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Analytical and Bioanalytical Chemistry (v.385, #7)

Focus on Bioanalytical Chemistry in Spain by Alfredo Sanz-Medel (pp. 1153-1154).

Molecularly imprinted polymers applied to the clean-up of zearalenone and α-zearalenol from cereal and swine feed sample extracts by Javier L. Urraca; María Dolores Marazuela; María C. Moreno-Bondi (pp. 1155-1161).

A molecularly imprinted polymer prepared using 1-allylpiperazine (1-ALPP) as the functional monomer, trimethyltrimethacrylate (TRIM) as the crosslinker and the zearalenone (ZON)-mimicking template cyclododecanyl-2,4-dihydroxybenzoate (CDHB) has been applied to the clean-up and preconcentration of this mycotoxin (zearalenone) and a related metabolite, α-zearalenol (α-ZOL), from cereal and swine feed sample extracts. The extraction of ZON and α-ZOL from the food samples was accomplished using pressurized liquid extraction (PLE) with MeOH/ACN (50:50, v/v) as the extraction solvent, at 50 °C and 1500 psi. The extracted samples were cleaned up and preconcentrated through the MIP cartridge and analyzed using HPLC with fluorescence detection (λ _exc=271/ λ _em=452 nm). The stationary phase was a polar endcapped C₁₈ column, and ACN/MeOH/water 10/55/35 (v/v/v, 15 mM ammonium acetate) at a flow rate of 1.0 mL min⁻¹ was used as the mobile phase. The method was applied to the analysis of ZON and α-ZOL in wheat, corn, barley, rye, rice and swine feed samples fortified with 50, 100 and 400 ng g⁻¹ of both mycotoxins, and it gave recoveries of between 85 and 97% (RSD 2.1–6.7%, n=3) and 87–97% (RSD 2.3–5.6%, n=3) for α-ZOL and ZON, respectively. The method was validated using a corn reference material for ZON.

Keywords: Zearalenone; α-Zearalenol; Molecularly imprinted polymer; MISPE; Cereal; Swine feed

Optimization of an analytical methodology for the determination of alkyl- and methoxy-phenolic compounds by HS-SPME in biomass smoke by Francisco J. Conde; Ana M. Afonso; Venerando González; Juan H. Ayala (pp. 1162-1171).

A sampling and analysis method for the determination of 21 phenolic compounds in smoke samples from biomass combustion has been developed. The smoke is used to make smoked foods, following an artisanal procedure used in some parts of the Canary Islands. The sampling system consists of a Bravo H air sampler, two impingers, each one containing an aqueous solution of sodium hydroxide 0.1 mol L⁻¹, followed by a silica gel trap. The variables optimized to reach the best sampling conditions were volume of absorbent solution and sampling flow. Under the optimum conditions, 100 mL of absorbent solution of NaOH 0.10 mol L⁻¹ and 2 L min⁻¹ for the sampling flow, sampling efficiencies are higher than 80%. Analysis of phenolic compounds was carried out by headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography–mass spectrometry (GC-MS). Five different fiber coatings were employed in this study. By means of a central composite design, extraction time, salt concentration, and pH of the solution were optimized: 65-μm carbowax–divinylbenzene, extraction time 90 min, concentration in NaCl of 35% (m/v), and pH 2 yielded the highest response. Detection limits of phenol and their alkyl derivatives, guaiacol and eugenol, are between 1.13 and 4.60 ng mL⁻¹. 3-Methoxyphenol, 2,6-dimethoxyphenol, and vanillin have detection limits considerably higher. Good linearity (R ²≥0.98) was observed for all calibration curves in the established ranges. The reproducibility of the method (RSD, relative standard deviation) was found to oscillate between 7 and 18% (generally close or lower than 10%).

Keywords: Smoked foods; Phenolic compounds; Headspace analysis; Solid-phase microextraction; Central composite design; Gas chromatography–mass spectrometry

Development of a rapid extraction procedure for speciation of arsenic in chicken meat by Daniel Sánchez-Rodas; José Luis Gómez-Ariza; Vanesa Oliveira (pp. 1172-1177).

A rapid extraction procedure has been developed for speciation of arsenic in chicken tissue. Water, methanol–water (1:1), and methanol–chloroform (1:1) were tested as extraction media. Individual use of an ultrasonic bath, a microwave oven, or an ultrasonic probe was not sufficient for quantitative recovery of As(III), dimethylarsinate, monomethylarsonate, As(V), and arsenobetaine in spiked samples of chicken tissue. A new extraction procedure using a methanol–water mixture and a microwave oven then an ultrasonic probe enabled extraction of the arsenic species in 7 min with efficiencies ranging from 80 to 100%. HPLC–UV–HG–AFS was used for the determinations. The extraction procedure was 100% efficient when applied to real samples of chicken tissue. AsB (48±5 μg As kg ⁻¹) and one containing-arsenic feed additive, Nitarsone (227±5 μg As kg ⁻¹) were detected.

Keywords: Arsenic; Speciation; Chicken; Ultrasonic bath; Microwave oven; Ultrasonic probe; HPLC; AFS

Lead ultra-trace on-line preconcentration and determination using selective solid phase extraction and electrothermal atomic absorption spectrometry: applications in seawaters and biological samples by E. Vereda Alonso; M. T. Siles Cordero; A. García de Torres; J. M. Cano Pavón (pp. 1178-1185).

In this work, a new chelating resin [1,5-bis (2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide immobilised on aminopropyl-controlled pore glass (550 Å; PSTH-cpg) was synthesised and packed in a microcolumn which replaced the sample tip of the autosampler arm. The system was applied to the preconcentration of lead. When microliters of 10% HNO₃, which acts as elution agent, pass through the microcolumn, the preconcentrated Pb(II) is eluted and directly deposited in a tungsten-rhodium coated graphite tube. With the use of the separation and preconcentration step and the permanent modifiers, the analytical characteristics of the technique were improved. The proposed method has a linear calibration range from 0.012 to 10 ng ml⁻¹ of lead. At a sample frequency of 36 h⁻¹ with a 90 s preconcentration time, the enrichment factor was 20.5, the detection and determination limits were 0.012 and 0.14 ng ml⁻¹, respectively and the precision, expressed as relative standard deviation, was 3.2% (at 1 ng ml⁻¹). Results from the determination of Pb in biological certified reference materials were in agreement with the certified values. Seawaters and other biological samples were analysed too.

Keywords: Electrothermal atomic absorption spectrometry; On-line preconcentration; Lead; Permanent chemical modified; Seawaters; Biological samples

A sequential injection electronic tongue employing the transient response from potentiometric sensors for anion multidetermination by M. Cortina; A. Duran; S. Alegret; M. del Valle (pp. 1186-1194).

Intelligent and automatic systems based on arrays of non-specific-response chemical sensors were recently developed in our laboratory. For multidetermination applications, the normal choice is an array of potentiometric sensors to generate the signal, and an artificial neural network (ANN) correctly trained to obtain the calibration model. As a great amount of information is required for the proper modelling, we proposed its automated generation by using the sequential injection analysis (SIA) technique. First signals used were steady-state: the equilibrium signal after a step-change in concentration. We have now adapted our procedures to record the transient response corresponding to a sample step. The novelty in this approach is therefore the use of the dynamic components of the signal in order to better discriminate or differentiate a sample. In the developed electronic tongue systems, detection is carried out by using a sensor array formed by five potentiometric sensors based on PVC membranes. For the developed application we employed two different chloride-selective sensors, two nitrate-selective sensors and one generic response sensor. As the amount of raw data (fivefold recordings corresponding to the five sensors) is excessive for an ANN, some feature extraction step prior to the modelling was needed. In order to attain substantial data reduction and noise filtering, the data obtained were fitted with orthonormal Legendre polynomials. In this case, a third-degree Legendre polynomial was shown to be sufficient to fit the data. The coefficients of these polynomials were the input information fed into the ANN used to model the concentrations of the determined species (Cl⁻, $${ ext{ NO}}^{{ ext{ - }}}_{{ ext{3}}} $$ and $${ ext{HCO}}^{{ ext{ - }}}_{{ ext{3}}} $$ ). Best results were obtained by using a backpropagation neural network trained with the Bayesian regularisation algorithm; the net had a single hidden layer containing three neurons with the tansig transfer function. The results obtained from the time-dependent response were compared with those obtained from steady-state conditions, showing the former superior performance. Finally, the method was applied for determining anions in synthetic samples and real water samples, where a satisfactory comparison was also achieved.

Keywords: Electronic tongue; Artificial neural network; Sequential injection analysis; Sensor array; Anion multidetermination; Transient response

Impedimetric genosensors for the detection of DNA hybridization by A. Bonanni; M. J. Esplandiu; M. I. Pividori; S. Alegret; M. del Valle (pp. 1195-1201).

Impedance spectroscopy is proposed as the transduction principle for detecting the hybridization of DNA complementary strands. In our experiments, different DNA oligonucleotides were used as model gene substances. The gene probe is first immobilized on a graphite-epoxy composite working electrode based genosensor. Detection principle is based on changes of impedance spectra of a redox marker, the ferro/ferricyanide couple, after hybridization with target DNA. Resistance offered to the electrochemical reaction serves as the working signal, allowing for an unlabelled gene assay.

Keywords: DNA biosensor; Impedance; Capacitance; Unlabelled DNA

Flow screen-printed amperometric detection of p-nitrophenol in alkaline phosphatase-based assays by Pablo Fanjul-Bolado; María Begoña González-García; Agustín Costa-García (pp. 1202-1208).

p-Nitrophenyl phosphate is one of the most widely used substrates for alkaline phosphatase in ELISAs because its yellow, water-soluble product, p-nitrophenol, absorbs strongly at 405 nm. p-Nitrophenol is also electroactive; an oxidative peak at 0.97 V (vs. an Ag pseudoreference electrode) is obtained when a bare screen-printed carbon electrode is used. When an amperometric detector was coupled to a flow-injection analysis system the detection limit achieved for p-nitrophenol was 2×10⁻⁸ mol L⁻¹, almost two orders of magnitude lower than that obtained by measuring the absorbance of the compound. By use of this electrochemical detection method, measurement of 7×10⁻¹⁴ mol L⁻¹ alkaline phosphatase was achieved after incubation for 20 min. The feasibility of coupling immunoassay to screen-printed carbon electrode amperometric detection has been demonstrated by performing an ELISA for detection of pneumolysin, a toxin produced by Streptococcus pneumoniae, which causes respiratory infections. The method is simple, reproducible, and much more sensitive than traditional spectrophotometry.

Keywords: Alkaline phosphatase; p-Nitrophenyl phosphate/p-nitrophenol; Screen-printed carbon electrode; Flow-injection analysis

Bienzyme sensors based on novel polymethylferrocenyl dendrimers by J. Losada; M. Zamora; P. García Armada; I. Cuadrado; B. Alonso; C. M. Casado (pp. 1209-1217).

Amperometric bienzyme electrodes with horseradish peroxidase (HRP) and glucose oxidase (GOx) co-immobilized on polymethylferrocenyl dendrimers deposited onto platinum electrodes have been used for determination of the hydrogen peroxide produced by the oxidase during the enzymatic reaction. The redox dendrimers consist of flexible poly(propylenimine) dendrimer cores functionalised with octamethylferrocenyl units. The effects of dendrimer generation, the thickness of the dendrimer layer, substrate concentration, interferences, and reproducibility on the response of the sensors were investigated. The new bienzyme biosensors respond to substrate at work potential values between 200 and 50 mV (vs. SCE), have good sensitivity, and are resistant to interferences. Figure

Keywords: Polymethylferrocene; Dendrimers; Bienzyme electrodes; Horseradish peroxidase (HRP); Glucose oxidase; Amperometric biosensor

A simplified LC–DAD method with an RP-C₁₂ column for routine monitoring of three sulfonamides in edible calf and pig tissue by M. Gratacós-Cubarsí; M. Castellari; A. Valero; J. A. García-Regueiro (pp. 1218-1224).

Use of an RP-C₁₂ analytical column with a mobile phase at pH 4.5 enabled excellent chromatographic separation and quantification of sulfadiazine (SDZ), sulfamerazine (SMR), and sulfamethazine (SMZ) in edible calf and pig tissue (muscle and liver). Tissue samples were extracted with acetonitrile, centrifuged without further clean-up, and analyzed by LC–DAD. The proposed conditions are useful for a rapid and reliable screening of the SDZ, SMR, and SMZ content of calf and pig tissue at concentrations lower than the maximum residue level (MRL) (LOQ between 27 and 55 ppb). Separation of some possible SMZ metabolites should be further investigated.

Keywords: HPLC; Sulfonamides; Sulfamethazine; Muscle; Liver

A liquid chromatography–fluorimetric method for the in vitro estimation of the skin penetration of disodium phenyldibenzimidazole tetrasulfonate from sunscreen formulations through human skin by A. Balaguer; A. Salvador; A. Chisvert; M. Meliá; M. Herráez; O. Díez (pp. 1225-1232).

Disodium phenyldibenzimidazole tetrasulfonate (PDT) is a new organic UV filter with hydrophilic properties used in modern sunscreen spray formulations. The aim of this work was to develop and validate an analytical method that can be used to study skin absorption of PDT from sunscreens. Results obtained in vitro for human skin showed a low level of absorption. The proposed in vitro method employs a diffusion cell. Sunscreen lotion was applied onto pretreated human skin, which was then placed in the cell. PDT was collected in a receptor liquid, the surface of which was in contact with the skin. The solutions obtained were diluted appropriately and analyzed by liquid chromatography without any interference. The analytical features of chromatographic determination with fluorimetic detection were suited to this analytical problem, since this method gave a limit of detection of 1 ng ml⁻¹. Phenol red (PR) was used as a marker to check the skin integrity, and a sensitive method based on sequential injection on-line solid-phase extraction coupled with spectrophotometric detection was developed for determining this marker in the receptor liquid in order to screen the cells.

Keywords: Disodium phenyldibenzimidazol tetrasulfonate (PDT); Human skin penetration; In vitro; Liquid chromatography–fluorimetric detection

Renewable stationary phase liquid magnetochromatography: determining aspartame and its hydrolysis products in diet soft drinks by E. Barrado; J. A. Rodríguez; Y. Castrillejo (pp. 1233-1240).

A new chromatographic modality that does not require high pressures and also allows renewal of the stationary phase as desired is reported. The technique is based on a thin layer paramagnetic stationary phase (Fe₃O₄–SiO₂) retained on the inner wall of a minicolumn through the action of an external magnetic field, which also plays an important role in separating the analytes. Accordingly, the name “renewable stationary phase liquid magnetochromatography”, or RSP-LMC, has been proposed for it. The technique was used to separate and quantify the sugar substitute α-aspartame and its constituent amino acids (hydrolysis products), L-aspartic acid and L-phenylalanine, in diet fizzy soft drinks. When the results obtained for α-aspartame were compared with those obtained using HPLC as a reference method, no significant differences were observed. The system proposed is fully automated, making it an economic, competitive alternative to conventional methods of determining α-aspartame and its amino acid components.

Keywords: Chromatography; Low pressure; Magnetic field intensity; Renewable stationary phase; Aspartame

Design of a method for generation of gas-phase hydroxyl radicals, and use of HPLC with fluorescence detection to assess the antioxidant capacity of natural essential oils by D. Pezo; J. Salafranca; C. Nerín (pp. 1241-1246).

The use of natural antioxidants is of increasing importance in the human diet, because they are recognised as compounds essential to health which minimize or delay the aging process. Despite apparent simplicity, however, it is very difficult to measure and quantify such properties, for which a robust analytical method is required. Because oxidation usually is caused by the presence of OH· radicals, a new method involving the in-situ, vapour-phase generation of these radicals and their quantification in the presence and absence of potential antioxidant extracts has been developed. The oxidant atmosphere generated from hydrogen peroxide is carried by an air stream through an empty quartz chamber in which UV radiation promotes the formation of radicals by a photochemical reaction. The products then pass through a cartridge containing the essential oil, finally bubbling into an impinger containing an aqueous solution of salicylic acid, at pH 4.5, which reacts with the OH· radicals forming 2,5-dihydroxybenzoic acid. This solution is quantified by RP-HPLC using UV and fluorescence detectors connected in series. Detection and quantification limits for OH· radicals were approximately 0.01 pg g⁻¹ air. Description and optimization of the method are discussed, as also is the antioxidant performance of an extract of ginger (Zingiber officinale R.), which reduced the oxidation process by up to 92%.

Keywords: Hydroxyl radicals; Salicylic acid; Zingiber officinale R. ; Antioxidant evaluation; HPLC–fluorescence

Rapid and quantitative extraction method for the determination of chlorophylls and carotenoids in olive oil by high-performance liquid chromatography by Raquel Mateos; José A. García-Mesa (pp. 1247-1254).

Colour is an organoleptic characteristic of virgin olive oil and an important attribute that affects the consumer perception of quality. Chlorophylls and carotenoids are the main pigments responsible for the colour of virgin olive oil. A simple analytical method for the quantitative determination of chlorophylls and carotenoids in virgin olive oils has been developed. The pigments were isolated from small samples of oil (1.0 g) by solid-phase extraction using diol-phase cartridges (diol-SPE), and the extract was analysed by reverse-phase HPLC with diode-array UV detection. Chromatographic peak resolution, reproducibility (coefficient of variation (C.V.) <4.5%) and recovery (>98.4%) for each component were satisfactory. A comparative study of the proposed method was performed versus classical liquid-liquid extraction (LLE) with N,N′-dimethylformamide and solid-phase extraction using a C18 column (C18-SPE). While 96.4% of the pigments were recovered by LLE, only 51.3% were isolated by C18-SPE in comparison to diol-SPE. Likewise, a higher alteration of pigment composition was observed when such LLE and C18-SPE procedures were used. In this sense, a higher ratio of pheophytin in comparison to that isolated by the diol-SPE procedure was achieved with both extraction procedures, indicating a greater extent of the pheophytinization reaction. Therefore, quantification of pigments from virgin olive oil by diol-SPE followed by RP-HPLC was found to be rapid, simple, required only a small amount of sample, consumed only small amounts of organic solvents, and provided high recoveries, accuracy and precision.

Keywords: Carotenoids; Chlorophylls; Virgin olive oil; HPLC; Solid-phase extraction

Comparison of two quantitative GC–MS methods for analysis of tomato aroma based on purge-and-trap and on solid-phase microextraction by J. Beltran; E. Serrano; F. J. López; A. Peruga; M. Valcarcel; S. Rosello (pp. 1255-1264).

Two analytical procedures, one based on purge-and-trap and the other on solid phase microextraction, both followed by GC–MS measurement using an ion-trap mass spectrometer in the electron impact mode, have been developed for determination and quantitation of up to 39 aroma compounds in fresh tomatoes. The method based on purge-and-trap for isolation of the volatile compounds uses Tenax as adsorbent and a hexane–diethyl ether mixture as solvent for elution. The method was validated for linearity, precision (better than 20% for most compounds), and limit of detection, which was approximately 1 ng g⁻¹. This method enabled identification of up to 30 compounds in real samples. Use of SPME was considered as an alternative, to simplify sample treatment while maintaining the information level for the samples (e.g. the number of compounds detected) and quality of quantitation. A procedure based on SPME using a Carboxen/polydimethylsiloxane fibre was developed and validated for determination of 29 aroma compounds; precision was better than 20% and limits of detection ranged from 4 to 30 ng g⁻¹.

Study of the microbiodegradation of terpenoid resin-based varnishes from easel painting using pyrolysis–gas chromatography–mass spectrometry and gas chromatography–mass spectrometry by María Teresa Doménech-Carbó; Laura Osete-Cortina; Juana de la Cruz Cañizares; Fernando Bolívar-Galiano; Julio Romero-Noguera; María Antonia Fernández-Vivas; Inés Martín-Sánchez (pp. 1265-1280).

The alterations produced by microbiological attack on terpenoid resin-based varnishes from panel and canvas paintings have been evaluated using pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) and gas chromatography–mass spectrometry (GC–MS). The proposed methods include the on-line derivatisation of drying oils and diterpenoid resins using hexamethyldisilazane during pyrolysis and the application of methyl chloroformate as a derivatisation reagent for triterpenoid resins in GC–MS. Two types of specimens, consisting of model oil medium prepared from linseed oil and model spirit varnishes prepared from colophony and mastic resins dissolved in turpentine, have been used as reference materials. For a series of specimens upon which different genera of bacteria and fungi were inoculated and encouraged to grow, analyses indicated that no mechanisms that commonly occur during the attack of enzymes on drying oils and terpenoid biodegraders were observed to occur in the oil medium and varnishes studied. Thus, the degradation pathways observed in the performed trials usually occur as consequence of natural ageing. Specific trials consisting of the application of biocides to uninoculated colophony varnish resulted in the identification of processes that produce undesirable degradation of the varnish due to interactions between the biocide and the varnish components. Finally, the studied biocides—Biotin, New-Des and Nipagine—generally exhibited good inhibiting effects on the microorganisms studied, although some interesting differences were found between them regarding the application method and type of biocide.

Keywords: Py–GC–MS; Terpenoid resin; Hexamethyldisilazane; Biocide; Painting microbiodegradation

Parallel factor analysis combined with PLS regression applied to the on-line monitoring of Pichia pastoris cultures by Anna Surribas; José Manuel Amigo; Jordi Coello; José Luis Montesinos; Francisco Valero; Santiago Maspoch (pp. 1281-1288).

Various key variables (biomass, substrate and product) of bioprocesses should be monitored in order to retrieve useful information on the system, with the biomass (the cell density) the principal target. Although several analytical methods have been adapted and used to monitor the evolution of cell density evolution in cultures, a general method for performing this determination has not yet been established, as each technique has its own advantages and drawbacks. In the present work, noninduced glycerol batch cultures (for which biomass and substrate are the key variables) were monitored using multiwavelength fluorescence spectroscopy. The data gathered were modelled via PARAFAC-PLS chemometric methodologies, resulting in important qualitative and quantitative information about the behaviours of different biogenic fluorophors in batch cultures of the yeast Pichia pastoris. This information was used to predict the target process variables in such cultures; this permitted the applicability of this combined technique to bioprocess monitoring to be assessed.

Keywords: PARAFAC; PLS; Pichia pastoris ; Biomass monitoring; On-line monitoring

Four-way calibration applied to the simultaneous determination of folic acid and methotrexate in urine samples by A. Muñoz de la Peña; I. Durán Merás; A. Jiménez Girón (pp. 1289-1297).

First-, second- and third-order calibration methods were investigated for the simultaneous determination of folic acid and methotrexate. The interest in the determination of these compounds is related to the fact that methotrexate inhibits the body’s absorption of folic acid and prolonged treatment with methotrexate may lead to folic acid deficiency, and to the use of folic acid to cope with toxic side effects of methotrexate. Both analytes were converted into highly fluorescent compounds by oxidation with potassium permanganate, and the kinetics of the reaction was continuously monitored by recording the kinetics curves of fluorescence emission, the evolution with time of the emission spectra and the excitation–emission matrices (EEMs) of the samples at different reaction times. Direct determination of mixtures of both drugs in urine was accomplished on the basis of the evolution of the kinetics of EEMs by fluorescence measurements and four-way parallel-factor analysis (PARAFAC) or multiway partial least squares (N-PLS) chemometric calibration. The core consistency diagnostic (CORCONDIA) was employed to determine the correct number of factors in PARAFAC and the procedure converged to a choice of three factors, attributed to folic acid, methotrexate and to the sum of fluorescent species present in the urine.

Keywords: Four-way parallel-factor analysis; Multiway partial least squares; Excitation–emission matrices; Methotrexate; Folic acid

Comparison of three strategies to evaluate uncertainty from in-house validation data. A case study: mercury determination in sediments by A. Guevara-Riba; A. Sahuquillo; J. F. López-Sánchez; R. Rubio (pp. 1298-1303).

In the present paper, three approaches are compared for the evaluation of the combined uncertainty in the determination of mercury in aquatic sediments by an aqua regia extraction procedure. For this, the data obtained in validation studies from five certified reference materials (CRMs), covering a range of concentrations from 0.8 to 130 mg kg⁻¹ of mercury and analysed by three atomic spectroscopic techniques (cold vapour generation atomic fluorescence spectrometry, CV-AFS, cold vapour generation atomic absorption spectroscopy, and inductively coupled plasma mass spectroscopy), were considered. The combined uncertainty was firstly assessed by considering separately the data obtained for each CRM analysed (approach A). Moreover, this assessment was also performed with two other calculation approaches (B and C) based on the pooled data obtained from the validation step. The comparison of the results obtained for the different techniques showed a clear bias effect when using CV-AFS with nitric acid as a diluent. In relation to the strategies tested for the combined uncertainty assessment, approach C proved to be the easiest and friendliest method for uncertainty assessment.

Keywords: Uncertainty; Certified reference materials; Mercury; Aquatic sediments

Selenium speciation from food source to metabolites: a critical review by Emmie Dumont; Frank Vanhaecke; Rita Cornelis (pp. 1304-1323).

Especially in the last decade, a vast number of papers on Se and its role in health issues have been published. This review gives a brief, critical overview of the main analytical findings reported in these papers. Of particular interest is the Se content in different food sources worldwide and the extent to which their consumption is reflected in the Se content of human tissues and body fluids. Several food sources, both natural (Brazil nuts, garlic, Brassica juncea) and Se-enriched (yeast-based supplements), are discussed as to origin, characteristics, Se metabolism and impact of their consumption on the human body. The continuous development of new and improvement of existing analytical techniques has provided different powerful tools to unravel the Se species and their function. An up-to-date literature study on Se speciation analysis is given, illustrating how analytical chemistry in its different facets aids in the identification of Se compounds and provides insight into the complete metabolic pathway of Se throughout the human body. This review includes a detailed image of the current state-of-the-art of Se speciation analysis in these food sources and in human tissues and body fluids.

Keywords: Selenium; Speciation; Analytical techniques; Food; Metabolites

Electrochemical oxidation of isoniazid catalyzed by (FcM)TMA at the platinum electrode and its practical analytical application by Zuo-Ning Gao; Xiao-Xia Han; Hui-Qin Yao; Bin Liang; Wan-Yi Liu (pp. 1324-1329).

The electrocatalytic oxidation of isoniazid (INH) by (ferrocenylmethyl)trimethylammonium [(FcM)TMA] at the platinum electrode in 0.10 M Na₂SO₄ aqueous solution was studied by cyclic voltammetry (CV). Although INH itself showed a very poor electrochemical response at the platinum electrode, the response could be greatly enhanced by using (FcM)TMA as a mediator, which enables a sensitive electrochemical determination of the substrate INH. The reaction rate constant for catalytic oxidation reaction was evaluated as (3.98±0.10)×10³ M⁻¹ s⁻¹ by using chronoamperometry (CA). Experimental conditions such as supporting electrolyte and its concentration, solution pH, and the concentrations of the catalyst (FcM)TMA and the substrate INH were investigated to maximize the current efficiency of the electrocatalytic oxidation. The method can be used for the sensitive practical determination of INH, and also opens an avenue for using (FcM)TMA as a mediator in electroanalytical determination which is very simple, cheap, and rapid. Furthermore, no sample pretreatment or time-consuming extraction steps are required prior to the analysis.

Keywords: Electrocatalytic oxidation; Isoniazid; (Ferrocenylmethyl)trimethylammonium; Platinum electrode; Analytical application

Mediator-free amperometric determination of glucose based on direct electron transfer between glucose oxidase and an oxidized boron-doped diamond electrode by Jing Wu; Yang Qu (pp. 1330-1335).

A mediator-free glucose biosensor, termed a “third-generation biosensor,” was fabricated by immobilizing glucose oxidase (GOD) directly onto an oxidized boron-doped diamond (BDD) electrode. The surface of the oxidized BDD electrode possesses carboxyl groups (as shown by Raman spectra) which covalently cross-link with GOD through glutaraldehyde. Glucose was determined in the absence of a mediator used to transfer electrons between the electrode and enzyme. O₂ has no effect on the electron transfer. The effects of experimental variables (applied potential, pH and cross-link time) were investigated in order to optimize the analytical performance of the amperometric detection method. The resulting biosensor exhibited fast amperometric response (less than 5 s) to glucose. The biosensor provided a linear response to glucose over the range 6.67×10⁻⁵ to 2×10⁻³ mol/L, with a detection limit of 2.31×10⁻⁵ mol/L. The lifetime, reproducibility and measurement repeatability were evaluated and satisfactory results were obtained.

Keywords: Biosensor; Glucose; Glucose oxidase (GOD); Oxidized boron-doped diamond electrode

Determination of norfloxacin in human urine by capillary electrophoresis with electrochemiluminescence detection by Biyang Deng; Caina Su; Yanhui Kang (pp. 1336-1341).

A fast and sensitive approach that can be used to detect norfloxacin in human urine using capillary electrophoresis with end-column electrochemiluminescence (ECL) detection of $${ ext{Ru}}{left( {{ ext{bpy}}} ight)}^{{2 + }}_{3} $$ is described. The separation column was a 75-μm i.d. capillary. The running buffer was 15 mmol L⁻¹ sodium phosphate (pH 8.2). The solution in the detection cell was 50 mmol L⁻¹ sodium phosphate (pH 8.0) and 5 mmol L⁻¹ $${ ext{Ru}}{left( {{ ext{bpy}}} ight)}^{{2 + }}_{3} .$$ The ECL intensity varied linearly with norfloxacin concentration from 0.05 to 10 μmol L⁻¹. The detection limit (S/N=3) was 0.0048 μmol L⁻¹, and the relative standard deviations of the ECL intensity and the migration time for eleven consecutive injections of 1.0 μmol L⁻¹ norfloxacin (n=11) were 2.6% and 0.8%, respectively. The method was successfully applied to the determination of norfloxacin spiked in human urine without sample pretreatment. The recoveries were 92.7–97.9%.

Keywords: Capillary electrophoresis; Electrochemiluminescence; Norfloxacin; Tris(2,2′-bipyridyl) ruthenium(II); Urine

Cobalt(II)-selective membrane sensor based on a [Me₂(13)dieneN₄] macrocyclic cobalt complex by Ashok Kumar Singh; Puja Saxena; Sameena Mehtab; Amit Panwar (pp. 1342-1346).

A new poly(vinyl chloride)-based membrane was fabricated with the cobalt(II) complex of 2,4-dimethyl-1,5,8,11-tetraazacyclotrideca-1,4-diene [Me₂(13)dieneN₄] as an ion carrier. The membrane composition was Co²⁺ complex/PVC/NaTPB/DBP 15:50:15:20 (w/w). The sensor exhibited a Nernstian response for Co²⁺ ions over a wide concentration range (7.94×10⁻⁶–1.0×10⁻¹ M) at pH 2.5–7.0, a response time of 10 s, and it could be used for 3 months without any significant divergence in potential. The proposed membrane sensor exhibited good selectivity for Co²⁺ over a wide variety of other metal ions and in mixtures containing up to 25% (v/v) non-aqueous content. The sensor was successfully used as an indicator electrode in the potentiometric titration of Co²⁺ with EDTA and the direct determination of Co²⁺ in real samples.

Keywords: Co²⁺-selective electrode; Macrocyclic complex; Poly(vinyl chloride); Potentiometry

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Analytical and Bioanalytical Chemistry (v.385, #7)