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Analytica Chimica Acta (v.581, #1)

Editorial Board (pp. co1).

Contents (pp. v-vi).

Calendar of forthcoming meetings (pp. n1).

Editorial Board (pp. co1).

Contents (pp. v-vi).

Electrocatalytic detection of insulin at RuOx/carbon nanotube-modified carbon electrodes by Joseph Wang; Tanin Tangkuaram; Suchera Loyprasert; Terannie Vazquez-Alvarez; Waret Veerasai; Proespichaya Kanatharana; Panote Thavarungkul (pp. 1-6).

A bilayer surface coating, prepared by electrodepositing ruthenium oxide (RuOx) onto a carbon nanotube (CNT) layer, offers dramatic improvements in the stability and sensitivity of voltammetric and amperometric measurements of insulin compared to the individual (CNT or RuOx) coated electrodes. The enhanced electrocatalytic activity towards insulin is indicated from lowering the potential of the oxidation process (starting around 0.35 versus Ag/AgCl) and the substantially higher sensitivity over the entire potential range. A wide linear dynamic range (10–800nM) was achieved with a detection limit of 1nM. The marked electrocatalytic activity of the RuOx/CNT coating towards insulin is coupled with a greatly enhanced stability. For example, the insulin amperometric response of the RuOx/CNT-coated electrodes is highly stable, with 97% of the initial activity remaining after 60min stirring of 2×10⁻⁶M solution (compared to significantly faster current diminutions at the RuOx- or CNT-coated surfaces). The results suggest great promise for miniaturized sensors and detectors for monitoring insulin.

Keywords: Insulin; Electrocatalysis; Carbon nanotubes; Ruthenium

Continuous glucose monitoring in interstitial fluid using glucose oxidase-based sensor compared to established blood glucose measurement in rats by Stefanie Woderer; Nadja Henninger; Claus-Dieter Garthe; Hans Martin Kloetzer; Martin Hajnsek; Ulrike Kamecke; Norbert Gretz; Bettina Kraenzlin; Johannes Pill (pp. 7-12).

Glucose monitoring is of importance for success of complex therapeutic interventions in diabetic patients. Its impact on treatment and glycemic control is demonstrated in large clinical trials. Up to eight blood glucose measurements per day are recommended. Notwithstanding, a substantial number of diabetic patients cannot or will not monitor their blood glucose appropriately. Considerable progress in control of disturbed metabolism in diabetic patients can be expected by continuous glucose monitoring. The aim of the study was to evaluate the performance of a new amperometric glucose oxidase-based glucose sensor in vitro and in vivo after subcutaneous implantation into rats.For in vitro testing current output of sensors was measured by exposure to increasing and decreasing glucose concentrations up to 472mgdL⁻¹ over a time period of 7 days. After subcutaneous implantation of sensors into interscapular region of male rats glucose in interstitial fluid was evaluated and compared to glucose in arterial blood up to 7 days. Hyper- and hypoglycaemia were induced by intravenous application of glucose and insulin, respectively. Current of each implanted sensor was converted into glucose concentration using the first blood glucose measurement only.A change of current with glucose of 0.35nAmg⁻¹dL⁻¹ indicates high sensitivity of the sensor in vitro. The response time (90% of steady state) was calculated by approximately 60s. Test strips for blood glucose measurement as reference for sensor readings was found as an appropriate and rapidly available method in rats by comparison with established hexokinase method in an automated lab analyzer with limits of agreement of +32.8 and −25.7mgdL⁻¹ in Bland-Altman analysis. In normo- and hypoglycaemic range sensor readings in interstitial fluid correlated well with blood glucose measurements whereas hyperglycaemia was not reflected by the sensor completely when blood glucose was changing rapidly.The data given characterize a sensor with high sensitivity, long term stability and short response time. A single calibration of the sensor is required only in measurement periods up to 7 days. The findings demonstrate that the sensor is a highly promising candidate for assessment in humans.

Keywords: Abbreviations; b.w.; body weight; GOD; glucose oxidase; ISF; interstitial fluid; MPC; 2-methacryloyloxyethyl phosphorylcholineGlucose biosensor; Continuous glucose monitoring; Glucose oxidase; Glucose in interstitial fluid; Blood glucose; Rat

A novel planar miniaturized potentiometric sensor for flow injection analysis of nitrates in wastewaters, fertilizers and pharmaceuticals by Saad S.M. Hassan; H.E.M. Sayour; Saeed S. Al-Mehrezi (pp. 13-18).

A novel all-solid-state miniaturized nitrate sensor is developed, characterized and used for flow injection analysis (FIA) of nitrates in various samples. The sensor incorporates silver bis(bathophenanthroline) nitrate [Ag(bath)₂NO₃] as an electroactive material in a plasticized PVC membrane. The sensing membrane (3mm×5mm) is immobilized on a wafer polyimide microchip (size 13.5mm×3.5mm) to offer a planar miniaturized design easily used in a single channel wall-jet flow injection system. Under hydrodynamic mode of operation (FIA) the sensor displays fast response, high sensitivity, long term stability and good selectivity for NO₃⁻ in the presence of many common associated anions. The calibration slope is 55.1±0.1mVdecade⁻¹ over the concentration range 1.0×10⁻¹ to 1.0×10⁻⁶molL⁻¹, the lower detection limit is 0.05μgmL⁻¹, the working pH is 2–9,and the output is 70–90samplesh⁻¹. Validation of the assay method reveals good performance characteristics and suggests application for routine determination of NO₃⁻ in industrial wastewaters, fertilizers and pharmaceuticals. The results agree fairly well with data obtained by the standard spectrophotometric methods.

Keywords: Miniaturized planar sensor; Nitrates; Silver bis(bathophenanthroline) nitrate; Potentiometry; Pharmaceutical analysis; Wastewaters; Fertilizer analysis; Flow injection analysis

Approach on quantitative structure–activity relationship for design of a pH neutral carrier containing tertiary amino group by Zhong Cao; Fu-Chun Gong; He-Ping Li; Zhong-Liang Xiao; Shu Long; Ling Zhang; San-Jun Peng (pp. 19-26).

The quantitative structure–activity relationship (QSAR) for neutral carriers used to prepare hydrogen ion sensors has been studied. A series of synthesized carrier compounds were taken as the training set. Five molecular structure parameters of the compounds were calculated by using CNDO/2 algorithm and used as feature variables in constructing QSAR model. The lower and upper limits of the linear pH response range were taken as the activity measure. The corresponding model equations were derived from the stepwise regression procedure. With the established QSAR model, a new pH carrier, (4-hydroxybenzyl) didodecylamine (XIII) was proposed and synthesized. The PVC membrane pH electrode based on carrierXIII with a wide pH linear response range of 2.0–12.5 was prepared. Having a theoretical Nernstian response slope of 57.2±0.3mV/pH ( n=5 at 25°C) without a super-Nernstian phenomenon, the sensor had low resistance, short response time, high selectivity and good reproducibility. Moreover, the sensor was successfully applied to detecting the pH value of serum samples.

Keywords: Quantitative structure–activity relationship (QSAR); Molecular structure parameter; Neutral carrier; Poly(vinyl chloride) (PVC) membrane pH electrode; Serum sample

Voltammetric determination of Cd²⁺ based on the bifunctionality of single-walled carbon nanotubes–Nafion film by Dong Sun; Xiafeng Xie; Yuepiao Cai; Huajie Zhang; Kangbing Wu (pp. 27-31).

In the presence of Nafion, single-walled carbon nanotubes (SWNTs) were easily dispersed into ethanol, resulting in a homogeneous SWNTs/Nafion suspension. After evaporating ethanol, a SWNTs/Nafion film with bifunctionality was constructed onto glassy carbon electrode (GCE) surface. Attributing to the strong cation-exchange ability of Nafion and excellent properties of SWNTs, the SWNTs/Nafion film-coated GCE remarkably enhances the sensitivity of determination of Cd²⁺. Based on this, an electrochemical method was developed for the determination of trace levels of Cd²⁺ by anodic stripping voltammetry (ASV). In pH 5.0 NaAc–HAc buffer, Cd²⁺ was firstly exchanged and adsorbed onto SWNTs/Nafion film surface, and then reduce at −1.10V. During the positive potential sweep, reduced cadmium was oxidized, and a well-defined stripping peak appeared at −0.84V, which can be used as analytical signal for Cd²⁺. The linear range is found to be from 4.0×10⁻⁸ to 4.0×10⁻⁶molL⁻¹, and the lowest detectable concentration is estimated to be 4.0×10⁻⁹molL⁻¹. Finally, this method was successfully employed to detect Cd²⁺ in water samples.

Keywords: Cadmium; Determination; Carbon nanotubes; Nafion; Chemically modified electrodes

Voltammetric determination of Cd²⁺ based on the bifunctionality of single-walled carbon nanotubes–Nafion film by Dong Sun; Xiafeng Xie; Yuepiao Cai; Huajie Zhang; Kangbing Wu (pp. 27-31).

Keywords: Cadmium; Determination; Carbon nanotubes; Nafion; Chemically modified electrodes

Simultaneous determination of guanosine and guanosine-5′-triphosphate in biological sample using gold nanoparticles modified indium tin oxide electrode by Rajendra N. Goyal; Munetaka Oyama; Anuradha Tyagi (pp. 32-36).

A nanogold modified indium tin oxide (ITO) electrode was used for the simultaneous determination of guanosine and GTP at pH 7.2. The electrode exhibited an effective catalytic response towards their oxidation and lowered the oxidation potential of guanosine by ∼120mV and GTP by ∼183mV. Linear concentration curves were obtained for guanosine with a detection limit of 9.8×10⁻⁸M and 5.5×10⁻⁸M for GTP. The concentration of guanosine and GTP were also estimated in the human blood plasma samples using gold nanoparticles modified ITO electrode with good reproducibility.

Keywords: Nanogold modified indium tin oxide electrode; Guanosine; Guanosine-5′-triphosphate; Differential pulse voltammetry; Blood sample

Ultra trace adsorptive stripping voltammetric determination of atrazine in soil and water using mercury film electrode by N. Maleki; G. Absalan; A. Safavi; E. Farjami (pp. 37-41).

In situ mercury film electrode produced in the presence of thiocyanate has been shown extremely useful for highly sensitive adsorptive stripping voltammetric measurements of atrazine down to sub-μgL⁻¹ level. Operational parameters have been optimized and the stripping voltammetric performance has been investigated using square wave scans. The adsorptive stripping response is linear over the range of 0.5–60μgL⁻¹ atrazine, with a detection limit of 0.024μgL⁻¹. The method has been applied to the determination of atrazine in soil and water samples.

Keywords: Atrazine determination; Adsorptive stripping; Mercury film electrode; Soil; Water

Ultra trace adsorptive stripping voltammetric determination of atrazine in soil and water using mercury film electrode by N. Maleki; G. Absalan; A. Safavi; E. Farjami (pp. 37-41).

Keywords: Atrazine determination; Adsorptive stripping; Mercury film electrode; Soil; Water

Modeling of nucleic acid adsorption on 3D prisms in microchannels by Yandong Hu; Dongqing Li (pp. 42-52).

Understanding nucleic acid adsorption in microchannels is critical to improve the efficiency of purifying and extracting nucleic acid (NA) from sample solutions by microfluidic technologies. Using a microchannel with 3D prismatic silica elements on the wall can dramatically increase the surface area-to-volume ratio, and hence facilitate the nucleic acid adsorption on the wall. In this study a theoretical model for modeling adsorption in a microchannel with a designed 3D surface structure was developed, and five dimensionless numbers were found to be the key parameters in the adsorption process. Extensive numerical simulations were conducted. Two flow modes, the electroosmotic flow (EOF) and pressure-driven flow (PDF), were investigated for their effect on the adsorption. It was found that the EOF is more desirable than PDF. The 3D prismatic elements can increases the NA molecule adsorption not only by providing more surface areas, but also by the induced pressure resisting the central bulk electroosmotic flow. Finally, the effects of adsorption kinetic parameters (i.e., the kinetic association/dissociation constants, the diffusion coefficient, the total site density, the loading concentration, and the channel height), on the adsorption process were discussed in detail.

Keywords: Numerical simulation; Nucleic acid assay; Adsorption; Three-dimensional prisms in microchannel

Modeling of nucleic acid adsorption on 3D prisms in microchannels by Yandong Hu; Dongqing Li (pp. 42-52).

Keywords: Numerical simulation; Nucleic acid assay; Adsorption; Three-dimensional prisms in microchannel

Determination of low level methyl tert-butyl ether, ethyl tert-butyl ether and methyl tert-amyl ether in human urine by HS-SPME gas chromatography/mass spectrometry by Licia Scibetta; Laura Campo; Rosa Mercadante; Vito Foà; Silvia Fustinoni (pp. 53-62).

Methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE) and tert-amyl methyl ether (TAME) are oxygenated compounds added to gasoline to enhance octane rating and to improve combustion. They may be found as pollutants of living and working environments. In this work a robotized method for the quantification of low level MTBE, ETBE and TAME in human urine was developed and validated. The analytes were sampled in the headspace of urine by SPME in the presence of MTBE-d12 as internal standard. Different fibers were compared for their linearity and extraction efficiency: carboxen/polydimethylsiloxane, polydimethylsiloxane/divinylbenzene, and polydimethylsiloxane. The first, although highly efficient, was discarded due to deviation of linearity for competitive displacement, and the polydimethylsiloxane/divinylbenzene fiber was chosen instead. The analysis was performed by GC/MS operating in the electron impact mode. The method is very specific, with range of linearity 30–4600ngL⁻¹, within- and between-run precision, as coefficient of variation, <22 and <16%, accuracy within 20% the theoretical level, and limit of detection of 6ngL⁻¹ for all the analytes. The influence of the matrix on the quantification of these ethers was evaluated analysing the specimens of seven traffic policemen exposed to autovehicular emissions: using the calibration curve and the method of standard additions comparable levels of MTBE (68–528ngL⁻¹), ETBE (<6ngL⁻¹), and TAME (<6ngL⁻¹) were obtained.

Keywords: Methyl; tert; -butyl ether; Ethyl; tert; -butyl ether; tert; -Amyl methyl ether; Urine; Solid phase microextraction; Biomarkers; Occupational exposure

Solid phase microextraction/gas chromatography/mass spectrometry integrated with chemometrics for detection of Salmonella typhimurium contamination in a packaged fresh vegetable by Ubonrat Siripatrawan; Bruce R. Harte (pp. 63-70).

A rapid method for detection of Salmonella typhimurium contamination in packaged alfalfa sprouts using solid phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS) integrated with chemometrics was investigated. Alfalfa sprouts were inoculated with S. typhimurium, packed into commercial LDPE bags and stored at 10+2°C for 0, 1, 2 and 3 days. Uninoculated sprouts were used as control samples. A SPME device was used to collect the volatiles from the headspace above the samples and the volatiles were identified using GC/MS. Chemometric techniques including linear discriminant analysis (LDA) and artificial neural network (ANN) were used as data processing tools. Numbers of Salmonella were followed using a colony counting method. From LDA, it was able to differentiate control samples from sprouts contaminated with S. typhimurium. The potential to predict the number of contaminated S. typhimurium from the SPME/GC/MS data was investigated using multilayer perceptron (MLP) neural network with back propagation training. The MLP comprised an input layer, one hidden layer, and an output layer, with a hyperbolic tangent sigmoidal transfer function in the hidden layer and a linear transfer function in the output layer. The MLP neural network with a back propagation algorithm could predict number of S. typhimurium in unknown samples using the volatile fingerprints. Good prediction was found as measured by a regression coefficient ( R²=0.99) between actual and predicted data.

Keywords: Solid phase microextraction; Gas chromatography/mass spectrometry (GC/MS); Chemometrics; Salmonella typhimurium; Detection

Optimization of solid-phase microextraction of volatile phenols in water by a polyaniline-coated Pt-fiber using experimental design by M. Mousavi; E. Noroozian; M. Jalali-Heravi; A. Mollahosseini (pp. 71-77).

Solid-phase microextraction (SPME) coupled to gas chromatography (GC) was applied to the extraction of phenol and some of its volatile derivatives in water samples. The SPME fiber consisted of a thin layer of polyaniline, which was electrochemically coated on a fine Pt wire. The stability of the coating was such that it could be used at temperatures as high as 325°C, without any deterioration. The effects of various parameters affecting the extraction efficiency were studied, simultaneously. From these, optimization of the extraction temperature, extraction time, coating thickness, sample pH, salt concentration and desorption time was carried out by means of a (2^6–2) fractional factorial design. It was found that the effects and interactions of five out of six factors were significant. However, the coating thickness showed a large main effect but an insignificant interaction effect, so it was kept constant. Also, the effect of desorption time was insignificant if sufficient time was allowed for desorption to take place. Therefore, a central composite design (CCD) with four remaining factors, i.e., sample pH, salt concentration, extraction time and sample temperature was performed and a response surface equation was derived. The statistical parameters of the derived model were r=0.97 and F=25.3. The optimum conditions were obtained using a grid method. Using the optimum conditions, the method was analytically evaluated. The detection limit, relative standard deviation, linear range and recovery were 1.3–12.8ngmL⁻¹, 2.2–5.3%, 0.01–5.0μgmL⁻¹, and 88–103%, respectively. The results showed the suitability of polyaniline-coated fiber in analyzing volatile phenolic compounds in water samples.

Keywords: Experimental design; Chemometrics; Solid-phase microextraction; Polyaniline; Gas chromatography; Phenols

Application of pressurized fluid extraction to determine cadmium and zinc in plants by A.R. Maurí-Aucejo; T. Arnandis-Chover; R. Marín-Sáez; M. Llobat-Estellés (pp. 78-82).

A procedure for the determination of Cd and Zn in plants is proposed. The metals are extracted by pressurized fluid extraction (PFE). Operational conditions are: pressure 1500psi, temperature 75°C, static time 5min, flush volume 35%, purge time 60s, cycles 1 and 1,2-diaminocyclohexane- N, N, N′, N′-tetraacetic acid (CDTA) 0.01M at pH 4.5 as extracting solution. Determination of Zn is carried out by flame atomic absorption spectroscopy and depending on the concentration level, Cd content is determined by flame or electrothermal atomic absorption spectroscopy. Certified samples of Virginia tobacco leaves, tea leaves, spinach leaves, poplar leaves, a commercial spinach sample ( Spinacea oleracea) and genetically modified Arabidopsis thaliana were analysed by the proposed procedure and also by microwave acid digestion and extraction with HCl–Triton X-100. Confidence intervals for Cd and Zn content obtained by the proposed procedure overlap with the certified values. The other procedures, however, provide inaccurate results for Cd. Recoveries obtained for a confidence level of 95% are 96±6% and 95±5% for Zn and Cd, respectively. Reproducibility of Zn by the proposed procedure is 7% ( n=8), similar to the other tests and the detection limit is 2.6μg. For Cd reproducibility is 8.5% ( n=8), better than with HCl–Triton X-100 and similar to acid digestion, the detection limit is 3.5ng of Cd.

Keywords: Pressurized fluid extraction; Cadmium; Zinc; Plants; Environmental

Application of pressurized fluid extraction to determine cadmium and zinc in plants by A.R. Maurí-Aucejo; T. Arnandis-Chover; R. Marín-Sáez; M. Llobat-Estellés (pp. 78-82).

Keywords: Pressurized fluid extraction; Cadmium; Zinc; Plants; Environmental

Simultaneous monitoring of inorganic cations, amines and amino acids in human sweat by capillary electrophoresis by Takeshi Hirokawa; Hikaru Okamoto; Yoshinori Gosyo; Takao Tsuda; Andrei R. Timerbaev (pp. 83-88).

The determination of cationic constituents of sweat is widely recognized as a difficult analytical task due to its complex composition and minute sample volumes available for the individual analysis. Capillary electrophoresis (CE) has been evaluated as a simple routine method to measure sweat metal cations, biogenic amines, and amino acids using a sampling procedure previously developed in one of collaborative teams. The carrier electrolyte, which consisted of 10mM 4-methylbenzylamine, 6.5mM α-hydroxyisobutyric acid, and 2mM 18-crown-6 at pH 4.25, allowed the separation of five cations (NH₄⁺, K⁺, Ca²⁺, Na⁺, Mg²⁺) and four amino acids (ornithine, histidine, lysine, arginine) to be completed in about 13min with a positive polarity of the applied voltage (30kV). By increasing the sample volume (due to employing hydrodynamic instead of hydrostatic injection mode), it was also possible to detect indirect UV signals of Zn²⁺, diethanolamine, and trithanolamine. Sweat samples were collected from the fingers and forearms of three healthy male volunteers and analyzed by CE. A good repeatability and reproducibility of peak area responses based on five intraday and three inter-day assays (average %R.S.D. less than 3.5 and 2.5, respectively) were obtained. The limits of detection were in the range of 3.2–5.8μM for alkali and alkaline-earth cations (hydrostatic injection) and 0.27–0.79μM for other target analytes (hydrodynamic injection). The analytical results for particular analytes were found to vary, depending on the sampling spot and individual, but in general correspond well to clinical concentration ranges.

Keywords: Human sweat; Capillary electrophoresis; Sampling; Cations; Amino acids; Amines

Development and validation of a high-throughput high-performance liquid chromatographic assay for the determination of caffeine in food samples using a monolithic column by Paraskevas D. Tzanavaras; Demetrius G. Themelis (pp. 89-94).

The present study reports the development and validation of a high-throughput high-performance liquid chromatographic (HPLC) assay for the determination of caffeine in food samples. The analyte was separated rapidly from sample matrix using a short monolithic column (50mm×4.6mm i.d.). The flow rate was 3.0mLmin⁻¹, while the mobile phase consisted of ACN/water (10:90, v/v). Caffeine was detected directly at 274nm. Under the optimal HPLC conditions, the sampling rate was 60h⁻¹. The assay was validated for linearity, LOD and LOQ, precision, selectivity and ruggedness. The case of external calibration versus standard addition for the analysis of real samples was also examined. The proposed assay was applied to the analysis of beverages and coffee samples.

Keywords: Caffeine; High-performance liquid chromatography; Monolithic column; Food samples; Validation

Determination of synthetic acaricides residues in beeswax by high-performance liquid chromatography with photodiode array detector by Sabine Adamczyk; Regina Lázaro; Consuelo Pérez-Arquillué; Antonio Herrera (pp. 95-101).

A multiresidue HPLC method for identification and quantification of the synthetic acaricides fluvalinate, coumaphos, bromopropylate and its metabolite 4,4′-dibromobenzophenone in beeswax has been developed. Different techniques were tested and modified. The method consists of a sample preparation with isooctane followed by solid phase extraction using Florisil columns. Determination of the synthetic acaricides is achieved by HPLC with a photodiode array detector. Analytical performance of the proposed method, including sensitivity, accuracy and precision was satisfactory. The LOD for the analytes varied between 0.1 and 0.2μgg⁻¹ wax and the recoveries between 70 and 110%. Relative standard deviation of the repeatability of the method is <15% and reproducibility is <31%.

Keywords: Multiresidue method; Fluvalinate; Coumaphos; Bromopropylate; 4,4′-Dibromobenzophenone; Beeswax; High-performance liquid chromatography

Combining high-performance liquid chromatography with on-line microdialysis sampling for the simultaneous determination of ascorbyl glucoside, kojic acid, and niacinamide in bleaching cosmetics by Cheng-Hui Lin; Hsin-Lung Wu; Yeou-Lih Huang (pp. 102-107).

We have used on-line microdialysis sampling coupled with high-performance liquid chromatography and UV–vis detection to simultaneously determine the contents of ascorbyl glucoside (AA-2G), kojic acid (KA), and niacinamide (VitB₃) in commercial bleaching cosmetics. Our results indicate that AA-2G, KA, and VitB₃ separated well within 4.5min on a reverse-phase Hypersil Fluophase PFP column when eluting with 0.020M phosphate buffer solution in 40% (v/v) methanol at pH 5.5. The calibration curves were linear over the ranges 0.068–304, 0.071–284, and 0.024–488μgmL⁻¹ for AA-2G, KA, and VitB₃, respectively, with correlation coefficients for the linear regression analyses falling within the range 0.9982–0.9999. The detection limits for AA-2G, KA, and VitB₃ were 0.01, 0.01, and 0.007μgmL⁻¹, respectively. The detection wavelength was robust when the levels of the analytes in the samples were high (0.1–2%). The analytes were all detected using ultraviolet light (254nm). The compounds diffuse through the membrane more readily when KA and VitB₃ are in their molecular forms and AA-2G is ionized. The recoveries were in the range 92–106% with good reproducibility (R.S.D.=3.9–8.7%). We used this procedure to assay six commercially available bleaching cosmetics; our results confirmed not only the precision of the method but also the claims made on the labels of the cosmetics. This approach provides a very simple means to determine the contents of AA-2G, KA, and VitB₃ in various dosages in bleaching cosmetics.

Keywords: Microdialysis sampling; High-performance liquid chromatography; Ascorbyl glucoside; Kojic acid; Niacinamide; Bleaching cosmetics

Validation of a high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of tetracyclines residues in bovine milk by Bernardete Ferraz Spisso; Ana Luiza de Oliveira e Jesus; Marcus Antônio Gonçalves de Araújo Júnior; Mychelle Alves Monteiro (pp. 108-117).

A high-performance liquid chromatography-fluorescence detection method was optimized and validated to determine tetracyclines residues in bovine milk. Post-column derivatization using metal complexation in non-aqueous reagent increased the fluorescence of chelates by a factor up to 2.54 compared to water (signal-to-noise ratio enhancement). Overall recoveries ranged from 61 to 115%, with RSD_r from 5 to 15% ( n=54). Detection limits ranged from 5 to 35μgkg⁻¹. Limits of quantification were established at 50μgkg⁻¹. Decision limits (CCα) were 109, 108 and 124μgkg⁻¹ and detection capabilities (CCβ) 119, 117 and 161μgkg⁻¹ for oxytetracycline, tetracycline and chlortetracycline, respectively. The method was applied successfully in a national monitoring program.

Keywords: Validation; Milk; Residues; Tetracyclines; Antibiotics

Estuarine water classification using EEM spectroscopy and PARAFAC–SIMCA by Gregory J. Hall; Jonathan E. Kenny (pp. 118-124).

The primary method for the prevention of the introduction of nonindigenous aquatic nuisance species in the U.S. is ballast water exchange (BWE). Our recent work focused on the use of the excitation emission matrix (EEM) spectroscopy of the colored dissolved organic matter (CDOM) to “fingerprint�? water as a function of its port of origin, and therefore provide a forensic tool for the enforcement of BWE regulations. In that work, we utilized N-way partial least squares with discriminant analysis (NPLS-DA), which models the data with an emphasis on differences among classes (ports of origin). In this work, EEMs of samples from three different U.S. ports were analyzed by parallel factor analysis (PARAFAC) coupled with soft independent modeling of class analogy (SIMCA) to provide an effective classification method with a low false positive rate. This coupling, which is shown for the first time in this work, can be a useful alternative to NPLS-DA in that PARAFAC–SIMCA decomposes the EEM signal into chemical components and utilizes the scores for these components in the classification scheme. This gives the user the option of removing the contributions of interfering or unidentifiable fluorescent components prior to classification.

Keywords: Colored dissolved organic matter (CDOM); Parallel factor analysis (PARAFAC); Soft independent model of class analogy (SIMCA); Ballast water; Ballast water exchange (BWE); Estuarine; Fluorescence

Estuarine water classification using EEM spectroscopy and PARAFAC–SIMCA by Gregory J. Hall; Jonathan E. Kenny (pp. 118-124).

The primary method for the prevention of the introduction of nonindigenous aquatic nuisance species in the U.S. is ballast water exchange (BWE). Our recent work focused on the use of the excitation emission matrix (EEM) spectroscopy of the colored dissolved organic matter (CDOM) to “fingerprint” water as a function of its port of origin, and therefore provide a forensic tool for the enforcement of BWE regulations. In that work, we utilized N-way partial least squares with discriminant analysis (NPLS-DA), which models the data with an emphasis on differences among classes (ports of origin). In this work, EEMs of samples from three different U.S. ports were analyzed by parallel factor analysis (PARAFAC) coupled with soft independent modeling of class analogy (SIMCA) to provide an effective classification method with a low false positive rate. This coupling, which is shown for the first time in this work, can be a useful alternative to NPLS-DA in that PARAFAC–SIMCA decomposes the EEM signal into chemical components and utilizes the scores for these components in the classification scheme. This gives the user the option of removing the contributions of interfering or unidentifiable fluorescent components prior to classification.

Fluorescence energy transfer probes based on the guanine quadruplex formation for the fluorometric detection of potassium ion by Satoru Nagatoishi; Takahiko Nojima; Elzbieta Galezowska; Agata Gluszynska; Bernard Juskowiak; Shigeori Takenaka (pp. 125-131).

Dual-labeled oligonucleotide derivative, FAT-0, carrying 6-carboxyfluorescein (FAM) and 6-carboxy-tetramethylrhodamine (TAMRA) labels at 5′- and 3′-termini of thrombin-binding aptamer (TBA) sequence 5′-GGTTGGTGTGGTTGG-3′ and its derivatives, FAT- n ( n=3, 5, and 7) were designed and synthesized. FAT- n derivatives contained a T_mA spacer ( m=2, 4, and 6, respectively) at 5′-end of TBA sequence. The probes were developed to estimate the spacer effect on FRET efficiency and to identify the best probe for sensing of K⁺. Circular dichroism (CD), UV–vis absorption, and fluorescence studies revealed that all FAT- n probes could form the intramolecular tetraplex structures after binding K⁺. Association constants of particular K⁺/FAT- n complexes were determined using different experimental approaches. Suitability of particular probes for sensitive monitoring of K⁺ in intra- and extracellular conditions was examined and discussed. Calibration graphs of fluorescence ratio were linear in the K⁺ concentration range of 2–10mM for extracellular conditions showing sensitivity of 1.2%mM⁻¹ K⁺ and for intracellular conditions in the range of 100–200mM with sensitivity of 0.49%mM⁻¹ K⁺.

Keywords: Fluorescence; Fluorescence resonance energy transfer; G-quadruplex; Potassium ion; Tetraplex; Thrombin-binding aptamer

Sensitive and selective spectrofluorimetric determination of chromium(VI) in water by fluorescence enhancement by Yu Xiang; Ling Mei; Na Li; Aijun Tong (pp. 132-136).

A new fluorogenic method for the selective and sensitive determination of chromium(VI) in acidic water using rhodamine B hydrazide was developed. This method was based on the oxidation of non-fluorescent rhodamine B hydrazide by potassium dichromate in acidic aqueous conditions to give rhodamine B, which was highly fluorescent, as a product. With the optimum condition described, the fluorescence enhancement at 585nm was linearly related to the concentration of chromium(VI) in the range of 5.0×10⁻⁸ to 2.0×10⁻⁶molL⁻¹ (2.60–104ngmL⁻¹) with a correlation coefficient of R²=0.9993 ( n=18) and a detection limit of 5.5×10⁻⁹molL⁻¹ (0.29ngmL⁻¹). The R.S.D. was 2.2% ( n=5). The proposed method was also applied to the determination of chromium(VI) in drinking water, river water and synthetic samples.

Keywords: Chromium(VI); Rhodamine B hydrazide; Fluorescence enhancement; Oxidation

Sensitive and selective spectrofluorimetric determination of chromium(VI) in water by fluorescence enhancement by Yu Xiang; Ling Mei; Na Li; Aijun Tong (pp. 132-136).

Keywords: Chromium(VI); Rhodamine B hydrazide; Fluorescence enhancement; Oxidation

Study of the properties of molecularly imprinted polymers by computational and conformational analysis by Ying Liu; Fang Wang; Tianwei Tan; Ming Lei (pp. 137-146).

In this paper, a simplified model was set up to give an insight into the properties of molecularly imprinted polymer (MIP) at molecular level using MMFF94 force field. Based on our model, the interaction energies (Δ Es) between monomers and template or its analogues were calculated, and the most possible conformations of template or its analogues interacting with monomers in the molar ratio 1/4 were found. The obtained results using the computational and conformational analysis showed that large Δ E meant more activity sites in the cavities in the resultant polymer giving high affinity and good selectivity, leading to a large imprinting factor and when the Δ E differences were small, the imprinting factors were mainly determined by the activity sites. These were well consistent with the experimental results, which confirmed the validity of the model and method proposed that were believed to benefit screening molecularly imprinted systems rapidly in an experiment-free way instead of trial-and-error approach. Considering the affinity and selectivity, 2,6-bisacrylamide pyridine was predicted to be the optimal monomer used to prepare paracetamol MIP for application in quantification of drugs from the Δ E and possible activity sites.

Keywords: Molecularly imprinted polymer; Interaction energy; Conformation; Activity site; Paracetamol

Study of the properties of molecularly imprinted polymers by computational and conformational analysis by Ying Liu; Fang Wang; Tianwei Tan; Ming Lei (pp. 137-146).

Keywords: Molecularly imprinted polymer; Interaction energy; Conformation; Activity site; Paracetamol

Determination of veterinary drug residues in chicken meat using corona discharge ion mobility spectrometry by M.T. Jafari; T. Khayamian; V. Shaer; N. Zarei (pp. 147-153).

A positive corona discharge ion mobility spectrometry (CD-IMS) has been evaluated for the determination of three residual veterinary drugs including furazolidone (FUR), chloramphenicol (CAP), and enrofloxacin (ENR) in poultry for the first time. Pretreatment included extraction of the drugs from samples and further treatment of the extracts by solid phase extraction (SPE) using C₁₈ sorbents. The limits of quantification (LOQs) were less than 20μgkg⁻¹ for all compounds. The calibration plots for these compounds were linear to about three orders of magnitude. The validity of the method was demonstrated by the analysis of spiked and real samples.

Keywords: Antibiotic; Furazolidone (CAS no. 67-45-8); Chloramphenicol (CAS no. 56-75-7); Enrofloxacin (CAS no. 93106-60-6); SPE; Corona discharge; Ion mobility spectrometry

Determination of veterinary drug residues in chicken meat using corona discharge ion mobility spectrometry by M.T. Jafari; T. Khayamian; V. Shaer; N. Zarei (pp. 147-153).

Keywords: Antibiotic; Furazolidone (CAS no. 67-45-8); Chloramphenicol (CAS no. 56-75-7); Enrofloxacin (CAS no. 93106-60-6); SPE; Corona discharge; Ion mobility spectrometry

Raman sensitivity enhancement for aqueous absorbing sample using Teflon-AF 2400 liquid core optical fibre cell by Yanjie Tian; Liuyang Zhang; Jian Zuo; Zuowei Li; Shuqin Gao; Guohui Lu (pp. 154-158).

The compatibility Teflon-AF 2400 liquid core optical fibre with resonance Raman spectroscopy (RRS-LCOF) was used to detect aqueous biomolecules. The maximum sensitivity enhancement factor for concentrations greater than the detection limit in a conventional cell was 10, and detection limit reduction of about 1000-fold have been achieved for the measurement of aqueous absorbing sample using Teflon-AF 2400 fibre Raman cell compared to the conventional cell. We were able to collect spectra of 2.5×10⁻⁹ and 2.5×10⁻¹⁰M aqueous β-carotene using 16.2mW of laser power and 10s integration time. This volume of a 2.5×10⁻¹⁰M aqueous solution corresponds to only 1.5fmol or 830fg of β-carotene. The results of this preliminary study indicate that RRS-LCOF has potential in bioanalytical and biomedical applications.

Keywords: Teflon-AF; Liquid core optical fibre; Resonance Raman spectroscopy; Aqueous solution

Sub-optimal wavelet denoising of coaveraged spectra employing statistics from individual scans by Roberto Kawakami Harrop Galvão; Heronides Adonias Dantas Filho; Marcelo Nascimento Martins; Mário César Ugulino Araújo; Celio Pasquini (pp. 159-167).

This paper proposes a novel wavelet denoising method, which exploits the statistics of individual scans acquired in the course of a coaveraging process. The proposed method consists of shrinking the wavelet coefficients of the noisy signal by a factor that minimizes the expected square error with respect to the true signal. Since the true signal is not known, a sub-optimal estimate of the shrinking factor is calculated by using the sample statistics of the acquired scans. It is shown that such an estimate can be generated as the limit value of a recursive formulation. In a simulated example, the performance of the proposed method is seen to be equivalent to the best choice between hard and soft thresholding for different signal-to-noise ratios. Such a conclusion is also supported by an experimental investigation involving near-infrared (NIR) scans of a diesel sample. It is worth emphasizing that this experimental example concerns the removal of actual instrumental noise, in contrast to other case studies in the denoising literature, which usually present simulations with artificial noise. The simulated and experimental cases indicate that, in classic denoising based on wavelet coefficient thresholding, choosing between the hard and soft options is not straightforward and may lead to considerably different outcomes. By resorting to the proposed method, the analyst is not required to make such a critical decision in order to achieve appropriate results.

Keywords: Wavelet transform; Denoising; Individual scans; Coaveraging process; Near-infrared spectroscopy; Diesel analysis

On-line flow injection solid sample introduction, leaching and potentiometric determination of fluoride in phosphate rock by Jamal A. Sweileh (pp. 168-173).

A flow injection method with on-line solid sample dissolution was developed for the determination of fluoride in phosphate rock. The fluoride was selectively leached (98–102.4 % recovery) from a 50-mg powdered phosphate rock sample with 0.50M citric acid. Using the zone sampling technique the fluoride in the buffered leachate was determined by injecting 87μL into the carrier stream using a fluoride ion-selective electrode detector. The sensing element of the electrode was housed in a home-made sleeve-type flow-through cell. On-line solid sample digestion with 0.50M citric acid at 55°C resulted in minimum dissolution of interfering iron and aluminum ions with improved accuracy and calibration linearity. The incorporation of relatively high level of fluoride in the carrier stream (40μgmL⁻¹) facilitated the determination of high levels of fluoride in phosphate rock (up to 4.1%) with out the need for excessive on-line dilution.The optimized flow system was applied for the determination of fluoride in phosphate rocks samples and a reference material at a rate of nine samples per hour with a relative standard deviation ( n=5) of 2.95–4.0 %. Comparison of the proposed flow injection method with the standard method, which involves steam distillation from sulfuric acid solution and manual titration with thorium nitrate, showed no evidence of bias at the 95% confidence level.

Keywords: On-line leaching; Flow injection; Solid sample introduction; Fluoride; Potentiometry; Phosphate rock

On-line flow injection solid sample introduction, leaching and potentiometric determination of fluoride in phosphate rock by Jamal A. Sweileh (pp. 168-173).

Keywords: On-line leaching; Flow injection; Solid sample introduction; Fluoride; Potentiometry; Phosphate rock

Automated measurement of permeation and dissolution of propranolol HCl tablets using sequential injection analysis by Stephan A. Motz; Jana Klimundová; Ulrich F. Schaefer; Stefan Balbach; Thomas Eichinger; Petr Solich; Claus-Michael Lehr (pp. 174-180).

Aim of this study was to automate sampling and quantification of the previously described apparatus for combined determination of dissolution and permeation through Caco-2 monolayer by means of sequential injection analysis (SIA). Native fluorescence of propranolol HCl in Krebs–Ringer buffer (KRB) was used for quantification. Sampling was done at three different locations within the apparatus at a high sampling frequency (approximately 60h⁻¹). Injection volume delivered to the fluorescence detector was 50μL for permeation monitoring and 25μL for dissolution monitoring. Linear regression for 50μL injection yielded a detection limit calculated as 0.04μgmL⁻¹ of propranolol HCl in KRB ( R²>0.999). However, linearity for dissolution monitoring was not given for the complete range of concentrations and first order polynomial calibration was established ( R²>0.9999). To conclude, the SIA system was able to monitor simultaneously dissolution and permeation of the immediate release propranolol HCl tablets and the authors succeeded in automating the apparatus for combined measurement of dissolution and permeation. In addition, the obtained data was consistent with data obtained by manual sampling followed by HPLC analysis.

Keywords: Dissolution; Permeation; Absorption; Caco-2 cells; Sequential injection analysis (SIA)

Development of in situ ion selective sensors for dissolution by Hugo Bohets; Koen Vanhoutte; Roy De Maesschalck; Paul Cockaerts; Bert Vissers; Luc J. Nagels (pp. 181-191).

The dissolution of formulations of the drugs dapoxetine, paliperidone, cinnarizine, tetrazepam, mebeverine, loperamide, galantamine and ibuprofen was studied by an in-line potentiometric measurement system. The transpose of a Nikolskii-Eisenman type function performed the conversion of potential to percentage of dissolution. A novel gradient membrane electrode was developed especially for dissolution, varying continuously in composition from an ionically conducting rubber phase to an electronically conducting solid state PVC/graphite composite. The gradient part had a thickness of 200μm. The electrodes life span exceeded 6 months. An ion exchange procedure was used to prepare them for one specific drug. This enabled us to use one universal electrode built to measure a wide array of drugs. The system parameters such as accuracy, reproducibility and linearity were presented with the data obtained for the drug dapoxetine. In dissolution, accurate measurements were possible from 10⁻⁹ to 10⁻³M concentrations, for high log P drugs. The effect of t₉₀ response times on the measurement error was estimated. The t₉₀ response times of the electrodes were concentration dependent, and varied between 50 and 10s for, respectively, 10⁻⁶ and 10⁻³M concentrations. Potential drift was studied in detail. The measurements performed with these electrodes showed an accuracy of 1%, and inter- and intra electrode variabilities of 0.6 and 1.7%, respectively. The electrodes were successfully applied in colloidal media containing suspended matter, typically formed during dissolution of tablets. The advantages and pitfalls of potentiometry over the presently used techniques for dissolution testing are discussed.

Keywords: Drugs; Potentiometry; In-line; Dissolution; Detection; Sensor

Development of in situ ion selective sensors for dissolution by Hugo Bohets; Koen Vanhoutte; Roy De Maesschalck; Paul Cockaerts; Bert Vissers; Luc J. Nagels (pp. 181-191).

Keywords: Drugs; Potentiometry; In-line; Dissolution; Detection; Sensor

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Analytica Chimica Acta (v.581, #1)