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Analytica Chimica Acta (v.592, #1)

Contents (pp. v).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n1).

25,000-fold pre-concentration in a single step with liquid-phase microextraction by Tung Si Ho; Terje Vasskog; Trude Anderssen; Einar Jensen; Knut Einar Rasmussen; Stig Pedersen-Bjergaard (pp. 1-8).

Hollow fiber protected liquid-phase microextraction (LPME) was developed for large sample volume extractions in a single step, with special emphasis on extraction of basic drugs from environmental waters. Five antidepressant drugs were extracted from 1100 or 100mL water samples, through approximately 50μL of dihexyl ether immobilized in the pores in the wall of a porous hollow fiber (liquid membrane), and into 20μL of 10mM HCl or HCOOH as the acceptor solution. Extractions were performed for 60 or 120min supported by magnetic stirring at 800rpm, and hereafter the acceptor solution was directly injected in HPLC-UV or HPLC-MS. Compared with earlier work on LPME from small sample volumes, both closing the hollow fiber and the type of liquid membrane was found to be critical for large volume extractions. The hollow fibers were carefully closed with a small piece of metal wire, dihexyl ether was used as the liquid membrane, and pH in the sample was adjusted to 11.8 with NaOH. Recoveries from 1100mL samples were in the range 33–49%, and enrichments were in the range 18,000–27,000 after 120min of extraction. With HPLC-MS, the drugs were detected down to the 5–30pgL⁻¹ level. Within-day precision was within 12.4–20.6% R.S.D. ( n=6), whereas between-day precision was within 17.6 and 37.2% R.S.D. Linearity was obtained in the range 1–500ngL⁻¹ with r²-values between 0.982 and 0.994. The proposed LPME system was utilized to detect the five antidepressants in wastewater from the city of Tromsø in Northern Norway.

Keywords: Sample preparation; Liquid-phase microextraction; Three-phase extraction; Basic drugs; Large sample volumes; Environmental samples

Microwave-assisted headspace single-drop microextration of chlorobenzenes from water samples by Lorena Vidal; Claudia E. Domini; Nuria Grané; Elefteria Psillakis; Antonio Canals (pp. 9-15).

A one-step and in-situ sample preparation method used for quantifying chlorobenzene compounds in water samples has been developed, coupling microwave and headspace single-drop microextraction (MW-HS-SDME). The chlorobenzenes in water samples were extracted directly onto an ionic liquid single-drop in headspace mode under the aid of microwave radiation. For optimization, a Plackett–Burman screening design was initially used, followed by a mixed-level factorial design. The factors considered were: drop volume, aqueous sample volume, stirring speed, ionic strength, extraction time, ionic liquid type, microwave power and length of the Y-shaped glass-tube. The optimum experimental conditions found from this statistical evaluation were: a 5μL microdrop of 1-hexyl-3-methylimidazolium hexafluorophosphate exposed for 20min to the headspace of a 30mL aqueous sample, irradiated by microwaves at 200W and placed in a 50mL spherical flask connected to a 25cm Y-shaped glass-tube. Under the optimised experimental conditions, the response of a high performance liquid chromatographic system was found to be linear over the range studied and with correlation coefficients ranging between 0.9995 and 0.9999. The method showed a good level of repeatability, with relative standard deviations varying between 2.3 and 8.3% ( n=5). Detection limits were found in the low μgL⁻¹ range varying between 0.016 and 0.039μgL⁻¹. Overall, the performance of the proposed method demonstrated the favourable effect of microwave sample irradiation upon HS-SDME. Finally, recovery studies from different types of environmental water samples revealed that matrix had little effect upon extraction.

Keywords: Chlorinated aromatic compounds; Microwave-assisted; Liquid phase microextraction; Ionic liquid; Experimental design; Water analysis; Sample pretreatment

Extractive liquid–liquid spectrophotometric procedure for the determination of thiocyanate ions employing the ion pair reagent amiloride monohydrochloride by A.S. Bashammakh; S.O. Bahaffi; A.A. Al-Sibaai; H.O. Al-Wael; M.S. El-Shahawi (pp. 16-23).

An accurate, inexpensive and less laborious liquid–liquid extractive spectrophotometric procedure for the determination of thiocyanate ions in aqueous media has been developed. The method has been based upon the formation of a yellow colored complex ion associate of the ion-pairing reagent 1-(3, 5 -diamino -6 -chloropyrazinecarboxyl) guanidine hydrochloride monohydrate, namely amiloride hydrochloride, DPG⁺·Cl⁻ and the thiocyanate ions in aqueous media containing HNO₃ (0.5molL⁻¹) and subsequent extraction with 4-methyl-2-pentanone. The absorption electronic spectrum of the ion associate showed one well-defined peak at λ_max 366nm. The stoichiometric mole ratio of DPG⁺·Cl⁻ to the thiocyanate ions is 1:1.The effective molar absorptivity ( ɛ) of the ion associate at λ_max 366nm is 1.1±0.1×10⁴Lmol⁻¹cm⁻¹. The extraction constants ( K_d, K_ex, and β) enabled a simple and convenient use of the developed binary ion associate for the extractive spectrophotometric determination of traces of thiocyanate ions in the aqueous media. Beer's law and Ringbom's plots are obeyed in the concentration range 0.05–10 and 0.1–7μgmL⁻¹ of the thiocyanate ions, respectively with a relative standard deviation of ±2.3%. The calculated lower limits of detection (LOD) and quantitation (LOQ) of the developed procedure for the thiocyanate ions were found equal to 0.02 and 0.066μgmL⁻¹, respectively. The developed method has been applied for the determination of trace amounts of thicyanate ions in tap-, waste- and natural water samples and compared successfully with the reported methods at the 95% confidence level. The proposed method was also applied successfully for the determination of thiocyanate ions in saliva samples.

Keywords: Thiocyanate determination; Chemical equilibrium; Amiloride hydrochloride; Solvent extraction; Spectrophotometry; Wastewater and biological samples

Investigation on the interaction of tetrachloride fluorescein–bovine serum albumin-β-cyclodextrin and the determination of protein by flow injection analysis by Xiashi Zhu; Yanyan Hu; Aiqin Gong (pp. 24-29).

In this paper, a simple and sensitive flow injection analysis (FIA) for the determination of protein with spectroscopic probe was developed. This method was based on the investigation of the interaction of tetrachloride fluorescein (2,4,5,7-tetrachloro-3,6-fluorandiol)–bovine serum albumin (BSA), the coupling reaction of protein with tetrachloride fluorescein (TCFS) which was used as a spectroscopic probe in the presence of β-cyclodextrin (β-CD). The interaction mechanism and the main factors affecting the determination were investigated in details. Under the optimum conditions, the linear range and detection limit were 0.0–28.0μgmL⁻¹ and 0.76μgmL⁻¹, respectively. The proposed method has been used to determine albumin in serum albumin with satisfactory results.

Keywords: Bovine serum albumin; Tetrachloride fluorescein; β-Cyclodextrin; Flow injection analysis

Direct determination of glyphosate using hydrophilic interaction chromatography with coulometric detection at copper microelectrode by Cláudia F.B. Coutinho; Lincoln F.M. Coutinho; Luiz H. Mazo; Suzana L. Nixdorf; Carlos A.P. Camara; Fernando M. Lanças (pp. 30-35).

A simple, rapid, and low-cost coulometric method for direct detection of glyphosate using hydrophilic interaction chromatography is presented. The principle of detection is based on the enhancement of the anodic current of copper microelectrode in the presence of complexing agents, such as glyphosate, with the formation of a soluble Cu(II) complex. Under optimized conditions, the limit of detection (S/R=3) for glyphosate was 0.1mgL⁻¹ (0.59μM) without any preconcentration method. The calibration curve has been found linear in all concentration range tested (from limit of detection to 34mgL⁻¹) with an excellent correlation coefficient (0.9999). The present method was successfully applied for the determination of glyphosate in fruit juices without any kind of extraction, clean-up, or preconcentration step, with recoveries of 92 and 90% for apple and grape juice, respectively.

Keywords: Hydrophilic interaction chromatography; Coulometric detection; Glyphosate analysis; Copper(II) complex

Fabrication and characterization of Meldola's blue/zinc oxide hybrid electrodes for efficient detection of the reduced form of nicotinamide adenine dinucleotide at low potential by S. Ashok Kumar; Shen-Ming Chen (pp. 36-44).

We report the synthesis and the electrochemical properties of hybrid films made of zinc oxide (ZnO) and Meldola's blue dye (MB) using cyclic voltammetry (CV). MB/ZnO hybrid films were electrochemically deposited onto glassy carbon, gold and indium tin oxide-coated glass (ITO) electrodes at room temperature (25±2°C) from the bath solution containing 0.1M Zn(NO₃)₂, 0.1M KNO₃ and 1×10⁻⁴MMB. The surface morphology and deposition kinetics of MB/ZnO hybrid films were studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical quartz crystal microbalance (EQCM) techniques, respectively. SEM and AFM images of MB/ZnO hybrid films have revealed that the surfaces are well crystallized, porous and micro structured. MB molecules were immobilized and strongly fixed in a transparent inorganic matrix. MB/ZnO hybrid films modified glassy carbon electrode (MB/ZnO/GC) showed one reversible redox couple centered at formal potential ( E⁰′) −0.12V (pH 6.9). The surface coverage ( Γ) of the MB immobilized on ZnO/GC was about 9.86×10⁻¹²molcm⁻² and the electron transfer rate constant (ks) was determined to be 38.9s⁻¹. The MB/ZnO/GC electrode acted as a sensor and displayed an excellent specific electrocatalytic response to the oxidation of nicotinamide adenine dinucleotide (NADH). The linear response range between 50 and 300μM NADH concentration at pH 6.9 was observed with a detection limit of 10μM (S/N=3). The electrode was stable during the time it was used for the full study (about 1 month) without a notable decrease in current. Indeed, dopamine (DA), ascorbic acid (AA), acetaminophen (AP) and uric acid (UA) did not show any interference during the detection of NADH at this modified electrode.

Keywords: Meldola's dye; Zinc oxide; Nicotinamide adenine dinucleotide oxidation; Electrocatalysis; Modified electrodes; Sensor

Use of chemically modified thermoresponsive copolymers for the detection of C-reactive protein by Vidya Raj; P.R. Hari; K. Sreenivasan (pp. 45-50).

Fluorescence intensity of N-isopropylacrylamide-glycidyl methacrylate (NIPAAm–GMA) copolymer conjugated with fluoreseinamine isomer1 was found to decrease considerably in the presence of NIPAAm–GMA copolymer containing O-phosphorylethanolamine (PEA), the specific ligand of C-reactive protein (CRP). The decrease in the emission intensity was reasoned due to the quenching of the fluorescence through the interaction of the polymer chains. The emission intensity was, however, found to increase rapidly when CRP was added in to the solution containing the polymers. The intensity of fluorescence emission was increased by five-fold in the presence of CRP as low as 20ngmL⁻¹. Albumin, the major blood protein, did not show any interference in the emission. The presence of a low molecular protein, cytochrome c, on the fluorescence spectra was also studied and this protein also found not have any influence in binding of CRP onto the ligand indicating that other proteins irrespective of their molecular weights did not influence the measurement. A definite correlation was found between the concentration of CRP and the fluorescence intensity. The method appears to be very sensitive and easy to perform. The study reflects, for the first time, the scope of using copolymeric combinations for the measurement of CRP without the use of antibody.

Keywords: C-reactive protein; N; -Isopropyl acrylamide; Glycidyl methacrylate; O; -Phosphorylethanolamine; Fluoreseinamine isomer1

Characterisation of antibodies to chloramphenicol, produced in different species by enzyme-linked immunosorbent assay and biosensor technologies by Terence Fodey; Grace Murilla; Andrew Cannavan; Christopher Elliott (pp. 51-57).

Six polyclonal antisera to chloramphenicol (CAP) were successfully raised in camels, donkeys and goats. As a comparison of sensitivity, IC₅₀ values ranged from 0.3ngmL⁻¹ to 5.5ngmL⁻¹ by enzyme-linked immunosorbent assay (ELISA) and from 0.7ngmL⁻¹ to 1.7ngmL⁻¹ by biosensor assay. The introduction of bovine milk extract improved the sensitivity of four of the antisera by ELISA and two by biosensor assay; a reduction in sensitivity of the remaining antisera ranged by a factor of 1.1–2.6. Porcine kidney extract reduced the sensitivity of all the antisera by a factor ranging from 1.1 to 7 by ELISA and a factor of 1.5 to 4 by biosensor. A low cross-reactivity with thiamphenicol (TAP) and florfenicol (FF) was displayed by antiserum G2 (1.2% and 18%, respectively) when a homologous ELISA assay format was employed. No cross-reactivity was displayed by any of the antisera when a homologous biosensor assay format was employed. Switching to a heterologous ELISA format prompted three of the antisera to display more significant cross-reactivity with TAP and FF (53% and 82%, respectively, using D1). The heterologous biosensor assay also increased the cross-reactivity of D1 for TAP and FF (56% and 129%, respectively) and of one other antiserum (G1) to a lesser degree. However, unlike the ELISA, the heterologous biosensor assay produced a substantial reduction in sensitivity (by a factor of 6 for D1).

Keywords: Abbreviations; CAP; chloramphenicol; TAP; thiamphenicol; FF; florfenicol; ELISA; enzyme-linked immunosorbent assay; HRP; horseradish peroxidase; HSA; human serum albumin; SPE; solid-phase extraction; SPR; surface plasmon resonance; NHS; N; -hydroxysuccinimide; EDC; 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochlorideChloramphenicol; Thiamphenicol; Florfenicol; Antibody production; Enzyme-linked immunosorbent assay; Biosensor

Preparation of monoclonal antibodies against a derivative of semicarbazide as a metabolic target of nitrofurazone by Aizhong Gao; Qiaolin Chen; Yu Cheng; Jing Lei; Lingwen Zeng (pp. 58-63).

Monoclonal antibodies (McAb) were produced to detect semicarbazide (SEM), a metabolite as a marker residue of nitrofurazone in animal food production. A carboxyphenyl derivative (CPSEM) of SEM was synthesized following derivatisation with 4-carboxybenzaldehyde (CBA). CPSEM was purified by recrystallization and conjugated to bovine serum albumin (BSA) or ovalbumin (OVA) as immunogen or coating antigen, respectively. Hybridomas were obtained by fusing mouse myeloma cells SP2/0 with splenocytes from the mice immunized with CPSEM–BSA. Hybridomas 1F10 and 4F2 secreting antibodies against CPSEM were obtained and subcloned. Ascites of monoclonal antibodies were prepared by injecting 1×10⁶ cells of hybridoma 1F10 into mice abdomen. McAb obtained from hybridoma 1F10 was highly specific for CPSEM and had no cross-reaction with various nitrofuran metabolites and a range of veterinary drugs. The sensitivity of the McAb to SEM was 0.01ngmL⁻¹ and the IC₅₀ value was 1.3ngmL⁻¹ (SEM in the form of CPSEM). McAb 1F10 is suitable to develop an immunoassay for SEM with sufficient sensitivity for monitoring nitrofurazone residues.

Keywords: Monoclonal antibodies; Semicarbazide; Nitrofurazone; Nitrofurazone metabolites

Enzyme immunoassay for semicarbazide—The nitrofuran metabolite and food contaminant by Kevin M. Cooper; Jeanne V. Samsonova; Laura Plumpton; Christopher T. Elliott; D. Glenn Kennedy (pp. 64-71).

Semicarbazide (SEM), the marker residue for the banned nitrofuran veterinary antibiotic nitrofurazone (NFZ), has been detected regularly in foods (47% of recent nitrofuran EU Rapid Alerts involve SEM). However, the validity of SEM as a definitive marker for NFZ has been undermined by SEM arising from other sources including azodicarbonamide, a plastics blowing agent and flour treatment additive. An inexpensive screening test for SEM in food matrices is needed—all SEM testing currently uses expensive LC–MS/MS instrumentation. We now report the first production of antibodies against derivatised SEM. A novel carboxyphenyl SEM derivative was used to raise a polyclonal antibody that has been incorporated into a semi-quantitative microtitre plate ELISA, validated according to the criteria set out in Commission Decision 2002/657/EC, for use with chicken muscle. The antibody is highly specific for derivatised SEM, cross-reactivity being 1.7% with NFZ and negligible with a wide range of other nitrofurans and poultry drugs. Samples are derivatised with o-nitrobenzaldehyde and simultaneously protease digested before extraction by cation exchange SPE. The ELISA has a SEM detection capability (CC_β) of 0.25μgkg⁻¹ when a threshold of 0.21μgkg⁻¹ is applied to the selection of samples for confirmation (lowest observed 0.25μgkg⁻¹ fortified sample, n=20), thus satisfying the EU nitrofurans’ minimum required performance limit of 1μgkg⁻¹. NFZ-incurred muscles (12) containing SEM at 0.5–5.0μgkg⁻¹ by LC–MS/MS, all screened positive by this ELISA protocol which is also applicable to egg and chicken liver.

Keywords: Semicarbazide; Nitrofurazone; Nitrofurans; Enzyme-linked immunosorbent assay; Chicken; Azodicarbonamide

Quantitative structure–retention relationship for the Kovats retention indices of a large set of terpenes: A combined data splitting-feature selection strategy by Bahram Hemmateenejad; Katayoun Javadnia; Maryam Elyasi (pp. 72-81).

A data set consisting of a large number of terpenoids, the widely distributed compounds in nature that are found in abundance in higher plants, have been used to develop a quantitative structure property relationship (QSPR) for their Kovats retention index. QSPR models are usually obtained by splitting the data into two sets including calibration (or training) and prediction (or validation). All model building steps, especially feature selection procedure, are performed using this initial splitting, and therefore the performances of the resulted models are highly dependent on the initial data splitting. To investigate the effects of data splitting on the feature selection in the current article we proposed a combined data splitting-feature selection (CDFS) methodology for QSPR model development by producing several different training/validation/test sets, and repeating all of the model building studies. In this method, data splitting is achieved many times and in each case feature selection is performed. The resulted models are compared for similarity and dissimilarity between the selected descriptors. The final model is one whose descriptors are the common variables between all of resulted models. The method was applied to QSPR study of a large data set containing the Kovats retention indices of 573 terpenoids. A final 8-parametric multilinear model with constitutional and topological indices was obtained. Cross-validation indicated that the model could reproduce more than 90% of variances in the Kovats retention data. The relative error of prediction for an external test set of 50 compounds was 3.2%. Finally, to improve the results, structure–retention relationships were followed by nonlinear approach using artificial neural networks and consequently better results were obtained.

Keywords: Terpenoids; Quantitative structure property relationship; Kovats index; Data splitting; Feature selection; Combined data splitting-feature selection

Multivariate methods on the excitation emission matrix fluorescence spectroscopic data of diesel–kerosene mixtures: A comparative study by O. Divya; Ashok K. Mishra (pp. 82-90).

Quantitative determination of kerosene fraction present in diesel has been carried out based on excitation emission matrix fluorescence (EEMF) along with parallel factor analysis (PARAFAC) and N-way partial least squares regression ( N-PLS). EEMF is a simple, sensitive and nondestructive method suitable for the analysis of multifluorophoric mixtures. Calibration models consisting of varying compositions of diesel and kerosene were constructed and their validation was carried out using leave-one-out cross validation method. The accuracy of the model was evaluated through the root mean square error of prediction (RMSEP) for the PARAFAC, N-PLS and unfold PLS methods. N-PLS was found to be a better method compared to PARAFAC and unfold PLS method because of its low RMSEP values.

Keywords: Excitation emission matrix fluorescence (EEMF); Parallel factor analysis (PARAFAC); N; -way partial least squares regression (; N; -PLS)

Comparative proteomic analysis of B. cenocepacia using two-dimensional liquid separations coupled with mass spectrometry by Kyu H. Park; John J. LiPuma; David M. Lubman (pp. 91-100).

Burkholderia cenocepacia is an important respiratory pathogen in persons with cystic fibrosis. We compared the proteomes of clinical and environmental isolates of B. cenocepacia by using a 2D liquid separation method coupled with mass spectrometry. Proteome maps of four B. cenocepacia isolates were generated. In the first dimension, 5mg of protein from each isolate was fractionated by chromatofocusing (CF) in the range of pH 4.0–7.0. In the second dimension, each CF fraction was separated by NPS-RP-HPLC. Results of the 2D liquid separation were visualized as 2D UV maps, which allowed direct comparison of proteomes with high resolution and reproducibility. From the proteomic comparison of the four isolates, 38 of 96 differentially abundant proteins were identified by peptide mass fingerprinting and MS/MS sequence analysis using a partially annotated B. cenocepacia protein database. Many of the identified proteins in the clinical isolates are involved in gene translation and bacterial virulence such as transmissibility, resistance, and quorum sensing.

Keywords: B. cenocepacia; Bacterial proteomics; Two-dimensional liquid separation; Proteome mapping; Virulence factor; Peptide mass fingerprinting

Rapid uranium preconcentration and separation method from fresh water samples for total U and²³⁵U/²³⁸U isotope ratio measurements by ICP-MS by K. Tagami; S. Uchida (pp. 101-105).

A simple and rapid method using TRU resin cartridges (Eichrom Technologies, Inc., USA) and quadrupole ICP-MS for total uranium (U) and²³⁵U/²³⁸U isotope ratio measurements in fresh water samples was investigated. After U extraction on the resin by sample solution loading, three alkaline reagents, tetramethyl ammonium hydroxide (TMAH), NaOH and NH₄OH were studied for U elution behavior from the resin cartridges and applicability of these eluates was evaluated with respect to direct introduction to ICP-MS. Among the studied eluants, TMAH showed the best results with high U recovery and no counting interferences with internal standard elements such as thallium and bismuth. Moreover, U in water samples was separated from many major and minor elements with the TRU cartridges. Almost all U was concentrated in 10mL of 0.014M TMAH in 2h using 200mL of water sample.

Keywords: TRU resin cartridge; Vacuum box extraction system; Uranium isotope ratio; Quadrupole inductively coupled plasma mass spectrometry; Tetramethyl ammonium hydroxide

Diffusive gradients in thin films technique for uranium measurements in river water by Weijia Li; Chunsheng Li; Jiujiang Zhao; R. Jack Cornett (pp. 106-113).

The diffusive gradients in thin films technique (DGT) was used for uranium measurements in water. DGT devices with Dowex resin binding phase (Dow DGT) were tested in synthetic river water, which gave 84% response to total uranium concentration. The devices were also deployed in natural river water and compared to devices with other types of binding phases, Chelex 100 resin beads imbedded in polyacrylamide hydrogel (Chelex DGT) and DE 81 anion exchange membrane (DE DGT), deployed in the same location at the same time. The measurement by Dow DGT was the lowest among the different types of the DGT devices, 45% of total uranium, while measurement by DE DGT was the highest, 98% of total uranium. The results achieved by the three types of DGT devices were explained by three DGT working mechanisms, equilibrium between complexes of resin/uranyl carbonates and complexes of resin/competitive ligands in water, effective reduction of uranyl carbonate concentration by the binding phase and dissociation of UO₂(CO₃)₂²⁻ and UO₂(CO₃)₃⁴⁻ within the diffusive layer in a DGT device. It is hoped that by deploying the DGT devices with different binding phases in natural waters, additional information on uranium speciation could be obtained.

Keywords: Diffusive gradients in thin films; Uranyl carbonate; Binding phase

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Analytica Chimica Acta (v.592, #1)