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Analytica Chimica Acta (v.593, #2)

Contents (pp. iii).

Calendar of forthcoming meetings (pp. n3).

Editorial Board (pp. co1).

Novel analytical procedures for screening of drug residues in water, waste water, sediment and sludge by Wolfgang W. Buchberger (pp. 129-139).

Traces of pharmaceuticals are continuously introduced into the aquatic environment mainly by sewage treatment plant effluents. Final data about their impact on the ecosystem are still partly missing. Progress in instrumental analytical chemistry has resulted in the availability of methods that allow a monitoring of these pollutants at ngL⁻¹ levels. In this review the state-of-the-art of residue analysis of pharmaceuticals by chromatographic and electrophoretic techniques is summarized. Improvements in detection limits over the past years have mainly been due to sophisticated mass spectrometric detection techniques. Furthermore, robust sample preparation and preconcentration protocols based on solid-phase extraction and related procedures have contributed significantly to the achievements observed so far. This review also covers several immunochemical approaches which may serve as an inexpensive alternative for quick screening of samples.

Keywords: Pharmaceuticals; Environmental analysis; Water; Sediment; Sludge; Review

Modelling of retention of pesticides in reversed-phase high-performance liquid chromatography: Quantitative structure-retention relationships based on solute quantum-chemical descriptors and experimental (solvatochromic and spin-probe) mobile phase descriptors by Angelo Antonio D’Archivio; Fabrizio Ruggieri; Pietro Mazzeo; Enzo Tettamanti (pp. 140-151).

A quantitative structure-retention relationship (QSRR) analysis based on multilinear regression (MLR) and artificial neural networks (ANNs) is carried out to model the combined effect of solute structure and eluent composition on the retention behaviour of pesticides in isocratic reversed-phase high-performance liquid chromatography (RP-HPLC). The octanol–water partition coefficient and four quantum chemical descriptors (the total dipole moment, the mean polarizability, the anisotropy of the polarizability and a descriptor of hydrogen-bonding based on the atomic charges on acidic and basic chemical functionalities) are considered as solute descriptors. In order to identify suitable mobile phase descriptors, encoding composition-dependent properties of both methanol- and acetonitrile-containing mobile phases, the Kamlet–Taft solvatochromic parameters (polarity–dipolarity, hydrogen-bond acidity and hydrogen-bond basicity, π^*, α and β, respectively) and the¹⁴N hyperfine-splitting constant ( a_N) of a spin-probe dissolved in the eluent are examined. A satisfactory description of mobile phase properties influencing the solute retention is provided by a_N and β or alternatively π^* and β. The two seven-parameter models resulting from combination of a_N and β, or π^* and β, with the solute descriptors were tested on a set of 26 pesticides representative of 10 different chemical classes in a wide range of mobile phase composition (30–60% (v/v) water–methanol and 30–70% (v/v) water–acetonitrile). Within the explored experimental range, the acidity of the eluent, as quantified by α, is almost constant, and this parameter is in fact irrelevant. The results reveal that a_N and π^*, that can be considered as interchangeable mobile phase descriptors, are the most influent variables in the respective models. The predictive ability of the proposed models, as tested on an external data set, is quite good ( Q² close to 0.94) when a MLR approach is used, but the modelling capability can be further improved using an artificial neural network.

Keywords: Quantitative structure-retention relationships; Electron spin resonance; Artificial neural network; Reversed-phase high-performance liquid chromatography; Pesticides; Mobile phase

Determination of sulfonamides in milk after precolumn derivatisation by micellar liquid chromatography by Mónica Ana Raviolo; Maria Rambla-Alegre; Jenifer Clausell-Tormos; Maria-Elisa Capella-Peiró; Samuel Carda-Broch; Josep Esteve-Romero (pp. 152-156).

A simple method to identify and determine six sulfonamides (sodium sulfacetamide, sulfamethizole, sulfaguanidine, sulfamerazine, sulfathiazole and sulfamethoxazole) in milk by micellar liquid chromatography (MLC) is reported. The assay makes use of a precolumn diazotisation-coupling derivatisation including the formation of an azo dye that can be detected at 490nm. Furthermore, the use of MLC as an analytical tool allows the direct injection of non-purified samples. The separation was performed with an 80mM SDS-8.5% propanol eluent at pH 7. Analysis times are below 16min with a complete resolution. Linearities ( r>0.9999), as well as intra- and inter-day precision (below 2.7%), were studied in the validation of the method. The limits of detection and quantification ranged from approximately 0.72 to 0.94 and 2.4 to 3.1ngmL⁻¹, respectively. The detection limit was below the maximum residue limit established by the European Community. Finally, recoveries in spiked milk samples were in the 83–103% range.

Keywords: Sulfonamides; Azo dye precolumn derivatisation; Micellar liquid chromatography; Milk

Analysis of phenylurea and propanil herbicides by solid-phase microextraction and liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection by Ahmed R. Mughari; P. Parrilla Vázquez; M. Martínez Galera (pp. 157-163).

This study examines the application of solid-phase microextraction coupled with high performance liquid chromatography combined with post-column photochemically induced fluorimetry derivatization and fluorescence detection (SPME–HPLC–PIF–FD) for the determination of four phenylurea herbicides (monolinuron, diuron, linuron and neburon) and propanil in groundwater. Direct immersion (DI) SPME was applied using a 60μm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber for the extraction of the pesticides from groundwater samples. An AQUASIL C₁₈ column (150mm×4.6mm i.d., 5μm) was used for separation and determination in HPLC. The method was evaluated with respect to the limits of detection (LODs) and the limits of quantification (LOQs) according to IUPAC. The limits of detection varied between 0.019μgL⁻¹ and 0.034μgL⁻¹. Limits of quantification ranged between 0.051μgL⁻¹ and 0.088μgL⁻¹. These values meet the recommended limits for individual pesticides in groundwater (0.1μgL⁻¹) established by the EU. Recoveries ranged between 86% and 105% and relative standard deviation values between 2% and 8%.

Keywords: Solid-phase microextraction; Phenylurea herbicides; Photochemically induced fluorescence; Liquid chromatography separation; Groundwater

Molecularly imprinted solid phase extraction for the selective HPLC determination of α-tocopherol in bay leaves by F. Puoci; G. Cirillo; M. Curcio; F. Iemma; U.G. Spizzirri; N. Picci (pp. 164-170).

A new sorbent for molecularly imprinted solid phase extraction (MISPE) was synthesized to extract and purify α-tocopherol (α-TP) from vegetable sources. Molecularly imprinted polymers (MIP) were synthesized using methacrylic acid (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking agent using a photo-polymerization procedure. A thermo-polymerization was also performed but no imprinting effect in the resulting materials was raised.The proposed MISPE protocol could overcome the drawback of traditional detection methods, which require pre-treatments of the samples. The possibility to obtain the selective recognition of α-TP from natural samples in aqueous mixtures represents one of the main advantages of our materials. Our procedure involves the direct HPLC injection of eluate without any treatment and above all the use of no toxic and biocompatible organic solvents.After the evaluation of the selectivity of the α-TP imprinted polymers, the performance of these materials as solid phase extraction (SPE) sorbents was investigated. Our MISPE–HPLC procedure has a high sensitivity, LOD and LOQ were 3.49×10⁻⁷ and 1.16×10⁻⁶molL⁻¹, respectively, as well as good precision (intraday precision below 3.3% and interday precisions below 6.5%) and recovery (60%). Thus, it can be successfully used for the purification of α-TP from bay leaves.

Keywords: α-Tocopherol; MIP; Selective extraction; Bay; Food analysis

Simultaneous estimation of zeta potential and slip coefficient in hydrophobic microchannels by H.M. Park; T.W. Kim (pp. 171-177).

Electroosmotic flows through hydrophobic microchannels experience velocity slip at the channel wall, which increases the volumetric flow rate at a given electric potential gradient. The conventional method of zeta potential estimation using the volumetric flow rate may yield quite inaccurate zeta potential unless the velocity slip is appropriately taken care of. In the present investigation we develop a method for simultaneous estimation of zeta potential and velocity slip coefficient in the electroosmotic flow through a hydrophobic microchannel using velocity measurements. The relevant inverse problem is solved through the minimization of a performance function utilizing a conjugate gradient method. The present method is found to estimate the zeta potential and slip coefficient accurately even with noisy velocity measurements.

Keywords: Lab-on-a-chip; Electroosmosis; Zeta potential; Slip coefficient

Selective and sensitive hydroxypropyl-beta-cyclodextrin based sensor for simple monitoring of (+)-catechin in some commercial drinks and biological fluids by Deia Abd El-Hady (pp. 178-187).

(+)-Catechin (CAT) was considered as a polyphenolic compound abundantly contained in plants. It exerts protective effect against cancer, inflammatory and cardiovascular diseases. These protective effects are mainly attributed to its antioxidative activity by scavenging free radicals. Therefore, the need of simple, selective and sensitive monitoring of (+)-catechin in commercial drinks and biological fluids is crucial. A new selective and sensitive voltammetric quantification of (+)-catechin was investigated at low cost hydroxypropyl-beta-cyclodextrin modified carbon paste sensor in acidic solutions. The constructed sensor was treated in simple and fast manner to increase its stability for catechin determination. The effect of solution and instrumental parameters was investigated by using osteryoung square-wave anodic voltammetry (OSWAV) at pH 2.20 and differential pulse cathodic voltammetry (DPCV) at pH 4.40 in 0.10M Britton-Robinson buffer. Acidic solutions were chosen to increase the stability of (+)-catechin, reduce its adsorption on the sensor surface and increase the selectivity of proposed method. Cyclic voltammetry (CV) was used to elucidate the electrochemical mechanism of catechin at the modified electrochemical sensor. A linear range up to 7.20 and 4.20μgmL⁻¹ of catechin was achieved in anodic and cathodic voltammetry, respectively. The method gave reproducible and reliable results with 1.50(gmL⁻¹ catechin (S.D. 0.062). Limit of detection of 0.12 and 0.30ngmL⁻¹ and limit of quantification (LOQ) of 1.10 and 2.80ngmL⁻¹ were easily achieved using anodic and cathodic voltammetry, respectively. Selectivity of the proposed procedure was estimated by testing recovery and adding the most interfering metal ions and/or organic compounds. The proposed method was applied successfully to selective determination of catechin in some commercial drinks like tea, cocoa and coffee with acceptable recovery range (98–102%). The extraction of catechin was rather simple, making it suitable for studies with a large number of commercial samples. Furthermore, the application to urine samples without pretreatment was achieved and statistically confirmed at 95% confidence level. It was easy to analyze catechin in urine down to 0.55ngmL⁻¹.

Keywords: Voltammetry; Hydroxypropyl-beta-cyclodextrin; Sensor; Selective; Catechin; Drinks; Urine

Different experimental results for the influence of immersion angle on the resonant frequency of a quartz crystal microbalance in a liquid phase: With a comment by Dazhong Shen; Qi Kang; Xiaoyu Li; Hongmei Cai; Yuandong Wang (pp. 188-195).

This paper presents different experimental results of the influence of an immersion angle ( θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (Δ F) versus ( ρη)^1/2, the square root of the product of solution density ( ρ) and viscosity ( η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large ( ρη)^1/2 region (0–55wt% sucrose solution as an example, with ρ value from 1.00 to 1.26gcm⁻³ and η value from 0.01 to 0.22gcm⁻¹s⁻¹, respectively), the slope of the plot of Δ F versus ( ρη)^1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase.

Keywords: Quartz crystal microbalance; Immersion angle; Longitudinal wave; Viscodensity

Immersion angle dependence of the resonant-frequency shift of the quartz crystal microbalance in a liquid: Effects of longitudinal wave by Minoru Yoshimoto; Satoshi Kobirata; Hideo Aizawa; Shigeru Kurosawa (pp. 196-198).

We investigated the effects of the longitudinal wave on the immersion angle dependence of the resonant-frequency shift, Δ F, of the quartz crystal microbalance, QCM. In order to study exactly the effects, we employed the three types of cells: normal cell, cell with the glass beads and cell with sponge. The longitudinal wave exists in the normal cell. On the other hand, both the cell with the glass beads and the cell with sponge eliminate the longitudinal wave. As results, we have found that the tendencies of Δ F are the same in the three types of cells. That is, we conclude that the longitudinal wave does not have effects on the immersion angle dependence of Δ F.

Keywords: Quartz crystal microbalance; Immersion angle; Longitudinal wave

Computer-assisted prediction of pesticide substructure using mass spectra by Qing Xiong; Yuxi Zhang; Menglong Li (pp. 199-206).

Mass spectral classifiers of 16 substructures that are present in basic structures of pesticides have been investigated to assist pesticide residues analysis as well as screening of pesticide lead compounds. Mass spectral data are first transformed into 396 features, and then Genetic Algorithm-Partial Least Squares (GA-PLS) as a feature selection method and Support Vector Machine (SVM) as a validation method are implemented together to get an optimization feature set for each substructure. At last, a statistical method which is AdaBoost algorithm combined with Classification and Regression Tree (AdaBoost-CART) is trained to predict the 16 substructures presence/absence using the optimization mass spectral feature set. It is demonstrated that the optimum feature sets can be used to predict the 16 pesticide substructures presence/absence with mostly 85–100% in recognition success rate instead of the original 396 features.

Keywords: Feature selection; Mass spectra; Classification; Genetic Algorithm-Partial Least Squares; AdaBoost algorithm combined with Classification and Regression Tree

Matrix assisted laser desorption ionization-time of flight mass spectrometry analysis of hyaluronan oligosaccharides by Shinobu Sakai; Kana Hirano; Hidenao Toyoda; Robert J. Linhardt; Toshihiko Toida (pp. 207-213).

A new method is presented for the identification of oligosaccharides obtained by enzymatic digestion of hyaluronan (HA) with bacterial hyaluronidase (E.C. 4.2.2.1, from Streptomyces hyalurolyticus) using matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOFMS). Mixtures containing HA oligosaccharides of tetrasaccharide (4-mer)–34-mer were analyzed using this method. The carboxyl groups of the glucuronate residues in the prepared HA oligomers, were modified as the acidic form (COOH), sodium salts (COONa), organic ammonium salts, or methylesters before MALDI-TOFMS measurement. Among these samples, the methylester form of glucuronate residues in HA oligosaccharides, prepared by methylation using trimethylsilyl diazomethane, afforded high sensitivity for spectra. This simple modification method for carboxyl group methylation of acidic polysaccharides [Hirano et al., Carbohydr. Res., 340, (2005) 2297–2304] provides samples suitable for MALDI-TOF mass spectrometric analysis throughout a significantly enhanced range of masses.

Keywords: Hyaluronan oligosaccharide; Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOFMS); Methylester

Determination of the dose–depth distribution of proton beam using resazurin assay in vitro and diode laser-induced fluorescence detection by Min Jung Kim; Sukdeb Pal; Yu Kyung Tak; Kyeong-Hee Lee; Tae Keun Yang; Su-Jae Lee; Joon Myong Song (pp. 214-223).

In this study the dose–depth distribution pattern of proton beams was investigated by inactivation of human cells exposed to high-LET (linear energy transfer) protons. The proton beams accelerated up to 45MeV were horizontally extracted from the cyclotron, and were delivered to the cells acutely through a home made prototype over a range of physical depths (in the form of a variable water column). The biological systems used here were two in vitro cell lines, including human embryonic kidney cells (HEK 293), and human breast adenocarcinoma cell line (MCF-7). Cells were exposed to unmodulated proton beam radiation at a dose of 50Gy similar to that used in therapy. Resazurin metabolism assay was investigated for measurement of cell response to irradiation as a simple and non-destructive assay. In the resazurin reduction test the non-fluorescent probe dye is reduced to pink and highly fluorescent resorufin. The dose–depth distribution of proton beam obtained based on the highly sensitive laser-induced fluorometric determination of resorufin was found to coincide well with the data collected using conventional film based dosimetry. The resazurin method yielded data comparable with the optical micrographs of the irradiated cells, showing the least cell survival at the measured Bragg-peak position of 10mm. In addition, fused silica capillary was used as a sample container to increase the probability for irradiated laser beam to probe and excite resorufin in small sample volume of the capillary. The developed method has the potential to serve as a non-destructive, sample-thrifty, and time saving tool to realize more realistic, practical dose–depth distribution of proton beam compared to conventional in vitro cell viability assessment techniques.

Keywords: Proton beam; Dose–depth distribution; Bragg-peak; Resazurin; Resorufin; Laser-induced fluorescence

Prediction of the retention in thin layer chromatography screening systems by atomic contributions by Łukasz Komsta (pp. 224-237).

A novel atomic-contribution system for predicting ofRM values is presented and validated on 13 thin layer chromatography screening systems on silica gel, where the large experimental datasets (198–761RM values) are available. TheRM is predicted with error less than 0.5 in majority of solutes (besides several outliers), which corresponds to difference inRF equal to 0.28 in the worst case. The system was validated by dividing the data into training and validation datasets, proving its accuracy. The main reason of larger errors in outliers are: large conjugated heterocycles, quarternary ammonium cations, large amount of polar atoms or very simple but unique molecules. The calculations are very easy and can be performed on free software or even manually. The presented method can be used in the retention prediction of new solutes in existing chromatographic screening systems.

Keywords: Quantitative Structure-Property Relationship (QSPR); Quantitative Structure-Retention Relationship (QSRR); Thin layer chromatography (TLC); Screening; Atomic contributions

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Analytica Chimica Acta (v.593, #2)