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Analytica Chimica Acta (v.540, #2)

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

Contents (pp. iii-iv).

Calendar of forthcoming meetings (pp. n5-n6).

Filler Ad.: ACAEES (pp. ii).

Digestion treatments and risks of Cr(III)–Cr(VI) interconversions during Cr(VI) determination in soils and sediments—a review by Maurizio Pettine; Silvio Capri (pp. 231-238).

Threshold values for Cr(VI) in various types of solid matrices have been set up to protect human health and biota. To ascertain the compliance of solids with these limits different types of extractants and different conditions of pH and temperature have been proposed in the literature. These extraction procedures are reviewed and their potentialities in quantitatively extracting Cr(VI) from solids without inducing undesired Cr(VI)–Cr(III) interconversions during the extraction are carefully evaluated. This evaluation takes into account the knowledge of the kinetics of most important redox reactions of chromium gathered in recent years. Among possible Cr(VI) reductants made available during the digestion, a number of species including Fe(II), sulphide, sulfite and humic matter were considered, while oxidants included hydrogen peroxide, dissolved oxygen, manganese oxides. Theoretical calculations suggest that pH higher than 10, high temperature and high concentrations of carbonate and magnesium ions minimize Cr(III)–Cr(VI) interconversions. The EPA Method 3060A meets these basic requirements. However, the applicability of this method to the analysis of Cr(VI) in soil and sediment samples, whose extracts may suffer from the interference by humic matter, is questionable.

Keywords: Solid matrices; Chromium extraction; Kinetics of chromium reactions; Chromium analysis

Removal of humic matter interference in the determination of Cr(VI) in soil extracts by the diphenylcarbazide method by Maurizio Pettine; Silvio Capri (pp. 239-246).

Alkaline digestion of soil samples, which is recommended for minimizing Cr(III)–Cr(VI) interconversions during the extraction of Cr(VI), may also solubilize humic matter (HM). The latter is responsible for both positive and negative interference in the analysis of Cr(VI) in the extract by the diphenylcarbazide (DPC) method. Humic compounds indeed absorb light at 540nm as the Cr-DPC product and are also able to rapidly reduce Cr(VI) under the pH conditions of the standard DPC method. To prevent any risk of interference and make the DPC method applicable to soil extracts, a new protocol is proposed. This consists of three successive steps: (1) extraction of Cr(VI) by the U.S.EPA method 3060A in the presence of Mg²⁺; (2) batch removal of solubilised HM by the XAD-7 sorbent at pH 3.0±0.1 with 3–5min contact time; (3) analysis of Cr(VI) with the DPC method at pH 3.0±0.1. The application of this new protocol to the soil product SQC-012 Lot 4 certified by R.T. Corporation (RTC, USA) gave significantly lower Cr(VI) concentrations and smaller variability compared to certified values (46.5±2.3 instead of 153±32.6mg/kg). The new protocol was validated by Cr(VI) and Cr(III) spikes either to the soil/extractant suspension or to the exctract. Cr(VI) results in the wide range of acceptance limits (104–202mg/kg) reported by RTC were only obtained when the U.S.EPA method 3060A without the addition of Mg²⁺ and DPC analysis at pH 1.0 were applied. The latter procedure appears questionable since it leads to largely variable results which reflect the complex role played by humic matter in the determination of Cr(VI) and the instability of Cr(III) during the extraction.

Keywords: Chromium soil extraction; Humic matter interference; Chromium (VI) determination

Analytical procedures for the determination of selected major (Al, Ca, Fe, K, Mg, Na, and Ti) and trace (Li, Mn, Sr, and Zn) elements in peat and plant samples using inductively coupled plasma-optical emission spectrometry by Atindra Sapkota; Michael Krachler; Christian Scholz; Andriy K. Cheburkin; William Shotyk (pp. 247-256).

A simple, robust and reliable analytical procedure for the determination of Al, Ca, Fe, K, Li, Mg, Mn, Na, Sr, Ti, and Zn in peat and plant materials by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed. A microwave heated high pressure autoclave was used to digest powdered sample aliquots (approximately 200mg) with different acid mixtures including nitric acid (HNO₃), tetrafluoroboric acid (HBF₄) and hydrogen peroxide (H₂O₂). The optimized acid mixture for digestion of plant and peat samples consisted of 3mL HNO₃ and 0.1mL HBF₄, in addition to H₂O₂ which was sub-boiled into the PTFE digestion tubes during heating of the autoclave. Using HNO₃ alone, recoveries of Al and Ti were too low by 40 and 160%, respectively, because HNO₃ could not fully liberate the analytes of interest from the silicate fraction of the plant and peat matrix. However, for all other elements (such as Mn, Sr, and Zn), the use of HBF₄ was less critical. The accuracy of the analytical procedure developed was evaluated with peat and plant reference materials of different origin and composition. The ICP-OES instrument was optimized using solutions of plant reference materials considering RF power, nebulizer pressure, auxiliary gas flow and rinse time. Scandium was used as an online internal standard (IS) as it provided accurate results and showed less than 3% drift in sensitivity over time which was lower compared to other potential IS such as Rh (20%) and In (6%). The combination of most sensitive and less sensitive wavelengths allowed to obtain low detection limits and highest possible dynamic range. The achieved procedure detection limits ranged from 0.05μgg⁻¹ (Li) to 15μgg⁻¹ (Ca) and allowed a precise quantification of all elements. Comparative X-ray fluorescence spectrometric measurements of solid peat and plant samples generally agreed well with results obtained by digestion/ICP-OES. To overcome interferences caused by Na, K, and Li, a solution of 10μgg⁻¹ CsCl₂ was successfully used as an ionization buffer. The good agreement between the found and certified concentrations in plant and peat reference materials indicates that the developed analytical procedure is well suited for further studies on the fate of major elements in plant and peat matrices.

Keywords: Microwave digestion; ICP-OES; Plant; Peat; Major elements

Analysis of cigarette smoke by laser desorption mass spectrometry by Vincent Carr�; Fr�d�ric Aubriet; Jean-Fran�ois Muller (pp. 257-268).

Laser desorption ionization Fourier transform ion cyclotron mass spectrometry (LDI–FTICRMS) has been successfully applied for the characterization of tobacco smokes. The versatily of analysis allows inorganic and organic tobacco smoke constituents to be identified. As a function of ion detection mode and laser irradiance experimental conditions, inorganic nitrate and sulfate as well as nicotine and associated nicotine, tobacco-specific nitrosamine, polycyclic aromatic hydrocarbon, polyoxygenated compounds are highlighted. The high mass resolution and the high mass accuracy attained by LDI–FTICRMS measurements allow the unambiguous assignment of detected species for m/z<250 to be achieved.

Keywords: Tobacco; Laser desorption mass spectrometry; Mainstream cigarette smoke; Particulate matter; Organic and inorganic characterization; FTICRMS

Determination of trace elements in ambient aerosol samples by Natalie J. Pekney; Cliff I. Davidson (pp. 269-277).

A microwave-assisted digestion procedure using HNO₃, HF, and H₂O₂ has been developed for analysis of elements in ambient particulate matter (PM). The samples are collected on cellulose filters and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS is calibrated with external standards, and recovery of analytes is tested with NIST SRM 1648 Urban Dust. This method has been used to quantify the airborne concentrations of a large number of elements, including Ag, As, Ba, Be, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, K, Li, Mg, Mn, Mo, Ni, Pb, Rb, Se, Sb, Sr, Ti, Tl, V, and Zn. For the majority of these elements, recovery of the NIST SRM is within 15% of the certified values.

Keywords: Trace elements; Atmospheric aerosols; Inductively coupled plasma-mass spectrometry; Microwave digestion; Cellulose filter

Detection of antisperm antibody in human serum using a piezoelectric immunosensor based on mixed self-assembled monolayers by Guangyu Shen; Hua Wang; Shuzhen Tan; Jishan Li; Guoli Shen; Ruqin Yu (pp. 279-284).

A novel piezoelectric immunosensor based on mixed self-assembled monolayers (mixed SAMs) formed by short-chain amine- and carboxyl-terminated thiols has been developed to immobilize antigens onto gold electrodes for detecting antisperm antibody (AsAb) in human serum samples. The properties and the enhanced performance of the affinity biosensor interface based on mixed SAMs are investigated. Most importantly, analytical results of several human serum samples using the developed technique are in satisfactory agreement with those given by the enzyme-linked immunosorbent assay (ELISA) method in the concentration ranging from 32.3 to 300.0mU/ml. It means the procedure proposed in this paper is likely to have a great potential in research and may play an important clinical role in a few years later.

Keywords: Piezoelectric immunosensor; Mixed self-assembled monolayer; Antisperm antibody

Monoclonal antibody-based ELISA for the quantification of nitrofuran metabolite 3-amino-2-oxazolidinone in tissues using a simplified sample preparation by Iva Diblikova; Kevin M. Cooper; D. Glenn Kennedy; Milan Franek (pp. 285-292).

A sensitive and specific monoclonal ELISA for the determination of tissue bound furazolidone metabolite 3-amino-2-oxazolidinone (AOZ) is described. The procedure enables the detection of AOZ in matrix supernatant after homogenisation, protease treatment, acid hydrolysis and derivatisation of AOZ released from the tissue by o-nitrobenzaldehyde. The formed p-nitrophenyl 3-amino-2-oxazolidinone (NPAOZ) is determined by ELISA calibrated with matrix-matched standards in the concentration range of 0.05–5.0μgI⁻¹. The assay was validated according to criteria set down by Commission Decision 2002/657/EC for the performance and validation of analytical methods for chemical residues. Detection capability, set on the basis of acceptance of no false negative results, was 0.4μgkg⁻¹ for shrimp, poultry, beef and pork muscle. This sensitivity approaches the established confirmatory LC–MS/MS able to quantify tissue-bound AOZ at levels as low as 0.3μgkg⁻¹. An excellent correlation of results obtained by ELISA and LC/MS–MS within the concentration range 0–32.1μgkg⁻¹ was found in the naturally contaminated shrimp samples ( r=0.999, n=8). A similar correlation was found for the incurred poultry samples within the concentration range of 0–10.5μgkg⁻¹ ( r=0.99, n=8).

Keywords: Immunoassay; Nitrofurans; AOZ; Extraction; Edible tissues; Validation

Enzyme-based microtiter plate assay for γ-aminobutyric acid: Application to the screening of γ-aminobutyric acid-producing lactic acid bacteria by Tadayuki Tsukatani; Tomoko Higuchi; Kiyoshi Matsumoto (pp. 293-297).

An enzyme-based microtiter plate assay for γ-aminobutyric acid (GABA) was developed. GABA was quantified using γ-aminobutyrate glutamate aminotransferase and succinic semialdehyde dehydrogenase in the presence of NADP⁺ and α-ketoglutarate. The NADPH produced by the series of enzymatic reactions was measured spectrophotometrically at 340nm. A linear relationship between absorbance and the concentration of GABA was obtained in the ranges from 5.0×10⁻⁴ to 1.0×10⁻²M. The relative standard deviation for 10 successive measurements was 0.9% at the 10mM GABA level. This analytical method was applied to the screening of GABA-producing lactic acid bacteria in de Man–Rogosa–Sharpe (MRS) medium. The proposed method enables one to assay 96 samples for an hour without the pre-treatment of samples. The method is by far superior to the traditional HPLC method from the point of view of rapidity and simplicity.

Keywords: γ-Aminobutyric acid; Microtiter plate; Enzyme; GABase; Lactic acid bacteria

Gold nanoparticle arrays directly grown on nanostructured indium tin oxide electrodes: Characterization and electroanalytical application by Jingdong Zhang; Munetaka Oyama (pp. 299-306).

This work describes an improved seed-mediated growth approach for the direct attachment and growth of mono-dispersed gold nanoparticles on nanostructured indium tin oxide (ITO) surfaces. It was demonstrated that, when the seeding procedure of our previously reported seed-mediated growth process on an ITO surface was modified, the density of gold nanospheres directly grown on the surface could be highly improved, while the emergence of nanorods was restrained. By field emission scanning electron microscopy (FE-SEM) and cyclic voltammetry, the growth of gold nanoparticles with increasing growth time on the defect sites of nanostructured ITO surface was monitored. Using a [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ redox probe, the increasingly facile heterogeneous electron transfer kinetics resulting from the deposition and growth of gold nanoparticle arrays was observed. The as-prepared gold nanoparticle arrays exhibited high catalytic activity toward the electrooxidation of nitric oxide, which could provide electroanalytical application for nitric oxide sensing.

Keywords: Gold nanoparticles; Indium tin oxide electrode; Improved seed-mediated growth approach; Electrocatalysis; Nitric oxide

Phenylurea herbicides-selective polymer prepared by molecular imprinting using N-(4-isopropylphenyl)- N′-butyleneurea as dummy template by Jincheng Wang; Rongbo Guo; Jiping Chen; Qing Zhang; Xinmiao Liang (pp. 307-315).

A phenylurea herbicides-selective molecularly imprinted polymer (MIP) was prepared using N-(4-isopropylphenyl)- N′-butyleneurea as a dummy template and toluene as a porogen. The experimental results showed that the optimum molar ratio of template, functional monomer (MAA) and cross-linker (EDMA) was 1:8:20. Scatchard analysis showed that two classes of binding sites were formed in the imprinted polymer with dissociation constants of 26.81μmoll⁻¹ and 1.428mmoll⁻¹. The affinity and selectivity of MIP for phenylurea herbicides were studied. Among the 14 phenylurea herbicides tested, the MIP prepared showed obviously high affinity and selectivity for 10 chemicals (monuron, diuron, isoproturon, fenuron, chlortoluron, difenoxuron, metoxuron, neburon, buturon and fluometuron) with dichloromethane containing 10% hexane as mobile phase while non-imprinted polymer showed very low affinity for all the phenylurea herbicides tested. The experimental and calculated results also indicated that the size and property of the group at the N′ position of phenylurea molecules have great influence on the affinity of MIP for them and the recognition site is mainly located at the N′ position of phenylurea herbicides.

Keywords: Molecularly imprinted polymer; Phenylurea herbicides; N; -(4-Isopropylphenyl)-; N; ′-butyleneurea; Dummy template

Determination of acetone, hexanal and heptanal in blood samples by derivatization with pentafluorobenzyl hydroxylamine followed by headspace single-drop microextraction and gas chromatography–mass spectrometry by Ning Li; Chunhui Deng; Ning Yao; Xizhong Shen; Xiangmin Zhang (pp. 317-323).

In the study, we developed a simple, rapid, sensitive, and inexpensive method for determination of the disease biomarkers of acetone, hexanal and heptanal in human blood. For the first time, derivatization of carbonyls with O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine (PFBHA) was combined with headspace single-drop microextractin (HS-SDME) and gas chromatography-mass spectrometry (GC–MS) and applied to the analysis of acetone, hexanal, and heptanal in human blood. At first, acetone, hexanal and heptanal in blood were derivatized with PFBHA and formed oximes in several seconds. Sequentially, the oximes were headspace extracted and concentrated by a microdrop solvent. Finally, the extracted oximes were analyzed by GC–MS. HS-SDME conditions and method validations were studied. Due to needing of only 2μl organic solvent, short extraction time of 8min, and simple operation, derivatization-HS-SDME was shown to be a rapid, simple, and inexpensive technique for analysis of acetone, hexanal, and heptanal in human blood. Moreover, it had low detection limit values from 0.24 to 0.62nM, and good reproducibility (R.S.D. less than 12%).

Keywords: Derivatization; Carbonyls; Blood analysis; Single-drop extraction; Headspace analysis

On-line preconcentration of some rare earth elements in water samples using C₁₈-cartridge modified with l-(2-pyridylazo) 2-naphtol (PAN) prior to simultaneous determination by inductively coupled plasma optical emission spectrometry (ICP–OES) by Nader Bahramifar; Yadollah Yamini (pp. 325-332).

The on-line column preconcentration technique with inductively coupled plasma optical emission spectroscopy (ICP–OES) has been developed using a cartridge filled with octadecyl silica modified by l-(2-pyridylazo) 2-naphtol (PAN). The aim of this method was to determine some rare earth elements (REEs) (Ce, Dy, La, Sm, and Y) and uranium in water samples. Sample solutions were passed through the C₁₈-modified column. The adsorbed cations were subsequently eluted from the column and transferred into the plasma with nitric acid solution for simultaneous determination of them. Sample pH, amount of PAN as a complexing agent, sampling and eluting flowrates and concentration of the eluent were optimized. Detection limits based on three times of standard deviations of blank by 10 replicates were in the range of 11ngl⁻¹ for Dy to 69ngl⁻¹ for U. Sample throughput was 10 samplesh⁻¹. The proposed method was applied to determine REEs in natural water samples. Recoveries of the REEs from natural water samples were between 95 and 106% with percent relative standard deviation (%R.S.D.) of 1.0–7.9%.

Keywords: Rare earth elements; On-line solid phase extraction; Inductively coupled plasma optical emission spectrometry

Simultaneous on-line preconcentration and determination of trace metals in environmental samples by flow injection combined with inductively coupled plasma mass spectrometry using a nanometer-sized alumina packed micro-column by Jun Yin; Zucheng Jiang; Gang Chang; Bin Hu (pp. 333-339).

A flow injection (FI) on-line preconcentration procedure by using a nanometer-sized alumina packed micro-column coupled to inductively coupled plasma mass spectrometry (ICP-MS) was described for simultaneous determination of trace metals (V, Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb) in the environmental samples. The effects of pH value, sample flow rate, preconcentration time, and interfering ions on the preconcentration of analytes have been investigated. Under the optimized operating conditions, the adsorption capacity of the nanometer-sized alumina for V, Cr, Mn, Co, Ni, Cu, Zn, Cd and Pb were found to be 11.7, 13.6, 15.7, 9.5, 12.2, 13.3, 17.1, 17.7 and 17.5mgg⁻¹, respectively. With 60s preconcentration time and 60s elution time, an enrichment factor of 5 and the sampling frequency of 15h⁻¹ were obtained. The proposed method has been applied to the determination of trace metals in environmental certified reference materials and natural water samples with satisfactory results.

Keywords: Nanometer-sized alumina; Flow injection; On-line preconcentration; ICP-MS; Metal ions; Environmental samples

Elimination of matrix effects for headspace solid-phase microextraction of important volatile compounds in red wine using a novel coating by Mingming Liu; Zhaorui Zeng; Yun Tian (pp. 341-353).

In this paper, hydroxy-terminated silicone oil-butyl methacrylate-divinylbenzene (OH-TSO-BMA-DVB) copolymer was first synthesized and used as stationary phase with the aid of γ-methacryloxypropyltrimethoxylsilane (KH-570) as bridge in solid-phase microextraction (SPME) using sol–gel method and cross-linking technique. It has high extraction efficiency for both polar alcohols and fatty acids and nonpolar esters in comparison with commercial PDMS, PDMS-DVB and PA fibers. A simple and sensitive headspace SPME-gas chromatography (HS-SPME-GC) method using the novel fiber was presented for the simultaneous analysis of both polar alcohols and fatty acids and nonpolar esters in wine. To check the matrix effects, various model wine matrices, including distilled water; 11.5% ethanol/water (v/v) solution; a concentrated synthetic wine; a ‘volatile-free’ wine and a real wine were investigated in detail. Matrix effects were compensated for by using internal standard method and selecting the ‘volatile-free’ wine as working standard. The method presented in this study showed satisfactory linearity, precision, detection limits and accuracy. The recoveries obtained ranged from 85.87 to 104.2%, and the relative standard deviation values were below 9%. The results obtained indicated that the present method is a validated and accurate procedure for the simultaneous determination of both polar and nonpolar aroma compounds in wine.

Keywords: Sol–gel; Butyl methacrylate; Divinylbenzene; Solid-phase microextraction; Wine; Volatile organic compounds; Matrix effects

Microwave-assisted extraction of OCPs, PCBs and PAHs concentrated by semi-permeable membrane devices (SPMDs) by V. Yus�; A. Pastor; M. de la Guardia (pp. 355-366).

Microwave-assisted extraction (MAE) has been evaluated as an alternative to dialysis for extraction of some water-borne hydrophobic contaminants sampled by semi-permeable membrane devices (SPMDs). Seven organochlorine pesticides (OCPs), 11 polychlorinated biphenyls (PCBs) and 13 polycyclic aromatic hydrocarbons (PAHs) were accumulated in SPMDs at nanogram levels and extracted with three 3-min irradiation cycles with 33mL of a solvent mixture hexane–water (10:1,v/v) in each cycle. The developed MAE method gave for all analytes investigated statistically comparable extraction yields with those found by dialysis carried out with a total volume of 250mL hexane for 48h at room temperature. The recoveries of all the targeted contaminants were in the range of 65–105% with variation coefficients not exceeding 19%. The applicability of the MAE extraction was tested in field SPMDs samples deployed for 15 days in a sewage-treatment process. Our results show that MAE provides a remarkable reduction of time and solvent volume when used as an extraction method in the analysis of SPMDs.

Keywords: Semi-permeable membrane device; SPMD; Microwave-assisted extraction; MAE; Organochlorine pesticides; Polychlorinated biphenyls; Polycyclic aromatic hydrocarbons

Development and validation of liquid chromatography–mass spectrometry method for the determination of telmisartan in human plasma by Ben-mei Chen; Yi-zeng Liang; Ya-li Wang; Fu-Liang Deng; Ping Zhou; Fang-qiu Guo; Lan-fang Huang (pp. 367-373).

A sensitive liquid chromatographic–electrospray ionization mass spectrometric method was developed and validated for fast determination of telmisartan in human plasma. Plasma of 0.1mL was deprotienated with methanol, centrifugation, evaporation to dryness and dissolving in mobile phase, samples were separated using a Hypersil-Keystone C18 reversed-phase column (150mm×2.1mm i.d., 5μm), together with a mobile phase containing of acetonitrile–10mM ammonium acetate (42:58, v/v), 0.2% acetic acid and was isocratically eluted at a flow rate of 0.2mL/min. Telmisartan and its internal standard, valsartan, were measured by electrospray ion source in positive selective ion monitoring mode. The method demonstrated linearity from 1 to 2000ng/mL ( r=0.9988). The limit of quantification for telmisartan in plasma was 1ng/mL with good accuracy and precision. The mean sample extract recovery of the method were higher than 82 and 78% for telmisartan and internal standard (IS), respectively. The within-run and between-run precision ranged from 3.4 to 8.9% and 5.9 to 11.2% (relative standard deviation, R.S.D.), respectively.

Keywords: Telmisartan; LC–MS; Electrospray ionization

Liquid chromatographic tandem mass spectrometric determination of trandolapril in human plasma by Constantinos Pistos; Maria Koutsopoulou; Irene Panderi (pp. 375-382).

A liquid chromatographic tandem mass spectrometric method for the determination of trandolapril in human plasma has been developed and fully validated. The article describes, in detail, the bioanalytical procedure and summarizes the validation results obtained. The samples were extracted using HLB Oasis solid-phase extraction cartridges. The chromatographic separation was performed on X-Terra C8 MS column (150mm×4.6mm i.d., 5μm particle size) using a mobile phase consisting of acetic acid 20mM and triethylamine 4.3mM/acetonitrile (40:60 (v/v)), pumped isocratically at 0.35ml/min.The analytes were detected using a micromass quattro micro triple quadrupole mass spectrometer with positive electrospray ionization in multiple reaction-monitoring (MRM) mode. Tandem mass spectrometric detection enabled the quantitation of trandolapril down to 2.0ng/ml. Calibration graphs were linear ( r better than 0.996, n=9) in the concentration ranges 2.0–750ng/ml and the intra- and inter-day R.S.D. values were less than 3.83 and 3.86% for trandolapril.

Keywords: Trandolapril; Human plasma; Tandem mass spectrometry

High-performance liquid chromatographic assay of phosphate and organophosphorus pesticides using a post-column photochemical reaction and fluorimetric detection by Tom�s P�rez-Ruiz; Carmen Mart�nez-Lozano; Virginia Tom�s; Jes�s Mart�n (pp. 383-391).

A sensitive method for the post-column reaction detection of organophosphorus pesticides is described. The method relies on photolysis of the organocompounds by irradiation with a low-pressure mercury lamp (main spectral line, 254nm) in the presence of peroxydisulfate. The resultant orthophosphate was reacted with molybdate to form molybdophosphoric acid, which subsequently reacted with thiamine to generate thiochrome. Finally, the fluorescence intensity of thiochrome was measured at 440nm with excitation at 375nm. Factors affecting the rate of these reactions were optimized so that its contribution to the total band-broadening was negligible.This detection system was used for the determination of phosphate, acephate and methamidophos, which were separated on an ODS column by isocratic reversed phase chromatography with acetonitrile–water as the mobile phase. A linear relationship between analyte concentration and peak area was obtained within the range 0.016–7.0μgml⁻¹ with correlation coefficients greater than 0.9995 and detection limits between 4 and 12ngml⁻¹. Intra- and inter-day precision values of about 1.2% R.S.D. ( n=10) and 2.1% R.S.D. ( n=30), respectively, were obtained.Pesticide residues below ngml⁻¹ levels could be determined in environmental waters when a preconcentration device was coupled on-line with the HPLC system. Detection limits as low as 0.01ngml⁻¹ were achieved for only 250ml of sample. In the analyses of vegetables and grains, the detection limit was about 1μgkg⁻¹.

Keywords: High-performance liquid chromatography; Organophosphorus pesticides; On-line photo-oxidation; Molybdophosphoric acid reaction; Fluorescence detection

Hydroxypropyl-β-cyclodextrin effect on the fluorescence of auxin and skatole and on the simultaneous determination of binary mixtures of indole compounds in urine by first derivative spectrofluorimetry by Raquel E. Galian; A. Guillermo Bracamonte; Alicia V. Veglia (pp. 393-401).

The effect of hydroxypropyl-β-cyclodextrin (HPβCD, β-cyclodextrin (βCD) derivative) was determined on the fluorescence emission spectra of skatole (3-methylindole,MI) and auxin (indole 3-acetic acid,IA). The experiments were conducted at excitation wavelength ( λ_ex)=280nm, in aqueous solutions at different pH values, with and without HPβCD as receptor. The enhanced fluorescence in the presence of the receptor showed a 1:1 host–guest interaction and the values of the association constants K_A were between 100 and 200mol⁻¹L. The effects of methanol and propanol with and without receptor were also studied. The limit of detection ( L_D) for the HPβCD enhanced fluorimetric method at pH = 7.00 were 0.279 and 0.765ngmL⁻¹ forMI andIA, respectively. For the determination of indole compounds with closely overlapping spectral bands a zero-crossing first derivative spectrofluorimetric method with or without HPβCD is described. Binary mixtures ofMI orIA with melatonin ( N-acetyl-5-methoxytryptamine,M) or 5-methoxytryptamine (5-methoxy-3-(2-aminoethyl)indole,5M) were analysed in the presence of HPβCD. In the absence of receptor, binary mixtures ofMI withIA andM with5M were determined. The matrix effect was evaluated in urine samples by the method of standard addition. Good apparent recoveries were found for each indolic compound by the direct method (98–105% with R.S.D. 0.5–5%) and for mixtures of them by the first derivative method (90–105% with R.S.D. 1–5%) indicating the applicability of them with the advantage of their simplicity, low cost in materials, no time consuming and no requirement of the use of a sophisticate calibration program.

Keywords: Hydroxypropyl-β-cyclodextrin complexes; Skatole; Auxin; Fluorimetric determination; Indole mixtures

Optimization of conditions for flow-through partial-filling affinity capillary electrophoresis to estimate binding constants of ligands to receptors by Abby Brown; Robert Desharnais; Bidhan C. Roy; Sanku Malik; Frank A. Gomez (pp. 403-410).

This work details the determination of the minimal injection time of ligand required in flow-through partial-filling affinity capillary electrophoresis (FTPFACE) to estimate binding constants of ligands to receptors. Two model systems are examined in this study: carbonic anhydrase B (CAB, EC 4.2.1.1) and arylsulfonamides, and vancomycin from Streptomyces orientalis andd-Ala-d-Ala peptides. Using CAB, a minimal injection time of 0.07min at high pressure was determined that provided for the accurate and reproducible measurement of binding constants. In the FTPFACE technique, the capillary is first partially filled with a zone of ligand followed by a sample plug containing receptor and non-interacting standards. Upon application of a voltage the receptor and standards flow into the zone of ligand where a dynamic equilibrium is achieved between receptor and ligand. Continued electrophoresis results in the receptor and standards flowing through the domain of the ligand plug prior to detection. Analysis of the change in the relative migration time ratio (RMTR) of the receptor, relative to the non-interacting standards, as a function of the concentration of ligand, yields a value for the binding constant. In the present study, variable injection times of 4-carboxybenzenesulfonamide (CBSA) were examined to determine the minimal injection time needed to establish an equilibrium between CAB and ligand. A mathematical relationship was derived that correlated injection time and ligand concentration to the change in RMTR and comparisons made between the experimental and calculated values. Binding constants were obtained for a series of arylsulfonamide ligands andd-Ala-d-Ala terminus peptides to CAB and Van, respectively. The results support the use of FTPFACE to estimate affinity constants under variable experimental conditions.

Keywords: Affinity capillary electrophoresis; Binding constants; Carbonic anhydrase B; Vancomycin

Horizontal attenuated total reflection applied to simultaneous determination of ash and protein contents in commercial wheat flour by Marco F. Ferr�o; Celso U. Davanzo (pp. 411-415).

Partial least-squares (PLS) regression was used to generate various models for the determination of both the protein and the ash contents of wheat flours by using spectroscopic data in the mid-infrared region obtained with a horizontal attenuated total reflectance (HATR) accessory. One hundred samples of wheat flour were used as purchased in the market: 55 for constructing the calibration model and 45 as external samples. The protein content varied between 8.85 and 13.23% and the ash content, between 0.330 and 1.287%, as determined by reference methods. Raw spectra and those corrected by multiplicative signal correction (MSC), first and second derivative spectra, were used as data for building the models. Different pre-treatments, such as mean centered and/or variance scaled (VS) methods, were tested and compared. Very good models were built as judged by the correlation coefficients ( R²), root mean square error of calibration (RMSEC), root mean square error of validation (RMSEV) and root mean square error of prediction (RMSEP) that were obtained. Best results were achieved with MSC treated spectra.

Keywords: Horizontal attenuated total reflection; FT-IR; PLS regression; Wheat flour; Protein content; Ash content

Erratum to “Non-covalent imprinting of phosphorous esters�? by Andrew J. Hall; Francesca Lanza-Sellergren; Panagiotis Manesiotis; B�rje Sellergren (pp. 417-417).

Author Index (pp. 419-421).

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Analytica Chimica Acta (v.540, #2)