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Analytica Chimica Acta (v.555, #2)

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

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n1-n2).

Development of headspace solid-phase microextraction-gas chromatography–mass spectrometry methodology for analysis of terpenoids in Madeira wines by J.S. C�mara; M. Arminda Alves; J.C. Marques (pp. 191-200).

A dynamic headspace solid-phase microextraction methodology was developed for analysis of varietal aroma compounds in must and Madeira wine samples, a spirit wine with an ethanol content of 18% (v/v). The factors with influence in the headspace solid-phase microextraction efficiency such as: fibre coating, extraction time and temperature, pH, ionic strength, ethanol content, desorption time and temperature, were optimised and the method validated. The best results were obtained for a 85μm polyacrylate fibre, with a 60min headspace for must and 120min for wine samples, in a 2.4ml sample at 40°C with 30% of NaCl. The extract is injected in the splitless mode in a GC–MS Varian system, Saturn III, and separated on a Stabilwax capillary column. The linear dynamic range of the method covers the normal range of occurrence of analytes in wine with typical r² between 0.985 (β-ionone) and 0.998 (linalool) for musts and between 0.980 (α-terpineol) and 0.999 (linalool) for must and wine samples, respectively. For must samples the reproducibility ranges from 2.5% (citronellol) to 14.4% (nerolidol) (as R.S.D.), and from 4.8% (citronellol) to 14.2% (nerolidol) for wine samples. The analysis of spiked samples has shown that matrix effects do not significantly affect method performance. Limits of detection obtained are in low μgl⁻¹ range for all compounds analysed in this study.

Keywords: Solid-phase microextraction; Optimisation; Varietal compounds; Must; Wine

In-tube silylation in combination with thermal desorption gas chromatography-mass spectrometry for the determination of hydroxy polycyclic aromatic hydrocarbons in water by Nobuyasu Itoh; Hiroaki Tao; Takashi Ibusuki (pp. 201-209).

For the determination of hydroxy polycyclic aromatic hydrocarbons (OH-PAHs), a simple and sensitive method based on the silylation of OH-PAHs using N, O-bis(trimethylsilyl)trifluoro acetamide (BSTFA) in combination with thermal desorption gas chromatography-mass spectrometry (TD-GC–MS) is described. This method was performed by way of direct silylation in a TD unit (in-tube silylation) coupled to a GC inlet. Both a good detection limit (4.1–1200pgL⁻¹, S/N=3) and higher precision (relative standard deviation<4% on average) were achieved for 21 OH-PAHs studied using the full scan mode ( m/ z=40–550). These good results were due to the highly efficient derivatization of the OH-PAHs, which was attributed to not only the moisture-free environment and programmable heating in the TD tube for the in-tube silylation, but also to the constant vapor generation of BSTFA using a capillary introduction method. Although recoveries of 21 OH-PAHs from the spiked 3% NaCl solution ranged between 9 and 304%, those of 11 OH-PAHs fell between 70 and 130% (R.S.D.<11%). Thus, the present method was applied to a seawater sample collected from an industrial port, and nine OH-PAHs including 1- and 2-OH-fluorenone and 1,8- and 2,6-OH-anthraquinone were determined at concentrations of 0.49–5.8ngL⁻¹. Along with these OH-PAHs, significant amounts of several long chain fatty acids (C₁₂, C₁₆, C₁₈, C₂₀ and C₂₂) and bisphenol A were also identified in the seawater sample using reference data in a library of mass spectra (match factor: >80%).

Keywords: GC–MS; Hydroxy polycyclic aromatic hydrocarbon (OH-PAH); BSTFA; Thermal desorption (TD); Water sample

Direct chiral resolution and its application to the determination of fungicide benalaxyl in soil and water by high-performance liquid chromatography by Donghui Liu; Peng Wang; Wenfeng Zhou; Xu Gu; Zhenshan Chen; Zhiqiang Zhou (pp. 210-216).

A simple chiral high-performance liquid chromatography (HPLC) method with ultraviolet (UV) and circular dichroism (CD) detection was developed and validated for measuring benalaxyl enantiomers using ( R, R) Whelk-O 1 column. The effects of mobile phase composition and column temperature on the entioseparation were investigated. A CD detector was used to determine the elution order of the enantiomers. Excellent resolution was easily obtained using n-hexane-polar organic alcohols mobile phase. The chiral recognition mechanism was also discussed. Based on the developed chiral HPLC method, enantioselective analysis methods for this fungicide in environment matrix (soil and water) were developed and validated. Good linearities were obtained over the concentration range of 0.25–25mgL⁻¹ for both enantiomers. Liquid–liquid extraction and solid phase extraction (SPE) were used for the enrichment and cleanup of soil and water samples. Recoveries for the two enantiomers were 79–91% at 0.02, 0.04 and 0.2mgkg⁻¹ levels from soil, and 89–101% at 0.0025, 0.01 and 0.05mgL⁻¹ levels from water. Run-to-run and day-to-day assay precisions were below 10% for both enantiomers at concentrations of 0.5, 1 and 5mgL⁻¹. Individual detection limits of the two enantiomers were both 2ng. Limits of detection (LOD) were 0.004mgkg⁻¹ in soil and 0.001mgL⁻¹ in water.

Keywords: Benalaxyl; Enantioselective analysis; HPLC; Soil; Water

Multiple chromatographic fingerprinting and its application to the quality control of herbal medicines by Xiao-Hui Fan; Yi-Yu Cheng; Zheng-Liang Ye; Rui-Chao Lin; Zhong-Zhi Qian (pp. 217-224).

Recently, chromatographic fingerprinting has become one of the most powerful approaches to quality control of herbal medicines. However, the performance of reported chromatographic fingerprinting constructed by single chromatogram sometimes turns out to be inadequate for complex herbal medicines, such as multi-herb botanical drug products. In this study, multiple chromatographic fingerprinting, which consists of more than one chromatographic fingerprint and represents the whole characteristics of chemical constitutions of the complex medicine, is proposed as a potential strategy in this complicated case. As a typical example, a binary chromatographic fingerprinting of “ Danshen Dropping Pill�? ( DSDP), the best-sold traditional Chinese medicine in China, was developed. First, two HPLC fingerprints that, respectively, represent chemical characteristics of depsides and saponins of DSDP were developed, which were used to construct binary chromatographic fingerprints of DSDP. Moreover, the authentication and validation of the binary fingerprints were performed. Then, a data-level information fusion method was employed to capture the chemical information encoded in two chromatographic fingerprints. Based on the fusion results, the lot-to-lot consistency and frauds can be determined either using similarity measure or by chemometrics approach. The application of binary chromatographic fingerprinting to consistency assessment and frauds detection of DSDP clearly demonstrated that the proposed method was a powerful approach to quality control of complex herbal medicines.

Keywords: Multiple chromatographic fingerprinting; Data fusion; Quality control of herbal medicines; Danshen Dropping Pill; Salvia miltiorrhiza; Bunge; Panax notoginseng

The high throughput analysis of N-methyl carbamate pesticides in fruits and vegetables by liquid chromatography electrospray ionization tandem mass spectrometry using a short column by Tomomi Goto; Yuko Ito; Sadaji Yamada; Hiroshi Matsumoto; Hisao Oka; Hisamitsu Nagase (pp. 225-232).

We developed a new analysis method for the nine N-methyl carbamate pesticides in fruits and vegetables using ESI LC/MS/MS with direct sample injection into a short column. After extraction of the pesticides with ethyl acetate from sample, the extract is evaporated to dryness and redissolved in ultra pure water before injection into LC/MS/MS. The method needs no cleanup steps. The average recoveries from fruits and vegetables fortified at the level of 0.01μg/g ranged from 56.0 to 119.1% with the coefficients of variation ranging from 0.2 to 7.6% for intra-day ( n=5×3 days) and from 0.8 to 18.4% for inter-day ( n=15). At the fortified level of 0.5μg/g, the recoveries ranged from 67.7 to 119.3% with the coefficients of variation ranging from 0.5 to 7.8% for intra-day ( n=5×3 days) and from 0.9 to 14.8% for inter-day ( n=15). The method is considered to be satisfactory for the monitoring of the carbamate pesticide residues in fruits and vegetables, suggesting that the present method is applicable to other pesticide residues in foods.

Keywords: High throughput analysis; N; -Methyl carbamate pesticides; Fruits; Vegetables; ESI LC/MS/MS

Determination of cyclamate in foods by high performance liquid chromatography–electrospray ionization mass spectrometry by Ziqiang Huang; Jinyu Ma; Bo Chen; Ying Zhang; Shouzhuo Yao (pp. 233-237).

A high sensitive method for determination of cyclamate in foods by ion-pair high-performance liquid chromatography–electrospray ionization mass spectrometry was developed and validated. The separation was achieved on a C₈ column with 5mM tris(hydroxymethyl)aminomethane aqueous solution (pH 4.5, adjusted by acetic acid) as mobile phase with an isocratic mode. The quantification of target compound was completed using a selected ion recording (SIR) at m/ z 178 obtained from ESI-mode. Tiopronin was used as internal standard for the quantification of cyclamate. The correlation coefficient of the calibration curve were better than 0.996, in the range of 50–5000ng/mL. The limit of detection is 5ng/mL, the limit of quantification is 20ng/mL. The inter- and intra-day accuracy, precision were investigated in detail. The method can be used to monitor effectively the content of the artificial sweetener in foods. The method has obvious merits such as high sensitivity, specificity and simply versus other methods reported.

Keywords: Cyclamate; Artificial sweetener; HPLC–ESI MS

A environmentally friendly reversed-phase liquid chromatography method for phthalates determination in nail cosmetics by D. De Orsi; L. Gagliardi; R. Porr�; S. Berri; P. Chimenti; A. Granese; I. Carpani; D. Tonelli (pp. 238-241).

A simple and rapid analytical method was developed for the determination of phthalates, usually employed in nail cosmetic products. The method is based on an ultrasonic extraction of the sample with ethanol–water (90:10, v/v) followed by HPLC separation and quantitation. HPLC was carried out using a C18 column and spectrophotometric detection at 254nm. A linear gradient elution was performed with ethanol–water starting from 50 to 95% ethanol in 30min. Standard calibration curves were linear for all the analytes over the concentration range 5–200μgml⁻¹ with LOD values of about 0.5μgml⁻¹.The proposed green analytical method has been successfully applied for the analysis of commercial samples in order to check the presence of phthalates and to determine their concentration.

Keywords: Phthalates; HPLC; Cosmetic products; Quality control; Green analytical chemistry

Determination ofl-ascorbic acid in wines by direct injection liquid chromatography using a polymeric column by Paulo Lopes; Jessica Drinkine; C�dric Saucier; Yves Glories (pp. 242-245).

A rapid method for the identification and quantification ofl-ascorbic acid in wines by direct injection liquid chromatography equipped with a UV detection was developed. The levels of ascorbic acid were determined using a polymeric PLRP-S 100A (5μm) column (150mm×4.6mm) with a mobile water/trifluoroacetic acid (99/1, v/v) phase. The method is rapid (less than 5min) and sensitive (LOQ of 5mgL⁻¹). The calibration curve of ascorbic acid was linear ( r=0.999) over a concentration range between 1 and 200mgL⁻¹. Repeatability was less than 2.5% and the recovery over 95%.

Keywords: Liquid chromatography; l; -ascorbic acid; Wine

Highly sensitive fluorescence detection with Hg-lamp and photon counter in microchip capillary electrophoresis by Qin Yan; Rong Sheng Chen; Jie-Ke Cheng (pp. 246-249).

A microchip capillary electrophoresis system with highly sensitive fluorescence detection is reported. The system was successfully constructed using an inverted fluorescence microscope, a highly sensitive photon counter, a photomultiplier tube (PMT) and a capillary electrophoresis microchip. This system can be applied to the fluorescence detection with various wavelengths (300–600nm). Different fluorescence reagents require different excitation wavelengths. The wavelengths of UV light (300–385nm), blue light (450–480nm) and green light (530–550nm) are employed to excite Titan yellow, fluorescence-5-isothiocyanate (FITC) and Rhodamine 6G, respectively. The detection limit (S/N=3) of FITC is 7×10⁻¹⁰M, which is 2–3 orders of magnitude lower than that obtained with the lamp-based fluorescence and PMT detection system and approaches the data gained by the laser-induced fluorescence detection. The linear relationship is excellent within the range of concentration 1.3×10⁻⁹ to 6.5×10⁻⁸M FITC. It offers a new method to widen the application of the lamp-based fluorescence detection.

Keywords: Microchip capillary electrophoresis; Photon counter; Fluorescence detection; Fluorescence-5-isothiocyanate (FITC)

Characterization of lignin using multi-angle laser light scattering and atomic force microscopy by Aarti V. Gidh; Stephen R. Decker; Chun H. See; Michael E. Himmel; Clint W. Williford (pp. 250-258).

Small differences in the isolation techniques of lignin can result in significant changes in its molecular structure and configuration. Light scattering (evaluated at 18 different angles in a plane), Atomic Force Microscopy (AFM) and Near Infrared Spectroscopy (NIR) proved very effective for evaluating the characteristics of lignin. Zimm plots were generated using Zimm, Debye and Berry formalisms to evaluate the weight average molecular weight (MW), radius of gyration ( r_g), hydrodynamic radius ( r_h) and second virial coefficient ( A₂). Two types of lignin and nine different solvents were used for the study, to analyze the conformation of lignin molecules in different solvents expected to be used in lignin degradation and subsequent analysis. Absolute MW and r_g decreased and the d n/d c increased when the solvent used for lignin was changed from water to sodium hydroxide. The two types of lignin also exhibited different values for all the above estimated parameters. This study also highlighted the differences between the unlyophilized and lyophilized lignin in terms of aggregation, pH dependence and stability over time. This aggregation has never been seen on a ultraviolet (UV) or refractive index (RI) detector that has been used so far for liquid chromatography (LC) reducing the reliability of lignin depolymerization data obtained without light scattering.

Keywords: Abbreviations; NL; NREL lyophilized lignin; NREL; second batch of NREL lyophilized lignin; LL; NREL unlyophilized lignin; pH 12; lignin dissolved in 0.1; N NaOH titrated down to pH 12; pH 14; untitrated 0.1; N NaOHLignin; Characterization; Aggregation; Molecular conformation; Multi-angle laser light scattering; Atomic force microscopy; Depolymerization

Detection of malathion by the CO₂ laser: Potentials and limitations by Dubravka S. Maravić; Milan S. Trtica; Šćepan S. Miljanić; Bojan B. Radak (pp. 259-262).

Possibilities of on-line non-contact detection of the vapour of the commercially available pesticide malathion by the CO₂ laser were investigated, using a photoacoustic technique developed in our laboratory. A set of laser/vapour spectral coincidences in the usual range of CO₂ laser wavelengths were obtained, the samples being: the commercial product Etiol available on the market, solvent, emulsifiers, and neat malathion, all with air added to a mid-pressure of about 100mbar and to atmospheric pressure. Relative contributions of the components in the product are discussed. A detection limit of 0.002vol.% of the product in air was estimated.

Keywords: Laser spectroscopy; CO; ₂; laser; Photoacoustics; Pesticides; Malathion; Etiol; Organophosphorous

Gold colloid analysis by inductively coupled plasma-mass spectrometry in a single particle mode by C. Degueldre; P.-Y. Favarger; S. Wold (pp. 263-268).

Analysis in a single particle mode of gold colloids in water has been performed by inductively coupled plasma-mass spectrometry (ICP-MS). The signal induced by the flash of ions due to the ionization of a colloid in the plasma torch can be measured for the ions¹⁹⁷Au⁺ by the mass spectrometer without interferences. The intensity of the MS signal is recorded in time scan. The recorded peak distributions were analysed as a function of the colloid size for five monodisperse colloids (80–250nm). This study describes the experimental conditions to analyse gold colloids in a single particle mode. The size detection limit is around 25nm corresponding to 0.15fg colloids and one particle per ml may be detected during a 1min time scan within standard procedure.

Keywords: Single particle analysis; Inductively coupled plasma-mass spectrometry; ICP-MS; Gold colloid; Colloid size

Qualitative and quantitative analysis of quaternary ammonium alkaloids from Rhizoma Corydalis by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry coupled with a selective precipitation reaction using Reinecke salt by Zhi-hong Cheng; Yin-long Guo; Hao-yang Wang; Guo-qiang Chen (pp. 269-277).

A major problem hampering the use of MALDI-MS for quantitative measurements is the inhomogeneous distribution of analytes and matrices in sample preparations. In this study, an aerospray method was utilized for sample preparation method to improve sample homogeneity across stainless steel targets for quantitative analysis of quaternary ammonium alkaloids (QAAs). A selective precipitation reaction with Reinecke salt known to selectively trap QAAs was used to facilitate the separation and purification of QAAs from the complex crude plant extracts. Palmatine and berberine as the representative QAAs in commercial Rhizoma Corydalis were successfully quantified by introducing an internal standard with similar molecular properties as analytes. The LODs were found to be 0.07fmol, for palmatine, and 0.24fmol, respectively, for berberine. The content of QAAs of three commercial Rhizoma Corydalis was between 0.201 and 0.245% for palmatine, and 0.049–0.057% for berberine. Furthermore, MS/MS experiments based on the accurate-mass measurements were carried out by infrared multiphoton dissociation (IRMPD) for QAAs and the corresponding tertiary alkaloids, which offered additional selectivity for this quantitative analysis method. In the fragmentation of precursor ions from QAAs, only cleavage of substituted groups attached to the A- or D-ring was observed, while cleavage between B- and C-ring from tertiary alkaloids had occurred. This study offers a perspective into the utility of MALDI-FTMS as an alternate quantitative tool for QAAs, especially in complex plant extracts.

Keywords: MALDI-MS; Corydalis yanhusuo; Quantitative analysis; Reinecke salt; Aerospray

Chemical shifts as a novel measure of interactions between two binding sites of symmetric dialkyldimethylammonium bromides to α-cyclodextrin by Noriaki Funasaki; Seiji Ishikawa; Shun Hirota (pp. 278-285).

Complex formation of α-cyclodextrin (α-CD) with decyltrimethylammonium (DeTAB), N, N-dioctyldimethylammonium (DOAB), and N, N-didecyldimethylammonium bromides (DDeAB) was investigated by proton NMR spectroscopy. Analysis of chemical shifts yielded macroscopic 1:1 and 1:2 binding constants ( K₁ and K₂) and chemical shift differences (Δ δ_SD and Δ δ_SD2) for the 1:1 and 1:2 complexes of DeTAB, DOAB, and DDeAB with α-CD. The K₁ and K₂ values of DDeAB were quantitatively explained on the basis of the assumption that the microscopic 1:1 binding constant of DDeAB is identical to the observed K₁ value of DeTAB. The K₂ value of DDeAB was also explained in terms of its observed K₁ value and the independent binding of two alkyl chains. Furthermore, the Δ δ_SD and Δ δ_SD2 values for protons of DDeAB and α-CD were quantitatively explained on the basis of the assumption that the geometry of the decyl group of DDeAB in an α-CD cavity is identical to that of DeTAB. The Δ δ_SD value was also explicable on the basis of the same geometric assumption and the observed Δ δ_SD2 value for this system. Similar results were obtained for the 1:1 and 1:2 DOAB–α-CD complexes.

Keywords: Chemical shift; Microscopic binding constant; α-Cyclodextrin; Symmetric double chain surfactant

Robustness of calibration models based on near infrared spectroscopy for the in-line grading of stonefruit for total soluble solids content by M. Golic; K.B. Walsh (pp. 286-291).

The utility of near infrared spectroscopy as a non-invasive technique for the assessment of internal eating quality parameters of stonefruit (peaches, nectarines and plums) was assessed. Calibration model performance for the attributes of total soluble solids (TSS) was encouraging (typical R²>0.88, RMSECV 0.53–0.88%TSS, SDR_CV 2.9–3.7). Model performance was acceptable using a combined multi-variety peach–nectarine data set, but it was advantageous to maintain a separate multi-variety plum model. Model robustness to temperature was achieved by including into the calibration set samples scanned at a range of temperatures, with less than 5% of total population required to be treated in this way. Similarly, where models incorporated the range of TSS seen in the validation population, prediction performance was good. Model performance was stable over several seasons in terms of R² (typical R²>0.8), with bias corrected SEP varying in proportion to population S.D. Prediction bias for new populations could be corrected by model updating or direct bias adjustment.

Keywords: NIR; Stonefruit; Peach; Nectarine; Plum; Total soluble solids content; Robustness

Microtiter plate assay for phosphate using a europium–tetracycline complex as a sensitive luminescent probe by Axel Duerkop; Matejka Turel; Aleksandra Lobnik; Otto S. Wolfbeis (pp. 292-298).

A new luminescent europium probe is presented for the determination of phosphate (P) in microtiter plate format. The assay is based on the quenching of the luminescence of the europium–tetracycline (EuTc) 1:1 complex by phosphate using a reagent concentration of 20.8μmol/L. The probe is excited at 400nm and displays a large Stokes’ shift of 210nm. The emission maximum is located at 616nm. The system works best at neutral pH 7 and is therefore suitable for phosphate determination in biological and biochemical systems. The linear range of the calibration plot is from 5×10⁻⁶mol/L to 7.5×10⁻⁴mol/L of phosphate, and the limit of detection is 3μmol/L.

Keywords: Phosphate; Microplate assay; Luminescence; Lanthanide

Fluorescence resonance energy transfer disposable sensor for copper(II) by C. Cano-Raya; M.D. Fern�ndez-Ramos; L.F. Capit�n-Vallvey (pp. 299-307).

A disposable sensor has been developed for the measurement of copper(II) concentration in aqueous solution based on a change in the fluorescence of porphyrazine 2,7,12,17-tetra- tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine (TP). The sensor was constructed by spin-coating a polyester support with a PVC solution containing TP, a plasticizer, the chelating agent Zincon and the ion-pairing benzetonium chloride. The measurement principle is based on the radiationless resonance energy transfer (RET) from TP immobilized in membrane, and acting as fluorescence donor, to Zincon acting as an acceptor induced by copper(II). The absorption spectrum of the Zincon–Cu(II) complex presents adequate overlapping with the emission spectrum of TP, producing a useful analytical signal by the RET process.The disposable sensor responds to copper(II) irreversibly over a dynamic range from 0.039 to 14μmolL⁻¹ (2.5–890μgL⁻¹) with a sensor-to-sensor reproducibility (relative standard deviation RSD) of 1.9%, aslogaCu2+, at the medium level of the range and a response time of 10min. The performance of the optical disposable sensor was tested for the analysis of copper in different types of natural waters (river, well, spring and swimming pool), validating results against a reference procedure.

Keywords: Disposable sensor; Copper determination; Resonance energy transfer; Fluorescence; Water analysis

Design and characterization of a lactate biosensor based on immobilized lactate oxidase onto gold surfaces by A. Parra; E. Casero; L. V�zquez; F. Pariente; E. Lorenzo (pp. 308-315).

The design and characterization of a lactate biosensor and its application to the determination of this analyte in wine and beer are described. The biosensor is developed through the immobilization of lactate oxidase (LOx) using two different strategies including direct adsorption and covalent binding. The characterization of the resulting lactate oxidase monolayers was performed in aqueous phosphate buffer solutions using atomic force microscopy (AFM) and quartz crystal microbalance (QCM) techniques. In presence of lactate and using hydroxymethylferrocene as a redox mediator, biosensors obtained by either direct adsorption or by covalent binding exhibit a clear electrocatalytic activity, and lactate could be determined amperometrically at 300mV versus SSCE. Results obtained under these conditions give a linear current response versus lactate concentration up to 0.3mM, with a detection limit of 10μM of lactate and a sensitivity of 0.77±0.08μAmM⁻¹. Finally, biosensors were applied to the determination of lactate in wine and beer. The results obtained are in good agreement with those obtained by a well-established enzymatic-spectrophotometric assay kit.

Keywords: Lactate oxidase biosensor; Hydroxymethylferrocene; AFM; QCM

Entrapment of plant invertase within novel composite of agarose–guar gum biopolymer membrane by Dipali Bagal; Meena S. Karve (pp. 316-321).

Invertase or β-d-Fructofuranosidase (E.C.3.2.1.26) was extracted from Cucumis melo. L. fruit (Family-Cucurbitaceae). Soluble, plant invertase enzyme was immobilized in novel composite of agarose–guar gum biopolymer matrix in the form of hydrophilic, porous membranes. The immobilized invertase was characterized for sucrose hydrolytic activity and leakage from the matrix support. The efficiency of immobilization was found to be 91% with negligible leaching. The kinetic parameters K_m and V_max for free and immobilized invertase were also determined. Immobilized invertase was optimally active in the wide pH range of 4.5–6.5. The immobilization process also enhanced the thermal stability of enzyme up to 65°C. Immobilized invertase membranes showed excellent storage stability with shelf life of 110 days. Entrapped invertase showed better operational stability and reusability up to 12 cycles. The fluorescence spectra of the composite membranes were studied and compared with that of soluble enzyme. All these characteristics of the immobilized invertase membranes make them suitable for the fabrication of biosensors.

Keywords: Acid invertase; Immobilization; Agarose–guar gum composite; Sucrose

A novel barium polymeric membrane sensor for selective determination of barium and sulphate ions based on the complex ion associate barium(II)–Rose Bengal as neutral ionophore by A.M. Othman; M.S. El-Shahawi; M. Abdel-Azeem (pp. 322-328).

A simple, long life, rapid response and sensitive barium(II)–PVC membrane sensor that typically follows Nernstian behavior has been developed for the assay of barium(II) ions. The developed sensor has been made by incorporating the complex ion associate of barium(II)–Rose Bengal (Ba–RB) as an ionophore into a plasticized PVC matrix. The sensor is stable and exhibited fast potential response of 20s and gave a good linear response with a Nernstian slope of 28.5±0.4mV/decade of activity within the concentration range 5×10⁻⁵ to 10⁻¹M over a wide range of pH 4.5–10.0 for barium(II) ions. The developed sensor showed comparatively good selectivity for barium(II) ions with respect to other alkali, alkaline earth, transition and heavy metal ions. The plasticizer o-nitrophenyloctyl ether controlled significantly the calibration slope and the lifetime of the fabricated sensor. The proposed sensor was used successfully for the analysis of barium(II) ions in wastewater samples and in lithophone pigment with excellent recovery percentages in the range 98.9–99.8±1.6%. The determination of sulphate in fresh and potable water samples with the developed sensor has been also achieved successfully. The described sensor provides a reliable means with good correlation with the data obtained by atomic absorption spectrometry (AAS) and other spectrophotometric methods for the analysis of trace amounts of barium(II) and/or sulphate ions in different matrices.

Keywords: Barium(II) ions; Sulphate ions; PVC membrane sensor; Wastewater; Pigment

Al(III)-selective electrode based on newly synthesized xanthone derivative as neutral ionophore by Abdollah Yari; Leila Darvishi; Mojtaba Shamsipur (pp. 329-335).

The suitability of a xanthone derivative, 1-hydroxy-3-methyl-9 H-xanthen-9-one (HMX) as a neutral ionophore for the preparation of a polyvinylchloride (PVC) membrane electrode for aluminum(III) ions was investigated. The prepared electrode exhibits a Nernstian response for Al³⁺ ions over a wide concentration range (1.0×10⁻⁶ to 1.6×10⁻¹M) with a limit of detection 6.0×10⁻⁷M. It has a relatively fast response time and can be used for at least three months without any considerable divergence in potentials. The proposed membrane electrode revealed very good selectivity for Al³⁺ ions over a wide variety of other cations and could be used at a working pH range of 3.0–8.5. It was used as an indicator electrode in potentiometric titration of aluminum ions with EDTA and in the determination of Al³⁺ in different real samples.

Keywords: Al(III) ion-selective electrode; PVC membrane; Xanthone; Potentiometry

Highly selective and sensitive thiocyanate membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine by Hassan Ali Zamani; Farhad Malekzadegan; Mohammad Reza Ganjali (pp. 336-340).

A highly selective membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine (NOBP) is presented. The proposed electrode shows very good selectivity for thiocyanate ions over a wide variety of common inorganic and organic anions. The sensor displays a near Nernstian slope of −58.7±0.6mV per decade. The working concentration range of the electrode is 1.0×10⁻⁶ to −1.0×10⁻¹M with a detection limit of 5.7×10⁻⁷M (33.06ng/mL). The response time of the sensor in whole concentration ranges is very short (<10s). The response of the sensor is independent on the pH range of 4.3–9.8. The best performance was obtained with a membrane composition of 30% PVC, 65% dibutyl phthalate, 3% NOBP and 2% hexadecyltrimethylammonium bromide. It was successfully applied to direct determination of thiocyanate in biological samples, and as an indicator electrode for titration of thiocyanate ions with AgNO₃ solution.

Keywords: Potentiometry; NOBP; PVC membrane; Thiocyanate-selective electrode

Electrooxidation of the antiviral drug valacyclovir and its square-wave and differential pulse voltammetric determination in pharmaceuticals and human biological fluids by Bengi Uslu; Sibel A. Özkan; Zühre Şentürk (pp. 341-347).

The electrochemical properties of valacyclovir, an antiviral drug, were investigated in pH range 1.8–12.0 by cyclic, differential pulse and square-wave voltammetry. The drug was irreversibly oxidized at a glassy carbon electrode in one or two oxidation steps, which are pH-dependent. For analytical purposes, a very resolved diffusion controlled voltammetric peak was obtained in Britton–Robinson buffer at pH 10.0 using differential pulse and square-wave modes. Limits of detection were 1.04×10⁻⁷ and 4.60×10⁻⁸M for differential pulse and square-wave voltammetry, respectively. The applicability to direct assays of tablets, spiked human serum and simulated gastric fluid, was described.

Keywords: Valacyclovir; Cyclic voltammetry; Differential pulse voltammetry; Square-wave voltammetry; Glassy carbon electrode; Tablet; Biological fluids

Hierarchical classification designs for the estimation of different sources of variability in proficiency testing experiments by Pedro Araujo; Livar Fr�yland (pp. 348-353).

An approach to the estimation of possible different sources of variation found in proficiency testing experiments is described. Four errors namely, technique, analyst, laboratory and geographical location are considered and calculated by using a rational experimental design based on hierarchical classification. The treatment of the confidence of the design over different experimental arrangements is explored and visualised by calculating a function that depends only on the design and not on the experimental response. An illustrative example based on simulated data is used to show how the theory could be applied in practice.

Keywords: Proficiency testing (PT); Experimental design; Hierarchical classification; Sources of variability; Accreditation; Performance parameter; Quality assurance; Quality control; Confidence of the experimental design

Preliminary chemometric study of minerals and trace elements in Spanish infant formulae by C. Sola-Larra�aga; I. Navarro-Blasco (pp. 354-363).

The concentrations of minerals (Na, K, P, Ca and Mg) and trace elements (Fe, Zn, Cu, Mn, Se, Al, Cd and Pb) in a total of 105 different infant formulae (starter, follow-up, premature, specialised and soya formulae) marketed in Spain were determined by atomic spectrometry (flame and electrothermal) and inductively coupled plasma emission spectroscopy after acid-microwave decomposition. On the basis of the elements distribution, a preliminary chemometric study with the use of pattern recognition methods was carried out. Hierarchical cluster analysis (HCA), principal component analysis (PCA), as unsupervised exploratory techniques, and linear discriminant analysis (LDA), were applied to characterise, classify and distinguish the different types of infant formulae. The HCA results showed that mineral and trace element content data support adequate information to obtain the infant formula differentiation. PCA permitted the reduction of 13 variables to four principal components accounting for 61.9% of the total variability. This four-factor model interprets reasonably well the correlations of these studied elements. The obtained element associations may be attributed to the composition of matrix ingredients, the contamination during elaboration, the additives and mineral supplements added and the present tendency of standardization in the manufacture of infant formulae. The application of LDA gave a 77.1% of infant formulae correctly assigned with three clearly differentiated and two overlapped groups. The use of discriminant functions, as a complementary tool, to distinguish the different types depending on protein matrix of infant formula, is also discussed. This survey shows that HCA, PCA and LDA techniques appear useful tools for the characterisation and classification of infant formulae using their elemental profile.

Keywords: Infant formulae; Atomic spectrometry; Pattern recognition; Multivariate analysis; Cluster analysis; Principal component analysis; Linear discriminant analysis

Phenanthrene degradation in subcritical water by Yu Yang; Frank Hildebrand (pp. 364-369).

Subcritical water (<374°C and <221bar) has unique characteristics such as dramatically decreased dielectric constant, surface tension, and viscosity with increasing temperature, allowing for dissolution and reaction of organics in high-temperature water to occur. Additionally, the dissociation constant of water at temperatures of 200–300°C is three orders of magnitude greater than that of ambient water, which may also contribute to the reactivity of subcritical water with certain organic compounds. In this study, the degradation and oxidation of phenanthrene in subcritical water were investigated. Both deionized water and water with 3% hydrogen peroxide were used in the degradation and oxidation studies. The effect of temperature on degradation efficiency has been determined with a temperature range of 100–350°C. When the temperature was increased from 150 to 350°C, the amount of phenanthrene degraded varied from 6 to 243μg in each milliliter of deionized water. However, these quantities were increased to 195μg at 150°C and 3680μg at 350°C in each milliliter of water with 3% hydrogen peroxide. Several degradation products including phenol, benzoic acid, and ketones were identified by using gas chromatography/mass spectrometry (GC/MS).

Keywords: Phenanthrene; Ketones; Phenol; Benzoic acid; Subcritical water; GC/FID; GC/MS; Degradation; Oxidation

Automatic flow system for the sequential determination of copper in serum and urine by flame atomic absorption spectrometry by Cristina M.P.V. Lopes; Agostinho A. Almeida; Jo�o L.M. Santos; Jos� L.F.C. Lima (pp. 370-376).

In this work, a fully automated flow system exploiting the advantages of the association of multi-pumping, multicommutation, binary sampling and merging zones, to accomplish the sequential determination of copper in serum and urine by flame atomic absorption spectrometry, is described. The developed flow system allowed multiple tasks, such as serum samples preparation (samples and standard solutions viscosity adjustment), serum copper (SCu) measurement, urine copper (UCu) pre-concentration and its subsequent elution and measurement, to be carried out sequentially. The implemented flow manifold presented a modular configuration consisting on two quasi-independent modules, each one accountable for a specific sample manipulation and whose combined operation under computer control enabled the determination of copper in a wide concentrations range.Once optimised and with a sample consumption of about 0.250mL of serum and 7mL of urine, the developed flow system allowed linear calibration plots up to 5mgL⁻¹ with a detection limit of 0.035mgL⁻¹ for SCu and linear calibration plots up to 300μgL⁻¹ with a detection limit of 0.67μgL⁻¹ for UCu. The sampling rate varied according to the module employed and was about 360determinationsh⁻¹ (SCu module), 12determinationsh⁻¹ (UCu module) or 24determinationsh⁻¹ (12 urine and 12 serum samples; UCu and SCu modules simultaneously). Repeatability studies (R.S.D.%, n=10) showed good precision for UCu at concentrations of 25μgL⁻¹ (2.54%), 50μgL⁻¹ (0.90%) and 100μgL⁻¹ (1.62%) as well as for SCu at concentrations of 0.25mgL⁻¹ (8.11%), 1mgL⁻¹ (3.11%) and 5mgL⁻¹ (0.90%). A comparative evaluation showed a good agreement between the results obtained in the analysis of UCu and SCu ( n=18) by both the developed methodology and the reference procedures. Accuracy was further evaluated by means of the analysis of reference samples (Seronorm™ Trace Elements Urine and Seronorm™ Trace Elements Serum) and the obtained results complied with the certified values.

Keywords: Copper; Serum; Urine; Flame atomic absorption spectrometry; Multi-pumping flow system

A flow sampling strategy for the analysis of oil samples without pre-treatment in a sequential injection analysis system by Paula C.A.G. Pinto; M. L�cia M.F.S. Saraiva; Jos� L.F.C. Lima (pp. 377-383).

The present work describes a sequential injection analysis (SIA) system adapted to direct analysis of oil samples. In this way, the flow system was designed by incorporation, in the SIA system, of an injection valve that was responsible for the sample insertion. With the developed sampling strategy the sample pre-treatment outside the flow system is avoided and also the problems associated with viscous samples in flow systems.The developed SIA system was applied to the determination of iron (Fe(III)) in edible oil samples and was based on the formation of a red complex ( λ=510nm) between Fe(III) and thiocyanate in organic medium. A mixture of methanol:chloroform (85:15) was used as carrier solution and possible refractive index associated with the spectrophotometric detection was avoided by introduction of a mixing chamber in the flow system. The presented methodology produced 4.2ml of effluent and consumed 150μl of sample and 0.95mg of thiocyanate per determination.Linear calibration plots were obtained for Fe(III) concentrations up to 25mgl⁻¹ and the detection limit of the determination was 0.31mgl⁻¹. The developed methodology exhibited a good precision, with an R.S.D.<3.5% ( n=15) and a determination frequency of 20 determinations h⁻¹. The results of the analysis were evaluated by recovery studies (96.5–104.5%) and by the analysis of two AOCS reference samples.

Keywords: Sequential injection analysis; Edible oil; Sampling strategy; Organic medium; Iron

Method study for the preparation of a wet sediment quality control material by A. Guevara-Riba; R. Rubio; G. Rauret; H. Muntau; A. Sahuquillo (pp. 384-390).

Quality control materials (QCMs) to be used in daily quality control in environmental laboratories are required to be similar to real samples in terms both of composition and of physical state. The present paper describes in detail the procedure of preparation and the results of homogeneity and stability studies performed on wet sediments QCMs. For this purpose, two sediments with different matrix composition were selected and the main factors involved in the preparation of the material were carefully studied and established with the aim of guaranteeing long-term stability of the QCM: pre-treatment steps, homogenisation, bottling and storage. The results obtained from the homogeneity and from 12 months of stability studies for Cd, Cr, Cu, Ni, Pb and Zn following the aqua regia extraction procedure (ISO 11466), showed that the wet sediment QCMs we have developed are feasible, constituting a new and useful material among the aquatic sediments for quality control purposes in monitoring.

Keywords: Quality control material; Reference materials; Wet sediment; Trace metals analysis; Homogeneity studies; Stability studies

Gravimetric analysis of high purity tellurium for purity evaluation by Toshihiro Suzuki; Akiharu Hioki (pp. 391-394).

Gravimetric analysis was utilized for purity evaluation of high purity tellurium, which was a raw material of a tellurium standard solution. Using a method in which tellurium was precipitated as elemental tellurium with hydrazinium after dissolution of the high purity tellurium, an avoidable positive error (ca. 0.02%) was observed. It seems that a cause of the positive error is oxidation of the tellurium or occlusion of the solvent during the precipitation. On the other hand, when the precipitated elemental tellurium was further converted into tellurium oxide by heating at 600�C, the positive error disappeared. Finally, the purity of the starting tellurium was evaluated from the recovery of tellurium oxide with sufficient accuracy for a raw material of a tellurium standard solution (0.017% expanded uncertainty ( k=2)).

Keywords: Tellurium; Tellurium oxide; Gravimetric analysis; Hydrazinium; Uncertainty; Primary method of measurement

Author Index (pp. 395-398).

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Analytica Chimica Acta (v.555, #2)