Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.539, #1-2)

Contents (pp. v-vii).

Calendar of forthcoming meetings (pp. n1-n3).

Outside front cover - Editorial Board (pp. co1).

Selection of orthogonal chromatographic systems based on parametric and non-parametric statistical tests by P�ter Forlay-Frick; Elke Van Gyseghem; K�roly H�berger; Yvan Vander Heyden (pp. 1-10).

The orthogonal/similar character of 38 chromatographic systems using retention factor data of 68 drug substances was determined using different parametric and non-parametric methods. Non-parametric methods can be recommended, as the majority of retention data cannot be considered as normally distributed.The generalized pairwise correlation method (GPCM) with different statistical tests was applied to examine the similarity/orthogonality of the tested systems. Beside this, the Pearson's (product moment) correlation coefficient, the Spearman's rho and the Kendall's tau were also used as conventional correlation parameters. The Williams’ t-test (as a parametric statistical test), and the Conditional Fisher's, the McNemar's and the Chi-square tests (as non-parametric statistical tests) were used for hypotheses testing. Except for the selection using correlation coefficients all other measures are non-parametric. A new procedure was applied to establish orthogonality of the chromatographic systems. From the different correlation measures so-called orthogonality ratios were calculated. The ratios originating from GPCM with McNemar's test was found to be the best to select orthogonal (dissimilar) and similar systems. The method was compared with various alternatives to validate the findings (among others with the ratios from Pearson's correlation coefficients). The non-parametric options for correlation coefficients (Spearman's rho and Kendall's tau) are found not to be sensitive enough to define the orthogonality of these chromatographic systems.

Keywords: HPLC; Variable selection; Pairwise correlations; Non-parametric methods; Generalized pairwise correlation method; Spearman's rho; Kendall's tau

The identification of phenolic compounds by a gas chromatographic method on three capillary columns with the same non-polar stationary phase by Jadwiga Jaroszyńska; Tomasz Ligor (pp. 11-15).

The reproducibility and repeatability of retention indices values of phenolic compounds studied on several capillary columns with the same methyl–5% phenylsiloxane stationary phase indicated that various mode of such columns could be of use for the confirmative analysis. The application of three columns with manufactures’ symbols of PE-5ms, PE-5ht and DB-5 has made it possible to identify 16 of free phenolic compounds present in pine needles.

Keywords: Confirmation analysis; Gas chromatography; Phenolic compounds; Plant sample; Pine needles

Development and evaluation of headspace gas chromatography method for the analysis of carbonyl compounds in spirits and vodkas by Piotr Sowiński; Waldemar Wardencki; Monika Partyka (pp. 17-22).

The objective of this study was to develop and assess a method for the determination of aldehydes in alcoholic beverages using o-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine derivatization followed by headspace analysis (HS) coupled with electron capture detection (ECD). Suitable operating conditions for headspace sampling (volume of headspace phase, time and temperature of sample thermostating, ethanol concentration in sample and addition of salt) were determined. The new method is reproducible, for nearly all compounds at ppb and sub-ppb levels the relative standard deviation (R.S.D.) was in the range between 2 and 11%. The method limits of detection (MDL) for the individual aldehydes varied from 0.016 to ca. 4.3μgl⁻¹. The procedure was applied for the determination of aldehydes in real alcoholic beverages (vodkas).

Keywords: Carbonyl compounds; Headspace analysis; Spirits; o; -PFBHA; Derivatization

Synthesis and chromatographic properties of α-Schiff bases (6-imino)-β-cyclodextrin bonded silica for stationary phase of liquid chromatography by Zhi-Ming Zhou; Min Fang; Cong-Xuan Yu (pp. 23-29).

Two new chiral stationary phases (CSPs), 6-deoxyisopropylimino-β-cyclodextrin bonded on the silica gel (YBCDs) and heptakis[2,6- o-diamyl-6-deoxyisopropylimino]-β-cyclodextrin bonded on the silica gel (WYBCDs), were prepared. The chromatographic properties of two CSPs (YBCDs and WYBCDs) were tested. Good resolutions for disubstituted benzene isomers were obtained with YBCDs.l- andd-amino acids mixtures were well separated on both YBCDs and WYBCDs. The influence of pH of aqueous triethylammonium acetate buffer (TEAA) was also studied on the two CSPs. Experimental results show that WYBCDs enhances the retention of amino acids. It is proposed that the amylation modification above the cyclodextrin (CD) partially occludes the mouth of the CD cavity and sterically influences the formation of inclusion complexes, leading to the change in solute retention.

Keywords: HPLC; Schiff base; Cyclodextrin; CSPs

Determination of robenidine in eggs by liquid chromatography with UV spectrophotometric detection by Geraldine Dowling; Michael O’Keeffe; Malcolm R. Smyth (pp. 31-34).

A method has been developed to analyse for robenidine drug residues in eggs. Egg samples were extracted with acetonitrile and the sample extracts were defatted with hexane and aliquots of the extracts were analysed by liquid chromatography with UV spectrophotometric detection (317nm). The method was validated according to the criteria defined in Commission Decision 2002/657/EC. The validation parameters linearity, precision, recovery, specificity, decision limit (CC α) and detection capability (CC β) were determined. The decision limit was 10μgkg⁻¹ and the detection capability was 17μgkg⁻¹. The results of the inter-assay study, which was performed by fortifying egg samples ( n=6) at three levels in three separate assays, show mean recoveries to be between 79 and 105%. The precision of the method, expressed as CV (%) values for the within-laboratory repeatability, was ≤13.5%.

Keywords: Robenidine; Residue analysis; Egg; Method validation; Liquid chromatography with UV spectrophotometric detection

Microextraction in packed syringe/liquid chromatography/electrospray tandem mass spectrometry for quantification of olomoucine in human plasma samples by Mohamed Abdel-Rehim; Patrik Skansen; Marina Vita; Zuzana Hassan; Lars Blomberg; Moustapha Hassan (pp. 35-39).

Olomoucine is a purine analogue that selectively inhibits cyclin-dependent kinases. Malfunction of these enzymes has been associated with several diseases, including cancer. Olomoucine was introduced recently into clinical trials. The aim of the present investigation was to develop a simple, fast and sensitive method for the determination of olomoucine in plasma samples.The determination of olomoucine in plasma and urine was performed using micro extraction in packed syringe (MEPS) as sample preparation method on-line with high-performance liquid chromatography and tandem mass spectrometry (LC–MS/MS). In MEPS, the sampling sorbent was 1mg polystyrene polymer that was inserted in a 250-μL syringe. Roscovitine was used as internal standard. The limit of detection (LOD) for olomoucine was 0.5ng/mL and the lower limit of quantification (LLOQ) was set to 1.0ng/mL. The accuracy values of quality control samples (QC) were between ±15%, and precision (R.S.D.) had a maximum deviation of 10%. The standard curve was obtained within the concentration range 0.5–2000ng/mL in both plasma and urine. The regression correlation coefficients ( R²) for plasma and urine samples were ≥0.999 for all runs. The present method is miniaturized, fully automated and robust that can be easily used for pharmacokinetic and pharmacodynamic studies of olomoucine.

Keywords: Microextraction in packed syringe; Sample preparation; Polystyrene sorbent; Olomoucine; Plasma; LC–MS/MS

Determining leaching of bisphenol A from plastic containers by solid-phase microextraction and gas chromatography–mass spectrometry by Chia-Min Chang; Chi-Chi Chou; Maw-Rong Lee (pp. 41-47).

This study evaluates solid-phase microextraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS) to determine trace levels of bisphenol A in water and leached from plastic containers. The extraction using headspace post-derivatization with bis(trimethylsilyl) trifluoroacetamide (BSTFA), containing 1% trimethylchlorosilane (TMCS) vapor, following SPME was compared with extraction without derivatization. The SPME experimental procedures to extract bisphenol A in water were optimized with a relatively polar polyacrylate (PA)-coated fiber, an extraction time of 50min and desorption at 300°C for 2min. Headspace derivatization following SPME was performed using 7μL of BSTFA with 1% TMCS at 65°C for 30s. The precision was 5.2% without derivatization and 9.0% headspace derivatization. The detection limit was determined to be at the ng/L level. When SPME was used following headspace derivatization, the detection limit was one order of magnitude better than that achieved without derivatization. The results of this study reveal the adequacy of SPME–GC–MS method for analyzing bisphenol A leached from plastic containers. The concentrations of bisphenol A leached from plastic containers into water ranged from 0.7 to 78.5μg/L.

Keywords: Bisphenol A; Solid-phase microextraction; Plastic containers; GC–MS

Simultaneous derivatization and extraction of amphetamine-like drugs in urine with headspace solid-phase microextraction followed by gas chromatography–mass spectrometry by Kan-Jung Chia; Shang-Da Huang (pp. 49-54).

A sensitive and solvent-free procedure for the determination of amphetamine-like drugs, amphetamine (AM), methamphetamine (MeAM), methylen-dioxyamphetamine (MDA), methylen-dioxymethamphetamine (MDMA) and methylen-dioxyethylamphetamine (MDEA) in urine samples was developed using solid-phase microextraction (SPME) with an on-fiber derivatization device. In this study, the amphetamine-like drugs were derivatized with heptafluorobutyric anhydride (HFBA) and heptafluorobutyric chloride (HFBCl) and determined by means of a gas chromatography–mass spectrometer with selected ion storage (SIS) detection. An improved design was used for sample preparation. The test specimen was placed in an 8ml vial along with additives (KOH and NaCl), a glass insert with twelve holes containing the derivatizing reagents was inserted into the vial, and the vial was then sealed tightly. A SPME device with a 100μm polydimethylsiloxane fiber was inserted into the vial and the fiber was exposed to the headspace in the insert, then the vial was heated and stirred at 95°C and 600rpm for 30min for evaporation/adsorption/derivatization. The SPME needle was finally removed and inserted into the GC injection port to desorb the analytes.The influence of several parameters on the efficiency of microextraction (type of fiber coating, extraction time, extraction temperature, etc.) was investigated. The SPME method developed provides good sensitivity with a calibration range from 0.5 to 1000ngml⁻¹ for MDA, and 0.1–1000ngml⁻¹ for AM, MA, MDMA and MDEA. The method detection limits (MDLs) are in the range 0.016–0.193ngml⁻¹ with the studied drugs. This method was also successfully tested on real samples of urine from people who were suspected of using amphetamines.

Keywords: Solid-phase microextraction; Derivatization; Amphetamine; Urine

Solid-phase microextraction with on-fiber derivatization for the determination of hydroxy-polychlorinated biphenyl compounds in urine by Jee Eun Hong; Heesoo Pyo; Song-Ja Park; Won Lee (pp. 55-60).

A sensitive and solvent-free procedure for the determination of hydroxy metabolites of polychlorinated biphenyls (PCBs) in urine samples was studied using solid-phase microextraction (SPME) followed by on-fiber silylation and gas chromatography/mass spectrometry (GC/MS) determination. The analytical procedure involved headspace adsorption with coated fiber and headspace derivatization with bis(trimethylsilyl)-trifluoroacetamide (BSTFA) in a sample vial. Experimental SPME parameters such as selection of coating material, addition of salt, extraction time and temperature of adsorption were optimized. The optimum extraction conditions for hydroxy-PCBs were obtained with a polydimethylsiloxane/divinylbenzene (PDMS/DVB) coated fiber at 90°C for 60min in urine, added 10% sodium chloride. Derivatization of the hydroxy-PCBs with BSTFA was performed on the SPME fiber at 60°C for 10min. The calibration curves for derivatized forms showed good linearity in the range of 0.01–10ngmL⁻¹ and method detection limits proved to be 0.01–0.1ngmL⁻¹ in 2mL of urine.

Keywords: Hydroxy-polychlorinated biphenyl compounds; Gas chromatography/mass spectrometry; Derivatization; Headspace; Solid-phase microextraction; Urine

Solid phase extraction using immobilized yeast Saccharomyces cerevisiae for determination of palladium in road dust by Beata Godlewska-Żyłkiewicz; Magdalena Kozłowska (pp. 61-67).

A solid phase extraction procedure using a yeast Saccharomyces cerevisiae immobilized in calcium alginate beads is proposed for the determination of Pd in road dust. Palladium was separated from the matrix elements by selective retention on the column at acidic pH (pH 1–1.5) followed by subsequent elution with 1ml of thiourea (TU) solution (0.3moll⁻¹ TU in 0.25moll⁻¹ HC1) and determination by graphite furnace atomic absorption spectrometry (GFAAS). The limit of detection was 7ngg⁻¹. The method validation was performed by analysis of certified reference material SARM-7 (platinum ore). The concentration of Pd in road dust samples collected in Bialystok (Poland) determined by the evaluated method is in the range 114.2–215.5ngg⁻¹. The analysis of data shows inhomogeneous distribution of Pd in road dust.

Keywords: Palladium; Immobilized yeast; Matrix separation; Road dust; GFAAS

Immobilized salen ( N, N′-bis (salicylidene) ethylenediamine) as a complexing agent for on-line sorbent extraction/preconcentration and flow injection–flame atomic absorption spectrometry by Shayessteh Dadfarnia; Ali Mohammed Haji Shabani; Fatema Tamaddon; Maryam Rezaei (pp. 69-75).

The microcolumn of salen I ( N, N′-bis (salicylidene) ethylenediamine) immobilized on surfactant-coated alumina has been used for on-line preconcentration of copper and lead with a flow injection–flame atomic absorption spectrometry (FI–AAS). Various parameters affecting the deposition/elution processes in the FI–AAS system was optimized. Deposition of analytes was affected at pH of ∼9, and injection of nitric acid (250μl 2moll⁻¹) served to elute retained species to AAS. A good relative standard deviation of 4.5 and 3.8% at 30μg l⁻¹( n=7), high enrichment factors of 100 and 75, and detection limits of 0.3, 2.6μgl⁻¹ (3S) for Cu(II) and Pb(II) were obtained, respectively. The method was applied to water samples, multivitamin tablet and standard reference alloys (C12E41 and C12X3500) and accuracy was assessed through recovery experiment and independent analysis by furnace AAS, or comparing the results with the accepted values.

Keywords: On-line preconcentration; Flow injection–AAS; Salen (; N; ,; N; ′-bis (salicylidene) ethylenediamine); Microcolumn; Immobilized salen

Determination of residues of quinolones in pig muscle by M.P. Hermo; D. Barr�n; J. Barbosa (pp. 77-82).

This paper presents the comparison between two analytical methods used for the determination of quinolones in pig muscle. The procedures involve the extraction of the quinolones from the tissues by traditional extraction and using microwave-assisted extraction (MAE), a step for clean-up and preconcentration of the analytes by solid phase extraction and subsequent liquid chromatography separation with UV absorbance detection. MAE has proven to be an alternative to classical extraction to extract quinolones from pig muscle below the maximum residue limit (MRLs) established by European Community, because less interfering substances were observed and cleaner extracts were obtained and in consequence LOD and LOQ determined are slightly lower than those obtained with classical extraction.

Keywords: Liquid chromatography; Microwave-assisted extraction (MAE); Pig muscle and quinolones

Molecularly imprinted solid phase extraction using stable isotope labeled compounds as template and liquid chromatography–mass spectrometry for trace analysis of bisphenol A in water sample by Migaku Kawaguchi; Yoshio Hayatsu; Hisao Nakata; Yumiko Ishii; Rie Ito; Koichi Saito; Hiroyuki Nakazawa (pp. 83-89).

We have developed a molecularly imprinted polymer (MIP) using a stable isotope labeled compound as the template molecule and called it the “isotope molecularly imprinted polymer�? (IMIP). In this study, bisphenol A (BPA) was used as the model compound. None imprinted polymer (NIP), MIP, dummy molecularly imprinted polymer (DMIP) and IMIP were prepared by the suspension polymerization method using without template, BPA, 4- tert-butylphenol (BP) and bisphenol A-d₁₆ (BPA-d₁₆), respectively. The polymers were subjected to molecularly imprinted solid phase extraction (MI-SPE), and the extracted samples were subjected to liquid chromatography–mass spectrometry (LC–MS). Although the leakage of BPA-d₁₆ from the IMIP was observed and that of BPA was not observed. The selectivity factors of MIP and IMIP for BPA were 4.45 and 4.43, respectively. Therefore, IMIP had the same molecular recognition ability as MIP. When MI-SPE with IMIP was used and followed by LC–MS in the analysis of river water sample, the detection limit of BPA was 1 ppt with high sensitivity. Moreover, the average recovery was higher than 99.8% (R.S.D.: 3.7%) by using bisphenol A-¹³C₁₂ (BPA-¹³C₁₂) as the surrogate standard. In addition, the IMIP were employed in MI-SPE of BPA in river water sample by LC–MS. The concentration of BPA in the river water sample was determined to be 32pgml⁻¹. We confirmed that it was possible to measure trace amounts of a target analyte by MI-SPE using IMIP.

Keywords: Isotope molecularly imprinted polymer (IMIP); Molecularly imprinted solid phase extraction (MI-SPE); Bisphenol A (BPA); Liquid chromatography–mass spectrometry (LC–MS)

Discrimination of epimeric disaccharides by templated polymers by Susanne Striegler (pp. 91-95).

Efficient differentiation of epimeric disaccharides with templated poly(acrylates) is achieved. The rebinding event of the sugar epimersd-lactulose (1) andd-lactose (2) is based on shape recognition in unbuffered aqueous solution at neutral pH. A high-fidelity imprint of the disaccharide structures and functionality during material preparation has been demonstrated to be only achievable in a very narrow space around the immobilized binding site. Selectivity factors of 4.3 are observed in saturation competition experiments applying equimolar amounts of1 and2. Investigation of the coordination behavior of a copper(II) complex as functional monomer reveals defined 1:1 complex formation with both disaccharides in solution.

Keywords: Carbohydrate; Copper(II) complex; Molecular recognition; Templated polymer

An allosteric model for the binding of bilirubin to the bilirubin imprinted poly(methacrylic acid-co-ethylene glycol dimethylacrylate) by Mei-Jywan Syu; You-Ming Nian (pp. 97-106).

During liver failure, hyperbilirubinemia occurred and the bilirubin level can be very high. Bilirubin concentration for a healthy adult is approximately 0.3mg/dL. The detection of bilirubin concentration can be important to indicate the liver function. Molecular imprinting technique was applied in this work using bilirubin molecule as the target template. Therefore, bilirubin imprinted poly(methacrylic acid-co-ethylene glycol dimethylacrylate) (poly(MAA-co-EGDMA)) was synthesized. The bilirubin imprinted polymer showed specific binding toward bilirubin rather than its analogue biliverdin. The binding results from bilirubin solution, biliverdin solution, and bilirubin/biliverdin mixture solution performed by bilirubin imprinted polymer particles were all obtained. The binding capacity of the target molecule, bilirubin, to the imprinted poly(MAA-co-EGDMA) was reduced because of the presence of biliverdin. On the contrary, the binding of bilirubin analogue, biliverdin, was slightly enhanced by the presence of bilirubin. The experimental results were further used for simulation to obtain the binding isotherms. The computational analysis proved that the binding kinetics could not be properly explained by Langmuir model as it was often reported to be. Instead, an allosteric model was proposed in this work. The simulation results showed that the binding kinetics was well described by the allosteric model. For the specific adsorption of bilirubin by the molecularly imprinted polymer (MIP) from the bilirubin/biliverdin mixture solution, a competitive allosteric model could well interpret the data. The maximum binding amount of bilirubin in single-compound solution, 0.476mg/g MIP, was higher than that obtained in bilirubin/biliverdin mixture solution, 0.442mg/g MIP. The binding constant of bilirubin in single solution, 170mg/dL, was smaller than that in bilirubin/biliverdin mixture, 192mg/dL. Instead, for the non-specific adsorption of biliverdin by the MIP from the bilirubin/biliverdin mixture solution, an enhanced allosteric model was proposed. Excellent simulation results were achieved. The binding parameters of the proposed models for this system were also obtained and discussed.

Keywords: Bilirubin; Molecular imprinting; Bilirubin imprinted poly(methacrylic acid-co-ethylene glycol dimethylacrylate); Biliverdin; Allosteric model; Competitive; Enhanced

Synthesis and characterization of creatinine imprinted poly(4-vinylpyridine- co-divinylbenzene) as a specific recognition receptor by Hsuan-Ang Tsai; Mei-Jywan Syu (pp. 107-116).

In this study, molecularly imprinted poly(4-vinylpyridine- co-divinylbenzene) (poly(4-VP- co-DVB)) as the specific receptor of creatinine was prepared by heated polymerization. 4-Vinylpyridine (4-VP) was used as the functional monomer. Creatinine was used as the template and divinylbenzene (DVB) was the cross-linking agent. After polymerization, water was applied to remove the imprinted creatinine from the polymer. Approximately 72% of the imprinted creatinine template was extracted. Solid-state¹³C NMR was used to analyze qualitatively the imprinting effect of the synthetic polymer. Adsorption results of creatinine by the imprinted poly(4-VP- co-DVB) and the corresponding non-imprinted polymer were compared. Maximum imprinting ratio of 4.56, defined as the maximum binding capacity of the MIP to that of non-MIP, was achieved. The adsorption kinetics could be precisely described by Langmuir isotherms. The kinetic parameters, Q_m and K_m, with the respective values of 11.95mg/g and 0.11dL/g were obtained. Imprinting ratio of the creatinine imprinted poly(4-VP- co-DVB) was also obtained. Selectivity factors of the imprinted poly(4-VP- co-DVB) defined as the binding of creatinine with respect to the other analogs ranging from 2.0 to 4.0 were obtained. The major detection interference of creatinine for clinical applications may come from creatine. Therefore, the creatinine/creatine binary competitive adsorption experiment was also carried out to evaluate the specific recognition ability of the polymer. The binding specificity of the imprinted poly(4-VP- co-DVB) toward creatinine was thus confirmed.

Keywords: Molecularly imprinted poly(4-vinylpyridine-; co; -divinylbenzene); Creatinine; Solid-state; ¹³; C NMR; Adsorption; Langmuir isotherms; Creatine

Automatic selective determination of caffeine in coffee and tea samples by using a supported liquid membrane-modified piezoelectric flow sensor with molecularly imprinted polymer by Mohammed Zougagh; Angel R�os; Miguel Valc�rcel (pp. 117-124).

An on-line supported liquid membrane-piezoelectric detection based on molecularly imprinted polymer (SLM-PZ-MIP) manifold was developed and applied to the quantitative determination of caffeine in coffee and tea samples. The proposed assembly provides all the advantages of an on-line system as regards automation, in addition to good selectivity, acceptable sensitivity and precision. The slurry sample was directly placed in SLM unit located in the loop of an injection valve, and the caffeine released from the sample passed through the membrane ( n-undecane/hexyl ether) into an acidic acceptor stream. The caffeine is quantified by using a quartz crystal modified with a molecularly imprinted polymer (MIP). The method shows a linear range between 10 and 1000ngml⁻¹, with a relative standard deviation of ±5% (at 50ngml⁻¹). Satisfactory results were found by analysing real coffee and tea samples.

Keywords: Supported liquid membrane; Molecularly imprinted polymer; Piezoelectric sensor; Caffeine; Coffee; Tea

Solid-phase molecularly imprinted on-line preconcentration and voltammetric determination of sulfamethazine in milk by A. Guzm�n-V�zquez de Prada; P. Mart�nez-Ruiz; A.J. Reviejo; J.M. Pingarr�n (pp. 125-132).

The synthesis and evaluation of a molecularly imprinted polymer (MIP) as a selective solid-phase extraction sorbent, coupled to voltammetric detection, for the efficient preconcentration and determination of sulfamethazine in milk is reported. The polymer was prepared using sulfamethazine as the template molecule, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linking monomer in the presence of acetonitrile as the solvent. The detection of sulfamethazine was carried out by square wave voltammetry (SVW) at a glassy carbon electrode in a MeOH:acetic acid (9:1) medium. This solvent mixture was also used for the elution of the analyte from the MIP microcolumns. Optimisation of the variables involved in the sulfamethazine binding/extraction process was carried out (solvent used for rebinding, pH of the rebinding solution, eluent volume, analyte and eluent flow rates). Using solid-phase extraction cartridges, containing 0.16–0.18g of MIP, an eluent volume of 2ml and a sample volume of 90ml, resulted in a nominal enrichment factor of 45, which was sufficient to analyse sulfamethazine at the maximum level permitted by the Codex Alimentarius Commission in milk (25mg1⁻¹). The selectivity of the MIP was evaluated by considering different substances with molecular structures similar to sulfamethazine. Sulfamethazine was determined in milk samples spiked at two concentration levels: 696mg1⁻¹ in the buttermilk obtained after milk deproteinisation, and 25mg1⁻¹ both in the buttermilk and in the milk before deproteinisation. Recoveries of practically 100% were achieved in all cases.

Keywords: Molecularly imprinted polymers (MIPs); Preconcentration; Solid-phase extraction; Sulfamethazine; Voltammetric detection

Real-time monitoring of a pharmaceutical process reaction using a membrane interface combined with atmospheric pressure chemical ionisation mass spectrometry by Rebecca Clinton; Colin S. Creaser; Duncan Bryant (pp. 133-140).

A single-stage membrane-based interface has been developed for real-time mass spectrometric monitoring of the starting materials and products of a highly concentrated pharmaceutical process reaction mixture. The interface was directly connected to the atmospheric pressure chemical ionisation source of a quadrupole mass spectrometer (APCI-MS). Dilution of the concentrated reaction mixture was achieved in a single-step by using the interface with a precision of 3.2% for replicate samples. The combination of the membrane inlet with APCI-MS is demonstrated for the Michael addition reaction of phenylethylamine and acrylonitrile in ethanol using a hydrophobic polyvinylidene fluoride microporous membrane. The reaction was monitored throughout its course, allowing the endpoint to be determined based on the relative concentrations of the reaction precursors and products. The device required minimal analyst intervention, reducing sample preparation and handling prior to on-line real-time MS analysis.

Keywords: APCI-MS; Membrane interface; Michael addition reaction; Process monitoring

Rapid and decisive determination of Cr⁶⁺ using electrospray ionization mass spectrometry by K. Minakata; M. Suzuki; O. Suzuki (pp. 141-143).

Cr⁶⁺ complexed with diethyldithiocarbamate (DDC) was extracted into 0.1 volume of octanol in the presence of citric acid. The extracted compound was determined to be CrOH(DDC)₃⁺ by electrospray ionization mass spectrometry. The peak at m/ z 513 derived from⁵²Cr was so high that only 5pg of Cr⁶⁺ could be determined in 10min.

Keywords: Chromium; Electrospray ionization; Mass spectrometry; Diethyldithiocarbamate

A comparison of pyrolysis–gas chromatography–mass spectrometry and fourier transform infrared spectroscopy for the characterisation of automative paint samples by D. Thorburn Burns; K.P. Doolan (pp. 145-155).

It has been shown that by using pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS), it is possible to discriminate between a variety of base coat, solid paint and clear coat samples of automotive paints in commercial use from a wide range of car manufacturers. Some of the solid paints and clear coats were pairs of samples indistinguishable by fourier transform infrared spectroscopy (FT-IR).

Keywords: Pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS); Fourier transform infrared (FT-IR) spectroscopy; Automotive paints; Base coat; Solid paint; Clear coatAbbreviations; PAMMEpentanoic acid methyl methyl ester; PABEpentanoic acid butyl ester; PAMBEpentanoic acid methyl butyl ester on the pyrograms

The discrimination of automotive clear coat paints indistinguishable by Fourier transform infrared spectroscopy via pyrolysis–gas chromatography–mass spectrometry by D. Thorburn Burns; K.P. Doolan (pp. 157-164).

It has been shown that by using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS), it is possible to discriminate between a variety of automotive clear coat paints, indistinguishable by Fourier transform infrared spectroscopy (FT-IR).

Keywords: Pyrolysis–gas chromatography–mass spectrometry; Fourier transform infrared spectroscopy; Automotive paint; Clear coat

Module for real time non-invasive control of the electroosmotic flow in microfluidic systems by Laszlo Szekely; Ruth Freitag (pp. 165-171).

A module is introduced that allows setting and maintaining the flow rate in microfluidic systems (analytical chips) using electroosmotic flow (EOF) for mobile phase propulsion. The sensing principle is compatible with any type of microanalytical device, where the mobile phase is drawn from a reservoir. It allows continuous monitoring of the EOF and does not require any manipulation or compositional changes (additives/heating) of the mobile phase. Instead the sensor optically records the speed of displacement of the liquid level in the chip reservoirs as the liquid flows out. Readings are taken with a frequency of 1000Hz allowing flow rate measurements in less than 0.4s. Based on these measurements, the flow rate can be maintained to a preset value (‘flow control’) using a simple control circuit/algorithm that compares the actual with the desired flow rate and adjusts the former if necessary via the applied field strength. The potential of the module to stabilize the flow after disturbances is demonstrated.

Keywords: Electroosmotic flow; Microfluidic systems; Mobile phase propulsion; Capillary electrophoresis

A pulsed sequential injection analysis flow system for the fluorimetric determination of indomethacin in pharmaceutical preparations by Paula C.A.G. Pinto; M. L�cia M.F.S. Saraiva; Jo�o L.M. Santos; Jos� L.F.C. Lima (pp. 173-179).

This works reports the development of a pulsed flow sequential injection analysis (SIA) system based on the utilisation of pulse generating solenoid micro-pumps, which replace the conventional solutions propelling units commonly used in SIA systems. The influence on sample/reagent zones interpenetration and reaction zone formation of the reproducible pulsed flow produced by micro-pumps operation, which is characterised by a chaotic solutions movement, was comparatively evaluated with the typical laminar flow conditions of conventional SIA systems.The enhanced sample/reagent mixing provided by the controlled pulsed flow was favourably applied in the implementation of a SIA methodology for the fluorimetric determination of indomethacin in pharmaceutical preparations upon alkaline hydrolysis in micellar medium. Linear calibration plots were obtained for indomethacin concentrations up to 10⁻⁵moll⁻¹ with a 3 σ detection limit of about 1.6×10⁻⁸moll⁻¹. The obtained results complied with those furnished by the reference procedure (RD≤2.3%) and exhibited good reproducibility (RSD<1.2%, n=15). Sampling rate was about 30 samples per hour.

Keywords: Pulsed flow; SIA; Solenoid micro-pump; Indomethacin; Micellar medium; Fluorimetry

Sequential injection absorption spectrophotometry using a liquid-core waveguide: Determination of p-arsanilic acid in natural waters by Aaron R. Roerdink; Joseph H. Aldstadt III (pp. 181-187).

We describe the development, optimization, and application of a novel method for the quantification of p-arsanilic acid ( p-ASA), an organoarsenical that is widely used as an animal feed additive, at μgL⁻¹ levels in surface water samples. The method is based on sequential injection–long pathlength absorbance spectrophotometry (SI–LPAS). This method incorporates the selective reactivity of p-ASA with p-dimethylaminobenzaldehyde (DMAB, “Ehrlich's Reagent�?) in the presence of other common environmental organoarsenicals, such as dimethylarsenic acid (DMAA), monomethylarsonic acid (MMAA), and 3-nitro-4-hydroxyphenylarsonic acid (3-NHPAA, Roxarsone). Optimal reaction conditions were studied, namely the pH dependence of the reaction (pH=1.4), volumes of reagent and sample, reagent concentration, reaction time, reaction temperature, and flow rates. A calibration model that was linear over four orders of magnitude was prepared, where y ( A₄₅₀, peak height)=0.139×(mgL⁻¹)+0.0275 ( R²=0.9984). The limit of detection was 21.2μgL⁻¹ (3Ω), and the analysis time was <8min/sample. A study of the response of the method to other organoarsenicals demonstrated that the method is selective for p-ASA ( t-test, t=0.622, t_c=3.707 at the 99% confidence limit). For an authentic surface water sample from a swine farm that was fortified with p-ASA to 0.500mgL⁻¹, a recovery of 100.5% and an average precision ( n=4) of 13.7% relative standard deviation were observed.

Keywords: Sequential injection; Liquid-core waveguide; Arsenic; Solid-phase extraction; p; -Arsanilic acid (CASRN 98–50–0); p; -Dimethylaminobenzaldehyde (CASRN 100–10–7)

Multisyringe flow injection analysis of stable and radioactive yttrium in water and biological samples by Y. Fajardo; E. G�mez; F. Garcias; V. Cerd�; M. Casas (pp. 189-194).

A novel multisyringe flow injection (MSFIA) method for the determination of stable and radioactive yttrium by means of a liquid–liquid extraction has been developed. An on-line column containing di-2-ethylhexylphosphoric acid (HDEHP) – a highly selective extractant for the analyte – adsorbed on a C18 support is employed to carry out the isolation from the matrix. Stable and radioactive yttrium concentrations are determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and by a low background proportional counter, respectively. The proposed method shows important advantages because the manual handling of radioactive samples is avoided and throughput is increased. Moreover, as the extractant can be reused, cost per analysis and waste generation are reduced. The lower limit of detection (LLD) of stable yttrium is 10μgl⁻¹, whereas for⁹⁰Y is 0.05Bq. The automated isolation process yields a yttrium recovery close to 100% with a relative standard deviation of 2.3% ( n=10). Our methodology has been successfully applied to different spiked water and biological samples.

Keywords: Yttrium; Radioactivity; MSFIA; Water; Biological samples

Insecticide identification using a flow injection analysis system with biosensors based on various cholinesterases by Bogdan Bucur; Madalina Dondoi; Andrei Danet; Jean-Louis Marty (pp. 195-201).

This work presents an automatic method able to identify the presence of neurotoxic insecticides using omethoate as a model compound. The acetylcholinesterase (AChE)-based biosensors used to detect the neurotoxic insecticides present two shortcomings: the weak limit of detection (LOD) and the lack of selectivity. An appropriate LOD is obtained in our work by using two sensitive AChEs from Drosophila melanogaster ( Dm): the wild type (wt- Dm) and the E69W mutant. To discriminate between the insecticides and all other interferences, we use a FIA system that provides analytical information acquired from two enzymes: (i) the sensitive Dm-AChEs and (ii) an omethoate-resistant AChE from Electric Eel (Eel), which is equally affected by the matrix. The enzymes were immobilised on screen-printed electrodes by entrapment in a photocrosslinkable PVA-SbQ polymer used with a FIA system with three channels, each one of them simultaneously analysing the same sample using biosensors based on different AChEs. The biosensor based on the wt- Dm had a LOD of 2×10⁻⁶M omethoate, while the one based on the E69W mutant permitted to lower the LOD to 1×10⁻⁷M. Interferences produced by mercury and hypocloryte were successfully discriminated. Environmental water samples were also analysed.

Keywords: Recombinant acetylcholinesterase (AChE); Omethoate; Selective insecticide detection; Flow injection analysis (FIA); Screen-printed electrode (SPE)

Determination of mercury(II) at trace levels by gas-diffusion flow injection analysis with amperometric detection by Nazanin Amini; Terence J. Cardwell; Robert W. Cattrall; Spas Kolev (pp. 203-207).

A gas-diffusion flow injection (GD-FI) system for the determination of Hg(II) in aqueous samples at trace levels is described. The analytical procedure involved injection of Hg(II) samples and standards into a 1.5M H₂SO₄ stream which was subsequently merged with a reagent stream of 0.6% SnCl₂ in 1.5M H₂SO₄ to reduce Hg(II) to metallic mercury. The gas-diffusion cell was thermostated at 85°C to enhance the vaporization of mercury. The mercury vapour diffused across a Teflon membrane into an acceptor stream containing 0.050M KNO₃ where it was detected amperometrically at a gold electrode set at +600mV versus Ag/AgCl reference electrode. Under optimal conditions, the flow injection method is characterized by a linear calibration range between 0 and 80μgl⁻¹, a detection limit of 900ngl⁻¹ and a sampling rate of 12 samples per hour. The flow injection system was successfully applied to the determination of mercury in freshwater samples containing colored compounds and suspended particulates and to digested sediment and soil samples. Satisfactory agreement with results obtained by cold vapour atomic absorption spectrometry was observed.

Keywords: Gas-diffusion; Flow injection; Mercury determination; Cold vapour; Ameprometric detection

Carbon-nanotubes doped polypyrrole glucose biosensor by Joseph Wang; Mustafa Musameh (pp. 209-213).

We report on the one-step preparation route of amperometric enzyme electrodes based on incorporating a carbon-nanotube (CNT) dopant and the biocatalyst within an electropolymerized polypyrrole film. Cyclic voltammetric growth profiles indicate that the anionic CNT is incorporated within the growing film for maintaining its electrical neutrality. The entrapment of the CNT has little effect upon the electropolymerization rate and redox properties of the resulting film. The CNT dopant retains its electrocatalytic activity to impart high sensitivity and selectivity. Linearity prevails up to ca. 50mM glucose, with a slight curvature thereafter. Relevant parameters of the film preparation were examined and optimized. Such an electropolymerization avenue represents a simple, one-step route for preparing enzyme electrodes and should further facilitate the widespread production of CNT-based electrochemical biosensors.

Keywords: Enzyme electrode; Carbon nanotubes; Nanobiocomposites; Glucose sensor; Polypyrrole; Enzyme immobilization

Amperometric sensor for glucose based on electrochemically polymerized tetraruthenated nickel-porphyrin by Maria do Socorro Maia Quintino; Herbert Winnischofer; Marcelo Nakamura; Koiti Araki; Henrique Eisi Toma; L�cio Angnes (pp. 215-222).

Glassy carbon and gold electrodes were modified with tetraruthenated Ni-porphyrin by electropolymerization in alkaline medium and characterized by cyclic voltammetry, UV–vis spectroscopy and MAC-mode scanning probe microscopy (SPM). The half-wave potentials and current intensities associated with the Ni^III/Ni^II process were strongly pH-dependent. The modified electrodes were successfully employed as sensors for glucose in alkaline medium, based on the catalytic activity of the Ni^III/Ni^II centers. Glucose quantification was carried out by means of cyclic voltammetry or amperometry coupled to batch injection analysis (BIA). The BIA-amperometry technique revealed more efficiency than cyclic voltammetry, lowering the detection limit to 3.6×10⁻⁷molL⁻¹, and providing a larger, linear working range (2.5×10⁻⁶ to 1.0×10⁻³molL⁻¹), better repeatability (RSD=1.1% for 25 injections of 2.5×10⁻⁵molL⁻¹), and higher sampling frequency (60samplesh⁻¹). The new sensor was successfully employed for the analysis of glucose in parentheral nutrition solutions and the results were in good agreement with the ones obtained by spectrophotometry, utilizing a modified Benedict's test.

Keywords: Nickel-porphyrin; Electrocatalytic oxidation; Glucose quantification; Cyclic voltammetry; Amperometry; Batch injection analysis

Development of anion selective polymer membrane electrodes based on lutetium(III) porphyrins by Matthew S. Messick; Sandeep K. Krishnan; Matthew K. Hulvey; Erich D. Steinle (pp. 223-228).

Liquid polymer membrane electrodes based on lutetium(III) porphyrins are examined as anion-selective electrodes. The lanthanide metal ion, incorporated into tetraphenylporphyrin or octaethylporphyrin, is added to a plasticized poly(vinyl chloride) membrane. The selectivity coefficients of the resulting membrane electrodes differ from the traditional Hofmeister series, with a preference towards the salicylate anion, while discriminating thiocyanate and iodide. Through separate incorporation of lipophilic ionic additives, the lutetium(III) porphyrin-based electrodes were determined to function via a neutral carrier mechanism. As a result, the addition of cationic (quaternary ammonium) salts to the membrane enhances the response characteristics of the electrodes. An initial study to determine the feasibility of utilizing these electrodes in clinical determinations of salicylate is also demonstrated. Membrane composition and sample pH are varied to optimize salicylate response in the clinical range of salicylate concentrations.

Keywords: Ion-selective polymer electrode; Anion sensor; Lutetium(III) porphyrin; Salicylate; Ionic sites

Construction and evaluation of As(V) selective electrodes based on iron oxyhydroxide embedded in silica gel membrane by J.A. Rodr�guez; E. Barrado; M. Vega; F. Prieto; J.L.F.C. Lima (pp. 229-236).

Two As(V) selective electrodes (with and without inner reference solution) have been developed using selective membranes based on iron oxyhydroxide embedded on silica gel mixed with ultrapure graphite at a 2/98 (w/w) ratio. The active component of the membrane was synthesised by means of the sol-gel technique and characterized by X-ray and FTIR spectroscopy. This compound shows a great affinity towards As(V) ions adsorbing 408mgg⁻¹. Using 1moll⁻¹ phosphate buffer (at a 1/1, v/v ratio) to adjust the pH and the ionic strength to 7 and 0.5moll⁻¹, respectively, the calibration curve is linear from 1.0×10⁻¹ to 1.0×10⁻⁶moll⁻¹ As(V), with a practical detection limit of 4×10⁻⁷moll⁻¹ (0.03mgl⁻¹) and a slope close to 30mVdecade⁻¹. The effect of potentially interfering ions was investigated. The accuracy and precision of the procedure have been tested on arsenic-free drinking water samples spiked with known amounts of arsenic and on groundwater samples containing high levels of arsenic. Total arsenic in these samples was determined after oxidation of As(III) with iodine at pH 7. The results of total As were comparable to those generated by ET-AAS.

Keywords: Arsenic(V) selective electrodes; Potentiometry; Iron oxyhydroxides; Silica gel; Adsorption

“Electrochemical Index�? as a screening method to determine “total polyphenolics�? in foods: A proposal by Antonio J. Blasco; M.C. Rogerio; M.C. Gonz�lez; A. Escarpa (pp. 237-244).

A new screening protocol based on electrochemical analysis is proposed to determine total polyphenolics in foods. The protocol is based on the use of a flow injection analysis system with a glassy carbon electrode. Using a wide and representative group of food samples and by comparison with a spectrophotometric protocol, the “Electrochemical Index�? is defined as the total polyphenolic content obtained by electrochemistry. The new electrochemical protocol is introduced as alternative to traditional procedures as a new screening protocol to measure the “total natural antioxidant�? content.

Keywords: Electrochemical Index; Total polyphenolics; Electrochemical detection; Natural antioxidants

Voltammetric determination of inorganic As(III) and total inorganic As in natural waters by Antonella Profumo; Daniele Merli; Maria Pesavento (pp. 245-250).

The paper describes a voltammetric method for the determination of As(III) and total inorganic As at ppb and sub ppb level using cathodic stripping voltammetry. This method is based on the formation of a copper-arsenic intermetallic at HDME during the preconcentration step.Sodium dithionite is used for the reduction of As(V) to As(III). As(III) is then determined in HBr supporting electrolyte. Compared to the procedures described in previous literature, the determination of total inorganic arsenic in such conditions needs shorter deposition times and less amount of copper. Moreover, better linear response current versus concentration and peaks repeatability are obtained. In the described working conditions LOQ for As(III) and As(V) are 0.010 and 0.020ppb respectively, for a deposition time of 300s. Standard deviation for 1ppb arsenic concentration ( n=7) is 5%. The method was applied to thermal, spring and sea waters and accuracy was verified by a recovery test on spiked samples. Total arsenic concentrations are in good agreement with those obtained in ICP-OES-HG.

Keywords: Trivalent arsenic; Pentavalent inorganic arsenic; Total inorganic arsenic; Cathodic stripping voltammetry

A novel homogeneous assay format utilising proximity dependent fluorescence energy transfer between particulate labels by Antti Valanne; Hanne Lindroos; Timo L�vgren; Tero Soukka (pp. 251-256).

Particle labels feature considerably higher specific activity than small molecule labels due to high number of label molecules incorporated in one unit. We developed a novel homogeneous assay relying on time-resolved detection of fluorescence energy transfer between particulate labels. The long-lifetime fluorescent Eu(III)-chelate-doped donor nanoparticles and the prompt near-infrared fluorescent TransFluoSphere™ acceptor particles possess high specific activity, resulting in great sensitivity potential. The proximity required in fluorescence energy transfer was achieved via antibody–antigen interactions, where the model analyte was prostate specific antigen (PSA), and donor and acceptor particles were coated with monoclonal anti-PSA-antibodies specific for discrete PSA epitopes. Due to long-lived donor emission and near-infrared acceptors, the sensitized acceptor emission was detectable in delayed measurement window free of autofluorescence. Due to these properties and low non-specific binding of the particles, the detection limit of below 0.1ng/mL PSA and low variations, typically 0.1–7%, were achieved. The developed homogeneous assay setup is applicable to sensitive indirect competitive or non-competitive high-throughput screening.

Keywords: Homogeneous immunoassay; Fluorescence energy transfer; Particulate labels; Time-resolved detection

Direct determination of paracetamol in powdered pharmaceutical samples by fluorescence spectroscopy by Altair B. Moreira; Hueder P.M. Oliveira; Teresa D.Z. Atvars; Iara L.T. Dias; Graciliano O. Neto; Elias A.G. Zagatto; Lauro T. Kubota (pp. 257-261).

The native fluorescence of paracetamol (PA) in the solid state is demonstrated, allowing the development of a rapid, simple and rugged method for direct analysis of pharmaceutical formulations. It is easily adaptable to any spectrofluorimeter, and no chemical treatment of the sample is needed. The fluorescence measurements ( λ_ex=333nm; λ_em=382nm) are performed directly on the powdered sample, the active substance being diluted in lactose, maize starch, poly(vinylpyrrolidone), talc and stearic acid. The influence of the ingredients of PA formulations is discussed. Fluorescence intensity is linearly dependent on PA concentration within the 100–400mgg⁻¹ range. The analytical frequency is 200h⁻¹. Detection and quantification limits were estimated within the 13.0–16.7 and 43.1–55.7mgg⁻¹ ranges for samples with different ingredient proportions. The method was applied to pharmaceutical formulations and the relative standard deviation of results was <2.7% ( n=20) for all tested ingredient proportions. Results were compared with those obtained by a method recommended by the British Pharmacopoeia and no statistical difference between methods was found at the 95% confidence level.

Keywords: Solid-phase analysis; Fluorescence spectroscopy; Paracetamol; Acetaminophen

A crosslinked matrix of thylakoids coupled to the fluorescence transducer in order to detect herbicides by Pierre Euzet; Maria Teresa Giardi; Regis Rouillon (pp. 263-269).

A new method to detect photosynthetic herbicides has been developed. It is based on the fluorescence activity of spinach thylakoids immobilised in a matrix of crosslinked albumin-glutaraldehyde. Among all the tested parameters, it was the area over the fluorescence curve (FA) which showed the greatest modification in the presence of herbicides. So that was therefore selected for the experiments. The optimal area was measured at 25°C in a 10mM phosphate buffer, pH 5.5. After immobilisation, the value of fluorescence area retained 77% of the activity after a 240-day storage at −18°C. A good operational stability was given by the measuring of the fluorescence area every 10min during 180min at +5 and +25°C. The limits of detection were determined for various photosynthesis inhibiting herbicides (corresponding to a 10% inhibition of FA). The greatest sensitivity for the detection of the phenylurea diuron (0.35μg/L) was recorded and the order of sensitivity among the triazines and triazinones chemical classes were, respectively, metribuzin (2μg/L), atrazine (3.5μg/L), and cyanazine (10μg/L). It was also possible to detect low concentrations of diuron in environmental water samples except for highly concentrated salt waters which modified the fluorescence activity of the thylakoid matrix. The results suggest that this system could be useful for monitoring of pollutants and environmental pre-screening.

Keywords: Fluorescence area; Thylakoids; Immobilisation by BSA-Glu; Herbicides; Photosynthesis; Water sources

The enhancement effect of CaCl₂ on solid substrate room temperature phosphorescence of polyhalogenated derivatives of fluorescein and application in immunoassay by Ya-Lan Wu; Long-Di Li; Jia-Ming Liu; Guo-Hui Zhu (pp. 271-275).

It was found that the solid substrate room temperature phosphorescence (SS-RTP) signal of some polyhalogenated derivatives of fluorescein (including eosin5-isothiocyanate) on a polyamide membrane can be enhanced obviously when an external inorganic salt was introduced into the system. The enhancement effect (RTP intensity and the ratio of signal to noise) of CaCl₂ was much more notable than those of typical heavy atom perturbers in phosphorimetry, such as Pb(AC)₂ and Hg(NO₃)₂, etc. According to that, a solid substrate room temperature phosphorescence immunoassay (SS-RTP-IA) with eosin5-isothiocyanate as a marker and CaCl₂ as an enhancer for the determination of human complement 3 was developed. On a polyamide membrane, SS-RTP signals ( λ_ex/ λ_em=532nm/685nm) of the immune complex are in linear correlation to the amount of human C3 in the range of 0.156–5.00pg/spot (the sample volume was 0.4μL/spot, corresponding concentration was 0.391–12.5ng/mL). The regression equation of working curve can be expressed as Δ I_p (Δ I_p= I_sample− I_blank)=1.57+0.633 m_C3 (pg/spot), correlation coefficient r=0.998. The detection limit calculated as 3 S_b/ k is 0.12pg/spot. The method was directly applied to the determination of human complement 3 in human serums with satisfactory results. These results proved sufficiently that eosin-ITC is a good phosphorescent marker, while CaCl₂ was used as the enhancer. Obviously, the results will expand the application area of these luminescent molecules, and using CaCl₂ instead of Pb(AC)₂ as a phosphorescence enhancer is more favorable for environment.

Keywords: Solid substrate room temperature phosphorescence immunoassay; Polyhalogenated derivatives of fluorescein; Eosin-ITC; CaCl; ₂; as an enhancer; Human complement 3

Determination of recombinant human tumor necrosis factor-α in serum by chemiluminescence imaging by Lirong Luo; Zhujun Zhang; Lifeng Ma (pp. 277-282).

A simple, sensitive and high throughput chemiluminescence (CL) imaging method was described for the determination of recombinant human tumor necrosis factor-α (rh TNF-α). The proposed method has the advantage of showing the specificity of enzyme-linked immunosorbent assays (ELISA), sensitivity of enhanced chemiluminescence (ECL), and high throughput of CL imaging method. In this system, 96 well transparent microtiter plates were used as solid phase materials. The method was based on the use of two monoclonal antibodies against rh TNF-α, one “capture�? antibody and one labeled with horseradish peroxidase (HRP), in a “sandwich�? ELISA format. A cooled CCD camera has been applied to image the weak chemiluminescence from the ECL. The CL intensity was proportional with the concentration of rh TNF-α in the range of 9.0–312.0pgml⁻¹ and the detection limit was 1pgml⁻¹. The proposed method has been successfully applied to the determination of rh TNF-α in human serum, the reliability of the assay method was established by parallel determination and by standard-addition method (R.S.D.=4.7%, recoveries=94–108%).

Keywords: Recombinant human tumor necrosis factor-α; Enhanced chemiluminescence; Enzyme-linked immunosorbent assays; Imaging

A new application of X-ray scattering using principal component analysis – classification of vegetable oils by Gisele G. Bortoleto; Luiz Carlos M. Pataca; Maria Izabel M.S. Bueno (pp. 283-287).

This work describes an innovative technique based on X-ray scattering applied to classify complex organic matrices of different vegetable oils. This new, very simple and rapid procedure is based on taking a 1mL aliquot of sample, depositing it on the thin Mylar™ film of a sample cell and submitting it to irradiation for 100s in a conventional EDXRF equipment. The resulting spectra are processed through Principal Component Analysis (PCA), a chemometric tool, and a very convenient classification is obtained as a function of the origin of the oil. This classification can be used to verify oil adulterations, for example. The X-ray fluorescence spectrometer is a common bench equipment, with a Rh tube as source of the X-rays.Vegetable oils from corn, canola, soybean, sunflower and olive (extra virgin and others) were analysed and classifications were obtained using information from the scattered radiation. For the corn, canola, soybean and sunflower oil analyses, the PC1×PC4 score plots show distinct groups for each oil. These differences related to the variable fatty acid contents in the samples. Considering the discrimination between extra virgin and other olive oils, the PC1×PC2 scores plot shows two groups of samples. The main difference between them can be attributed to the total absence of water in extra virgin olive oils, since this first extraction is performed at room temperature without any kind of reagent. The technique is very useful to rapidly classify vegetable oil samples at very low cost, with the possibility of performing the measurements in situ with a portable instrument.

Keywords: X-ray scattering; Principal components analysis; Vegetable oils

A chemometric investigation of the effect of the process parameters during maleic anhydride pulsed plasma polymerization by F. Siffer; A. Ponche; P. Fioux; J. Schultz; V. Roucoules (pp. 289-299).

Plasma polymerization is a good candidate to functionalise solid surfaces. In particular, pulsed plasma polymerization produces polymer thin films with good structural retention of the monomer. The present work consists in a systematic investigation of the influence of parameters during maleic anhydride pulsed plasma polymerization. The following parameters have been considered in the present study: on-time polymerization, off-time polymerization and peak power. After preliminary experiments based on a factorial design, a central composite design was applied to optimise the three factors. Predicted and experimental response as anhydride groups retention, thickness and roughness of plasma polymer thin films were compared. The film chemical structures were obtained using X-ray photoelectron spectroscopy (XPS), the film thickness by ellypsometry measurements and the film roughness by AFM analysis.

Keywords: Plasma polymerization; Full factorial design; Central composite design; Surface analysis

Automated turbidimetric determination of cyclamate in low calorie soft drinks and sweeteners without pre-treatment by Natalia E. Llamas; Mar�a S. Di Nezio; Miriam E. Palomeque; Beatriz S. Fern�ndez Band (pp. 301-304).

A flow injection turbidimetric method for determination of cyclamate in low calorie soft drinks and sweeteners without pre-treatment is proposed. It was based on the oxidation of the sulphamic group of cyclamate, to sulphate by addition of nitrite. Then, a precipitate of sulphate was obtained by reaction with barium chloride, in presence of poly(vinyl alcohol) (PVA) in perchloric acid solution, at 30°C. The analytical signal was measured at 420nm.The method presented a linear range between 0.015 and 0.120% (w/v) and the calibration graph was S=(7.792±0.179) X−(0.114±0.012), R²=0.999. A reproducibility of 5.9% was obtained from nine calibration graphs that were carried out on different days and with different conditions (standard solution, reagents solution, etc.). The detection and quantification limits were 0.006 and 0.02% (w/v), respectively, the sample throughput 45h⁻¹ (by considering the wash cycle and the time consuming to eliminate the clean solution from the system). The obtained results were agreement with that obtained with the standard method.

Keywords: Cyclamate; Sweeteners; FIA; Turbidimetric

o-Tolidine: A new reagent for a simple nephelometric determination of anionic surfactants by J.G. March; M. Gual; A.D. Frontera (pp. 305-310).

Simple light scattering methods (batch, flow injection, sequential injection) for the determination of anionic active matter in detergents based on a novel reaction are reported. The methods are based on formation of a solid phase by association of anionic surfactants and protonated o-tolidine. Measurements were carried out with a conventional spectrofluorimeter at 400nm, and dodecylbenzene sulfonic acid (DBS) was selected as the reference anionic surfactant. Influence of the main parameters affecting the characteristics of the methods was studied by the univariate method. The optimized methods provided linear ranges from 1.6 to 300mgl⁻¹ DBS with a repeatability within the 1.2–2.6% range. Reaction time for the manual method is 45s and sampling frequency for FIA and SIA were estimated as 68 and 20h⁻¹, respectively. The methods were applied to commercial samples and results successfully compared with a volumetric recommended method. The proposed methods are simple, fast and neither require sample preparation nor any organic solvent.

Keywords: Anionic surfactants determination; o; -Tolidine; Nephelometry; Sequential injection analysis; Flow injection analysis

A colorimetric method for fluoride determination in aqueous samples based on the hydroxyl deprotection reaction of a cyanine dye by Chang-Qing Zhu; Jin-Long Chen; Hong Zheng; Yu-Qin Wu; Jin-Gou Xu (pp. 311-316).

A new highly sensitive and selective colorimetric method for fluoride determination in water is described. The novel reagent for this method is a cyanine dye (C₁) on which the hydroxyl group has been protected by reaction with tert-butyldimethylsilane (TBS) to form the silanated dye, C₂. C₂ is selectively attacked by fluoride ions to reform C₁. C₁ has an absorption maximum at 600nm with a molar absorptivity of about 200,000. Under optimized conditions, absorbance at 600nm is proportional to fluoride concentration up to about 1×10⁻⁴mol/L with a detection limit of 1.0×10⁻⁷mol/L. Because of the specific affinity of fluoride for the TBS functional group on C₂, there is little interference by other ions. The method has been successfully applied for fluoride determinations in local rainwater samples. Results determined by the proposed method agree favorably with those determined by a fluoride ion selective electrode method.

Keywords: Fluoride ion; Cyanine; Hydroxyl deprotection reaction; Colorimetric method

Kinetic method for the determination of trace amounts of copper(II) in water matrices by its catalytic effect on the oxidation of 1,5-diphenylcarbazide by Gast�n Adri�n Crespo; Francisco Javier Andrade; Fernando Alberto I��n; Mabel B. Tudino (pp. 317-325).

The chemical reaction between Cu(II) and 1,5-diphenylcarbazide (DPC) is revised from an analytical perspective. It is shown that instead of a Cu–DPC complex, an oxygen mediated DPC oxidation to diphenylcarbazone (DPCO) is the main reaction involved where Cu(II) acts as catalyst. Therefore, the signal observed corresponds to the oxidation product DPCO. Under certain specific conditions a chelate complex between Cu(II) and DPCO can also be observed. Kinetic parameters of these reactions are calculated. These results set the basis for the development of analytical methodologies for the determination of Cu(II) at ultra-trace levels. Since the study of interferences revealed Mg(II) as the most serious, an optimised flow injection system which allows the in-lineelimination of Mg(II) is presented. The limit of detection ( k=3) calculated for 10 blank replicates is 0.05μgL⁻¹ (injection volume 20μL), the analytical sensitivity equals 48μg⁻¹L and the sample throughput is 120h⁻¹. Obtained results for Cu(II) determination in natural waters as well as the validation of the analytical methodology will be given and discussed.

Keywords: Cu; DPC; Catalytic oxidation; Spectrophotometric determination

Comparison of ultra-violet and inductively coupled plasma-atomic emission spectrometry for the on-line quantification of selenium species after their separation by reversed-phase liquid chromatography by Fotios N. Tsopelas; Maria Th. Ochsenk�hn-Petropoulou; Ioannis G. Mergias; Lambrini V. Tsakanika (pp. 327-333).

An analytical approach for selenium speciation using liquid chromatography (LC) coupled with ultra-violet (UV) and inductively coupled plasma-atomic emission spectrometry (ICP-AES) was developed. The separation of the investigated selenium species, selenites, selenates, selenomethionine, selenocystine, selenocystamine and dimethyldiselenide was accomplished in less than 6min on a BIO Wide Pore RP-18 column using sodium salt of n-octanesulfonic acid as ion-pairing modifier. The on-line detection of the separated selenium species was performed using UV spectrometry at the optimum wavelength of 192nm, obtained by the UV spectra of the investigated individual selenium species. ICP-AES was also used as element specific on-line detector, after its coupling with the chromatographic system. The UV and ICP-AES detectors were compared for their suitability, including sensitivity and detection limits, for the on-line quantification of the six selenium species. The developed LC–UV as well as LC–ICP-AES techniques were successfully applied to a selenized yeast candidate reference material, after its enzymatic extraction with protease XIV. It was found that the described LC–UV technique is suitable for the determination of selenomethionine, the main selenium compound in the yeast, with an accuracy of 5%, although the UV detector is not element specific and it is rarely used for selenium speciation. This finding can prove valuable for routine laboratories to perform selenium speciation in such materials.

Keywords: Reversed-phase liquid chromatography; Ultra-violet spectrometry; Selenium speciation; Selenized yeast; Selenomethionine; Inductively coupled plasma-atomic emission spectrometry

Electrochemical hydride generation atomic fluorescence spectrometry for the simultaneous determination of arsenic and antimony in Chinese medicine samples by Wang-bing Zhang; Wu-er Gan; Xiang-qin Lin (pp. 335-340).

A new method for the simultaneous determination of As and Sb by using AFS coupled with a newly designed electrochemical hydride generator has been developed. The hydride generator is a tubular electrolytic cell of 28mm i.d. and 45mm length, which consists of a graphite tube cathode and a platinum anode. Gaseous hydrides of As and Sb are generated at the cathode. Through a gas–liquid separator, the hydrides are directly transported to the atomizer by an Ar flow for determination. A detection limit of 0.50 and 0.30μgl⁻¹ (3 σ) for As and Sb in synthetic samples containing10mgl⁻¹ Cu, Ni and Co was obtained, respectively. The precision ( n=11) for 50μgl⁻¹ As and Sb was 2.1 and 1.5%, respectively. The method was successfully applied for determination of total As and Sb in Chinese medicine samples.

Keywords: Electrochemical hydride generation; Atomic fluorescence spectrometry; Arsenic and antimony; Traditional Chinese medicine

Relationship between sensory analysis and near infrared spectroscopy in Australian Riesling and Chardonnay wines by Daniel Cozzolino; Heather E. Smyth; Kate A. Lattey; Wies Cynkar; Les Janik; Robert G. Dambergs; I. Leigh Francis; Mark Gishen (pp. 341-348).

The aim of this work was to investigate the relationship between sensory analysis and visible and near infrared spectroscopy in two Australian white wine varieties (namely unwooded Chardonnay and Riesling). A total of 120 samples (2 varieties×3 replicates×20 commercial labels) were scanned in transmission mode in the visible and near infrared range (400–2500nm). For the purposes of this study four aroma descriptors generated from a sensory descriptive analysis study: estery, honey, passionfruit, lemon-citrus and two palate properties :overall flavour and sweetness were selected for investigation. Calibration models between sensory properties and spectra were developed using partial least squares regression (PLS1 and PLS2) with cross validation. The correlation coefficients ( R_cal) were greater than 0.70 for estery, lemon and honey, and less than 0.50 for passionfruit, overall flavour and sweetness in both calibration and cross validation. Therefore, this work demonstrates that some relationships between sensory data and both visible and near infrared spectra exists to assess sensory properties in the white wine varieties. Further work will be carried out with a larger set of data including additional sensory properties in different white wine varieties in order to validate the method.

Keywords: Sensory properties; Near infrared reflectance; Spectroscopy; Unwooded Chardonnay; Riesling; Partial least squares; Chemometrics; Aroma; Palate

Evaluation of paper-based diffusive gradients in thin film samplers for trace metal sampling by Bronwyn L. Larner; Andrew J. Seen (pp. 349-355).

Diffusive gradients in thin films (DGT) samplers rely on diffusion of metals through a permeable diffusion layer of known thickness for in situ measurement of trace metals in natural waters, with the principal diffusion layer used to date being based on polyacrylamide hydrogels. Alternative diffusion layers based on commercially available chromatography paper have been investigated and applied as a diffusion layer in DGT samplers, with Cd diffusion coefficients being within 20% of the value in polyacrylamide hydrogels. Cd diffusion coefficients were, however, found to increase with decreasing ionic strength at ionic strengths ≤5×10⁻⁴molL⁻¹ NaNO₃, but unlike the polyacrylamide diffusion layer the chromatography paper showed reproducible behaviour at these low ionic strengths. Samples of the chromatography paper equilibrated with various ionic strength solutions containing Cd showed that the Cd was weakly bound by the paper, providing a potential explanation for the enhanced diffusion. The chromatography paper diffusion layer was also tested with a commercially available phosphate ion exchange binding phase where diffusion coefficients were determined for Cd, Cu, Pb, Zn, Co, Ni and Mn. The paper-based DGT samplers were found to be easier to prepare and handle than the polyacrylamide hydrogel based samplers, making them ideal for application as a routine monitoring technique.

Keywords: DGT; Trace metals; Chromatography paper; Ionic strength; Phosphate ion exchange membrane

Author Index (pp. 357-359).

Sections

Personal tools

Analytica Chimica Acta (v.539, #1-2)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.539, #1-2)