Check out our New Publishers' Select for Free Articles

Analytica Chimica Acta (v.594, #1)

Contents (pp. v-vi).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n1).

Amperometric biosensor based on Prussian Blue-modified screen-printed electrode for lipase activity and triacylglycerol determination by Ines Ben Rejeb; Fabiana Arduini; Aziz Amine; Mohamed Gargouri; Giuseppe Palleschi (pp. 1-8).

Lipase activity against triacylglycerols has been measured using an amperometric enzyme biosensor based on glycerol dehydrogenase/NADH oxidase. A Prussian Blue modified screen-printed electrode was selected as substrate for the two immobilised-enzyme systems due to their higher operative stability reported in previous works. Various parameters such as cofactor (flavin mononucleotide FMN) concentration (1mM), NAD⁺ coenzyme concentration (2mM), pH effect (phosphate buffer pH 6 to 8, Tris buffer pH 8–10) response time and storage stability were evaluated and optimised. The glycerol biosensor was then investigated for lipase activity. The system was challenged against an olive or sunflower oil real samples in order to detect fatty acids and the results were compared with those provided either by the manufacture or reference methods with good agreement.

Keywords: Screen-printed electrode; Prussian Blue; Lipase; Hydrolysis activity; Triacylglycerols

Polychlorinated biphenyls (PCBs) detection in milk samples by an electrochemical magneto-immunosensor (EMI) coupled to solid-phase extraction (SPE) and disposable low-density arrays by S. Centi; E. Silva; S. Laschi; I. Palchetti; M. Mascini (pp. 9-16).

An electrochemical immunosensor for polychlorinated biphenyl (PCB) detection based on graphite screen-printed low-density arrays and on magnetic beads is reported.The immunological reaction for the detection of PCBs is based on a direct competitive assay using alkaline phosphatase (AP) as enzymatic label. After the immunochemical recognition, the modified magnetic beads are captured by a magnet on the surface of the graphite working electrode. The electrochemical detection is thus achieved through the addition of the AP substrate (α-naphthyl-phosphate).Two different antibodies (sIgG anti-PCB28 and rIgG anti-PCB77) were tested and compared in terms of sensitivity and ability to recognise different congeners. The developed electrochemical magneto-immunosensor (EMI) was successfully combined with solid-phase extraction (SPE) for the analysis of PCBs in milk samples. In spiked samples a recovery of 80% was obtained. The proposed strategy offers great promise for rapid, simple, cost-effective, and on-site analysis of clinical, food and environmental samples, considering also that low-density arrays allow the simultaneous analysis of different processed samples.

Keywords: Disposable low-density array; Immunoassay; Magnetic separation; Polychlorinated biphenyls; Solid-phase extraction; Electrochemical detection

Improved performance of polyaniline-uricase biosensor by Kavita Arora; G. Sumana; Vibha Saxena; R.K. Gupta; S.K. Gupta; J.V. Yakhmi; M.K. Pandey; Subhash Chand; B.D. Malhotra (pp. 17-23).

Uricase has been covalently immobilized using glutaraldehyde as cross-linker onto electrochemically synthesized polyaniline (PANI) films. These PANI-uricase electrodes have been characterized using spectroscopic, cyclic voltammetry and impedance measurements. The morphology and covalent linkage of uricase lead to high enzyme loading and better shelf life. The value of the Michaelis–Menton constant obtained as 5.1×10⁻³mML⁻¹ for the immobilized uricase compared to 3.4×10⁻¹mML⁻¹ for the free uricase enzyme, suggests enhancement in affinity and/or activity of uricase attached to PANI. The influence of pH, temperature and concentration on electrode activity were studied. The enzyme electrodes were found to retain 95% of activity after 17–18 weeks when stored at 4°C. These electrodes have a response time of about 60s and have been used to measure uric acid concentration in serum. These PANI-uricase electrodes can be used for about 30 times for electrochemical measurements while retaining about 90% of its activity indicating improved performance.

Keywords: Conducting polymers; Polyaniline; Biosensor; Uric acid; Amperometric

Nanomolar detection of hydrogen peroxide on glassy carbon electrode modified with electrodeposited cobalt oxide nanoparticles by Abdollah Salimi; Rahman Hallaj; Saied Soltanian; Hussein Mamkhezri (pp. 24-31).

The electrochemical detection of H₂O₂ was investigated on a cobalt oxide nanoparticles modified glassy carbon electrode in phosphate buffer solution (pH 7). Cyclic voltammetry at potential range −1.1 to 1.1V from CoCl₂ natural aqueous solution produced well defined cobalt oxide nanopaparticles deposited on the surface of glassy carbon electrode. The surface of resulting electrode was characterized with SEM. The formation of cobalt oxyhydroxide film was investigated by cyclic voltammetry in alkaline and natural aqueous solution. The modified electrode showed well defined and stable redox couples in both alkaline and natural aqueous solution. The modified electrode showed excellent electrocatalytic activity for oxidation of hydrogen peroxide. The response to H₂O₂ on the modified electrode was examined using cyclic voltammetry and amperometry. The amperometric detection of hydrogen peroxide is carried out at 0.75V versus Ag/AgCl reference electrode in phosphate buffer solution with pH 7.4. The detection limit (S/N=3) was 0.4nM with linearity up to 6 orders of magnitude and sensitivity of 4.86μAμM⁻¹cm⁻². The response time of the electrode to achieve 95% of the steady-state current is <2s. No measurable reduction in analytical performance of the modified electrode was found by storing the electrode in ambient conditions for 20 days. This modified electrode recedes many advantages such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability of signal response during hydrogen peroxide oxidation. The immobilization of cobalt oxide nanoparticles on the surface of GC electrode appears to be a highly efficient method for the development of a new class of sensitive, stable and reproducible hydrogen peroxide electrochemical sensor.

Keywords: Electrodeposition; Cobalt oxide; Nanoparticles; Cyclic voltammetry; Electrocatalysis; H; ₂; O; ₂; Oxidation

Redox potential of tea infusion as an index for the degree of fermentation by P.C. Chen; F.S. Chang; I.Z. Chen; F.M. Lu; T.J. Cheng; R.L.C. Chen (pp. 32-36).

Redox potential of tea infusion is suggested as an index for the extent of tea fermentation. The potential was measured between platinum and Ag/AgCl electrode pair with a voltmeter with high input impedance (>1000GΩ). Phosphate buffer (10mM, pH 7.0) was used to extract the infusion and served as the supporting electrolytes for the electrochemical measurement. The reliability (the Nernst's behavior) for redox potential measurement was verified with a standard redox couple, ferricyanide/ferrocyanide. Tentative interferences from dissolved oxygen and the major coexisting reducing chemical, ascorbate, were discussed. Redox potential showed strong correlation with the fermentation process during indoor withering process. Eleven kinds of tea with different fermentation extents including Sencha, Pilochun, Pouchong, Formosa oolong tea, Lipton™ green tea, Lipton™ black tea, and Taiwanese black tea were tested.

Keywords: Potentiometric; Redox potential; Tea; Fermentation degree; Indoor withering

Cholinesterase-based dipstick assay for the detection of organophosphate and carbamate pesticides by Hwa-Young No; Young Ah Kim; Yong Tae Lee; Hye-Sung Lee (pp. 37-43).

A cholinesterase (ChE)-based dipstick-type assay for the class-specific detection of organophosphate (OP) and carbamate (CM) pesticides was developed. The principle of the assay is based on inhibition of the activity of a ChE by these two families of pesticides, which is dependent on the concentration of pesticides. The proposed assay system is composed of a test strip with an acetylcholinesterase (AChE)-coated membrane and an enzyme substrate solution. The assay protocol involves incubation of the enzyme-coated strip in the pesticide-containing sample solution followed by incubation of the sample-treated strip in a chromogenic enzyme substrate solution. The color intensity is estimated by the naked eye or a reflectometer. Of the membranes tested as the enzyme support, Hybond N⁺ was the most suitable. Among the compounds tested as the enzyme substrate, indophenyl acetate was the best. The detectable concentration range of the dipstick assay for the OP and CM pesticides was 10⁻⁶–10² and 10⁻⁶–10⁰μgmL⁻¹, respectively. The sensitivity of the dipstick assay to the oxidized form of parathion (paraoxon) was higher than to parathion. The strip showed a large matrix effect with pesticide-spiked lettuce samples, whereas it showed a small matrix effect with pesticide-spiked rice samples.

Keywords: Organophosphate pesticide; Carbamate pesticide; Cholinesterase; Dipstick

Voltammetric characterization of metal sulfide particles and nanoparticles in model solutions and natural waters by Elvira Bura-Nakić; Damir Krznarić; Darija Jurašin; George R. Helz; Irena Ciglenečki (pp. 44-51).

Voltammetric scans in sulfidic natural waters often reveal reduction peaks in the range −0.9 to −1.35V versus Ag/AgCl. These peaks have been attributed to iron sulfide complexes or clusters. However, sols containing CuS nanoparticles now also are known to produce reduction peaks in this range. Here we investigate the voltammetric behavior of two additional metal sulfides at the Hg electrode in 0.55M NaCl+0.03M NaHCO₃ electrolyte, pH=8.5. We show that Pb and Hg sulfides, either as suspended powders or as precipitated nanoparticles, also yield cathodic peaks between −0.9 and −1.35V, similar to peaks obtained with CuS and FeS. For precipitated nanoparticles, the position and shape of these reduction peaks change with ageing. Freshly formed nanoparticles produce less negative reduction peaks than aged nanoparticles. Peaks from aged nanoparticles often consist of two or more superimposed reduction peaks. When all other experimental parameters are held constant, the amount of nanoparticle analyte accumulated on the electrode increases with the amount of ageing (≤1h). Addition of EDTA or acidification followed by purging can be used to distinguish PbS nanoparticles and Fe sulfide clusters from CuS and HgS nanoparticles or from colloidal S. This test was applied to interpret −0.9 to −1.35V reduction peaks observed in two meromictic lakes. In conjunction with other evidence, this test suggests that FeS clusters are present in one case whereas colloidal S is present in the other. Interpreting −0.9 to −1.35V voltammetric peaks observed in sulfidic natural waters requires caution, but these peaks are potentially rich sources of information about trace metal speciation.

Keywords: Voltammetry; Metal sulfides; Nanoparticles; Iron sulfide clusters; Colloidal sulfur; Anoxic lakes

Simultaneous determination of suspended particulate trace metals (Co, Ni, Cu, Zn, Cd and Pb) in seawater with small volume filtration assisted by microwave digestion and flow injection inductively coupled plasma mass spectrometer by Seiji Nakatsuka; Kei Okamura; Kazuhiro Norisuye; Yoshiki Sohrin (pp. 52-60).

A new technique for the determination of suspended particulate trace metals (P–metals >0.2μm), such as Co, Ni, Cu, Zn, Cd and Pb, in open ocean seawater has been developed by using microwave digestion coupled with flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS). Suspended particulate matter (SPM) was collected from 500mL of seawater on a Nuclepore filter (0.2μm) using a closed filtration system. Both the SPM and filter were completely dissolved by microwave digestion. Reagents for the digestion were evaporated using a clean evaporation system, and the metals were redissolved in 0.8M HNO₃. The solution was diluted with buffer solution to give pH 5.0 and the metals were determined by FI-ICP-MS using a chelating adsorbent of 8-hydroxyquinoline immobilized on fluorinated metal alkoxide glass (MAF-8HQ). The procedure blanks with a filter were found to be 0.048±0.008, 10.3±0.3, 0.27±0.05, 3.3±1.8, 0.02±0.03 and 0.85±0.09ngL⁻¹ for Co, Ni, Cu, Zn, Cd and Pb, respectively ( n=14). Detection limits defined as 3 times the standard deviation of the blanks were 0.023, 0.90, 0.14, 5.3, 0.078 and 0.28ngL⁻¹ for Co, Ni, Cu, Zn, Cd and Pb, respectively. Accuracy was evaluated using certified reference materials of chlorella (NES CRM No. 3) and marine sediment (HISS-1). The method was applied to the determination of vertical distributions for P–Co, Ni, Cu, Zn, Cd and Pb in the Western North Pacific.

Keywords: Suspended particulate matter; Trace metals; Seawater; Microwave digestion; Flow injection inductively coupled plasma mass spectrometry

Determination of trace rare earth elements in environmental samples by low temperature electrothermal vaporization inductively coupled plasma mass spectrometry after synergistic extraction with dimethylheptyl methyl phosphate and 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 by Jun Yin; Bin Hu; Man He; Zucheng Jiang (pp. 61-68).

Synergistic extraction of trace rare earth elements (REEs) from nitrate solutions using mixtures of dimethylheptyl methyl phosphate (P350) and 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 (PMBP) in hexamethylene has been investigated. The factors affecting the synergistic extraction of rare earth ions, such as pH, organic solvent and phase ratio of organic phase to aqueous phase were systematically studied. The synergistic enhancement factors of P350 and PMBP for REEs were calculated to be 4.3–5.8. After the synergistic extraction, the postextraction organic phase was directly introduced into the graphite furnace for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) determination. It was found that PMBP along with P350 has an obvious chemical modification for REEs, and the limits of detection (LODs) for 15 REEs were in the range of 0.02–0.09ngL⁻¹. The proposed method was found to be more suitable for the analysis of environmental samples with complex matrix.

Keywords: Rare earth elements; Synergistic extraction; Electrothermal vaporization inductively coupled plasma mass spectrometry; Environmental samples

Flow-injection interface for on-line coupling solid-phase extraction and X-ray fluorescence measurements by J.A. Pérez-Serradilla; M.D. Luque de Castro (pp. 69-74).

A flow-injection (FI) manifold including a solid-phase extraction (SPE) mini-column has been coupled on-line to an energy-dispersive X-ray fluorescence detector (EDXRFD) by locating a lab-modified 18-μL flow-cell, 10-mm path length, connected to the SPE column by PTFE tubing of 0.5mm i.d., in the X-ray spectrometer chamber. The optical window of the flow-cell was adjusted and fixed to the X-ray irradiation zone of the spectrometer. Two PTFE tubes connected the flow-cell to the FI device and were introduced into the spectrometer chamber by a small orifice without distortion nor modification of the instrument. The SPE–EDXRFD coupling was tested for Pb and Cd aqueous solutions using Dowex 50 cation-exchange resin as sorbent, and flushing the eluate through the flow-cell for monitoring. The LODs and LOQs thus obtained were 1 and 3.2μg for Pb and 1.8 and 4.8μg for Cd, respectively; values which allow using the approach for the analysis of waste water by injecting 20mL of sample into the FI manifold. The linear dynamic ranges are a function of the sample volume circulated through the mini-column. For a sample volume of 20mL the ranges are between 1 and 4000μg for Pb and between 1.8 and 2000μg for Cd. The method was validated by the standard addition method using ground-water samples. The SPE–EDXRFD coupling enables to carry out the study of those variables influencing the SPE process – namely, the effect of the sample volume flushed through the column, concentration of analytes in the sample, amount of resin packed, breakthrough volume of the resin, elution profiles, sample pH and retention and elution flow-rates – in an automatic, cheap, fast and precise way.

Keywords: Solid-phase extraction; Flow-injection; Energy-dispersive X-ray fluorescence spectrometry; Cadmium; Lead; On-line coupling; Ion-exchange; Dowex

Solvent exchange using hollow fiber prior to separation and determination of some antioxidants by high performance liquid chromatography by Mir Ali Farajzadeh; Jan Åke Jönsson (pp. 75-80).

This study presents a simple and rapid solvent exchange procedure using a hollow fiber. Antioxidants (Irganox 1010, Irganox 1076 and Irgafos 168) and solvents such as tetrahydrofuran (THF), carbon tetrachloride and toluene were selected as model compounds and sample solvents, respectively. After injection of the sample solution into the hollow fiber and solvent evaporation, the precipitated analytes in lumen and pores of the fiber were washed with methanol (the mobile phase for separation and determination by HPLC-diode array detection) and good chromatographic peaks were obtained. The effect of different parameters such as fiber length, volumes of sample and washing solvents were investigated and the optimum conditions were selected. The repeatability of the method was tested and it was found that the relative standard deviation (R.S.D.) was less than 10% for all analytes. Also enrichment factors of 3.03, 2.21 and 1.19 times were obtained for Irganox 1010, Irganox 1076 and Irgafos 168, respectively, when 200μL sample and 50μL methanol (washing solvent) were used.

Keywords: Hollow fiber; Solvent exchange; Antioxidants; High performance liquid chromatography

Evaluation of carbon nanotubes as a solid-phase extraction adsorbent for the extraction of cephalosporins antibiotics, sulfonamides and phenolic compounds from aqueous solution by Hongyun Niu; Yaqi Cai; Yali Shi; Fusheng Wei; Jiemin Liu; Shifen Mou; Guibin Jiang (pp. 81-92).

The adsorptive potential of carbon nanotubes (single-walled carbon nanotubes and multi-walled carbon nanotubes) for solid-phase extraction of three groups of highly polar compounds (namely cephalosporins antibiotics, sulfonamides and phenolic compounds) was tested in this article. The analytes were strongly retained by the carbon nanotubes. And acceptable recoveries were obtained with the addition of ammonium acetate into eluents. The effects of solution pH on the recoveries of the antibiotics and phenolic compounds were examined. To check the retention abilities of three groups of compounds on carbon nanotubes, fixed amount of each analyte was added to different volumes (up to 500mL) of aqueous solution, and then extracted by the sorbents. Comparative studies showed that the carbon nanotubes were much superior to C₁₈ for the extraction of the highly polar analytes. For the cephalosporins antibiotics and sulfonamides, the carbon nanotubes showed stronger retention capability than graphitized carbon blacks, but for some of the phenolic compounds graphitized carbon blacks seemed to be more suitable, indicating different retention mechanisms of these analytes. To further assess the enrichment ability of carbon nanotubes for highly polar compounds, the solid-phase extraction method of multi-walled carbon nanotubes packed cartridge was well developed, and the sulfonamides were used as model compounds. Under the optimal procedures, the detection limits of sulfonamides were in the range of 27–38ngL⁻¹. The spiked recoveries from several real water samples obtained for sulfathiazole and sulfadiazine ranged from 55% to 79% and 72% to 92%, respectively, while the recoveries of sulfapyridine and sulfamethazine were in the range of 85–102%.

Keywords: Carbon nanotubes; Solid-phase extraction; Highly polar compounds

Homogeneous liquid–liquid extraction of trace amounts of mononitrotoluenes from waste water samples by Homeira Ebrahimzadeh; Yadollah Yamini; Fahimeh Kamarei; Shahab Shariati (pp. 93-100).

Homogeneous liquid–liquid extraction method was studied based on a phase separation phenomenon in a ternary solvent system. According to this procedure, mononitrotoloenes were extracted by single-phase extraction in a water/methanol/chloroform, homogeneous ternary solvent system. Methanol and chloroform were used as consolute and extraction solvents, respectively. The homogeneous solution was broken by the addition of salt and a cloudy solution was formed. After centrifugation, the fine droplets of the extraction solvent were sedimented in the bottom of the conical test tube. Analysis of the extracts was carried out by gas chromatography. The optimization procedure was performed using Box-Behnken design. The variables involved were: sample and extraction solvent volumes, consolute solvent volume and phase separator reagent concentration. Optimum results were obtained under the following conditions: sample volume of 5mL, extraction solvent volume of 55μL, consolute solvent volume of 1mL and phase separator reagent concentration; 5% (w/v). Under these conditions, the enrichment factors of 354, 311 and 300, dynamic linear ranges of 0.5–500, 1–500 and 1–500μgL⁻¹, and limit of detections (LODs) of 0.09, 0.09 and 0.1μgL⁻¹ were obtained for o-nitrotoluene, m-nitrotoluene and p-nitrotoluene, respectively. Finally, the method was successfully applied to the extraction and determination of MNTs in the waste water samples in the range of micrograms per liter with R.S.Ds.<13.2%.

Keywords: Homogeneous liquid–liquid extraction; Box-Behnken design; Mononitrotoluenes; Gas chromatography

Estimation of source spectra profiles and simultaneous determination of polycomponent in mixtures from ultraviolet spectra data using kernel independent component analysis and support vector regression by Guoqing Wang; Yu-an Sun; Qingzhu Ding; Chunhong Dong; Dexue Fu; Cunhong Li (pp. 101-106).

A method that use kernel independent component analysis (KICA) and support vector regression (SVR) was proposed for estimation of source ultraviolet (UV) spectra profiles and simultaneous determination of polycomponents in mixtures. In KICA–SVR procedure, the UV source spectra profiles were estimated using KICA, then the mixing matrix of the components were calculated using the estimated sources, and the calibration model was build using SVR based on the calculated mixing matrix. A simulated UV dataset of three-component mixtures was used to test the ability of KICA for estimating source spectra profiles from spectra data of mixtures. It was found that KICA has the potential power to estimate pure UV spectra profiles, and correlation coefficient of estimated sources correspond to the real adopted ones are better compared with that by FastICA and Infomax ICA. An UV dataset of polycomponent vitamin B was processed using the proposed KICA-SVR method. The results show that the estimated source spectra profiles are correlative with the real UV spectra of the components and chemically interpretable, and accurate results were obtained.

Keywords: Kernel independent component analysis (KICA); Support vector regression (SVR); Estimaion of source spectra profiles; Polycomponent determination; Ultraviolet spectrum (UV)

The prediction of total anthocyanin concentration in red-grape homogenates using visible-near-infrared spectroscopy and artificial neural networks by L.J. Janik; D. Cozzolino; R. Dambergs; W. Cynkar; M. Gishen (pp. 107-118).

This study compares the performance of partial least squares (PLS) regression analysis and artificial neural networks (ANN) for the prediction of total anthocyanin concentration in red-grape homogenates from their visible-near-infrared (Vis-NIR) spectra. The PLS prediction of anthocyanin concentrations for new-season samples from Vis-NIR spectra was characterised by regression non-linearity and prediction bias. In practice, this usually requires the inclusion of some samples from the new vintage to improve the prediction. The use of WinISI LOCAL partly alleviated these problems but still resulted in increased error at high and low extremes of the anthocyanin concentration range. Artificial neural networks regression was investigated as an alternative method to PLS, due to the inherent advantages of ANN for modelling non-linear systems. The method proposed here combines the advantages of the data reduction capabilities of PLS regression with the non-linear modelling capabilities of ANN. With the use of PLS scores as inputs for ANN regression, the model was shown to be quicker and easier to train than using raw full-spectrum data. The ANN calibration for prediction of new vintage grape data, using PLS scores as inputs, was more linear and accurate than global and LOCAL PLS models and appears to reduce the need for refreshing the calibration with new-season samples. ANN with PLS scores required fewer inputs and was less prone to overfitting than using PCA scores. A variation of the ANN method, using carefully selected spectral frequencies as inputs, resulted in prediction accuracy comparable to those using PLS scores but, as for PCA inputs, was also prone to overfitting with redundant wavelengths.

Keywords: Artificial neural networks; ANN; Anthocyanin; Colour; Near infrared; NIR; Partial least squares; PLS; PCA; NN-PLS

Precision of micellar electrokinetic capillary chromatography in the determination of seven antibiotics in pharmaceuticals and feedstuffs by Rade Injac; Nina Kocevar; Samo Kreft (pp. 119-127).

Validation of analytical procedures is important for their efficient and reliable application. The International Conference on Harmonisation (ICH), Food and Drug Administration (FDA) and pharmacopoeia guidelines achieved a great deal in harmonising the definitions of the required validation characteristics. It is well known that poor reproducibility limits the practical implementation of capillary electrophoresis (CE). A precision study on four different MEKC methods was performed with 11 samples, containing seven antibiotics, by two analysts, in few days, on two capillary electrophoresis instruments. Five pharmaceutical preparations and three animal feeds were used. Precision was statistically analysed using migration time, peak area and height of each compound, as well as electroosmotic front (EOF). In 25 of 31 cases, the reproducibility of peak area, peak height and migration time was good (<5%). In most cases the reproducibility of peak area was much better than the reproducibility of peak height. The worst reproducibility that we observed was 12.7% for peak height and 7.6% for peak area.

Keywords: Precision; Micellar electrokinetic capillary chromatography; Antibiotics; Feedstuffes; Pharmaceuticals

Signal processing of GC–MS data of complex environmental samples: Characterization of homologous series by Maria Chiara Pietrogrande; Mattia Mercuriali; Luisa Pasti (pp. 128-138).

Identification and characterization of homologous series by GC–MS analysis provide very relevant information on organic compounds in complex mixtures. A chemometric approach, based on the study of the autocovariance function, EACVF_tot, is described as a suitable tool for extracting molecular–structural information from the GC signal, in particular for identifying the presence of homologous series and quantifying the number of their terms. A data pre-processing procedure is introduced to transform the time axis in order to display a strictly homogenous retention pattern: n-alkanes are used as external standard to stretch or shrink the original chromatogram in order to build up a linear GC retention scale. This addition can be regarded as a further step in the direction of a signal processing procedure for achieving a systematic characterization of complex mixture from experimental chromatograms. The EACVF_tot was computed on the linearized chromatogram: if the sample presents terms of homologous series, the EACVF_tot plot shows well-defined deterministic peaks at repeated constant interdistances. By comparison with standard references, the presence of such peaks is diagnostic for the presence of the ordered series, their position can be related to the chemical structure of the compounds, their height is the basis for estimating the number of terms in the series. The power of the procedure can be magnified by studying SIM chromatograms acquired at specific m/ z values characteristic of the compounds of interest: the EACVF_tot on these selective signals makes it possible to confirm the results obtained from an unknown mixture and check their reliability.The procedure was validated on standard mixtures of known composition and applied to an unknown gas oil sample. In particular, the paper focuses on the study of two specific classes of compounds: n-alkanes and oxygen-containing compounds, since their identification provides information useful for characterizing the chemical composition of many samples of different origin. The robustness of the method was tested in experimental chromatograms obtained under unfavorable conditions: chromatograms acquired in non-optimal temperature program conditions and chromatographic data affected by signal noise.

Keywords: Abbreviations; ACVF; autocovariance function; EACVF; experimental autocovariance function; EACF; experimental autocorrelation function; SC; single componentMulticomponent mixtures; Homologous series; Time axis linearization; Hydrocarbons

Determination of Sudan dye residues in eggs by liquid chromatography and gas chromatography–mass spectrometry by Limin He; Yijuan Su; Binghu fang; Xiangguang Shen; Zhenling Zeng; Yahong Liu (pp. 139-146).

A sensitive and cheap high performance liquid chromatography (HPLC) with ultraviolet-visible (UV-VIS) was developed for the determination of Sudan dyes (I, II, III, and IV) residues in various types of eggs. The chromatographic separation was achieved on a reverse phase C₁₈ column with gradient elution, using a mobile phase of 0.1% formic acid acetonitrile/0.1% formic acid aqueous solution; detector was set at 478nm for Sudan I and 520nm for Sudan II, III and IV. The suspected egg samples were derivatized with N, O- bis (trimethylsilyl) trifluoro-acetamide and confirmed by gas chromatography–mass spectrometry (GC–MS) in EI. Mass spectra of trimethylsilyl derivatives of the Sudan dyes were built up in EI mode. Recoveries of the Sudan dyes ranged between 79.8 and 95.7% in eggs by HPLC–UV, with all the relative standard deviations of less than 5%. Limit of detection (LOD), limit of quantification (LOQ) were in the range of 4.0–4.8 and 12.3–13.8μgkg⁻¹ in eggs, respectively. Identification and confirmation could be validated in the range of 2.0–4.2μgkg⁻¹ with the GC–MS method. This method is suitable for routine fast monitoring, screening and confirmation of Sudan dyes residues in eggs, as mandated by regulatory agencies.

Keywords: Sudan dyes; Eggs; Residues; High performance liquid chromatography (HPLC); Gas chromatography–mass spectrometry (GC–MS)

Sections

Personal tools

Analytica Chimica Acta (v.594, #1)

Sections

Personal tools

Local resources

Analytica Chimica Acta (v.594, #1)