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Analytica Chimica Acta (v.565, #2)

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

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n3).

Determination of low-aliphatic aldehyde derivatizatives in human saliva using polymer monolith microextraction coupled to high-performance liquid chromatography by Hui-Juan Zhang; Jing-Fang Huang; Hong Wang; Yu-Qi Feng (pp. 129-135).

In this study, a polymer monolith microextraction (PMME) using a poly (methacrylic acid–ethylene glycol dimethacrylate) (MAA–EGDMA) monolith in conjunction with high-performance liquid chromatography (HPLC) was developed for the determination of 2,4-dinitrophenylhydrazine (DNPH) derivatives of several aldehydes in human saliva. The conditions for the labeling reactions of aldehydes with DNPH and followed extraction of the derivatives were optimized. The precision, recovery and detection limits were evaluated with spiked saliva. The limits of detection ranged from 0.43 to 1.40μg/L. The inter-and intra-day relative standard deviations were less than 10%. The proposed method was successfully applied to the determination of aldehydes in saliva samples from a non-smoker, a passive smoker and a heavy smoker.

Keywords: Polymer monolith microextration; Monolithic capillary; Aldehydes; 2,4-Dinitrophenylhydrazine; HPLC

Extraction of biogenic amines and their dansyl derivatives with reverse microemulsions of bis [2-ethylhexyl] sulphosuccinate (AOT) prior to high-performance liquid chromatographic determination by L. Romero; S. Keunchkarian; M. Reta (pp. 136-144).

The ability of reverse microemulsions of the surfactant bis [2-ethylhexyl] sulphosuccinate (AOT) in heptane to extract and preconcentrate eight biogenic amines present in aqueous matrices has been explored. The “phase transfer�? method, in which the surfactant solution is contacted with an aqueous salt solution containing the analytes, has been used as the analytical methodology. The extraction efficiencies have been compared with those obtained by using the “cloud point�? extraction technique with Triton X-114 as surfactant, and with methylene chloride as a typical extracting solvent. In order to improve extraction and detection as compared with the underivatized amines, the fluorescent reagent dansyl chloride has been used to obtain the more hydrophobic and thus, easily extractable dansyl derivatives. Although extraction of most of the biogenic amines is high, extraction of their dansyl derivatives is practically 100%. The procedure was successfully applied to the analysis of commercial fruit juices. The analytical methodology is sensitive, fast, simple and reproducible. The LOD were in the vicinity of 1 and 2pmol, which is similar or better than other techniques. The micellar phase is compatible with reverse phase HPLC mobile phases, which allow direct injection of the analyte after extraction. This is an advantage over solid phase extraction (SPE), where incomplete recovery can occur. Moreover, AOT showed to be better extracting surfactant for biogenic amines (and their corresponding dansyl derivatives) than Triton X-114 at the same concentration.

Keywords: Micellar extraction; Reverse microemulsions; AOT; Biogenic amines; Triton X-114; Cloud point extraction

Preconcentration of copper using double-imprinted polymer via solid phase extraction by Ebru Birlik; Arzu Ersöz; Adil Denizli; Rıdvan Say (pp. 145-151).

The aim of this study is to prepare double-imprinted polymers which can be used for the selective removal of Cu(II) ions from synthetic waters. Chitosan-succinate (CS) was choosen as the metal complexing polymer. In the first step, chitosan was modified with succinic anhydrides. Modified chitosan was complexed with copper(II) ions and then reacted with 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS). In the prepared imprinted sorbent, both Cu(II) and AAPTS were used as templates. Then polymeric beads were crosslinked with tetraethoxysilane (TEOS). After that, the template (i.e., Cu(II) ions) was removed using 0.1M HNO₃ solution. These Cu(II)-imprinted microbeads were used in the adsorption–desorption process. The effect of initial concentration of metal, the adsorption equilibria and the pH of the medium on adsorption capacity of Cu(II)-imprinting sorbents were studied. The maximum adsorption capacity and the relative selectivity coefficients of imprinted beads for Cu(II)/Zn(II), Cu(II)/Ni(II) and Cu(II)/Co(II) were also calculated. The double-imprinted polymers could be used many times without decreasing their adsorption capacities significantly.

Keywords: MISPE; Double-imprinted; Copper determination; Chitosan; Preconcentration; Sol–gel

Application of a new water-soluble polyethylenimine polymer sorbent for simultaneous separation and preconcentration of trace amounts of copper and manganese and their determination by atomic absorption spectrophotometry by Fatemeh Sabermahani; Mohammad Ali Taher (pp. 152-156).

In this work, a water-soluble polymer, polyethylenimine (PEI) was used for the simultaneous separation and preconcentration of trace Cu and Mn prior to their determination by flame atomic absorption spectrometry. For this purpose, the sample and the PEI solution were mixed and the metal-bound polymer was precipitated by adding acetone. The precipitate was separated and dissolved in a minimum amounts of water and aspirated into a flame AAS. By increasing the ratio of the volumes of sample to water used in dissolving the precipitate, the analyte elements were concentrated as needed. The sorption is quantitative in the pH ≥6. Detection limits were 5.2μg/L for Cu and 5.4μg/L for Mn. This method is simple, fast and precise.

Keywords: New water-soluble polyethylenimine polymer sorbent; Simultaneous separation and preconcentration; Copper and manganese; Atomic absorption spectroscopy

Acid–base properties of silica-based ion-exchanger having covalently bonded aminodi(methylphosphonic) acid by V.N. Zaitsev; L.S. Kostenko; N.G. Kobylinskaya (pp. 157-162).

Acid–base properties of an organophosphorous silica-based ion-exchanger with covalently bonded complexone groups— N-propylaminodi(methylphosphonic) acid (AdPA-SiO₂) were studied. By comparison of AdPA-SiO₂ chemical analysis and data of pH and conductometric titration it was demonstrated that the composition of immobilised layer differ from sample to sample and might consist of 60–88% aminodi(methylphosphonic) acid and 12–40% of residual aminopropyl groups. Regardless of the multifunctional nature of AdPA-SiO₂ interfacial layer, its acid–base properties can be predicted. All studied AdPA-SiO₂ samples have the properties of strong multiprotic H₄L acids with pK₁<2.6. Incomplete transformation of amino groups to aminodiphosphonic acid plays the key role in determination of the conditions of AdPA-SiO₂ ionisation in neutral and weak-basic media. Linear correlation was found for pK₂ and amine-to-acid conversion degree ( ω) with pK₂=8.8−4.0 ω. It allows us to determine the conditions of AdPA ionisation for all AdPA-SiO₂ samples. The established correlation can be used to check the quality (the degree of interfacial layer heterogeneity) of AdPA-SiO₂. The final measurable ionisation constant for AdPA-SiO₂, pK₃=7.9±0.6 is 2-orders of magnitude higher then acidity constant for AdPA homogeneous analogue. It seems that such reduction is caused by increase of electro static interaction between movable counter-ions and negatively charged surface groups. Conductometric study of AdPA-SiO₂ also suggests firm fixation of counter-ions in the interfacial layer.

Keywords: Chemically modified silica; Complexing silicas; Ion-exchangers; Organophosphorus complexones; Acid–based heterogeneous equilibrium; Immobilised layer composition

Fast high performance liquid chromatography analysis in lipidomics: Separation of radiolabelled fatty acids and phosphatidylcholine molecular species using a monolithic C₁₈ silica column by J.-F. Merlin; J. Gresti; S. Bellenger; M. Narce (pp. 163-167).

HPLC procedures using conventional C₁₈ columns are usually used to separate simple and complex lipid mixtures but these methods of separation remain often laborious and very slow. Here, monolithic columns were successfully applied to separate lipids – radiolabelled fatty acid mixtures and individual phosphatidylcholine (PC) molecular species. For that, isocratic elution was performed using two Chromolith™ Performance RP-18e columns connected in series. Detection was achieved by online measurement of radioactivity for radiolabelled fatty acids and by UV absorbance at 205nm for PC molecular species. The performances of such silica rods were compared to conventional reverse-phase silica columns. Monolithic stationary phase separated radiolabelled fatty acids and PC molecular species two times and four times faster, respectively. In each analysis, monolithic columns allowed better separation efficiency per unit of time, with lower inlet pressure. The main advantages of this method for lipid separation are that, under isocratic conditions, it is simpler and much faster, while remaining accurate and selective when compared to conventional methods. Therefore, monolithic columns may represent a powerful tool for the near future in the field of lipidomics.

Keywords: Abbreviations; ACN; acetonitrile; ChCl3; chloroform; MeOH; methanol; PC; phosphatidylcholine; RP-HPLC; reverse-phase liquid chromatography; D6D; delta-6 desaturase; SCD1; stearoyl CoA desaturaseHPLC; Fatty acid; Desaturation; Phosphatidylcholine molecular species; Monolithic column; Lipidomics

2-(2-Phenyl-1 H-phenanthro-[9,10- d]imidazole-1-yl)-acetic acid (PPIA) and its application for determination of amines by high performance liquid chromatography with fluorescence detection and identification with mass spectroscopy/atmospheric pressure chemical ionization by Jinmao You; Xianen Zhao; Yourui Suo; Honglun Wang; Yulin Li; Jing Sun (pp. 168-177).

A simple, sensitive, and mild method for the determination of amino compounds based on a condensation reaction with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC·HCl) as the dehydrant with fluorescence detection has been developed. Amines were derivatized to their acidamides with labeling reagent 2-(2-phenyl-1 H-phenanthro-[9,10- d]imidazole-1-yl)-acetic acid (PPIA). Studies on derivatization conditions indicated that the coupling reaction proceeded rapidly and smoothly in the presence of a base catalyst in acetonitrile to give the corresponding sensitively fluorescent derivatives with an excitation maximum at λ_ex 260nm and an emission maximum at λ_em 380nm. The labeled derivatives exhibited high stability and were enough to be efficiently analyzed by high-performance liquid chromatography. Identification of derivatives was carried out by online post-column mass spectrometry (LC/APCI–MS/MS) and showed an intense protonated molecular ion corresponding m/ z [MH]⁺ under APCI in positive-ion mode. At the same time, the fluorescence properties of derivatives in various solvents or at different temperature were investigated. The method, in conjunction with a gradient elution, offered a baseline resolution of the common amine derivatives on a reversed-phase Eclipse XDB-C₈ column. LC separation for the derivatized amines showed good reproducibility with acetonitrile–water as mobile phase. Detection limits calculated from 0.78pmol injection, at a signal-to-noise ratio of 3, were 3.1–18.2fmol. The mean intra- and inter-assay precision for all amine levels were <3.85% and 2.11%, respectively. Excellent linear responses were observed with coefficients of >0.9996. The established method for the determination of aliphatic amines from real wastewater and biological samples was satisfactory.

Keywords: HPLC; Amines; 2-(2-Phenyl-1; H; -phenanthro-[9,10-; d; ]imidazole-1-yl)-acetic acid (PPIA); Mass spectrometry

Reverse-phase high performance liquid chromatography for the determination of tiopronin in human plasma after derivatization with p-bromophenacyl bromide by Taomin Huang; Bei Yang; Yingjia Yu; Xiaowei Zheng; Gengli Duan (pp. 178-182).

In the study, we developed a simple, rapid and sensitive method for the determination of tiopronin (TP) in human plasma, which was based on derivatization with p-bromophenacyl bromide ( p-BPB) followed by liquid–liquid extraction and reverse-phase HPLC-UV detection. For the first time, the p-BPB was introduced into the derivatization of TP. The thiol group of TP was trapped with p-BPB to form a TP- p-BPB adduct, which can be very suitable for UV detection. From acidified plasma samples, the derivatized TP was extracted with 5mL dichloromethane. Effective chromatographic separation was achieved using a C18 column (DIAMONSIL 150mm×4mm i.d., 5μm) based on an acetonitrile–water–trifluoroacetic acid (40:59.88:0.12, v/v/v) elution at a flow-rate of 1mL/min. The IS and the derivatized TP were detected at 263nm. No endogenous substances were found to interfere. The limit of quantification for derivatized TP (TP- p-BPB) in plasma was 40ng/mL. The calibration curve for the derivatized TP showed linearity in the range 0.04–4μg/mL with a regression coefficient corresponding to 0.9991 and the coefficient of the variation of the points of the calibration curve being lower than 10%. Extraction recoveries of the derivatized TP in plasma were greater than 72%. The method was suitably validated and successfully applied to determination of TP in human plasma samples.

Keywords: Tiopronin (TP); Reverse-phase high performance liquid chromatography (HPLC); Derivatization; p; -Bromophenacyl bromide (; p; -BPB)

Separation of catecholamines by microchip electrophoresis with a simple integrated laser-induced fluorescence detector by Hai-Fang Li; ZongWei Cai; Jin-Ming Lin (pp. 183-189).

A simple microchip electrophoresis–laser-induced fluorescence device was constructed and used for separation and determination of catecholamines. On the fabricated glass chip, an extra optical fiber insertion channel, which was perpendicular and extremely close to the separation channel, was directly integrated by nothing operations more than design features on the photomask. The utilization of optical fiber to transmit the excitation light and the integration fiber channel make the fluorescence detection system simple and disposable. For electrophoresis, optimization of separation conditions was investigated for reaching high separation efficiency and sensitivity. A separation efficiency as high as 10⁶ theoretical plate numbers could be obtained for the analytes.

Keywords: Microchip electrophoresis; Laser-induced fluorescence; Optical fiber; Catecholamines

Simultaneous determination of organic acids in beverages by capillary zone electrophoresis by Inés Mato; José F. Huidobro; Jesús Simal-Lozano; M Teresa Sancho (pp. 190-197).

A rapid, reliable and simple capillary zone electrophoresis method for the determination of organic acids in beverages was developed. The complete separation of oxalic, formic, tartaric, malic, succinic, maleic, glutaric, pyruvic, acetic, lactic, citric, butyric, benzoic, sorbic, ascorbic and gluconic acids can be achieved in less than 3.5min with a simple electrolyte composed by phosphate as the carrier buffer (7.5mM NaH₂PO₄ and 2.5mM Na₂HPO₄), 2.5mM TTAOH as electroosmotic flow modifier and 0.24mM CaCl₂ as selectivity modifier, adjusting the pH at 6.40 constant value. Injection was performed in hydrodynamic mode (30s) and the detection mode was UV direct at 185nm. The running voltage was −25kV at thermostated temperature of 25°C. The method developed has been applied to several beverage samples with only a simple dilution and filtration treatment of the sample. The proposed method is fast because the separation time decrease two, four or, even, six times the separation times of the previous reported CZE methods. It is also simple and cheap due to a low consumption of chemicals and samples. These reasons permit it to be considered adequate for routine analysis of organic acids in beverage samples.

Keywords: Organic acids; Capillary zone electrophoresis; Direct UV detection; Beverage analysis

Development and validation of a method for the determination of trace alkylphenols and phthalates in the atmosphere by Zhiyong Xie; Julia Selzer; Ralf Ebinghaus; Armando Caba; Wolfgang Ruck (pp. 198-207).

An analytical method has been developed for the simultaneous extraction and determination of trace tertiary octylphenol ( t-OP), technical nonylphenol isomers (NP), nonylphenol monoethoxylate isomers (NP1EO) and seven phthalates in the atmosphere using gas chromatography–mass spectrometry (GC–MS). High volume samples were collected using a high-volume pump equipped with a PUF/XAD-2 column for air and glass fiber filter for particles. The detection limits of the method for alkylphenols (APs) and the phthalates ranged from 0.0006 to 0.034ngm⁻³ in air. The recoveries of t-OP, NP, NP1EO and the phthalates for the entire procedure were satisfactory (>69%). The method was successfully applied to the determination of the analytes in the atmosphere samples collected over land and the ocean. The concentrations of t-OP, NP, NP1EO showed decline trends from land to the open sea, and the phthalates present over land and the North Sea were comparable. It is suggested that the atmosphere is a significant pathway for the transport of alkylphenols and the phthalates in the environment.

Keywords: GC–MS; Nonyphenol; Tertiary octylphenol; Nonylphenol monoethoxylate; Phthalate; Atmosphere

Fractionation of chlorinated and brominated persistent organic pollutants in several food samples by pyrenyl-silica liquid chromatography prior to GC–MS determination by Belén Gómara; Carmen García-Ruiz; María José González; María Luisa Marina (pp. 208-213).

A high-performance liquid chromatography (HPLC) method using a column of 2-(1-pyrenyl) ethyldimethylsilylated silica was developed in this work in order to achieve satisfactory and reproducible fractionation of polychlorinated biphenyls (PCBs) from brominated flame retardants (BFRs) (polybrominated diphenylethers, PBDEs; and polybrominated biphenyls, PBBs). After the study of different chromatographic parameters (mobile phase composition and separation temperature were the most important) an isocratic elution with isooctane:toluene (98:2, v/v) at a flow-rate of 1mL/min, a temperature of 45°C, and UV-detection at 225nm was selected for fractionation of PCBs (time region, 4.0–5.8min) from PBDEs (5.8–9.0min) and from PBBs (5.8–11.0min). The applicability of this method to food samples was demonstrated by fractionating PCBs from PBDEs in three food samples (cheese, milk, and fish). Interferences from PCBs (present in real samples at much higher concentrations than PBDEs) were removed in this way. In addition, by analysing these samples by gas chromatography–mass spectrometry (GC–MS) with and without previous fractionation we were able to observe an improvement in detection sensitivity for PBDEs after HPLC fractionation.

Keywords: Brominated and chlorinated POPs; Fractionation; PYE; HPLC

Determination of chromium, iron and selenium in foodstuffs of animal origin by collision cell technology, inductively coupled plasma mass spectrometry (ICP-MS), after closed vessel microwave digestion by Vincent Dufailly; Laurent Noël; Thierry Guérin (pp. 214-221).

The determination of chromium (⁵²Cr), iron (⁵⁶Fe) and selenium (⁸⁰Se) isotopes in foodstuffs of animal origin has been performed by collision cell technology (CCT) mode using an inductively coupled plasma mass spectrometry (ICP-MS) as detector after closed vessel microwave digestion. To significantly decrease the argon-based interferences at mass to charge ratios ( m/ z): 52 (⁴⁰Ar¹²C), 56 (⁴⁰Ar¹⁶O) and 80 (⁴⁰Ar⁴⁰Ar), the gas-flow rates of a helium and hydrogen mixture used in the hexapole collision cell were optimised to 1.5mlmin⁻¹ H₂ and 0.5mlmin⁻¹ He and the quadrupole bias was adjusted daily between −2 and −15mV. Limits of quantification (LOQ) of 0.025, 0.086 and 0.041mgkg⁻¹ for Cr, Fe and Se, respectively, in 6% HNO₃ were estimated under optimized CCT conditions. These LOQ were improved by a factor of approximately 10 for each element compared to standard mode.Precision under repeatability, intermediate precision reproducibility and trueness have been tested on nine different certified reference materials in foodstuffs of animal origin and on an external proficiency testing scheme. The results obtained for chromium, iron and selenium were in all cases in good agreement with the certified values and trueness was improved, compared to those obtained in standard mode.

Keywords: Inductively coupled plasma mass spectrometry; Collision cell; Microwave digestion; Foodstuffs

Examination of precipitation chemistry and improvements in precision using the Mg(OH)₂ preconcentration inductively coupled plasma mass spectrometry (ICP-MS) method for high-throughput analysis of open-ocean Fe and Mn in seawater by Mak A. Saito; David L. Schneider (pp. 222-233).

The chemistry of magnesium precipitation preconcentration of Fe, Mn, and Co from seawater was investigated, and this analytical technique was adapted for use with the Element-2 inductively coupled plasma mass spectrometer (E2 ICP-MS). Experiments revealed that the scavenging efficiency of Mn using the precipitation protocol described here was ∼95% and similar to that previously observed with Fe. In contrast, the scavenging efficiency of Co was three-fold lower than that of Fe and Mn, resulting in poor recovery. An increase in sample size to 13mL led to several desired effects: (1) an increase in the Fe and Mn signals allowing a final dilution of samples to 0.5mL and the use of an autosampler, (2) an increase in precision to ∼1–2.5% R.S.D., and (3) an increase in signal relative to the blank. Experiments suggest metal concentration from seawater occurs during the formation of Mg(OH)₂ precipitate, whereas P was scavenged by adsorption onto the Mg(OH)₂ particles. Example vertical profiles are shown for dissolved Fe and Mn from the Equatorial Pacific.

Keywords: ICP-MS; Iron; Manganese; Cobalt; Magnesium co-precipitation; Seawater; Mg(OH); ₂

Aqueous ammonia as matrix effect suppressor in determination of noble metals by electrothermal atomic absorption spectrometry: A novel approach by Daria G. Filatova; Olga A. Shiryaeva; Nikita B. Zorov; Yuri A. Karpov (pp. 234-239).

A simple, fast and precise method for the electrothermal atomic absorption spectrometry (ETAAS) determination of Au(III), Ag(I), Pd(II) and Pt(IV) from a single aliquot at the level of 10⁻⁴% in complex samples was developed. The method is based on reducing the interfering effect of Al, Fe, Cu and Ni macrocomponents on determination of Au(III), Ag(I), Pd(II) and Pt(IV) by ETAAS by adjusting the acidic sample solution to pH 9–11 using aqueous ammonia. As a result, 98.4% of Al and 99.7% of Fe precipitated smoothly at room temperature and without additional reagents needed. Furthermore, Au(III), Ag(I), Pd(II) and Pt(IV) did not co-precipitate and remained in the soluble form as ammonia complexes. While soluble ammonia Ni and Cu complexes were also produced, they decomposed in a graphite furnace at 400°C and did not interfere with ETAAS determination of noble metals. In addition, the benefit of the ETAAS determination of Au(III), Ag(I) in the ammonia complexes is that there were no losses of Ag and Au due to the formation of insoluble AgCl and vaporization of gold and silver chlorides before atomization or incomplete dissociation in the gas phase when conventional sample treatment methods were used The relative standard deviations (R.S.D.) were in the range of 8–10% for determination of Au and Pd in aluminium catalysts, Ag in pure gold samples, and Pt in nickel tailings.

Keywords: Atomic absorption spectrometry; Matrix interferences; Electrothermal atomization; Ammonia complexes; Noble metals

Bienzymatic analytical microreactors for glucose, lactate, ethanol, galactose and l-amino acid monitoring in cell culture media by V. Vojinović; F.M.F. Esteves; J.M.S. Cabral; L.P. Fonseca (pp. 240-249).

A new alternative method for bioprocess monitoring based on bienzymatic analytical microreactors integrated in a flow injection analysis (FIA) system is described. Glucose-, alcohol-, lactate-, galactose- and l-amino acid oxidases (GO, AO, LacO, GalO and LAAO) and horseradish peroxidase (HRP) are immobilized on controlled pore glass (CPG) and used for the development of glucose, ethanol, lactate, galactose and amino acid sensors. The analytical methodology is based on HRP catalysed reaction of hydrogen peroxide produced by oxidases with phenol-4-sulfonic acid and 4-aminoantipyrine. The immobilized enzymes are characterized and used for preparation of the packed bed analytical microreactors. Shelf life and operational stability of the microeactors are determined. GO/HRP, AO/HRP and LAAO/HRP microreactors showed excellent shelf life, they could be stored and reused for more than 6 months with no or very little activity loss, while GalO/HRP and LacO/HRP could be stored for shorter periods of time (10–20 days). Operational stability of GO and LacO microreactors was very good: an equivalent to 16,900 FIA injections of 25μl to a LacO microreactor resulted in loss of half of its activity, immobilized GO was so stable that it was impossible to evaluate enzyme halflife. Immobilized GalO and LAAO lose their operational activity much faster: approximately 1400 and 8000 FIA injections of the respective substrate solution in a FIA set-up resulted in 50% activity loss. The methods with all the described microreactors were successfully validated using off-line samples from S. cerevisiae, E. coli and mesenchymal stem cell cultures with HPLC as the reference method.

Keywords: Monitoring; Analytical column; Biosensor; Galactose oxidase; Lactate oxidase; Alcohol oxidase; Glucose oxidase; Amino acid oxidase; Horseradish peroxidase; 4-Amino antipyrine

Amperometric simultaneous sensing system ford-glucose andl-lactate based on enzyme-modified bilayer electrodes by Naruhide Sato; Hirokazu Okuma (pp. 250-254).

An amperometric biosensor system which uses screen-printed electrodes to simultaneously detectd-glucose andl-lactate has been developed and applied for simple and rapid determination ofd-glucose andl-lactate levels in lactic fermenting beverages. The system was constructed from three-dimensionally layered electrodes. Taking into consideration the effects of easily oxidized substances contained in the samples, ferricyanide ions, which are electrochemically oxidized at a lower voltage, were chosen as a mediator. A linear relationship between steady-state current and concentration was found over a range of 1–100mM (d-glucose) and 1–50mM (l-lactate); the variation coefficients were 1.43% ( n=10) and 3.50% ( n=10) for thed-glucose andl-lactate sensors, respectively. When applied to lactic fermenting beverages, there was good agreement between the results obtained by the proposed sensing system and those obtained by the HPLC method. Using the proposed method, assays were completed within 5min.

Keywords: Screen-printed electrode; Biosensor; Simultaneous detection; d; -Glucose; l; -Lactate; Lactic fermenting beverage

Quality control of Metamitron in agrochemicals using Fourier transform infrared spectroscopy in the middle and near range by Javier Moros; Sergio Armenta; Salvador Garrigues; Miguel de la Guardia (pp. 255-260).

Two vibrational spectrometry-based methodologies were developed for Metamitron determination in pesticide formulations. Fourier transform-middle infrared (FT-MIR) procedure was based on the extraction of Metamitron by CHCl₃ and latter determination by peak area measurement between 1556 and 1533cm⁻¹, corrected with a two points baseline established from 1572 to 1514cm⁻¹. Fourier transform-near infrared (FT-NIR) determination was made after the extraction of Metamitron in acetonitrile and measuring the peak area between 6434 and 6394cm⁻¹ corrected using a two points baseline defined between 6555 and 6228cm⁻¹. Repeatability, as relative standard deviation, of 5 independent measurements at mgg⁻¹ concentration level, of 0.16% and 0.07% for MIR and NIR and a limit of detection of 0.03 and 0.004mgg⁻¹ were obtained for MIR and NIR, respectively.NIR determination provides a sample frequency of 120h⁻¹, higher than that found by MIR and liquid chromatographic methods (60 and 15h⁻¹, respectively). On the other hand, the NIR method reduces the solvent consumption and waste generation, to only 1ml acetonitrile per sample as compared with 3.4ml chloroform required for the MIR determination and 60ml acetonitrile used in the chromatographic reference procedure. So, vibrational procedures can be considered serious alternatives to long and time consuming chromatographic methods usually recommended for quality control of commercially available pesticide formulations.

Keywords: Metamitron; Fourier transform-middle infrared (FT-MIR) spectroscopy; Fourier transform-near infrared (FT-NIR) spectroscopy; Pesticide formulations; Agrochemicals

Flow injection determination of peroxide value in edible oils using triiodide detector by Bahruddin Saad; Wan Tatt Wai; Boey Peng Lim; Muhammad Idiris Saleh (pp. 261-270).

A flow injection analysis (FIA) method for the determination of peroxide value (PV) in edible oils is described. Oil sample (undiluted) and KI reagent were aspirated into a homemade reaction chamber where the redox reaction between iodide in the aqueous phase and hydroperoxides in the oil was effected by applying a short (typically 30s) vortex action. After allowing for the emulsified oil phase to be separated from the aqueous phase (bottom layer), an aliquot of the aqueous phase containing triiodide was next aspirated to the surface of a triiodide-selective membrane for detection. The optimized FIA procedure is linear over 0.35–28.0PV (mequiv.O₂/kg) with a detection limit of 0.32PV. Exhibiting good reproducibility (R.S.D. of 2.7% ( n=8) for the determination of 1.1PV) and sampling rate of 80samplesh⁻¹, the proposed method, unlike previous FIA procedures, completely eliminated the use of organic solvents (except the use of 2-propanol for cleaning of reaction chamber). Excellent correlation ( R²=0.9949) between the proposed method and the manual official AOCS method was found when applied to the determination of PV in diverse type of edible oils ( n=20).

Keywords: Peroxide value; Edible oil; Flow injection analysis; Triiodide electrode

Author Index (pp. 271-273).

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Analytica Chimica Acta (v.565, #2)