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Analytica Chimica Acta (v.536, #1-2)

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

Calendar of forthcoming meetings (pp. n1-n3).

A metabolomic investigation of splanchnic metabolism using¹H NMR spectroscopy of bovine blood plasma by H.C. Bertram; N.B. Kristensen; A. Malmendal; N.C. Nielsen; R. Bro; H.J. Andersen; D.L. Harmon (pp. 1-6).

This is the first study introducing an NMR-based metabolomic approach to elucidate metabolism in the portal-drained viscera and liver. High-resolution¹H NMR spectroscopy was performed on blood plasma obtained from the mesenteric artery, the hepatic portal vein and the hepatic vein of steers before and after interruminal infusion of short-chain fatty acids (SCFA). Partial least squares regression discriminant analysis (PLS-DA) on¹H NMR spectra obtained for arterial and portal plasma samples revealed increases in the intensities of spectral regions that could mostly be assigned to the methyl group of propionate, β-hydroxybutyrate as well as acetate in portal plasma samples compared with arterial plasma samples. PLS-DA on portal and hepatic plasma samples showed decreases in the intensities of spectral regions corresponding to the regions where methyl and methylene groups of n-butyrate, propionate, iso-butyrate, valerate, iso-valerate as well as lactate are reported to have chemical shifts. In addition, spectral differences likely to reflect a hepatic excretion of β-hydroxybutyrate and glucose were observed between portal and hepatic samples. All findings were supported by traditional biochemical analyses. Consequently, the present study clearly demonstrated the great potential of the NMR-based metabolomic approach for elucidating splanchnic metabolism. In addition, prediction of metabolite concentrations from the¹H NMR spectra obtained on plasma samples was investigated using PLS, which in relation to use¹H NMR spectra quantitatively revealed promising results with R-values in the region of 0.87–0.98.

Keywords: Volatile fatty acids; Rumen; Liver; Multivariate analysis; Chemometrics; Metabonomics

Structure–enantioselectivity relationship of hypnotic-sedative 1,4-disubstituted piperazine derivatives on cellulose tris(4-methylbenzoate) chiral stationary phase by Zdzislaw Chilmonczyk; Hanna Ksycińska; Malgorzata Lisowaka-Kuźmicz; Anna Jończyk; Maria Mazgajska; Malgorzata Jarończyk; Anna Strzelczyk; Hassan Y. Aboul-Enein (pp. 7-13).

Chromatographic behaviour of 19 chiral 1,4-disubstituted piperazine derivatives with hypnotic-sedative activity has been examined on cellulose tris(4-methylbenzoate) with hexane–isopropanol mobile phases. The chiral resolution has been obtained for of 14 (out of 19) compounds. While three of the resolved compounds (5,6 and10) did not undergo enantiodifferentiation ( α=1) at relatively high isopropanol content (50–10%) in hexane, however, enantiodifferentiation was possible ( α=1.06–1.40) at lower isopropanol contents. Enantioselectivity changes induced by isopropanol content variations were discussed in terms of the concept of true and apparent separation factors. The retention factors of the compounds were described with the aid of modified Soczewiński–Snyder equation. Theoretical calculations were carried out for the chiral stationary phase model, which stressed the importance of a solute and the stationary phase aromatic ring interactions.

Keywords: Liquid chromatography; Molecular dynamics simulation; Solute–chiral stationary phase interaction

Enantioseparation of alkyl tropate by high performance liquid chromatography using (2 R, 3 R)-di- n-propyl tartrate by Hongmei He; Xiuzhu Xu; Datong Zhang; Juanjuan Chen (pp. 15-20).

Optically active tartaric acid and its diester derivatives are well known as effective chiral selectors. In the current studies, a self-prepared diester of tartaric acid (2 R, 3 R)-di- n-propyl tartrate (DPT) was used as a chiral mobile-phase additive (CMPA) for the enantioseparation of seven kinds of alkyl tropate on a silica gel column by high performance liquid chromatography (HPLC). Four kinds of alkyl tropate were successfully enantioseparated using this chiral system, indicating that DPT is a novel useful chiral selector. The influences of mobile-phase composition and solute structure on enantioseparation were extensively studied. Although different types of alcoholic additive or various concentrations of alcoholic additive, DPT and dichloromethane in the mobile phase had great influence on the retention factor ( k′) and resolution ( R_s), the mobile-phase composition essentially had no effect on the separation factor ( α). In contrast, the structure of alkyl tropate greatly influenced the separation factor ( α). The results revealed that an increase in the bulkiness of the O-alkyl groups of tropic acid esters reduced the separation factors ( α), indicating that inhibition of the formation of effective hydrogen-bond interaction between DPT and solutes by the bulkiness of the O-alkyl group decreases the retentivity difference between the transient diasterieomeric complex pairs. Our observations suggested that the hydrogen-bond interactions between chiral additives and solutes might be the major chiral recognition mechanism for DPT as CMPA.

Keywords: (2; R; , 3; R; )-Di-; n; -propyl tartrate; Chiral mobile-phase additive; Alkyl tropate; Enantioseparation; High performance liquid chromatography

Detection of saponins in extract of Panax notoginseng by liquid chromatography–electrospray ionisation-mass spectrometry by Li Li; Rong Tsao; Jianpeng Dou; Fengrui Song; Zhiqiang Liu; Shuying Liu (pp. 21-28).

The liquid chromatography–electrospray ionisation-mass spectrometry (LC–ESI-MS) method was developed for the analyses and identification of saponins in plant extract from the root of Panax notoginseng (Burk.) F.H. Chen. The HPLC experiments were proceeded by means of a reversed-phase C18 column and a binary mobile phase system consisting of 0.2% acetic acid and acetonitrile under gradient elution conditions. Eight major peaks were separated and detected using both evaporative light scattering and MS detectors. The mass spectrometer was operated in the negative ion mode using electrospray ionization. The molecular ions, [ M−H]⁻ and the adduct ions [ M+AcO]⁻ of saponins were observed, and from which the molecular weights were obtained. A collision-induced dissociation (CID) experiment was carried out to aid the identification of the backbone and glycosidic linkage sites of the saponins. The identification of the saponins (peaks 1–7) in the extract of P. notoginseng was based on matching their retention times, the detection of the saponin molecular ions, and the fragment ions of the molecular ion obtained in the CID experiments with those of the authentic standards and data reported in the literature. The molecular structure of peak 8 was elucidated according to the fragmentation patterns and the literature reports.

Keywords: Panax notoginseng; Saponins; LC–ESI-MS; CID

Robustness tests on the United States Pharmacopoeia XXVI HPLC assay for ginsenosides in Asian and American ginseng using an experimental design by Yong-Guo Li; Hong Liu; Y. Vander Heyden; Ming Chen; Zheng-Tao Wang; Zhi-Bi Hu (pp. 29-38).

Ruggedness and robustness testing is applied prior to the transfer of a method to various laboratories. It is especially important for official methods that are widely and formally used. Ginsenosides (Rg₁, Re, Rf, Rb₁, Rg₂, Rc and Rd) occurring in Asian and American ginseng, were assayed using high-performance liquid chromatography (HPLC) methods issued by the United States Pharmacopoeia (USP XXVI and XXVII). They have a delicate system suitability to properly execute the method. A robustness test was carried out using an experimental design approach, in order to indicate the suitability of the method in a broad execution range. Seven factors are selected and examined by a fractional factorial design. Twelve responses, involving quantitation-related items, such as recovery of Rg₁ and Rb₁, and qualitative items, such as resolution ( R_s), theoretical plate number ( N), relative retention time (RRT) of two critical pairs, are measured. The calculated effects are both graphically and statistically interpreted to identify the significant factors. The robustness tests using fractional factorial design on the assay of ginsenosides provided an effective approach as part of a validation of the method on phytomedicines. It also indicated that methods with different selectivity, of which some are possibly unsuitable, could pass the existing system suitability limits.

Keywords: Robustness test; Ginsenosides; Asian ginseng; American ginseng; Fractional factorial design; System suitability parameters

HPLC separation of fullerenes on the stationary phases of two Lewis bases modified magnesia–zirconia by Qiong-Wei Yu; Yu-Qi Feng; Zhi-Guo Shi; Jun Yang (pp. 39-48).

Spherical particles (6–8μm) of magnesia–zirconia composite were prepared by means of sol–gel process. The composites were modified with 2,4,6-trinitrophenol and pyrenebutyric acid, respectively, and then used as charge-transfer stationary phases. The resulting stationary phases were characterized by elemental analysis, diffused reflectance FT-IR, nitrogen adsorption analysis and solid state NMR. The separation of C₆₀, C₇₀ and higher fullerenes was investigated on the two stationary phases. The influence of the mobile phase (toluene–cyclohexane) with different composition and the column temperature on the separation of C₆₀ and C₇₀ was examined, respectively. The retention time of C₆₀ and C₇₀ on the two stationary phases increases with decreasing toluene content in the mobile phase or with increasing the column temperature. Higher fullerenes can be separated well at 90°C using toluene as the mobile phase on the 2,4,6-trinitrophenol modified magnesia–zirconia. Based on the results of column loading capacity test, the magnesia–zirconia modified with 2,4,6-trinitrophenol and pyrenebutyric acid are probably considered as potential materials for the separation of fullerenes in large amounts.

Keywords: HPLC; 2,4,6-Trinitrophenol; Pyrenebutyric acid; Magnesia–zirconia; Stationary phase; Separation; Fullerenes

Stress degradation studies on etamsylate using stability-indicating chromatographic methods by Neeraj Kaul; Himani Agrawal; Abhijit Kakad; S.R. Dhaneshwar; Bharat Patil (pp. 49-70).

Two sensitive and reproducible methods are described for the quantitative determination of etamsylate in the presence of its degradation products. The first method was based on high-performance liquid chromatographic (LC) separation of the drug from its degradation products on the reversed phase, kromasil column [C₁₈ (5-μm, 25cm×4.6mm, i.d.)] at ambient temperature using a mobile phase consisting of methanol and water (50:50, v/v). Flow rate was 0.6mlmin⁻¹ with an average operating pressure of 180kgcm⁻² and retention ( t_R) time was found to be 2.93±0.05min. Quantitation was achieved with UV detection at 305nm based on peak area with linear calibration curves at concentration range 10–100μgml⁻¹. The second method was based on high-performance thin layer chromatographic (HPTLC) separation followed by densitometric measurement of spots at 305nm. The separation was carried out on Merck HPTLC aluminium sheets of silica gel 60 F₂₅₄ using toluene:methanol:chloroform (8.0:4.5:6.0, v/v/v) as mobile phase. This system was found to give compact spots for etamsylate after double development (retention factor, R_f value of 0.23±0.02). The second order polynomial regression analysis data was used for the regression line in the range of 500–6000ngspot⁻¹. Both methods have been successively applied to pharmaceutical formulation. No chromatographic interference from the tablet excipients was found. Both methods were validated in terms of precision, robustness, recovery and limits of detection and quantitation. The analysis of variance (ANOVA) and Student's t-test were applied to correlate the results of etamsylate determination in dosage form by means of HPTLC and LC method. Drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment and photo-degradation. As the proposed methods could effectively separate the drug from its degradation products, they can be employed as stability indicating one. Moreover, the proposed LC method was utilized to investigate the kinetics of the acidic, alkaline and oxidative degradation processes at different temperatures and the apparent pseudo first order rate constant, half-life and activation energy was calculated. In addition the pH-rate profile of degradation of etamsylate in constant ionic strength buffer solutions with in the pH range 2–11 was studied.

Keywords: Etamsylate; High-performance liquid chromatography; Reversed phase; High-performance thin layer chromatography; Method validation; Quantitative analysis; Student's; t; -test; Kinetics of degradation; pH-rate profile; Arrhenius plot; Activation energy

Classification and replacement test of HPLC systems using principal component analysis by Péter Forlay-Frick; Jenő Fekete; Károly Héberger (pp. 71-81).

Theoretical plate numbers and symmetry factor values have been measured for three solutes (benzoic acid, N, N-dimethyl-aniline and Vancomycin) in various chromatographic systems (stationary phases and different mobile phase compositions) with the aim of grouping the systems and studying the possibilities for replacement of columns and eluent compositions. The mobile phases consisted of acetonitrile or methanol modifier and KH₂PO₄–H₃PO₄ or triethylamine–H₃PO₄ aqueous buffer. The organic content of mobile phases was adjusted so that the log ks (logarithms of retention factor) of tested compounds vary in the range of 0.1–1.3 in case of all chromatographic systems and test compounds. Plate numbers and symmetry factors at all retention factor values (between log k=0.1–1.3 with 0.1 units) were subjected to principal component analysis (PCA). The input data were arranged in 13×28 data-matrices in case of all compounds separately for plate numbers and symmetry factors. Two principal components were retained in the model, which carry not less than 98% of the total variance. Principal component analysis showed which chromatographic systems (stationary and mobile phases) gave the same (similar) chromatographic parameters using three different kinds of compounds.Replacement of chromatographic systems is possible on the basis of measured chromatographic parameters using principal component analysis. The monofunctional test compounds provide only approximate information on the usefulness, classification and replacement of HPLC systems, if the aim is the separation of multifunctional solutes. Although the theoretical plate number (column efficiency) is negatively correlated with the symmetry factor, both are necessary for proper classification and characterization of stationary phases.

Keywords: Stationary phases; Principal component analysis; Classification; Reversed phase HPLC; Vancomycin; Chemometrics; Symmetry factor; Theoretical plate number

Analysis of heterocyclic amines in chicken by liquid chromatography with electrochemical detection by E. Bermudo; V. Ruiz-Calero; L. Puignou; M.T. Galceran (pp. 83-90).

The present paper describes a method based on liquid chromatography with electrochemical detection (LC–ECD) for the determination of heterocyclic amines (HAs) in food samples. In order to obtain extracts clean enough to quantify heterocyclic amines by liquid chromatography with electrochemical detection, an additional purification step based on a cationic exchanger (CBA) as sorbent was included in a clean-up performed by several solid-phase extraction steps. Two different mobile phases, acetonitrile–50mM ammonium acetate (10:90) at pH 5.25, and acetonitrile–50mM ammonium acetate (30:70) at pH 6.0, were used for the LC separation of polar and less polar amines. Optimum working potentials were +1000 and +950mV for polar and less polar HAs, respectively. The obtained figures of merit showed detection limits of 5–79pg for standards, 2–30ngg⁻¹ for beef extract and 0.3–2.9ngg⁻¹ for fried chicken sample, and day-to-day precisions of 1.2–7.6% for standards and 2.8–10.4% for fried chicken sample. The applicability of the LC–ECD method has been demonstrated by the determination of the amines in griddled and fried chicken.

Keywords: Heterocyclic amines; Food; LC–ECD

Comparison of milk residue profiles after oral and subcutaneous administration of benzimidazole anthelmintics to dairy cows by L. Moreno; F. Imperiale; L. Mottier; L. Alvarez; C. Lanusse (pp. 91-99).

The current experimental work reports on the comparison of the milk residue profile of the benzimidazole (BZD) anthelmintics after their administration by the oral and subcutaneous (SC) routes to dairy cows. The cows were distributed in four groups and treated as follows—Group 1: oxfendazole (OFZ) by oral route (5mgkg⁻¹); Group 2: albendazole (ABZ) by oral route (5mgkg⁻¹); Group 3: albendazole sulphoxide (ABZSO) by SC administration (3mgkg⁻¹); Group 4: OFZ by SC route (3mgkg⁻¹). After drug administrations milk samples were collected and frozen at −20°C until analyzed by liquid chromatography (LC). A complete validation of the analytical methodology was accomplished. Regression curves were linear over the concentrations examined and the correlation coefficients ( r) ranged between 0.994 and 0.999. The mean extraction recovery range between 77 and 97%. Residual concentrations of OFZ, fenbendazole sulphone (FBZSO₂) and FBZ were recovered in milk after OFZ oral administration. OFZ reached the highest concentration in milk (0.39±0.10μgml⁻¹) at 12h post-treatment, being detected up to 72h post-treatment. In contrast, FBZ was not detected in cow milk and FBZSO₂ was the main analyte recovered from the milk with the maximum milk residues (0.042±0.003μgml⁻¹) achieved at after 36h following the SC injection of OFZ. ABZSO and ABZSO₂ were the metabolites recovered in milk following oral (ABZ) and SC (ABZSO) treatments in dairy cows. ABZSO₂ was the analyte recovered at the highest residual concentration (0.86±0.33μgml⁻¹) at 12h after oral administration of ABZ. However, ABZSO was the main compound measured in cow milk following its SC injection (0.18μgml⁻¹) at 12h post-treatment. Overall, the total milk residue levels (sum of parent drug and metabolites) were higher after oral compared to parenteral treatments in dairy cows. These results reported here are discussed according to the acceptable maximum residue limits (MRLs) established for BZD compounds in cow milk.

Keywords: Milk residues; Albendazole; Albendazole sulphoxide; Oxfendazole; Oral administration; Subcutaneous administration

Investigations on the antioxidant activity of fruit and vegetable aqueous extracts on superoxide radical anion using chemiluminescence techniques by T. Triantis; A. Stelakis; D. Dimotikali; K. Papadopoulos (pp. 101-105).

A sensitive and simple method for measuring antioxidant activity was developed, based on antioxidant-dependant quenching of the chemiluminescence (CL) generated from 9-benzylacridine and potassium superoxide. This method was used to evaluate the antioxidant activity of fruit and vegetable aqueous extracts as well as of some pure phenolic compounds contained in fruits and vegetables. Coumaric, chlorogenic, caffeic, vanillic and ascorbic acids as well as (�)catechin, and 2-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox) were employed as antioxidants. It was found that the antioxidant activity of all fruit extracts is almost one order of magnitude higher than that of vegetables. Among the fruits, grapefruits show the highest antioxidant activity and pears the lowest. From the pure phenolic antioxidants, caffeic acid has the highest antioxidant activity (AA). The calculated antioxidant activities of fruit and vegetable extracts produced by the CL method are compared with other methods such as the ORAC, TEAC or DPPH method.

Keywords: Chemiluminescence; Antioxidants; Superoxide; Fruits and vegetables

Animal tissue-based chemiluminescence sensing of uric acid by Fangqiong Wu; Yuming Huang; Qian Li (pp. 107-113).

A new flow injection analysis method based on animal tissue as recognition element for chemiluminescence sensing of uric acid is proposed in this paper. The liver of the large white pig was used as molecular recognition element. Uric acid is oxidized by oxygen under the catalysis of urate oxidase in the tissue column to produce hydrogen peroxide, which can react with luminol in the presence of potassium hexacyanoferrate(III) to generate a CL signal. The experimental results show that the CL emission intensity was linear with uric acid concentration in the range of 0.001–3μgmL⁻¹ and the detection limit (3 σ) for uric acid was 4×10⁻⁴μgmL⁻¹. The biosensor detection system could be used continuously for 4h with less than 10% decrease in the response. More than 200 measurements were carried out during this time. A complete analysis, including sampling and washing, could be performed in 1min with a relative standard deviation of 4.47% for 1μgmL⁻¹ uric acid. The biosensor detection system has been applied successfully to the analysis of uric acid in plasma and urine samples.

Keywords: Chemiluminescence; Animal tissue; Biosensor detection system; Uric acid; Biological fluids

Chemiluminescent determination of vanadium(IV) using a cinchomeronic hydrazide–H₂O₂ system and flow injection analysis by J.A. Pradana P�rez; J.S. Durand Alegr�a; P. Fern�ndez Hernando; A. Narros Sierra (pp. 115-119).

This paper proposes a new chemiluminescent flow injection analysis (FIA) method for the determination of vanadium(IV) ions in aqueous media. The method is based on the chemiluminescent reaction that occurs between cinchomeronic hydrazide (CH) and hydrogen peroxide in a strongly alkaline medium, in which vanadium(IV) acts as a catalyst. The chemical and physical variables involved in the flow injection system are optimised using a modified simplex method. Vanadium ions can be detected in the 0.08 and 1.00μgmL⁻¹ range; the detection limit for a signal-to-noise ratio of 3 is 0.08μgmL⁻¹. Great variations in the quantum yield were observed when cobalt(II), chromium(III), copper(II) and/or nickel(II) were present in the reaction medium. The proposed method is selective and simple, and can be successfully used to analyse water samples without the need for separation or preconcentration processes.

Keywords: Cinchomeronic hydrazide; Vanadium(IV); Chemiluminescence; FIA

Selective determination of ammonium in water based on HPLC and chemiluminescence detection by S. Meseguer-Lloret; C. Molins-Legua; P. Camp�ns-Falc� (pp. 121-127).

A selective and sensitive method has been developed for liquid chromatographic determination of ammonium in water samples. The analyte is derivatized with Dansyl Chloride prior to injection into HPLC. Optimal solution derivatization conditions have been established. The dansyl derivative is separated with the aid of a chromatographic column and post-column mixed with peroxyoxalate (TCPO) and H₂O₂ in order to perform chemiluminescence detection. The detection limit achieved is 8μg/L and linear response from 0.027 to 0.750mg/L of ammonium was obtained. Ammonium ion was determined within 2.4min under optimum chromatographic conditions. The method is fast, and near 10 derivatized samples can be measured per hour. No interference of amines has been obtained. Accuracy studies gave % relative error below 9.8%, and precision studies gave %RSD between 2 and 8%. The method can be applied for amine and ammonium screening and quantification of ammonium in different kind of water samples: bottled, tap, lake, fountain, irrigation, waste and sea. Matrix effect was only found in seawater samples. The method was also applied to several samples after applying Kjeldahl treatment in order to obtain values of total Kjeldahl nitrogen.

Keywords: Ammonium; Water samples; Dansylation; Post-column chemiluminescence; HPLC; Total Kjeldahl nitrogen

Determination of hydroxyproline in rat urine by high-performance liquid chromatography with electrogenerated chemiluminescence detection using tris(2,2′-bipyridyl) ruthenium(II) by Tatsuya Ikehara; Naoko Habu; Ikuko Nishino; Hiroshi Kamimori (pp. 129-133).

A high-performance liquid chromatographic (HPLC) method for the determination of total urinary hydroxyproline (Hyp) in rat was developed and validated. Urine samples hydrolyzed with concentrated hydrochloric acid were filtered using a disposable centrifugal filter after the sample solutions had been adjusted to a slightly acidic condition by a buffer solution. Hyp in the fraction could be separated by column-switching HPLC and detected with electrogenerated chemiluminescence detection using tris(2,2′-bipyridyl) ruthenium(II) within an analysis time of 25min. The calibration curve gave good linearity in the concentration range of 30–1500nmol/ml, and the lower limit of quantification was 30nmol/ml. The recovery of Hyp from urine samples was more than 96%. Precision and accuracy including within- and between-run values were less than 6 and ±5%, respectively, in the assay range. We concluded that the present method could be used to measure Hyp in rat urine.

Keywords: Hydroxyproline; Rat urine; Electrogenerated chemiluminescence

Application of multivariate curve resolution for the study of folding processes of DNA monitored by fluorescence resonance energy transfer by Praveen Kumar; Kajal Kanchan; Raimundo Gargallo; Shantanu Chowdhury (pp. 135-143).

The study described in the present article used fluorescence resonance energy transfer (FRET) to monitor the folding of a 31-mer cytosine-rich DNA segment, from the promoter region of the human c-myc oncogene. Spectroscopic FRET data recorded during experiments carried out in different experimental conditions were individually and simultaneously analyzed by multivariate curve resolution. The simultaneous analysis of several data matrices allowed the resolution of the system, removing most of the ambiguities related to factor analysis. From the results obtained, we report the evidence of the formation of two ordered conformations in acidic and neutral pH values, in addition to the disordered structure found at high temperatures. These ordered conformations could be related to cytosine-tetraplex structures showing different degrees of protonation in cytosine bases.

Keywords: Multivariate curve resolution; FRET; c-myc

Flow injection on-line oxidizing fluorometry coupled to dialysis sampling for the study of carbamazepine–protein binding by Zhi-Qi Zhang; Guo-Xi Liang (pp. 145-151).

The mechanism of binding of carbamazepine (CBZ) with bovine serum albumin (BSA) has been investigated in vitro based on a new flow injection fluorometry coupled to the technique of dialysis sampling. The CBZ and BSA were mixed in different molar ratios in 0.050molL⁻¹ phosphate buffer (containing 0.9% NaCl), pH 7.4, and incubated at 37±0.5°C in a water bath. The dialysis sampler was utilized to sample free CBZ from mixed solution with a relative dialytic efficiency of 7.6%. Then the CBZ in dialysis solution was injected into carrier and on-line oxidized by lead dioxide solid-phase reactor into fluorescent product with a maximum excitation wavelength of 355nm and a maximum emission wavelength of 478nm. The fluorescence intensity measured was linear proportional with the concentration of free CBZ in mixed solution over the range of 1×10⁻⁵ to 2×10⁻⁴molL⁻¹ with the detection limit of 6×10⁻⁶molL⁻¹. According to the fluorescence measurement results from mixed solution, the association constant ( K) estimated for CBZ–BSA binding and the number of the binding site ( n) with Scatchard analysis were 1.08×10⁴Lmol⁻¹ and 0.94, respectively. Stern–Volmer plots indicated the presence of dynamic component in the quenching mechanism. The acting force was suggested to be mainly hydrophobic and the distance between the acceptor and donor was 3.12nm. The estimated binding parameters agreed well with literature values.

Keywords: Flow injection fluorometry; Dialysis sampling; Carbamazepine; Bovine serum albumin; Binding parameters

Fluorescence characteristics of several whey samples subjected to different treatments and conditions by Jos� A. Murillo Pulgar�n; Aurelia Ala��n Molina; M. Teresa Ala��n Pardo (pp. 153-158).

The total fluorescence spectra of several wheis, obtained from the corresponding mammals’ milk, subjected to different treatments and conditions, were recorded.Whey was obtained after two treatments of the milk: precipitation of insoluble protein fraction at pH 4.6, and separation of the soluble fraction, whey, using a filter paper.Wheis corresponding to: cow's milk (whole, skimmed or partially skimmed) at different heat treatments (raw milk, Pasteurization and UHT treatment), goat's milk, sheep's milk and human milk, were studied. In all cases, two fluorescent bands, in the UV region, were obtained.It was also studied if some chemical conditions (whey dilution, pH and ethanol concentration) modify or not the intensity and the position of the two fluorescent bands.A liquid chromatographic study with fluorescence detection showed that the two fluorescent amino acids tyrosine and tryptophan, which are present at soluble fraction of milk, are responsible for the intrinsic fluorescence of whey.

Keywords: Fluorescence; Liquid chromatography (LC); Milk; Whey

On the use of a small synthetic calibration set for the simultaneous spectrophotometric multivariate determination of Ca²⁺ and Mg²⁺ in groundwater: chemical and spectral considerations by Mar�a Agustina Gil Libarona; Fernando Alberto I��n (pp. 159-169).

A critical evaluation of chemical and spectral considerations for the simultaneous spectrophotometric determination of calcium and magnesium in groundwater samples with methylthymol blue (MTB) using a calibration set composed by synthetic standards is presented. The method is based upon the spectral changes observed in MTB spectra in the visible region (400–700nm) when concentrations of calcium and magnesium are varied. First-order multivariate calibration models were built using net analyte pre-processing followed by classical least-squared regression (NAP/CLS) method.The concentration of MTB, the pH of the solution at which the reaction is carried out and the spectral range were optimised. Based on theoretical concentration distribution plots, discussion of experimental effect of each chemical variable is provided. Through a suitable chemical and spectral optimisation and based on a factorial central composite design, we succeeded in obtaining excellent prediction results using a calibration set composed only by eight synthetic solutions in the analytical concentration range of 0–200 and 0–100mgL⁻¹ for Ca²⁺ and Mg²⁺, respectively. The developed methodology was applied to real groundwater samples from Great Buenos Aires area, with no pre-treatment except filtration of turbid samples, showing a very good agreement with the well-known flame atomic absorption spectrometry technique, which was used as reference method. Critical performance comparison with previous work is provided.

Keywords: Calibration set selection; Spectrophotometric simultaneous determination; MTB; Ca; Mg; Groundwater analysis

Study of the interaction of nucleic acid with europium(III) and CTMAB and determination of nucleic acids at nanogram levels by the second-order scattering by Fen Ding; Huichun Zhao; Shilv Chen; Jin Ouyang; Linpei Jin (pp. 171-178).

This paper firstly reports the second-order scattering (SOS) phenomenon in the nucleic acid system using a common spectrofluorometer. And a novel determination method of nucleic acids at nanogram level has been developed. Studies involving calf thymus DNA (ctDNA), fish sperm DNA (fsDNA) and yeast RNA (yRNA) showed that the SOS intensity of nucleic acids can be enhanced by La³⁺, Ce³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺ and Tb³⁺ ion, of which Eu³⁺ ion has the largest enhancement. And the intensity of the SOS is proportional to the concentration of nucleic acids. Maximum SOS peak at 550nm appeared at pH 7.5 and 6.0×10⁻⁵moll⁻¹ CTMAB (cetyltrimethylammonium bromide). Under the optimal conditions, the calibration graphs were linear in the range of 1.0×10⁻⁸ to 4.0×10⁻⁵gml⁻¹ for ctDNA, 6.0×10⁻⁹ to 2.0×10⁻⁶gml⁻¹ for fsDNA, and 8.0×10⁻⁹ to 1.0×10⁻⁶gml⁻¹ for yRNA, respectively. The detection limits were 1.7ngml⁻¹ for ctDNA, 0.36ngml⁻¹ for fsDNA and 0.21ngml⁻¹ for yRNA, respectively. In comparison with most other methods for the determination of nucleic acids, this method is more convenient, more sensitive and simpler. And the possible mechanism was proposed.

Keywords: Nucleic acids; Second-order scattering; Europium; CTMAB

Manipulate fluid in microchannels with thermo-responsive film by Tohru Saitoh; Ayahito Sekino; Masataka Hiraide (pp. 179-182).

The improvement of thermo-responsive wettability change on the glass surfaces poly( N-isopropylacrylamide) [PNIPAAm]-modified was investigated by the cooperative modification with hydrophobic octadecylsilane (ODS) or by the polymer modification on frosted surfaces. The water contact angle of PNIPAAm-modified glass surface was ca. 32° below the lower critical solution temperature (LCST, ca. 32°C) of PNIPAAm, while it was ca. 68° above LCST. In PNIPAAm–ODS system, the water contact angle above LCST increased to ca. 84°, but was still lower than 90° being the measure of water-repellency. On the other hand, higher wettability (water contact angle; ca. 24°) below LCST and water-repellency (water contact angle; ca. 104°) above LCST were obtained on the PINIPAAm-modifed frosted glass surfaces. When an optional portion beside the channel on a glass plate was warmed, the capillarity-based liquid flow in the channel was temporary stemmed at the prescribed portion. Furthermore, the flow switching at a T-junction in the channel was successfully achieved, when the opposite side of the channel that stream had to be directed was warmed.

Keywords: Poly(; N; -isopropylacrylamide); Contact angle; Water-repellency; Frosted glass; Michrochannel; Flow control

Sequential injection system incorporating a micro-extraction column for automatic fractionation of metal ions in solid samples by Roongrat Chomchoei; Manuel Mir�; Elo Harald Hansen; Juwadee Shiowatana (pp. 183-190).

Recently a novel approach to perform sequential extractions (SE) of elements in solid samples was developed by this group, based upon the use of a sequential injection (SI) system incorporating a specially designed extraction microcolumn. Entailing a number of distinct advantages as compared to conventional batch methods, this fully automated approach furthermore offers the potentials of a variety of operational extraction protocols. Employing the three-step sequential extraction BCR scheme to a certified homogeneous soil reference material (NIST, SRM 2710), this communication investigates four operating modes, namely uni-, bi- and multi-bi-directional flow and stopped-flow, allowing comparison of the metal fractionation profiles. Apart from demonstrating the versatility of the novel approach, the data obtained on the metal distribution in the various soil phases might offer valuable information as to the kinetics of the leaching processes and chemical associations in different soil geological phases. Special attention is also paid to the potentials of the microcolumn flowing technique for automatic processing of solid materials with variable homogeneity, as demonstrated with the sewage amended CRM483 soil which exhibits inhomogeneity in the particle size distribution.

Keywords: Sequential extraction; Sequential injection; Soil; Leaching kinetics; Microcolumn; Metal fractionation

Molecularly imprinted polymer thin films on quartz crystal microbalance using a surface bound photo-radical initiator by Theeraphon Piacham; �sa Josell; Hans Arwin; Virapong Prachayasittikul; Lei Ye (pp. 191-196).

The present work aims to study preparation of thin MIP films on a gold-coated QCM resonator in a well-controlled and reproducible manner. A surface-bound photo-radical initiator was used to furnish an imprinting polymerization in a dilute solution of template, functional monomer and crosslinker. Prior to polymerization, the photo-initiator was covalently coupled to a self-assembled monolayer of carboxyl terminated alkanethiol on a gold surface. With this approach we were able to control the thickness of the MIP film to be below 50nm, where the selective recognition of target analytes can be easily detected by the underlying quartz crystal resonator. When used in a flow injection analysis system, the assembled QCM sensor generated a large frequency change (>30Hz) upon encountering a small amount of analyte (0.19mM). The sensor had a very short response time (<1min), and displayed certain chiral selectivity towards the original template, ( S)-propranolol at a concentration higher than 0.38mM in aqueous solution.

Keywords: Molecular imprinting; Surface initiated polymerization; Quartz crystal microbalance; Propranolol

Investigation of different polymerization methods on the analytical performance of palladium(II) ion imprinted polymer materials by Sobhi Daniel; P. Prabhakara Rao; T. Prasada Rao (pp. 197-206).

Palladium(II) ion imprinted polymer (IIP) materials were prepared via bulk, precipitation and suspension polymerization methods using similar compositions. In these polymerization methods, the polymerization mixture consists of a ternary complex of palladium(II) imprint ion with 8-aminoquinoline (AQ), 4-vinyl pyridine (VP, monomer), 2-hydroxyethyl methacrylate (HEMA, functional monomer), ethylene glycoldimethacrylate (EGDMA, cross-linking monomer), 2,2′-azobisisobutyronitrile (AIBN, initiator) and 2-methoxy ethanol (Porogen). Various polymerization methods were carried out by thermal means and IIP materials thus obtained were leached with 50% (v/v) HCl to obtain leached IIP particles. Control polymer (CP) particles were similarly prepared by all the three polymerization methods. The above synthesized polymer particles were characterized physically and morphologically by using FTIR, TGA, CHN, X-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques. Furthermore, their capacity to rebind palladium(II) was investigated from dilute aqueous solutions and in presence of selected precious and transition elements (which are known to coexist with palladium in its mineral deposits). The rebinding studies of IIP particles obtained via bulk, precipitation and suspension methods reveal that (i) percent enrichment is quantitative with bulk and precipitation, and ∼72% only in case of suspension; (ii) retention capacities are 28.82, 20.16 and 18.76mg palladium(II)/g materials, respectively; (iii) selectivity for palladium(II) over other noble and transition elements lies in the order bulk∼precipitation>emulsion. Moreover, the IIP particles obtained by all three polymerization methods exhibit imprinting effect when compared with respective CP particles.

Keywords: Polymerization methods; Bulk; Precipitation; Suspension; Palladium(II); Ion imprinted polymers; Preconcentration and separation

On-line dynamic two-dimensional admicelles solvent extraction coupled to electrothermal atomic absorption spectrometry for determination of chromium(VI) in drinking water by Jing Nan; Xiu-Ping Yan (pp. 207-212).

An on-line dynamic two-dimensional admicelles solvent extraction system was coupled to electrothermal atomic absorption spectrometry (ETAAS) for determination of Cr(VI) in drinking water. As a two-dimensional solvent, admicelles were on-line-prepared by passing cetyltrimethylammonium bromide (CTAB) through a microcolumn packed with silica gel. The analyte Cr(VI) was on-line-complexed with pyrrolidine dithiocarbamate (PDC), and the resulting Cr(VI)–PDC was effectively adsolubilized in the admicelles of the microcolumn, and then quantitatively eluted with 30μl of acetonitrile for ETAAS determination. All the procedures including the formation and decomposition of admicelles and ETAAS determination were performed on-line, ensuring automatic determination of Cr(VI) in drinking water with a high precision. With a consumption of 2.1ml sample solution, a detection limit (3 σ) of 3.0ngl⁻¹, and an enhancement factor of 32 were obtained at a sample throughput of 31 samplesh⁻¹. The precision (R.S.D.) for 11 replicate measurements of 50ngl⁻¹ Cr(VI) was 2.5%. The developed methodology was demonstrated to be reliable and sensitive for automatic determination of ultratrace Cr(VI) in bottled drinking water samples.

Keywords: Two-dimensional solvent extraction; Admicelles; Electrothermal atomic absorption spectrometry; Chromium; Drinking water

Evaluation of commercial C18 cartridges for trace elements solid phase extraction from seawater followed by inductively coupled plasma-optical emission spectrometry determination by Jacobo Otero-Roman�; Antonio Moreda-Pi�eiro; Adela Bermejo-Barrera; Pilar Bermejo-Barrera (pp. 213-218).

Possibilities of the use of commercial C18 cartridges to separate and preconcentrate trace elements from seawater have been evaluated. Trace elements (Al, Cd, Cu, Fe, Mn, Ni, Pb, Sn, V and Zn) were previously complexed with 8-hydroxyquinoline, 8-HQ (5×10⁻⁴M as final concentration) at alkaline pH (8.0±0.1) and then they were eluted with 2.5ml of 2.0M nitric acid. Metals eluted from cartridges were measured by inductively coupled plasma-optical emission spectrometry (ICP-OES). Variables affecting the metal-8-HQ complexation such as pH and 8-HQ concentration, and affecting the metal-8-HQ complexes solid phase adsorption and elution (load and elution flow rates and concentration and volume of eluting solution) were studied in order to find compromise operating conditions for the simultaneous metals complexation, adsorption and elution. After studies of contamination of commercial C18 cartridges for trace metals, high reagent blanks were reached for Ti so that they are useless for the determination of this element. In addition, commercial C18 cartridges can be used at least seven times without loss of adsorption properties. Working with a seawater sample volume of 100ml and using an optimum nitric acid volume of 2.5ml for elution, a preconcentration factor of 40 was achieved, factor high enough to determine trace elements in unpolluted surface seawater samples by ICP-OES. Analytical performances, such as limits of detection and quantification, repeatability of the overall procedure and accuracy, by analyzing saline (CASS-3 and SLEW-3) and non-saline (TM-24) certified reference materials, were finally assessed.

Keywords: Commercial C18 cartridges; Solid phase extraction; Trace metals; Unpolluted surface seawater; Inductively coupled plasma-optical emission spectrometry

Steric effects of polymethylene chain of 4-acylbis(pyrazolones) on the solvent extraction of trivalent lanthanoids: synergistic effect with mono and bifunctional neutral organophosphorus extractants by Rani Pavithran; M.L.P. Reddy (pp. 219-226).

Various 4-acylbis(pyrazolones), namely 4-adipoylbis(1-phenyl-3-methyl-5-pyrazolone) (H₂AdBP=1), 4-suberoylbis(1-phenyl-3-methyl-5-pyrazolone) (H₂SuBP=2), 4-sebacoylbis(1-phenyl-3-methyl-5-pyrazolone) (H₂SbBP=3), 4-dodecandioylbis(1-phenyl-3-methyl-5-pyrazolone) (H₂DdBP=4) have been synthesized and examined their solvent extraction behavior towards trivalent lanthanoids (Nd³⁺, Eu³⁺ and Tm³⁺). The extraction of Ln³⁺ ions was found to increase monotonically with increasing atomic number of these metal ions.1–4 reagents showed an initial increase in the extraction efficiency of Ln³⁺ ion with increasing polymethylene chain length,(CH₂)_n, from n=4 to 8 and thereafter a decreasing trend, for n=10. The equilibrium constants ( K_ex) of the extracted complexes have been deduced by nonlinear regression analysis with the aid of suitable chemically based model developed by taking into account chemical mass action principles. The K_ex values were correlated with the polymethylene chain length, by measuring the distance between the carbonyl oxygen atoms connected to the polymethylene chain with the help of semi-empirical PM3 molecular modelling calculations. The synergistic effect on the addition of various neutral organophosphorus extractants to the metal–chelate system has also been investigated. Not only enhanced extraction efficiency, but also improved selectivity has been observed among these Ln³⁺ ions. The equilibrium constants of the synergistically extracted complexes have been correlated with the donor ability of the phosphoryl oxygen of the neutral organophosphorus extractants in terms of their³¹P NMR chemical shifts and their basicity values ( K_H=nitric acid uptake constant).

Keywords: Steric effect; 4-Acylbis(pyrazolones); Lanthanoids; Synergistic effects; Molecular modelling

An investigation into the retention profile and kinetics of sorption of the ternary complex ion associate of uranyl ions with crown ether and picric acid by the polyurethane foams by M.S. El-Shahawi; A.M. Othman; H.M. Nassef; M.A. Abdel-Fadeel (pp. 227-235).

The retention profile of uranyl ions from aqueous media by polyether-type-based polyurethane foams (PUFs) was studied to gain more information regarding the mechanism of uranyl ions extraction. The influence of pH, extraction time, picric acid (PC), crown ether (CE) and uranyl ions concentration on the sorption step by the PUFs was studied. The data revealed that the sorption of uranyl (II) ions involved formation of a ternary complex ion associate between uranyl (II) ions with crown ether and picric acid and its retention is highly dependent on the parameters studied. The dependency of the sorption percentage on the parameters was explained in a manner consistent with a “solvent extraction�? mechanism. The kinetics of uranyl ions sorption onto crown-ether-loaded PUFs was found fast and followed a first-order rate constant in the presence of picric acid in the aqueous phase. The sorption data were also followed Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms over the entire concentration range of uranyl ions employed. Thus, a dual-mode sorption mechanism involves absorption related to “solvent extraction�? and an added component for surface adsorption may be operated simultaneously. The proposed retention procedures were applied successfully for the determination of uranyl (II) ions and picric acid in aqueous media.

Keywords: Uranyl ions; Crown ether; Picric acid; Kinetics; Sorption isotherms; Polyurethane foams

Determination of essential oil in a traditional Chinese medicine, Fructus amomi by pressurized hot water extraction followed by liquid-phase microextraction and gas chromatography–mass spectrometry by Chunhui Deng; Ning Yao; Aiqin Wang; Xiangmin Zhang (pp. 237-244).

In this paper, for the first time, two sample techniques of pressurized hot water extraction (PHWE) and liquid-phase microextraction (LPME) were combined and applied to the analysis of essential oil in a traditional Chinese medicine (TCM), Fructus amomi. Essential oil in F. amomi samples (50.0mg) were extracted by PHWE equipment in dynamic mode, followed by extraction and concentration with headspace (HS)-LPME and detection by gas chromatography–mass spectrometry (GC–MS). The PHWE and HS-LPME parameters were optimized and the method repeatability was studied. The three active compounds of camphor, borneol and borneol acetate in the F. amomi sample from five different growing areas were quantitatively analyzed by internal standard method. Compared to steam distillation (SD), the proposed method required simple sample preparation, little sample mass and whole analysis time less than 40min. The present method provided good repeatability (R.S.D. <12.0%). It has been demonstrated that PHWE–LPME–GC–MS is a simple, rapid and low-cost method for determination of essential oils in TCMs and is a potential tool for TCM quality assessment.

Keywords: Pressurized hot water extraction; Liquid-phase microextraction; Essential oils; Extraction method; Traditional Chinese medicine; Fructus amomi

Application of continuous-flow liquid-phase microextraction to the analysis of volatile halohydrocarbons in water by Yalan Li; Taozhi Zhang; Pei Liang (pp. 245-249).

A novel method for the determination of four volatile halohydrocarbons (CHCl₃, CCl₄, C₂HCl₃ and C₂Cl₄) in water is developed by combined continuous-flow liquid-phase microextraction (CFME) with gas chromatography microelectron capture detection (GC-μECD). The effects of extraction solvent type and volume, flow-rate of sample solution, sample volume and salt concentration on the extraction performance were investigated and optimized. The developed protocol was found to yield a linear calibration curve in the concentration range from 0.02 to 20μgL⁻¹ for the target analytes, and the detection limits were found to be in the low μgL⁻¹ level, between 0.001 and 0.02μgL⁻¹. Good repeatabilities of extraction were obtained, with the R.S.D. values below 4.3%. The results demonstrated that the CFME followed with GC-μECD was a simple and reliable technique for the determination of volatile halohydrocarbons in water samples.

Keywords: Continuous-flow liquid-phase microextraction; Volatile halohydrocarbons; GC-μECD

On-line ion pair solid-phase extraction of electrokinetic multicommutation for determination of trace anion surfactants in pond water by Yan-Yun Hu; You-Zhao He; Li-Li Qian; Lei Wang (pp. 251-257).

An electrokinetic multicommutation system is presented in this paper for the preconcentration and determination of trace anion surfactants of alkylbenzenesulfonate (ABS) in pond water, including electro-osmotic pumping, on-line ion pair solid-phase extraction (IP-SPE), bubble removing and directly spectrophotometric determination. Tetrabutylammonium bromide (TBAB) as an ion-pairing reagent was added into sample solutions to improve ABS retention on C₁₈ extraction column. Several extraction parameters, including the concentration of different eluents and ion-pairing reagents, the retention and elution flow rate, and the eluent volume, were discussed in detail. A homemade gas–liquid separator was employed to remove bubbles from the eluate flow before spectrophotometric detection. In this way, the bubble interference in coupling reversed-phase SPE with spectrophotometry can be eliminated. For 15ml sampling volume, the detection limit of ABS, relative standard deviation and preconcentration factor of the proposed method were 10ngml⁻¹ (3 σ, N=7), 3.7% ( N=8), and 65, respectively.

Keywords: Electrokinetic multicommutation; Sequential injection analysis; Ion pair solid-phase extraction; Anionic surfactant

Semi-permeable membrane device efficiency for sampling free soluble fraction of polycyclic aromatic hydrocarbons by C. Mi�ge; C. Ravelet; J.P. Crou�; J. Garric (pp. 259-266).

Semi-permeable membrane devices (SPMDs) have been used for K_DOC (defined as the partition coefficient of hydrophobic organic contaminants between dissolved organic carbon and water) determination of five selected polycyclic aromatic hydrocarbons (PAHs) (fluoranthene, pyrene, benzo[b]fluoranthene, benzo[a]pyrene, benzo[e]pyrene). The Aldrich humic acid and the Suwannee river hydrophobic acid isolate (XAD8 isolate) were used as dissolved organic carbon. Uptake rate constants ( k_u and R_s) were evaluated and the SPMD method was calibrated based on a 3h exposure time. For the five PAHs, the linearity was checked for water PAH concentration from 1ng/L to 1μg/L. The analytical detection limits ranged from 2 to 50ng/L for the benzo[a]pyrene and the pyrene respectively. The proposed methodology is suitable for facile laboratory K_DOC measurement and produces results similar to previously published values.

Keywords: K; _DOC; Semi-permeable membrane device (SPMD); Polycyclic aromatic hydrocarbons (PAHs)

Pulsed amperometric detection of sulfide, cyanide, iodide, thiosulfate, bromide and thiocyanate with microfabricated disposable silver working electrodes in ion chromatography by Jun Cheng; Petr Jandik; Nebojsa Avdalovic (pp. 267-274).

The authors introduce a new type of silver electrodes. The new electrodes are designed to be disposable and as such they are used only for a limited period of time, usually 5–7 days, and then discarded. Manual polishing, which is required with non-disposable electrodes, is not necessary with disposable electrodes. This manuscript describes the development of pulsed amperometric detection waveforms that make it possible to utilize disposable silver electrodes in the chromatographic detection of sulfide, cyanide, iodide, thiosulfate, bromide and thiocyanate. Also discussed is an evaluation of analytical performance of the electrodes with the newly developed waveforms. The detection limits were found to be 1ppb (S²⁻), 2ppb (CN⁻), 5ppb (Br⁻, S₂O₃²⁻ and I⁻) and 10ppb (SCN⁻) for a 10μl injection volume. Calibration plots for S²⁻, CN⁻, Br⁻ and S₂O₃²⁻ are linear from their respective detection limits up to 50–100ppm. The linear calibration for I⁻ and SCN⁻ can be obtained from the detection limits up to 10ppm. Reproducible long-term performance was confirmed in a 2-week experiment with 10μl injections of 1ppm CN⁻.

Keywords: Disposable electrodes; Thin film electrodes; Silver electrodes; Ion chromatography; Pulsed amperometric detection; Sulfide; Cyanide; Bromide; Thiosulfate; Iodide; Thiocyanate

Solid-state electroanalytical characterization of the nonaqueous proton-conducting redox gel containing polyoxometallates by Adam Lewera; Grazyna Zukowska; Krzysztof Miecznikowski; Malgorzata Chojak; Wladyslaw Wieczorek; Pawel J. Kulesza (pp. 275-281).

A novel polymetacrylate-based redox-conducting polymeric gel, into which Keggin-type polyoxometallate, phosphododecatungstic acid (H₃PW₁₂O₄₀), had been incorporated, was electrochemically characterized in the absence of external liquid supporting electrolyte using an ultramicrodisk-working electrode. The phosphotungstate component (15wt.% of the gel block) was entrapped as the polar organic solvent solution within pores of the polymer matrix. H₃PW₁₂O₄₀ plays bifunctional role: it provides well-behaved redox centers and serves as strong acid (source of mobile protons). The solid-state voltammetric properties of the system are defined by the reversible one-electron transfers between phosphotungstate redox centers. The following parameters have been determined from the combination of potential step experiments performed in two limiting (radial and linear) diffusional regimes: the concentration of heteropolytungstate redox centers, 6×10⁻²moldm⁻³, and the apparent diffusion coefficient, 5×10⁻⁷cm²s⁻¹. The room temperature ionic (protonic) conductivity of the bulk gel was equal to 1.6×10⁻³Scm⁻¹. The charge propagation mechanism was found to be primarily controlled by physical diffusion of heteropolytungstate units within the gel pores rather than by electron hopping (self-exchange) between mixed-valence sites.

Keywords: Polymer gel; Crosslinked polymetacrylate; Polar aprotic solvent; Heteropolytungstate; Solid-state electroanalysis; Concentration of redox sites; Diffusion coefficient

Characterization of microorganisms by thermogravimetric analysis–mass spectrometry by A. Peter Snyder; Ashish Tripathi; Jacek P. Dworzanski; Waleed M. Maswadeh; Charles H. Wick (pp. 283-293).

A thermogravimetric analysis (TGA) system was interfaced to a mass spectrometry (MS) detector to investigate the thermal evolution of decomposition products from microorganisms. Traditionally, TGA–MS has been used to investigate the thermal parameters and chemical composition of materials such as the coal and lignin energy producing compounds and a wide range of technical organic polymers. The relative weight loss of biochemical species and compounds in bacteria from the TGA system allowed a comparison to the relative amounts of the same substances in bacteria from conventional microbiological extraction and isolation techniques. MS is shown to produce information rich total ion chromatogram profiles of thermal products from biochemical standards and microorganisms. The TGA thermal weight loss chromatogram (TWC) provides a degree of resolution, because the bacterial biochemical substances and components partition in a temporal fashion. Standard biochemical substances such as dipicolinic acid, polyhydroxybutyric acid, and peptidoglycan are produced in the same general temperature region in the TWC profile, and the compounds have similar mass spectra compared to those from microorganisms. Characterization of microorganisms was possible by the relation of their thermal events and extracted mass spectra to those of low and high mass model biochemical compounds.

Keywords: Gram-positive bacteria; TGA–MS; Thermogravimetric analysis; Mass spectrometry; Thermal programming; Biomarkers; Bacillus

Microwave-assisted volatilization of silicon fluorides for the determination of trace impurities in high purity silicon powder and quartz by ICP-MS by Ruey-Lin Ueng; Shiuh-Jen Jiang; Chia-Ching Wan; A.C. Sahayam (pp. 295-299).

Closed vessel microwave-assisted volatilization of silicon as fluoride in presence of vapors of HF and HNO₃, for the determination of trace impurities in high purity silicon powder and quartz, is reported. The volatilization of the matrix element from Si powder is 98.7% using vapors generated from 2:1 ratio of HF:HNO₃ whereas vapors generated from 5:1 ratio of HF:HNO₃ are used to volatilize 99% of Si from quartz. The recoveries of Mg, K, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ag, Cd, Ba and Pb after volatilization of matrix element are in the range 83–103% and 94–116% for Si powder and quartz, respectively, except for Ag (60–77% in both types samples). Determinations are carried out using inductively coupled plasma mass spectrometer with Dynamic Reaction Cell™ (DRC ICP-MS). The interferences due to the tailing of⁴⁰Ar⁺,³⁸Ar¹H⁺,⁴⁰Ar¹²C⁺ and⁴⁰Ar¹⁶O⁺ on the determination of³⁹K⁺,⁵²Cr⁺ and⁵⁶Fe⁺, respectively, have been reduced to insignificant levels in DRC mode using NH₃ as the reaction cell gas. Matrix volatilization using in situ-generated acid vapors in closed containers resulted in sub ngml⁻¹ experimental blanks. The method detection limits computed based on 3 σ variation in blank measurements ( n=5) are in the low or sub ngg⁻¹ level. The methods developed have been applied to determine trace impurities in high purity silicon powder and quartz samples.

Keywords: Microwave-assisted volatilization and dissolution system; High purity silicon powder and quartz; Dynamic reaction cell inductively coupled plasma-mass spectrometry

Erratum to “Fast matrix digestion with hot ethanolic alkali plus pyrogallol for polychlorinated dibenzo- p-dioxins, polychlorinated dibenzofurans and coplanar polychlorinated biphenyls analysis in biological samples�? by Hiroaki Otaka; Shunji Hashimoto (pp. 301-302).

Author Index (pp. 303-305).

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Analytica Chimica Acta (v.536, #1-2)

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Analytica Chimica Acta (v.536, #1-2)