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Analytica Chimica Acta (v.582, #1)

Editorial Board (pp. co1).

Contents (pp. v-vi).

Calendar of forthcoming meetings (pp. n1).

Contents (pp. v-vi).

Editorial Board (pp. co1).

Matrix-assisted laser desorption/ionization (MALDI) mechanism revisited by Wei Chao Chang; Ling Chu Lora Huang; Yi-Sheng Wang; Wen-Ping Peng; Huan Cheng Chang; Nien Yeen Hsu; Wen Bin Yang; Chung Hsuan Chen (pp. 1-9).

Although matrix-assisted laser desorption/ionization (MALDI) was developed more than a decade ago and broad applications have been successfully demonstrated, detailed mechanism of MALDI is still not well understood. Two major models; namely photochemical ionization (PI) and cluster ionization (CI) mechanisms have been proposed to explain many of experimental results. With the photochemical ionization model, analyte ions are considered to be produced from a protonation or deprotonation process involving an analyte molecule colliding with a matrix ion in the gas phase. With the cluster ionization model, charged particles are desorbed with a strong photoabsorption by matrix molecules. Analyte ions are subsequently produced by desolvation of matrix from cluster ions. Nevertheless, many observations still cannot be explained by these two models. In this work, we consider a pseudo proton transfer process during crystallization as a primary mechanism for producing analyte ions in MALDI. We propose an energy transfer induced disproportionation (ETID) model to explain the observation of an equal amount of positive and negative ions produced in MALDI for large biomolecules. Some experimental results are used for comparisons of various models.

Keywords: Matrix-assisted laser desorption/ionization; Ionization mechanism; Biopolymer ion

Focused microwave-assisted micellar extraction combined with solid-phase microextraction—gas chromatography/mass spectrometry to determine chlorophenols in wood samples by Verónica Pino; Juan H. Ayala; Venerando González; Ana M. Afonso (pp. 10-18).

This work describes the utilization of the focused microwave-assisted micellar extraction in combination with the solid-phase microextraction (SPME) to determine chlorophenols in wood samples. The influence of the nature of the surfactant in the extraction process, the optimization of the variables of the focused-microwave system, and the effect of the ageing time of the samples in the extraction efficiency of the method, have been assessed in this study. The overall method using the non-ionic surfactant POLE as extracting medium allows us to determine chlorophenols in wood samples achieving an average extraction efficiency of 104.1%, limits of detection ranging from 2 to 120ngg⁻¹, and intermediate precision values ranging between 3.5 and 13.2%. The proposed method is also characterized by short analysis times (around 5min for the microwaves extraction step) and by avoiding the use of organic solvents.

Keywords: Micellar media; Focused microwave-assisted extraction; Solid-phase microextraction; Chlorophenols; Gas chromatography-mass spectrometry

Determination of acrylamide in food by solid-phase microextraction coupled to gas chromatography–positive chemical ionization tandem mass spectrometry by Maw-Rong Lee; Li-Yo Chang; Jianpeng Dou (pp. 19-23).

A method has been developed to determine acrylamide in aqueous matrices by using direct immersion solid-phase microextraction (SPME) coupled to gas chromatography–positive chemical ionization tandem mass spectrometry (GC–PCI-MS–MS) in the selected reaction monitoring (SRM) mode. The optimized SPME experimental procedures to extract acrylamide in water solutions were: use of a carbowax/divinylbenzene (CW/DVB)-coated fiber at pH 7, extraction time of 20min and analyte desorption at 210°C for 3min. A detection limit of 0.1μgL⁻¹ was obtained. The linear range was 1–1000μgL⁻¹. The relative standard deviation was 10.64% ( n=7). The proposed analytical method was successfully used for the quantification of trace acrylamide in foodstuffs such as French fries (1.2μgg⁻¹) and potato crisps (2.2μgg⁻¹).

Keywords: Acrylamide; Solid-phase microextraction; Gas chromatography–mass spectrometry; Positive chemical ionization; French fries; Potato crisps

Headspace solid-phase microextraction of phthalic acid esters from vegetable oil employing solvent based matrix modification by Kateřina Holadová; Gabriela Prokůpková; Jana Hajšlová; Jan Poustka (pp. 24-33).

A new solvent-free analytical procedure based on headspace solid-phase microextraction (SPME) coupled to gas chromatography employing an electron capture detector (GC/ECD) or alternatively a mass spectrometric detector (GC/MSD) has been developed for the determination of phthalic acid esters (dimethyl-[DMP], diethyl-[DEP], di- n-butyl-[DnBP], butylbenzyl-[BBP], di-2-ethylhexyl-[DEHP] and di- n-octyl [DnOP] phthalate) in vegetable oils. Four different fiber coatings were evaluated, among them polydimethylsiloxane with a thickness of 100μm appeared to be the best choice for allowing extraction of the whole group of analytes. Various solvents were tested as sample matrix modification agents with the aim to facilitate the transfer of esters with low vapour pressure (DEHP and DnOP) from oil matrix into the headspace. The addition of methanol resulted in optimal set-up applicable for all phthalate esters. Temperature control and the way of sample stirring were recognized as critical points of the whole procedure. Primarily, because shaking rather than stirring of the sample is carried out using a CombiPal multipurpose sampler, the automation of the SPME method employing this instrument was found to be not fully suitable for efficient stripping of phthalates from the oil matrix into the sample headspace. Nevertheless, the optimized manual SPME method, encompassing GC/ECD or GC/MSD for the separation and detection of target analytes, offers a unique solution and showed acceptable performance characteristics: linear response in the range of 0.5–2mgkg⁻¹ and repeatability expressed as R.S.D. between 14 and 23% at the spiking level of 2mgkg⁻¹.

Keywords: Solid-phase microextraction; Phthalates; Di-2-ethylhexyl phthalate; Headspace analysis; Vegetable oil; Matrix modification

Poly(methyltetradecylsiloxane) immobilized onto silica for extraction of multiclass pesticides from surface waters by Anizio M. Faria; Liane Maldaner; César C. Santana; Isabel C.S.F. Jardim; Carol H. Collins (pp. 34-40).

A new material based on poly(methyltetradecylsiloxane) (PMTDS) thermally immobilized onto a silica support has been tested as a sorbent for the solid-phase extraction (SPE) from water of several pesticides used in soybean cultivation. The SPE methodology was developed and validated for six of these pesticides (imazethapyr, imazaquin, metsulfuron-methyl, bentazone, chlorimuron-ethyl and tebuconazole) according to the International Conference on Harmonization directives and the results were compared with those obtained with a commercial C18 SPE cartridge. The PMTDS-based sorbent gives results similar to the commercial sorbent with recoveries and precisions in agreement with directives for residue analysis. The quantification limits, after concentration, of all the pesticides evaluated were 1.0μgL⁻¹, below the levels imposed by the principal regulatory agencies. The PMTDS-based sorbent preparation is fast, easy and reproducible and the cartridges are less expensive than similar commercial SPE materials.

Keywords: Laboratory-made solid-phase extraction cartridges; Poly(methyltetradecylsiloxane); Herbicides; Soybeans; High-performance liquid chromatography-diode array detection

Multi-syringe flow injection solid-phase extraction system for on-line simultaneous spectrophotometric determination of nitro-substituted phenol isomers by Matías Manera; Manuel Miró; José Manuel Estela; Víctor Cerdà (pp. 41-49).

In this paper, a time-based multi-syringe flow injection (MSFI) approach is proposed for automated disk-based sorbent extraction of three nitro-substituted phenol isomers (2-, 3-, and 4-nitrophenol) followed by on-line simultaneous determination of individual species by diode-array spectrophotometry. The method involves the on-line enrichment of the targeted analytes from an acidic medium containing 0.1molL⁻¹ HCl onto a co-polymeric sorbent material, and the concurrent removal of potentially interfering matrix components. The nitrophenol isomers are subsequently eluted with an alkaline solution (0.7molL⁻¹ NaOH), whereupon the eluate is delivered to a diode-array spectrophotometer for recording of the spectral data in the UV–vis region. Deconvolution of strongly overlapped spectra was conducted with multivariate regression models based on multiple linear regression calibration. The analytical performance of the chemometric algorithm was characterized by relative prediction errors and recoveries.The MSFI manifold was coupled to a multiposition selection valve to set a rugged analyzer that ensures minimum operational maintenance via exploitation of membrane switching protocols. As compared with earlier methods for isolation/pre-concentration of nitro-substituted phenols based on liquid–liquid extraction, the proposed flow-through disk-based system should be regarded as an environmentally friendly approach because the use of harmful organic solvents is circumvented. Under the optimized chemical and physical variables, the 3 σ_blank detection limits for 2-, 3-, and 4-nitrophenol were 1.2, 3.2 and 0.3μmolL⁻¹ for a sample loading volume of 1.5mL, and the relative standard deviations were ≤5.0%. The flowing system, which is able to handle up to 135 samples automatically, was proven suitable for monitoring trace levels of the target isomers in mineral, tap, and seawater.

Keywords: Nitrophenol isomers; Multi-syringe flow injection analysis; Sorbent extraction; Multivariate regression modelling

The coupling of solid-phase microextraction/surface enhanced laser desorption/ionization to ion mobility spectrometry for drug analysis by Yan Wang; Sabatino Nacson; Janusz Pawliszyn (pp. 50-54).

The construction of a new solid-phase microextraction/surfaced enhanced laser desorption/ionization-ion mobility spectrometry (SPME/SELDI-IMS) device is reported here. A polypyrrole (PPY) coated SPME/SELDI fiber was employed as the extraction phase and SELDI surface to introduce analytes into the IMS. Analytes were directly ionized from the PPY coated fiber tip by a Nd:YAG laser without the addition of a matrix. Optimal experimental parameters, such as extraction conditions and laser parameters, were investigated. The use of a SPME/SELDI fiber simplified the sampling and sample preparation for IMS. Verapamil could be directly extracted from urine sample and analyzed by IMS without any further sample cleanup. This technique could be used for the analysis of drugs and other non-volatile compounds.

Keywords: Solid-phase micorextraction; Surface enhanced laser desorption/ionization; Ion mobility spectrometry; Verapamil; Polypyrrole

The coupling of solid-phase microextraction/surface enhanced laser desorption/ionization to ion mobility spectrometry for drug analysis by Yan Wang; Sabatino Nacson; Janusz Pawliszyn (pp. 50-54).

Keywords: Solid-phase micorextraction; Surface enhanced laser desorption/ionization; Ion mobility spectrometry; Verapamil; Polypyrrole

Determination of volatile phenols in wine using high-performance liquid chromatography with a coulometric array detector by R. Larcher; G. Nicolini; Chr. Puecher; D. Bertoldi; S. Moser; G. Favaro (pp. 55-60).

A new high-performance liquid chromatography method using a coulometric array detector to simultaneously analyse 4-ethylphenol, 4-ethylguaiacol, 4-vinylphenol, and 4-vinylguaiacol in wine was established. This procedure offers important advantages as it does not require sample preparation, with the exception of filtration, and performs chromatographic separation in short time, making control of wine production processes easier. The method is linear up to concentrations of 2000μgL⁻¹ and precise (R.S.D.<3%). Limits of detection are low (1–3μgL⁻¹) and suitable for analytical requirements in the oenological field. When compared to gas-chromatography-flame ionisation detection, the proposed method gives similar results with a shorter execution time.

Keywords: Wine; Vinylphenols; Ethylphenols; Electrochemical detector; Coulometric array

Fingerprint analysis of Dioscorea nipponica by high-performance liquid chromatography with evaporative light scattering detection by Chun-Zhao Liu; Hua-Ying Zhou; Qiong Yan (pp. 61-68).

High-performance liquid chromatographic method (HPLC) with evaporative light scattering detection (ELSD) coupled with microwave-assisted extraction (MAE) as an efficient sample preparation technique has been developed for fingerprint analysis of Dioscorea nipponica. The samples were separated with an Agilent C8 column using water (A) and acetonitrile (B) under gradient conditions (0–10min, linear gradient 20–40% B; 10–12min, linear gradient 40–42% B; 12–25min, isocratic 42% B) as the mobile phase at a flow rate of 1mLmin⁻¹ within 22min. The ELSD conditions were optimized at nebulizer-gas flow rate 2.7Lmin⁻¹ and drift tube temperature 90°C. Precision experiments showed relative standard deviation (R.S.D.) of peak area and retention time were better than 2.5%; inter-day and intra-day variabilities showed that R.S.D. was ranged from 0.78% to 4.74%. Limit of detection was less than 50μgmL⁻¹ and limit of quantification was less than 80μgmL⁻¹. Accuracy validation showed that average recovery was between 97.39% and 104.07%. The method was validated to achieve the satisfactory precision and recovery. Relative retention time and relative peak area were used to identify the common peaks for fingerprint analysis. There are nine common peaks in the fingerprint. The quality of seven batches of D. nipponica samples was evaluated to be qualified or unqualified by the parameters “difference�? and “total difference�? of common peaks. Furthermore, the contents of important medicinal compounds (dioscin, prodioscin and gracillin) in different batches of D. nipponica samples were determined simultaneously using the developed HPLC-ELSD method. The results indicated variation of the herb quality which might be related to different producing area, growing condition, climate, harvest time, drug processing and so on. The developed analytical procedure was proved to be a reliable and rapid method for the quality control of D. nipponica.

Keywords: Dioscorea nipponica; Evaporative light scattering detection; Fingerprint; High-performance liquid chromatography; Microwave-assisted extraction

Fingerprint analysis of Dioscorea nipponica by high-performance liquid chromatography with evaporative light scattering detection by Chun-Zhao Liu; Hua-Ying Zhou; Qiong Yan (pp. 61-68).

High-performance liquid chromatographic method (HPLC) with evaporative light scattering detection (ELSD) coupled with microwave-assisted extraction (MAE) as an efficient sample preparation technique has been developed for fingerprint analysis of Dioscorea nipponica. The samples were separated with an Agilent C8 column using water (A) and acetonitrile (B) under gradient conditions (0–10min, linear gradient 20–40% B; 10–12min, linear gradient 40–42% B; 12–25min, isocratic 42% B) as the mobile phase at a flow rate of 1mLmin⁻¹ within 22min. The ELSD conditions were optimized at nebulizer-gas flow rate 2.7Lmin⁻¹ and drift tube temperature 90°C. Precision experiments showed relative standard deviation (R.S.D.) of peak area and retention time were better than 2.5%; inter-day and intra-day variabilities showed that R.S.D. was ranged from 0.78% to 4.74%. Limit of detection was less than 50μgmL⁻¹ and limit of quantification was less than 80μgmL⁻¹. Accuracy validation showed that average recovery was between 97.39% and 104.07%. The method was validated to achieve the satisfactory precision and recovery. Relative retention time and relative peak area were used to identify the common peaks for fingerprint analysis. There are nine common peaks in the fingerprint. The quality of seven batches of D. nipponica samples was evaluated to be qualified or unqualified by the parameters “difference” and “total difference” of common peaks. Furthermore, the contents of important medicinal compounds (dioscin, prodioscin and gracillin) in different batches of D. nipponica samples were determined simultaneously using the developed HPLC-ELSD method. The results indicated variation of the herb quality which might be related to different producing area, growing condition, climate, harvest time, drug processing and so on. The developed analytical procedure was proved to be a reliable and rapid method for the quality control of D. nipponica.

Keywords: Dioscorea nipponica; Evaporative light scattering detection; Fingerprint; High-performance liquid chromatography; Microwave-assisted extraction

New methods for the direct determination of dissolved inorganic, organic and total carbon in natural waters by Reagent-Free™ Ion Chromatography and inductively coupled plasma atomic emission spectrometry by Andri Stefánsson; Ingvi Gunnarsson; Niels Giroud (pp. 69-74).

New methods have been developed and applied successfully for the determination of dissolved inorganic, organic and total carbon in water samples. The new methods utilize two instrumental setups, Reagent-Free™ Ion Chromatography (RF™-IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Dissolved inorganic carbon (DIC) was measured in untreated samples along with Cl⁻, F⁻ and SO₄²⁻ using RF™-IC and by in-line mixing with 0.1M HNO₃ to enhance CO₂ removal in the nebulizer, followed by ICP-AES analysis. Total dissolved carbon (TDC) was measured by in-line mixing with 0.1M NaOH following ICP-AES analysis. Dissolved organic carbon (DOC) was obtained as the difference between DIC and TDC. Only non-volatile organic carbon could be detected by the present method. The workable limits of detection obtained in the present study were 0.5mM (RF™-IC) and 0.1mM (ICP-AES) for dissolved inorganic and organic carbon, respectively. The power of the new methods lies in routine analysis of DIC and DOC in samples of natural waters of variable composition and salinity using analytical techniques and facilities available in most laboratories doing water sample analysis. The techniques are sensitive and precise, can be automated using gas-tight sample vials and auto-samplers, and are independent of most elemental interferences with the exception of chloride overload by saline samples when using RF™-IC. The new methods were successfully applied for analysis of DIC and DOC in selected samples of natural and synthetic waters.

Keywords: Chemical analysis; Dissolved inorganic carbon; Dissolved organic carbon; Inductively coupled plasma atomic emission spectrometry; Reagent-Free™ Ion Chromatography

Application of a validated stability-indicating densitometric thin-layer chromatographic method to stress degradation studies on moxifloxacin by Sanjay K. Motwani; Roop K. Khar; Farhan J. Ahmad; Shruti Chopra; K. Kohli; S. Talegaonkar (pp. 75-82).

A simple, sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic (HPTLC) method for densitometric determination of moxifloxacin both as a bulk drug and from pharmaceutical formulation was developed and validated as per the International Conference on Harmonization (ICH) guidelines. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase and the mobile phase consisted of n-propanol–ethanol–6M ammonia solution (4:1:2, v/v/v). Densitometric analysis of moxifloxacin was carried out in the absorbance mode at 298nm. Compact spots for moxifloxacin were found at R_f value of 0.58±0.02. The linear regression analysis data for the calibration plots showed good linear relationship with r=0.9925 in the working concentration range of 100–800ngspot⁻¹. The method was validated for precision, accuracy, ruggedness, robustness, specificity, recovery, limit of detection (LOD) and limit of quantitation (LOQ). The LOD and LOQ were 3.90 and 11.83ngspot⁻¹, respectively. Drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment and photodegradation. All the peaks of degradation products were well resolved from the standard drug with significantly different R_f values. Statistical analysis proves that the developed HPTLC method is reproducible and selective. As the method could effectively separate the drug from its degradation products, it can be employed as stability-indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of the acidic and alkaline degradation processes at different temperatures. Arrhenius plot was constructed and apparent pseudo-first-order rate constant, half-life and activation energy were calculated. In addition the pH-rate profile for degradation of moxifloxacin in constant ionic strength buffer solutions within the pH range 1.2–10.8 was studied.

Keywords: Moxifloxacin; High-performance thin-layer chromatography; Stability indicating; Stress degradation; Method validation; Kinetics of degradation; pH-rate profile

Front face fluorescence spectroscopy as a tool for the assessment of egg freshness during storage at a temperature of 12.2°C and 87% relative humidity by Romdhane Karoui; Robert Schoonheydt; Eddy Decuypere; Bart Nicolaï; Josse De Baerdemaeker (pp. 83-91).

The objective of this study was to investigate intrinsic fluorophores of thick albumen and egg yolk in order to assess egg freshness during storage at a temperature of 12.2°C and 87% relative humidity (RH). A total of 126 intact brown-shelled eggs of the same flock (29 weeks of age) were stored for 1, 6, 8, 12, 15, 20, 22, 26, 29, 33, 40, 47 and 55 days. The emission fluorescence spectra of aromatic amino acids and nucleic acids (AAA+NA) (excitation: 250nm; emission: 280–450nm), fluorescent Maillard reaction products (FMRP) (excitation: 360nm; emission: 380–580nm) and the excitation spectra of vitamin A (emission: 410nm; excitation: 270–350nm) were scanned on thick albumen and egg yolk. Among the intrinsic fluorophores, only the principal component analysis (PCA) applied on the vitamin A fluorescence spectra allowed a good identification of eggs as a function of their storage time. Factorial discriminant analysis (FDA) was then applied on the first five principal components (PCs) of the PCA applied on each spectral data set. Regarding AAA+NA recorded on thick albumen, correct classification of 69.4% and 63.9% was observed for the calibration and validation sets, respectively. Quite similar results were obtained on AAA+NA scanned on egg yolks. The best results were obtained with vitamin A fluorescence spectra since 97.7% and 85.7% of the calibration and validation sets was obtained, respectively. These results showed that vitamin A fluorescence spectra provide useful fingerprints, mainly allow the identification of eggs during storage and could be considered as a powerful intrinsic probe for the evaluation of egg freshness.

Keywords: Thick albumen; Egg yolk; Freshness; Fluorescence; Chemometric

Simultaneous determination of glycols based on fluorescence anisotropy by F. García Sánchez; A. Navas Díaz; M.M. López Guerrero (pp. 92-97).

Simultaneous determination of non-fluorescent glycols in mixtures without separation or chemical transformation steps is described. Two methods based in the measure of fluorescence anisotropy of a probe such as fluorescein dissolved in the analyte or analyte mixtures are described. In the first method, the anisotropy spectra of pure and mixtures of analytes are used to quantitative determination (if the fluorophor concentration is in a range where fluorescence intensity is proportional to concentration). In the second method, a calibration curve anisotropy–concentration based on the application of the Perrin equation is established. The methods presented here are capable of directly resolving binary mixtures of non-fluorescent glycols on the basis of differences on the fluorescence anisotropy of a fluorescence tracer. Best analytical performances were obtained by application of the method based on Perrin equation. This method is simple, rapid and allows the determination of mixtures of glycols with reasonable accuracy and precision. Detection limits are limited by the quantum yield and anisotropy values of the tracer in the solvents. Recovery values are related to the differences in anisotropy values of the tracer in the pure solvents. Mixtures of glycerine/ethylene glycol (GL/EG), ethylene glycol/1,2-propane diol (EG/1,2-PPD) and polyethylene glycol 400/1,2-propane diol (PEG 400/1,2-PPD) were analysed and recovery values are within 95–120% in the Perrin method. Relative standard deviation are in the range 1.3–2.9% and detection limits in the range 3.9–8.9%.

Keywords: Fluorescence anisotropy; Glycerine; Ethylene glycol; 1,2-Propane diol; Polyethylene glycol 400

Simultaneous determination of glycols based on fluorescence anisotropy by F. García Sánchez; A. Navas Díaz; M.M. López Guerrero (pp. 92-97).

Keywords: Fluorescence anisotropy; Glycerine; Ethylene glycol; 1,2-Propane diol; Polyethylene glycol 400

Flow injection chemiluminescence determination of nitrofurazone in pharmaceutical preparations and biological fluids based on oxidation by singlet oxygen generated in N-bromosuccinimide–hydrogen peroxide reaction by Jianxiu Du; Liang Hao; Yinhuan Li; Jiuru Lu (pp. 98-102).

A simple flow injection chemiluminescence (FI-CL) method was proposed for the determination of nitrofurazone. Strong CL signal was generated during the reaction of nitrofurazone with H₂O₂ and N-bromosuccinimide (NBS) in alkaline condition. The CL signal was proportional to the nitrofurazone concentration in the range 1.0×10⁻⁷ to 1.0×10⁻⁵gmL⁻¹. The detection limit was 2×10⁻⁸gmL⁻¹ nitrofurazone and the relative standard deviation was less than 4% (6.0×10⁻⁶gmL⁻¹ nitrofurazone, n=11). The proposed method was successfully applied to the determination of nitrofurazone in compound furacillin nasal drops, human plasma and urine samples. The CL reaction mechanism was also discussed briefly. Singlet oxygen generated in the reaction between H₂O₂ and NBS was suggested to be participated in the CL reaction.

Keywords: Nitrofurazone; Chemiluminescence; Flow injection; Singlet oxygen

Gas-diffusion flow injection determination of Hg(II) with chemiluminescence detection by Nazanin Amini; Spas D. Kolev (pp. 103-108).

A gas-diffusion flow injection method for the chemiluminescence detection of Hg(II) based on the luminol–H₂O₂ reaction was developed. The analytical procedure involved the injection of Hg(II) samples and standards into a 1.50M H₂SO₄ carrier stream, which was subsequently merged with a reagent stream of 0.60% (w/v) SnCl₂ in 1.50M H₂SO₄ to reduce Hg(II) to metallic Hg. The gas-diffusion cell was thermostated at 85°C to enhance the vaporisation of metallic Hg. Mercury vapour, transported across the Teflon membrane of the gas-diffusion cell into the acceptor stream containing 1.00×10⁻⁴M KMnO₄ in 0.30M H₂SO₄, was oxidised back to Hg(II). The acceptor stream was merged with a reagent stream containing 2.50M H₂O₂ in deionised water and then the combined stream was merged with another reagent stream containing 7.50×10⁻³M luminol in 3.00M NaOH at a confluence point opposite to the photomultiplier tube of the detection system. The chemiluminescence intensity of the luminol–H₂O₂ reaction was enhanced by the presence of Hg(II) in the acceptor stream. The corresponding increase was related to the original concentration of Hg(II) in the samples and standards. Under optimal conditions, the chemiluminescence gas-diffusion flow injection method was characterised by a linear calibration range between 1μgL⁻¹ and 100μgL⁻¹, a detection limit of 0.8μgL⁻¹ and a sampling rate of 12 samples per hour. It was successfully applied to the determination of mercury in seawater and river samples.

Keywords: Gas-diffusion flow injection analysis; Mercury determination; Cold vapour; Chemiluminescence detection; Luminol–permanganate reaction; Luminol–hydrogen peroxide reaction

Gas-diffusion flow injection determination of Hg(II) with chemiluminescence detection by Nazanin Amini; Spas D. Kolev (pp. 103-108).

Keywords: Gas-diffusion flow injection analysis; Mercury determination; Cold vapour; Chemiluminescence detection; Luminol–permanganate reaction; Luminol–hydrogen peroxide reaction

Production of artifact methylmercury during the analysis of certified reference sediments: Use of ionic exchange in the sample treatment step to minimise the problem by Alejandra Delgado; Ailette Prieto; Olatz Zuloaga; Alberto de Diego; Juan Manuel Madariaga (pp. 109-115).

Production of artifact methylmercury (MeHg⁺) during the analysis of two certified reference sediments, CRM-580 and IAEA-405, was investigated. Leaching of the analyte from the solid sample was achieved by ultrasound assisted acidic extraction. The aqueous leachate was either ethylated (NaBEt₄) or phenylated (NaBPh₄) using acetic/acetate or citric/citrate to buffer the solution. Preconcentration of the volatile compounds was carried out by extraction with an organic solvent ( n-hexane) or solid phase microextraction (SPME). MeHg⁺ was finally separated and detected by gas chromatography with atomic emission or mass spectrometry detection (GC–MIP-AED or GC–MS). In all the cases the concentrations obtained for MeHg⁺ in the CRM-580 were significantly higher than the certified value. For the IAEA-405, however, the MeHg⁺ concentration found was always statistically indistinguishable from the certified value. Experiments were also conducted with synthetic samples, such as aqueous mixtures of MeHg⁺ and inorganic mercury (Hg²⁺) or silica-gel spiked with both compounds. The methylation rates found (defined as the percentage of Hg²⁺ present in the sample which methylates to give artifact MeHg⁺) ranged from not observable (in certain synthetic aqueous mixtures) to 0.57% (analysis of CRM-580 under certain conditions). As the amount of Hg²⁺ available in the sample seems to be the main factor controlling the magnitude of the artifact, several experiments were conducted using an ionic exchange resin (Dowex M-41) in order to minimise the concentration of this chemical in the reaction medium. First, a hydrochloric leachate of the sample was passed through a microcolumn packed with the exchanger. Second, the resin was mixed with the sample prior to extraction with HCl. In both cases, the predominant Hg²⁺ species, HgCl₄²⁻, was adsorbed on the resin, whereas MeHg⁺, mainly as MeHgCl, remained in solution. Following the second option, a new method to analyse MeHg⁺ in conflictive matrices like certain sediments was proposed. This approach produced better results for the CRM-580, but a MeHg⁺ concentration slightly, but statistically significant, higher than the reference value was still obtained.

Keywords: Methylmercury; Sediments; Certified reference materials; Artifact methylmercury; Ionic exchange

A rapid and reliable method for Pb isotopic analysis of peat and lichens by laser ablation-quadrupole-inductively coupled plasma-mass spectrometry for biomonitoring and sample screening by M.E. Kylander; D.J. Weiss; T.E. Jeffries; B. Kober; A. Dolgopolova; R. Garcia-Sanchez; B.J. Coles (pp. 116-124).

An analytical protocol for rapid and reliable laser ablation-quadrupole (LA-Q)- and multi-collector (MC-) inductively coupled plasma-mass spectrometry (ICP-MS) analysis of Pb isotope ratios (²⁰⁷Pb/²⁰⁶Pb and²⁰⁸Pb/²⁰⁶Pb) in peats and lichens is developed. This technique is applicable to source tracing atmospheric Pb deposition in biomonitoring studies and sample screening. Reference materials and environmental samples were dry ashed and pressed into pellets for introduction by laser ablation. No binder was used to reduce contamination. LA-MC-ICP-MS internal and external precisions were <1.1% and <0.3%, respectively, on both²⁰⁷Pb/²⁰⁶Pb and²⁰⁸Pb/²⁰⁶Pb ratios. LA-Q-ICP-MS internal precisions on²⁰⁷Pb/²⁰⁶Pb and²⁰⁸Pb/²⁰⁶Pb ratios were lower with values for the different sample sets <14.3% while external precisions were <2.9%. The level of external precision acquired in this study is high enough to distinguish between most modern Pb sources. LA-MC-ICP-MS measurements differed from thermal ionisation mass spectrometry (TIMS) values by 1% or less while the accuracy obtained using LA-Q-ICP-MS compared to solution MC-ICP-MS was 3.1% or better using a run bracketing (RB) mass bias correction method. Sample heterogeneity and detector switching when measuring²⁰⁸Pb by Q-ICP-MS are identified as sources of reduced analytical performance.

Keywords: Laser ablation; Pb isotope; Environmental monitoring; Multi-collector; Biological sample; Peat; Lichen

Study and validity of¹³C stable carbon isotopic ratio analysis by mass spectrometry and²H site-specific natural isotopic fractionation by nuclear magnetic resonance isotopic measurements to characterize and control the authenticity of honey by J.F. Cotte; H. Casabianca; J. Lhéritier; C. Perrucchietti; C. Sanglar; H. Waton; M.F. Grenier-Loustalot (pp. 125-136).

Honey samples were analyzed by stable carbon isotopic ratio analysis by mass spectrometry (SCIRA-MS) and site-specific natural isotopic fractionation measured by nuclear magnetic resonance (SNIF-NMR) to first determine their potentials for characterizing the substance and then to combat adulteration. Honey samples from several geographic and botanical origins were analyzed. The δ¹³C parameter was not significant for characterizing an origin, while the ( D/ H)_I ratio could be used to differentiate certain single-flower varieties. Application of the official control method of adding a C₄ syrup (AOAC official method 998.12) to our authentic samples revealed anomalies resulting from SCIRA indices that were more negative than −1‰ (permil). A filtration step was added to the experimental procedure and provided results that were compliant with the natural origin of our honey samples. In addition, spiking with a C₄ syrup could be detected starting at 9–10%. The use of SNIF-NMR is limited by the detection of a syrup spike starting only at 20%, which is far from satisfying.

Keywords: Honey; Adulteration; Isotopic analyses; Stable carbon isotopic ratio analysis by mass spectrometry (SCIRA-MS); Site-specific natural isotopic fractionation measured by nuclear magnetic resonance (SNIF-NMR)

A multi-array sensor via the integration of acrylic molecularly imprinted photoresists and ultramicroelectrodes on a glass chip by Hui-Chi Huang; Sheng-Yu Huang; Chin-I Lin; Yu-Der Lee (pp. 137-146).

A novel multi-array sensor using molecularly imprinted photoresists (MIPhs) as the recognition element has been fabricated with good resolution, stability and selectivity. The versatility of MIPhs in patterning electrodes with desirable configurations has been demonstrated in our lab previously. Herein, the conventional three-electrode cell was miniaturized within a confined space by taking advantage of photolithography. A novel series of acrylic MIPhs with a resolution of 20μm were utilized to construct MIPh-based chips (MIPCs), which can discriminate albuterol from the interfering analogies, such as clenbuterol and terbutaline. Excellent selectivity toward these analytes ( β_Analytes) was obtained for the MIPCs as compared to the non-template MIPh-based and bare Pt chips. Furthermore, the peak currents of albuterol measured on MIPC have good linear relations with its concentrations in the two ranges of 1–50μM with the correlation coefficient ( R) of 0.9995, and 100–200μM with R of 0.9999 by differential pulse voltammetry (DPV). As the electrochemical cell on MIPC was reused 20 times, the peak current of albuterol changed from 2.453pA (pico-ampere) to 1.802pA with a relative standard deviation (R.S.D.) of 7.88%. The surface morphologies of molecularly imprinted and non-imprinted layers (observed by SEM and AFM) also displayed significantly different features. Because of small size, light weight and high specificity towards the template molecule, the multi-array sensor developed in this work is potentially useful for determining trace electroactive species either in vitro or in vivo.

Keywords: Albuterol; Differential pulse voltammetry; Molecularly imprinted photoresists; Photolithography; Multi-array; Ultramicroelectrodes

Ion imprinted polymer based sensor for monitoring toxic uranium in environmental samples by P. Metilda; K. Prasad; R. Kala; J.M. Gladis; T. Prasada Rao; G.R.K. Naidu (pp. 147-153).

In view of the extreme toxicity of uranium and consequent stringent limits fixed by WHO and various national governments, it is essential to monitor the uranium content in the environment which is at ultratrace levels. Conventional ionophore based ion selective electrodes, barring a few, have limitations in terms of sensitivity and selectivity for the above mentioned purpose. We now propose an ion imprinted polymer (biomimetic) based potentiometric sensor by dispersing the uranyl ion imprinted polymer particles in 2-nitrophenyloctyl ether (plasticizer), which is embedded in polyvinyl chloride matrix. The sensor responds to uranyl ion over a wide concentration range of 2.0×10⁻⁸ to 1.0×10⁻²M. The limit of detection was 2.0×10⁻⁸M. It showed a good selectivity for uranyl ion over alkali, alkaline earth, transition and heavy metal cations. The sensor is successfully tested for the monitoring of toxic uranium in tap and sea water samples.

Keywords: Uranium; Ion imprinted polymer; Sensors; Potentiometry; Natural and sea waters

Ion imprinted polymer based sensor for monitoring toxic uranium in environmental samples by P. Metilda; K. Prasad; R. Kala; J.M. Gladis; T. Prasada Rao; G.R.K. Naidu (pp. 147-153).

Keywords: Uranium; Ion imprinted polymer; Sensors; Potentiometry; Natural and sea waters

A hetero-core structured fiber optic pH sensor by Atsushi Seki; Hisakazu Katakura; Toshinori Kai; Mitsuhiro Iga; Kazuhiro Watanabe (pp. 154-157).

Novel spectroscopic sensor based on a hetero-core structured fiber optic is described in this paper. The hetero-core structured fiber optic consists of multi mode fibers and a short piece of single mode fiber which was inserted in the multi mode fibers. Phenol red and/or cresol red as pH sensitive dyes were immobilized on the surface of the hetero-core portion by using sol–gel method, and the pH change detection was performed by immersing the hetero-core portion into the solution. In the case that the cresol-red immobilized fiber was immersed in the alkaline and/or acidic solution, the peak wavelength of the propagating loss spectra were about 575 and 545nm, respectively. These propagating loss spectra were similar to that of the absorbance spectra of the dye solution. In the propagating loss spectra of phenol-red immobilized fiber, these spectra were similar to that of the dye solution. The colorimetric change of the dye in the support matrix was reversible, and the response time of the sensor was within 30s.

Keywords: Hetero-core fiber optic; pH sensor; Sol–gel method; Indicator dye

A hetero-core structured fiber optic pH sensor by Atsushi Seki; Hisakazu Katakura; Toshinori Kai; Mitsuhiro Iga; Kazuhiro Watanabe (pp. 154-157).

Keywords: Hetero-core fiber optic; pH sensor; Sol–gel method; Indicator dye

Nucleic acid biosensor for detection of hepatitis B virus using 2,9-dimethyl-1,10-phenanthroline copper complex as electrochemical indicator by Xue-Mei Li; Heng-Qiang Ju; Cai-Feng Ding; Shu-Sheng Zhang (pp. 158-163).

In this study, an electrochemical DNA biosensor was developed based on the recognition of target DNA by hybridization detection. The study was carried out using glassy carbon electrode (GCE) modified with lable-free 21-mer single-stranded oligonucleotides related to hepatitis B virus sequence via covalent immobilization and [Cu(dmp)(H₂O)Cl₂] (dmp=2,9-dimethyl-1,10-phenanthroline) as an electrochemical indicator, whose sizes are comparable to those of the small groove of native double-duplex DNA. The method, which is simple and low cost, allows the accumulation of copper complex within the DNA layer. Electochemical detection was performed by cyclic voltammetry and differential pulse voltammetry over the potential range where the [Cu(dmp)(H₂O)Cl₂] was active. Numerous factors affecting the probe immobilization, target hybridization, and indicator binding reactions were optimized to maximize the sensitivity and speed the assay time. With this approach, a sequence of the hepatitis B virus could be quantified over the ranges from 8.82×10⁻⁸ to 8.82×10⁻⁷M with a linear correlation of r=0.9937 and a detection limit of 7.0×10⁻⁸M. The [Cu(dmp)(H₂O)Cl₂] signal observed from probe sequence before and after hybridization with four bases mismatch containing sequence is lower than that observed after hybridization with complementary sequence.

Keywords: Hepatitis B virus; Electrochemical deoxyribonucleic acid biosensor; 2,9-Dimethyl-1,10-phenanthroline copper; Hybridization

Potentiometric determination of the total acidity of humic acids by constant-current coulometry by Giuseppe Palladino; Diego Ferri; Carla Manfredi; Ermanno Vasca (pp. 164-173).

A straightforward method for both the quantitative and the equilibrium analysis of humic acids in solution, based on the combination of potentiometry with coulometry, is presented. The method is based on potentiometric titrations of alkaline solutions containing, besides the humic acid sample, also NaClO₄ 1M; by means of constant current coulometry the analytical acidity in the solutions is increased with a high precision, until the formation of a solid phase occurs. Hence, the total acid content of the macromolecules may be determined from the e.m.f. data by using modified Gran plots or least-squares sum minimization programs as well. It is proposed to use the p K_w value in the ionic medium as a check of the correctness of each experiment; this datum may be readily obtained as a side-result in each titration. Modelling acid–base equilibria of the HA samples analysed was also performed, on the basis of the buffer capacity variations occurring during each titration. The experimental data fit, having the least standard deviation, was obtained assuming a mixture of three monoprotic acids (HX, HY, HZ) having about the same analytical concentration, whose acid dissociation constants in NaClO₄ 1M at 25°C were p K_HX=3.9±0.2, p K_HY=7.5±0.3, p K_HZ=9.5±0.2, respectively. With the proposed method the handling of alkaline HA solutions, the titration with very dilute NaOH or HCl solutions and the need for the availability of very small volumes of titrant to be added by microburettes may be avoided.

Keywords: Humic Acids; Coulometry; Potentiometry; Total acidity determination; Acid–base constants

Potentiometric determination of the total acidity of humic acids by constant-current coulometry by Giuseppe Palladino; Diego Ferri; Carla Manfredi; Ermanno Vasca (pp. 164-173).

Keywords: Humic Acids; Coulometry; Potentiometry; Total acidity determination; Acid–base constants

Comparison of two partial least squares infrared spectrometric methods for the quality control of pediculosis lotions by J. Moros; S. Garrigues; M. de la Guardia (pp. 174-180).

Two vibrational spectroscopy procedures have been developed and compared for the direct and simultaneous determination of piperonyl butoxide and tetramethrin, the active ingredients of alcoholic capillary lotions, for hair pediculosis diseases. Nine lotions, purchased from the Spanish market, were analyzed using both, attenuated total reflectance (ATR) and transmission FT-IR measurements, and based on the use of partial least squares (PLS) multivariate calibration. A reduced set of 15 matched standards (11 for calibration and 4 for validation) was employed using both measurement modes. The spectral wave number ranges between 1757 and 1712cm⁻¹ was selected to determine tetramethrin by both, transmittance and reflectance measurements. For the analysis of piperonyl butoxide the 1513–1479cm⁻¹ and 1576–1479cm⁻¹ regions were selected for ATR and transmission measurements, respectively. Results found for commercial samples compared well with those obtained by a liquid chromatography reference method that evidenced the applicability of the proposed strategy for the analysis of commercial formulations.

Keywords: Transmission; Attenuated total reflectance; Pediculosis lotions; Piperonyl butoxide; Tetramethrin; Partial least squares calibration

Comparison of two partial least squares infrared spectrometric methods for the quality control of pediculosis lotions by J. Moros; S. Garrigues; M. de la Guardia (pp. 174-180).

Keywords: Transmission; Attenuated total reflectance; Pediculosis lotions; Piperonyl butoxide; Tetramethrin; Partial least squares calibration

Direct orthogonal signal correction as data pretreatment in the classification of clinical lots of creams from near infrared spectroscopy data by J. Luypaert; S. Heuerding; D.L. Massart; Y. Vander Heyden (pp. 181-189).

Direct orthogonal signal correction (DOSC) is applied to correct for major variance sources such as temperature effects, time influences and instrumental differences in near infrared (NIR) data. The samples analysed are creams containing different concentrations of an active drug. The final aim is to classify the samples according to their concentration of active compound. Having performed DOSC on the data, it is not necessary anymore to apply sophisticated chemometric techniques to correct for temperature or time effects and to attribute the samples to their respective concentration classes. Moreover, the application of DOSC on the NIR spectra recorded on two different instruments shows that this method can be considered as a valuable alternative for the standardisation in classification applications. Since the applied algorithm tends to overfit, in a second part of this paper, a comparison is made with an algorithm designed by Westerhuis, which should overcome this problem. Although the calibration set results show that the overfitting has been partially corrected for by the latter algorithm, the test set results did not improve significantly.

Keywords: Direct orthogonal signal correction (DOSC); Classification; Near infrared (NIR) spectroscopy; Pharmaceuticals; Creams

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Analytica Chimica Acta (v.582, #1)