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Analytica Chimica Acta (v.618, #1)

Contents (pp. v-vi).

Editorial Board (pp. iii).

Multi-commutation in flow analysis: Recent developments and applications by Mário A. Feres; Paula R. Fortes; Elias A.G. Zagatto; João L.M. Santos; José L.F.C. Lima (pp. 1-17).

The concept of multi-commutation in flow analysis is revisited, and emphasis is given to recent methodological and applicative achievements. Multi-commutation is compatible with different flow patterns (unsegmented, segmented, pulsed, tandem) and amenable to concentration-oriented feedback mechanisms. Its exploitation has led to significant attainments mainly in relation to versatility of the flow system. Characteristics and potentialities of the multi-commuted flow systems are discussed, and guidelines for assisting methodological implementation are given.The number of applications has experienced remarkable increase during last years; therefore, the applicative part of this review is focused on the recent noteworthy applications, mainly in relation to environmental, agronomical, pharmaceutical, biological, food and industrial samples.

Keywords: Multi-commutation; Flow analysis; Tandem streams

Photodegradation study of decabromodiphenyl ether by UV spectrophotometry and a hybrid hard- and soft-modelling approach by Sílvia Mas; Anna de Juan; Sílvia Lacorte; Romà Tauler (pp. 18-28).

This work presents an exploratory study of the photochemical degradation process of decabromodiphenyl ether (decaBDE) and gives an interpretation of the kinetic pathway, species and effects of the key factors involved in the degradation process. Use of lowly brominated diphenyl ethers (PBDE) has been banned by the EU and there seems to be evidence of the photolytic degradation of highly brominated PBDEs into lowly brominated congeners. Hence, the importance of knowing the photodegradation process of decaBDE.The photodegradation was investigated under UV light by UV-spectrophotometric monitoring. A novel hybrid data analysis approach, based on the combination of hard- and soft-spectrophotometric multivariate curve resolution, was applied to elucidate the mechanism of the degradation process, to resolve kinetic profiles and pure spectra of the photodegradation products and to evaluate the rate constants. The photodegradation process could be described with a kinetic model based on three consecutive first-order reactions and a decrease of the degradation process was observed as solvent polarity increased. Complementary identification of photodegradation products by gas chromatography coupled to mass spectrometry using negative chemical ionization (GC-NCI–MS) is attempted.This work presents a novel attempt of describing in a comprehensive way the photochemical degradation process of decaBDE, with all successive steps and related rate constants. This study proves also the potential of the proposed hybrid data analysis methodology as a general strategy to interpret the evolution of these photochemical reactions.

Keywords: Decabromodiphenyl ether; Photodegradation process; Rate constants; Kinetic model; Hard- and soft-modelling multivariate curve resolution

Bioinformatical evaluation of modified nucleosides as biomedical markers in diagnosis of breast cancer by Dino Bullinger; Holger Fröhlich; Fabian Klaus; Hans Neubauer; Antje Frickenschmidt; Carsten Henneges; Andreas Zell; Stefan Laufer; Christoph H. Gleiter; Hartmut Liebich; Bernd Kammerer (pp. 29-34).

It is known that patients suffering from cancer diseases excrete increased amounts of modified nucleosides with their urine. Especially methylated nucleosides have been proposed to be potential tumor markers for early diagnosis of cancer. For determination of nucleosides in randomly collected urine samples, the nucleosides were extracted using affinity chromatography and then analyzed via reversed phase high-performance liquid chromatography (HPLC) with UV-detection. Eleven nucleosides were quantified in urine samples from 51 breast cancer patients and 65 healthy women.The measured concentrations were used to train a Support Vector Machine (SVM) and a k-nearest-neighbor classifier (k-NN) to discriminate between healthy control subjects and patients suffering from breast cancer. Evaluations of the learned models by computing the leave-one-out error and the prediction error on an independent test set of 29 subjects (15 healthy, 14 breast cancer patients) showed that by using the eleven nucleosides, the occurrence of breast cancer could be forecasted with 86% specificity and 94% sensitivity when using an SVM and 86% for both specificity and sensitivity with the k-NN model.

Keywords: Metabolomics; High performance liquid chromatography with ultraviolett detection (HPLC-UV); Nucleosides; Breast cancer; Support Vector Machine (SVM); k-Nearest-neighbor classifier (k-NN)

Study of interactions of concentrated marine dissolved organic matter with copper and zinc by pseudopolarography by Rudy Nicolau; Yoann Louis; Dario Omanović; Cédric Garnier; Stéphane Mounier; Ivanka Pižeta (pp. 35-42).

The interaction of dissolved organic matter (DOM) with copper and zinc in a concentrated seawater sample was characterised by pseudopolarography. Measurements performed at increased concentrations of copper(II) ions showed successive saturation of active DOM sites which indicate possible partition of copper between (i) free or labile complexes, (ii) reduced and released within the potential window of the method, and (iii) electroinactive copper complexes. Pseudopolarograms measured at pH 4 indicate a release of copper which was bound to the active sites of DOM that formed non-labile complexes. Variation of the peak position and half-peak width along the scanned deposition potentials and with the increasing concentration of copper bear the information about the complex electrochemical processes at the electrode surface and in the bulk of the solution. Pseudopolarograms of zinc showed a strong dependence of the peak current and the peak position along the scanned deposition potentials on pH values, indicating preferentially complexation of zinc with carboxylic-like active sites of DOM in the measured sample. Pseudopolarography is a valuable method in the trace metal complexation and speciation studies, serving as a fingerprint of the analysed sample.

Keywords: Dissolved organic matter; Pseudopolarography; Copper; Zinc; Metal speciation; Sea water

Electrosorption of Os(III)-complex at single-wall carbon nanotubes immobilized on a glassy carbon electrode: Application to nanomolar detection of bromate, periodate and iodate by Abdollah Salimi; Begard Kavosi; Ali Babaei; Rahman Hallaj (pp. 43-53).

A simple procedure was developed to prepare a glassy carbon electrode modified with single-wall carbon nanotubes (SWCNTs) and Os(III)-complex. The glassy carbon (GC) electrode modified with CNTs was immersed into Os(III)-complex solution (direct deposition) for a short period of time (60s). 1,4,8,12-Tetraazacyclotetradecane osmium(III) chloride, (Os(III)LCl₂)·ClO₄, irreversibly and strongly adsorbed on SWCNTs immobilized on the surface of GC electrode. Cyclic voltammograms of the Os(III)-complex-incorporated-SWCNTs indicate a pair of well defined and nearly reversible redox couple with surface confined characteristic at wide pH range (1–8). The surface coverage ( Γ) and charge transfer rate constant ( k_s) of the immobilized Os-complex on SWCNTs were 3.07×10⁻⁹molcm⁻², 5.5 (±0.2)s⁻¹, 2.94×10⁻⁹molcm⁻², 7.3 (±0.3)s⁻¹ at buffer solution with pH 2 and 7, respectively, indicate high loading ability of SWCNTs for Os(III) complex and great facilitation of the electron transfer between electroactive redox center and carbon nanotubes immobilized on the electrode surface. Modified electrodes showed higher electrocatalytic activity toward reduction of BrO₃⁻, IO₃⁻ and IO₄⁻ in acidic solutions. The catalytic rate constants for catalytic reduction bromate, periodate and iodate were 3.79 (±0.2)×10³, 7.32 (±0.2)×10³ and 1.75 (±0.2)×10³M⁻¹s⁻¹, respectively. The hydrodynamic amperometry of rotating modified electrode at constant potential (0.3V) was used for nanomolar detection of selected analytes. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantage of this sensor.

Keywords: Osmium complex; Carbon nanotube; Amperometry; Iodate; Periodate; Bromate

Sensitive adsorptive stripping voltammetric determination of paracetamol at multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode by Roohollah Torabi Kachoosangi; Gregory G. Wildgoose; Richard G. Compton (pp. 54-60).

A sensitive electroanalytical methodology for the determination of paracetamol using adsorptive stripping voltammetry (AdsSV) at a multiwalled carbon nanotube modified basal plane pyrolytic graphite electrode (MWCNT-BPPGE) is presented. Both cyclic voltammetric and square wave adsorptive stripping voltammetric techniques are compared. The adsorption occurs at open circuit potential with a 1min accumulation time. The effect of scan rate and pH were investigated and an optimal scan rate of 100mVs⁻¹ and a pH 7.5, 0.05M phosphate buffer solution (PBS) was used.Additions of paracetamol using cyclic voltammetry exhibits a linear detection range over a wide range of paracetamol concentrations (0.1–25μM) with a detection limit of 45nM (based on 3 σ). Additions of paracetamol using square wave adsorptive stripping voltammetry show two linear ranges for paracetamol detection. The first linear range is from 0.01μM to 2μM and the second linear range is from 2μM to 20μM. Using the first range of this calibration plot, a detection limit of 10nM is obtained for paracetamol. To the best of our knowledge, this limit of detection is the lowest limit of detection has been reported for paracetamol using electrochemical techniques.The method was then successfully utilised for the determination of paracetamol in a real sample of “ANADIN EXTRA” tablets and a recovery of 95% was obtained without interference from aspirin or caffeine. The proposed electroanalytical method using MWCNT-BPPGE is the most sensitive method for determination of paracetamol with lowest limit of detection to date. It has also advantages such as easy handling, resistance against surface fouling, and low cost.

Keywords: Paracetamol; Multiwalled carbon nanotubes; Basal plane pyrolytic graphite electrodes; Adsorptive stripping voltammetry; Cyclic voltammetry; Square wave voltammetry; pH

Coupled in-tube and on-fibre solid-phase microextractions for cleanup and preconcentration of organic micropollutants from aqueous samples and analysis by gas chromatography–mass spectrometry by Manju Gupta; Aradhana K.K.V. Pillai; Archana Jain; Krishna K. Verma (pp. 61-69).

Matrix interference removal is an important step when large volumes of aqueous samples are required to be processed to detect trace levels of analytes. A combination of two sample extraction methods has been used in this work with the aim of cleanup and preconcentration of analytes. For first objective, mild but preferential sorption of a range of analytes has been performed with in-tube solid-phase microextraction (SPME) using polytetrafluoroethylene (PTFE) tubing, and for the second, the eluate from in-tube SPME was subjected to on-fibre SPME using DVB/Caboxen/PDMS (30/50μm) fibre. Knitting of PTFE tubing created secondary flow pattern that enhanced radial diffusion and retention of organic analytes. Up to 2mgL⁻¹ of a broad range of substances that are not extracted by PTFE include nitrogen containing aromatic heterocyclic compounds, anilines, phenols and certain organophosphorus pesticides, thus providing a clean extract using this method of sample preparation. The proposed combination of in-tube and on-fibre SPME produced a rectilinear calibration graph over 0.03–150μgL⁻¹ of a range of analytes using 60mL of aqueous sample. The overall recovery of analytes was in the range 27–78%. The detection limits were between 6.1 and 21.8ngL⁻¹. The R.S.D. was in range 5.4–8.2% and 4.2–6.5% in the analysis of respectively 2 and 20μgL⁻¹ of analytes.

Keywords: Coupled in-tube and on-fibre solid-phase microextractions; Polytetrafluoroethylene tubing; Knotted; Divinylbenene/caboxen/polydimethylsiloxane; Organic micropollutants; Gas chromatography–mass spectrometry

Hollow-fibre liquid-phase microextraction: A simple and fast cleanup step used for PAHs determination in pine needles by Nuno Ratola; Arminda Alves; Nicolas Kalogerakis; Elefteria Psillakis (pp. 70-78).

A new, fast and simple cleanup procedure, based on hollow-fibre liquid-phase microextraction (HF-LPME) is described here, used for the determination of 13 polycyclic aromatic hydrocarbons (PAHs) in complex pine needle samples. Initially, pine needle samples were sonicated in a 20mL aqueous solution having a 20% (v:v) acetone content and 5mL of the sonicated liquid extract was then used for the HF-LPME cleanup step. Different experimental parameters (namely: type of organic solvent used as acceptor phase, effect and type of co-solvent, salt addition, sample agitation and sampling time) were controlled and optimized based on the response of GC–MS instrument under the SIM mode. Under the optimized experimental conditions found the typical chromatograms obtained revealed that despite the very complex matrix of pine needles the HF-LPME cleanup step greatly reduced if not eliminated the presence of interferents, resulting in chromatograms which contained very cleanly separated and readily evaluable PAH peaks. In addition, the proposed method was found to be linear in the concentration 10–2000ngg⁻¹ for most target analytes and the limits of detection for a S/N=3 ranged between 0.01 and 0.95ngg⁻¹ (dry weight). Furthermore, the repeatability and reproducibility were also found good. Finally, the proposed method was applied for the analysis of real pine needle samples taken for different parts of the island of Crete.

Keywords: Polycyclic aromatic hydrocarbons; Pine needles; Hollow fibre; Liquid-phase microextraction; Method optimization

Determination of benzoic acid and sorbic acid in food products using electrokinetic flow analysis–ion pair solid phase extraction–capillary zone electrophoresis by Fang Han; You-Zhao He; Lian Li; Guo-Ni Fu; Hai-Yang Xie; Wu-Er Gan (pp. 79-85).

An electrokinetic flow analysis system (EFA), consisting of one electroosmotic pump, five solenoid valves and one on-line homemade solid phase extraction (SPE) unit, combined with capillary zone electrophoresis (CZE) was proposed to determine benzoic acid and sorbic acid in food products. Tetrabutylammonium bromide (TBAB) was adopted as an ion pair reagent to improve the retention of the preservatives on C₈-bonded silica sorbent, which was also used to remove sample matrices. By using the SPE unit, the EFA–SPE–CZE system was able to perform the SPE operation and CZE separation simultaneously. With a modified interface of EFA and CZE, the buffer consumption was reduced to 130μL for each running. The preservatives were separated and determined under optimized conditions with p-hydroxybenzoic acid as an internal standard. The relative standard deviation (R.S.D.) of peak area for each analyte was less than 3.1% ( n=5) and the limits of detection (LODs) ranged from 10 to 20ngmL⁻¹ ( K=3, n=11).

Keywords: Electrokinetic flow analysis; Capillary zone electrophoresis; Ion pair solid phase extraction; Preservatives

Confirmatory analysis of Trenbolone using accurate mass measurement with LC/TOF-MS by M.H. Blokland; P.W. Zoontjes; S.S. Sterk; R.W. Stephany; J. Zweigenbaum; L.A. van Ginkel (pp. 86-93).

The use of accurate mass measurement as a confirmation tool is examined on a TOF-MS and compared with confirmation using a triple quadrupole mass spectrometer (QqQ-MS). Confirmation of the identity of a substance using mass-spectrometric detection has been described. However, the use of accurate mass measurement for confirmatory analysis has not been taken into account. In this study, criteria for confirmation with accurate mass are proposed and feasibility is demonstrated. Mass accuracy better than 3ppm of the quasi-molecular ion and a fragment and their relative ratios determined with LC/TOF-MS are compared to the criteria of two transition ions and their ratio of LC/QqQ-MS. The results show that these criteria can be met for Trenbolone in samples of bovine urine and that single MS accurate mass measurement is comparable to nominal mass MS/MS for confirmation. The increase in popularity and availability of LC/TOF-MS instruments and the ease, of which exact masses can be measured, make it important to formulate criteria for this type of instrumentation. It is shown in this study that accurate mass measurement can be used for confirmatory analysis. However, more experiments need to be conducted to demonstrate the applicability of accurate mass measurement in general for residue analysis.

Keywords: Accurate mass measurement; Exact mass; Time of Flight Mass Spectrometry; Triple Quadrupole mass spectrometry; Confirmation

Evaluation and optimization of high-throughput enzymatic assays for fastl-ascorbic acid quantification in fruit and vegetables by S. Vermeir; M.L.A.T.M. Hertog; A. Schenk; K. Beullens; B.M. Nicolaï; J. Lammertyn (pp. 94-101).

In this paper, we compare and evaluate the applicability of three UV–VIS absorbance based assays for high-throughput quantification of ascorbic acid in horticultural products. All the methods involve the use of a common enzyme (ascorbate oxidase) in combination with a different indicator molecule. The three methods were retrieved from literature: a direct oxidase-method, an OPDA coupled oxidase-method and a PMS-method, which is commercially available. The analysis in high-throughput context involved the analysis in microplates in combination with the use of an automated liquid handling system. We checked (i) the performance factors of the selected methods on standard solutions, (ii) the applicability of the defined methods in high-throughput context, and, (iii) the accuracy of the methods on real samples using HPLC as a reference technique. The OPDA-method was found to be the most appropriate method for the quantification of ascorbic acid in high-throughput context with a linear range between 7.0 and 950mgL⁻¹ and excellent correlation parameters (slopes close to 1, intercepts close to 0, R²>0.91) with the reference technique when real samples were analyzed. Finally, this method was optimized for assay cost and assay time. Hereto the enzymatic reaction was mathematically described using a model for enzyme kinetics, which was then used to calculate the optimal concentrations of ascorbate oxidase and OPDA. As a result of the modeling the amount of enzyme in the assay could be reduced with a factor 2.5 without affecting significantly the reaction time. In a last step the optimal concentrations were used for a successful validation with the HPLC-reference technique.

Keywords: Abbreviations; AA; ascorbic acid; AA; _int; intermediair complex of AA; AOX; ascorbate oxidase; CV; coefficient of variation; DHAA; dehydroascorbic acid; EDTA; ethylene-diamine-tetraacetate; LOD; limit of detection; LOQ; limit of quantification; MPA; meta; -phosphoric acid; OPDA; ortho; -phenylenediamine; PMS; 5-methyl-phenazinium methosulfate; PVPP; polyvinylpolypyrroldine; S.D.; standard deviation; seconds; s; MTT; 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromideAscorbic acid; Ascorbate oxidase; High-throughput analysis; UV–VIS-spectrophotometry; Fruit samples

Development and validation of a chiral HPLC method for rapid screening of allylic alcohol asymmetric epoxidation processes by Sonia Morante-Zarcero; Isabel del Hierro; Mariano Fajardo; Isabel Sierra (pp. 102-109).

A simple and rapid HPLC method has been developed using a polysaccharide chiral stationary phase (Chiralpak AD-H) for the resolution of glycidyl tosylate enantiomers. These compounds were obtained by asymmetric epoxidation of allyl alcohol with chiral titanium–tartrate complexes as catalyst after in situ derivatization of the intermediate glycidols. Separations were achieved using two types of mobile phase: a normal-phase ( n-hexane), and a polar-phase (methanol or acetonitrile). The influence of the type and concentration of organic modifier in the mobile phase (ethanol or 2-propanol), the flow rate and the column temperature was investigated. In normal-phase mode, the optimized conditions were: n-hexane/ethanol 70/30 (v/v) at a flow rate of 1.2mLmin⁻¹ and 40°C. In polar-phase mode, the optimized conditions were: methanol at a flow rate of 0.8mLmin⁻¹ and 20°C. In both cases, analysis time was ≤11min and the chiral resolution was ≥2. Nevertheless, due to the better Rs obtained in normal-phase mode, only this method was validated to avoid peaks overlapping in real samples. This method was found to be linear in the 5–300μgmL⁻¹ range ( R²>0.999) with an LOD of 1.5μgmL⁻¹ for both glycidyl tosylate enantiomers. Repeatability and intermediate precision at three different concentrations levels were below 0.5 and 7.2% R.S.D. for retention time and area, respectively. This method was applied successfully for the determination of glycidyl tosylate enantiomers after in situ derivatization of glycidols obtained in allylic alcohol asymmetric epoxidation processes with chiral titanium–tartrate complexes as catalysts.

Keywords: Chiral separation; HPLC; Polysaccharide chiral stationary phase; Glycidyl tosylate enantiomers; Asymmetric epoxidation

Comparability of composition of carbon functional groups in humic acids between inverse-gated decoupling and cross polarization/magic angle spinning¹³C nuclear magnetic resonance techniques by Akira Watanabe; Nobuhide Fujitake (pp. 110-115).

To find a certain relation between the composition of carbon functional groups of humic acids derived from liquid state¹³C nuclear magnetic resonance (NMR) spectra acquired with inverse-gated decoupling (IGD), known as a quantitative pulse sequence, and that by solid-state¹³C NMR with cross polarization/magic angle spinning (CPMAS) techniques, fifteen soil humic acid samples with a wide range of aromaticity were analyzed. Relationships between the proportions of humic acid carbon as alkyl, O-alkyl, and aromatic carbon assessed by the two methods could be regressed to y= ax ( r=0.932–0.956; P<0.005), respectively. The contents of alkyl, O-alkyl, and aromatic carbon assessed by CPMAS method were larger than those found by IGD method. However, the differences between the two methods were small and exclusive regression to y= x was also significant ( r=0.775–0.941; P<0.005). Aromaticity calculated from¹³C CPMAS NMR data also did not differ significantly from those computed from¹³C NMR spectra with IGD. These observations indicated the comparability of the relative content of carbon functional groups in humic acids except for carboxyl and carbonyl carbon.

Keywords: Aromaticity; ¹³; C nuclear magnetic resonance; Cross polarization magic angle spinning; Humic acids; Inverse-gated decoupling

Simultaneous immobilization of dehydrogenases on polyvinylidene difluoride resin after separation by non-denaturing two-dimensional electrophoresis by Youji Shimazaki; Mariko Kadota (pp. 116-119).

We detected mouse liver malate, sorbitol and aldehyde dehydrogenases by negative staining, analysis of malate and sorbitol dehydrogenase activities using each substrate, and electron transfers including nicotinamide adenine dinucleotide (NAD) and nitroblue tetrazolium in non-denaturing two-dimensional electrophoresis (2-DE) gel. Dehydrogenases were also identified by electrospray ionization tandem mass spectrometry (ESI-MS/MS) after 2-DE separation and protein detection by negative staining. Spots of dehydrogenases separated by 2-DE were excised, and simultaneously transferred and immobilized on polyvinylidene difuoride (PVDF) resin by electrophoresis. The dehydrogenase activities remained intact after immobilization . In conclusion, resin-immobilized dehydrogenases can be simultaneously obtained after separation by non-denaturing 2-DE, detection by negative staining and transferring to resins.

Keywords: Abbreviations; 2-DE; two-dimensional electrophoresis; ESI-MS/MS; electrospray ionization tandem mass spectrometry; PVDF; polyvinylidene difuoride; IEF; isoelectric focusing; TEMED; N; ,; N; ,; N; ′,; N; ′-tetramethylenediamine; NAD; β-nicotinamide adenine dinucleotide; PMS; phenazine methosulfate; NBT; nitroblue tetrazoliumNegative stain; Malate dehydrogenase; Sorbitol dehydrogenase; Aldehyde dehydrogenase; De novo sequencing

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Analytica Chimica Acta (v.618, #1)