Analytica Chimica Acta (v.537, #1-2)
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Sunscreen analysis by A. Salvador; A. Chisvert (1-14).
Although there are no official analytical methods for UV filters determination in sunscreen cosmetics, their maximum content are regulated by legislation, and then analytical methods to control these products are necessary. In this paper, analytical methods for UV filters determination in cosmetics, which can be found in the literature, are reviewed. The usefulness of the analytical methods, techniques and sample preparation is discussed. The analytical methods used for the determination of UV filters in other type of samples are commented upon. Moreover, a brief overview of the European Union legislation concerning UV filters is included.
Keywords: Review; UV filter; Sunscreen; Cosmetic;
An environmentally friendly (“green”) reversed-phase liquid chromatography method for UV filters determination in cosmetics by A. Salvador; A. Chisvert (15-24).
A green procedure based on reversed-phase liquid chromatography with gradient elution using environmentally friendly solvents, has been developed to determine 18 UV filters, which are most used in Europe nowadays as sunscreen in cosmetics. Samples were weighed and dissolved in ethanol. Two aliquots were taken from the initial sample solution to prepare two solutions, so analytes could be determined chromatographically in two groups (the most fat-soluble and the easily water-soluble ones) using a different gradient elution program for each group. The mobile phases were based on mixtures of ethanol and 1% acetic acid or 1% sodium acetate buffer pH 4.75. The same C18 stationary phase column was employed in both cases. The chromatographic variables such as mobile phase composition, pH, flow rate and temperature were studied and selected in order to achieve total separation of all the peaks involved. The proposed method has been validated by the analysis of 27 commercial sunscreen samples (with different cosmetic forms: cream, lipstick, makeup, sun water, lotion, milk) and two synthetic samples. The method allows any mixture of the 18 UV filters studied to be separated with a good resolution and determined without interference from cosmetic matrices, moreover it does not require the use of highly toxic organic solvents.
Keywords: UV filters; Sunscreens; Cosmetics; Liquid chromatography; Green chemistry;
Determination of disopyramide in human urine by capillary electrophoresis with electrochemiluminescence detection of tris(2,2′-bipyridyl) ruthenium (II) by Lanyun Fang; Xue-bo Yin; Xiuhua Sun; Erkang Wang (25-30).
Capillary electrophoresis (CE) with electrochemiluminescence detection (ECL) of disopyramide based on tris(2,2′-bipyridyl) ruthenium(II) was described. After CE separation using a 50 μm i.d. uncoated capillary column and 10 mM running buffer solution at 15 kV of separation potential, the analyte was detected at the surface of platinum disk electrode (300 μm in diameter) working electrode. Parameters influencing separation and detection were optimized in detail. Under optimal condition the detection limit was 2.5 × 10−8 mol L−1 (S/N = 3). The method can be successfully applied for the determination of disopyramide in human urine after an easy, rapid and cheap extraction procedure. Extraction recovery rates were between 92.3 and 96.9%.
Keywords: Capillary electrophoresis; Electrochemiluminescence; Disopyramide; Extraction;
High-performance liquid chromatographic assay of parabens in wash-off cosmetic products and foods using chemiluminescence detection by Qunlin Zhang; Mei Lian; Lijuan Liu; Hua Cui (31-39).
A new method for the simultaneous determination of parabens including methylparaben, ethylparaben, propylparaben, and butylparaben by high-performance liquid chromatography (HPLC) coupled with chemiluminescence detection was developed. The procedure was based on the chemiluminescent enhancement by parabens of the cerium(IV)–rhodamine 6G system in the strong sulfuric acid medium. The good separation of parabens was carried out with an isocratic elution using a mixture of methanol and water (60:40, v/v) within 8.5 min. Under the optimized conditions, a linear working range extends three orders of magnitude with the relative standard deviations of intra- and inter-day precision below 4.5%, and the detection limits were 1.9 × 10−9, 2.7 × 10−9, 3.9 × 10−9, and 5.3 × 10−9 g ml−1 for methylparaben, ethylparaben, propylparaben, and butylparaben, respectively. The chemiluminescence reaction was well compatible with the mobile phase of high-performance liquid chromatography. The proposed method has been successfully applied to the assay of parabens in wash-off cosmetic products and foods with the minimal sample preparation.
Keywords: High-performance liquid chromatography; Chemiluminescence; Paraben; Cerium(IV); Rhodamine 6G; Cosmetic product; Food;
Comparison of retention of native cyclodextrins and its permethylated derivatives on porous graphite carbon and silica C18 stationary phases by Arkadiusz Kwaterczak; Anna Bielejewska (41-46).
The retention of the solute in the stationary phase is the effect of interaction between the solute and the stationary phase and the solute and the mobile phase (solvatation phenomena). Additionally, the components of the mobile phase can modify the surface of the stationary phase, and thus the change the interaction between the solute and the stationary phase.The current paper presents a systematic comparison of retention of α-, β- and γ-cyclodextrins (CD) and its permethylated derivatives on the porous graphitic carbon and RP C18 columns. From temperature study, the contribution of ΔH and ΔS to ΔG has been discussed. The physico-chemical interactions of cyclodextrins seem to be similar only in the case of native cyclodextrins (except γ-CD) with the RP C18 column when enthalpy–entropy compensation can be observed. In the case of permethylated cyclodextrins and the RP C18 column, interactions are only similar for individual alcohols. For the PGC column, the influence of individual interactions on individual cyclodextrins seems to be different.
Keywords: Porous graphitic carbon column; Cyclodextrins; Temperature effects; Liquid chromatography; Retention mechanism;
Determination of free furfuryl alcohol in foundry resins by chromatographic techniques by Maria Teresa Oliva-Teles; Cristina Delerue-Matos; Maria Conceição M. Alvim-Ferraz (47-51).
Two chromatographic methods, gas chromatography with flow ionization detection (GC–FID) and liquid chromatography with ultraviolet detection (LC–UV), were used to determine furfuryl alcohol in several kinds of foundry resins, after application of an optimised extraction procedure. The GC method developed gave feasibility that did not depend on resin kind. Analysis by LC was suitable just for furanic resins. The presence of interference in the phenolic resins did not allow an appropriate quantification by LC. Both methods gave accurate and precise results. Recoveries were >94%; relative standard deviations were ≤7 and ≤0.3%, respectively for GC and LC methods. Good relative deviations between the two methods were found (≤3%).
Keywords: Foundry resins; Furfuryl alcohol; LC; GC;
Modelling retention in liquid chromatography of polyphenolic acids by N. Sanli; G. Fonrodona; J. Barbosa; G.A. Özkan; J.L. Beltran (53-61).
The retention behavior of a series of polyphenolic acids has been modeled in water–acetonitrile mobile phases, in order to optimize the chromatographic resolution between these compounds. The retention model is based on the relationships between retention factors of solutes with the pH and solvatochromic parameter of the mobile phase ( E T N ) , and between the dissociation constants of the compounds and the mole fraction of organic modifier. The retention of these ionizable compounds has been studied at three levels of acetonitrile percentage (10, 20 and 30%), and at six different pH values ranging between 3.5 and 7. Three different fitting procedures have been applied: model I consists of a nonlinear regression to all data points, whereas models II and III use only four and two data points, respectively, taken from the extreme pH / E T N values. The results obtained from these models indicate a good agreement between real and predicted retention factors for each compound, with errors about 5% for model I and about 10% for models II and III. The results of model III are of particular interest, because of only two experiments for each compound are needed to describe the retention behavior in a relatively large pH and percentage of acetonitrile intervals; this is especially valuable in the optimization of the mobile phase for chromatographic separation of several compounds.
Keywords: Retention modelling; Mobile phase composition; Polyphenolic acids; Benzoic acids; Cinnamic acids;
On-line cleanup of blanks by electrochemically modulated liquid chromatography for inductively coupled plasma-mass spectrometry by Towhid Hasan; Daniel Gazda; Marc D. Porter; R.S. Houk (63-68).
Electrochemically modulated liquid chromatography (EMLC) is used on-line to remove metal ions from the blank solution and improve detection limits in inductively coupled plasma-mass spectrometry (ICP-MS). The EMLC column contains glassy carbon particles held at an appropriate negative applied potential (E app). The supporting electrolyte and reference electrode are outside the porous stainless steel column to minimize contamination of the blank flow stream. Various metal ions, such as Tl+ and Pb2+, are retained at cathodic values of E app with an efficiency of 99% or better at liquid flow rates of 50–80 μl min−1. Other metals are retained at an E app that is moderately positive with respect to their standard reduction potentials. This latter observation suggests that surface functional groups on the carbon stationary phase are also important. The column can be cleaned easily by stripping the deposited metal at high anodic values of E app.
Keywords: Inductively coupled plasma (ICP); Inductively coupled plasma mass spectrometry (ICP-MS); Electrochemically modulated liquid chromatography (EMLC); Blanks; Background reduction;
Development of an immunochromatographic method to determine β-lactoglobulin at trace levels by Angel Puerta; Jose Carlos Diez-Masa; Mercedes de Frutos (69-80).
β-Lactoglobulin (βLG) is one of the main components of whey proteins. Among other reasons, its allergenic character makes necessary its determination in hypoallergenic foods and biopharmaceutical products at very low concentration making use of very sensitive methods. In this paper, the development of an enzyme linked immunoaffinity chromatographic (ELIAC) method in sandwich format is described. The optimized method includes the use of a minicolumn (4.9 mm × 1 mm) packed with Nucleosil® 4000-7OH derivatized with high density of antibody coverage, the employment of rabbit serum and Zwittergent® 3–12 as mobile phase additives, and the incubation of the sample containing βLG with anti βLG labeled with horseradish peroxidase prior to their injection into the immunochromatographic system. The method allows determination of βLG with a practical detection limit of 20.7 pM and a sensitivity of 1.05 × 109 AU mol−1 L. The application of this ELIAC method to determine βLG in a commercial hypoallergenic formula based on caseins is shown. The amount of allergen, 0.32 pmol βLG per gram of sample, is about 5 million times lower than that naturally occurring in cow's milk.
Keywords: β-Lactoglobulin; Enzyme linked immunoaffinity chromatography; ELIAC; Minicolumn; Hypoallergenic formula;
Immersed solvent microextraction and gas chromatography–mass spectrometric detection of s-triazine herbicides in aquatic media by Habib Bagheri; Faezeh Khalilian (81-87).
An immersed solvent microextraction (SME) method was successfully developed for the trace enrichment of s-triazine herbicides from aquatic media. A microdrop of butyl acetate was applied as the extraction solvent. After extraction, the microdrop was introduced directly into a gas chromatography–mass spectrometry (GC–MS) injection port. Some important extraction parameters such as type of solvent, extraction time, stirring rate, and temperature were investigated and optimized. The highest possible microdrop volume of 3 μl, a sampling temperature of 60 °C, and use of butyl acetate are major parameters to obtain high enrichment factors. The enrichment factor and linearity was studied by preconcentration of 1 ml of HPLC-grade, rice farm water and river water, spiked with a standard solution of triazines at a concentration range of 0.1–100 μg l−1 (R.S.D. < 11%). The correlation coefficient was satisfactory (r 2 > 0.98) for all the studied triazines. Detection limits were obtained using HPLC-grade and river water, i.e. 0.015–0.4 μg l−1. The effect of matrix on extraction efficiency was, also, studied using some real-life water samples.
Keywords: Immersed solvent microextraction; Gas chromatography–mass spectrometry; Triazine herbicides; Water analysis; Environmental analysis;
Use of second-order calibration for residue screening of some triazines in the presence of coeluting interferences by gas chromatography–selected ion mass spectrometry by Mehdi Jalali-Heravi; Maryam Vosough (89-100).
The quantities of residues of some triazines such as prometon, propazine, atrazine and simazine in complex matrices of apple samples were determined, using gas chromatography–selected ion mass (GC–SIM) spectrometry. Generalized rank annihilation method (GRAM) as a second-order calibration technique was used for screening, resolving and finally determining the amounts of the residues. Before the GRAM analysis, different steps of data preprocessing such as background correction, de-skewing and standardization for rank alignment was used for every target analyte. The de-skewing and rank alignment algorithms were used for bilinearity and trilinearity corrections, respectively. The two data matrices needed for the GRAM analysis were obtained from the sample solution, which contained different spiked levels of target analytes, and standard addition solution GC–SIM data. By using the GRAM method we were able to obtain the mass chromatograms and the true ion abundance ratio of each target analyte and precisely quantify the residue amounts of triazines in the different sample solutions by using only one standard data matrix. Unambiguous detection of a target analyte by this method was compared with the traditional approach of measuring peak height that fails to accurately detect the target because of severe coeluting interferences. Finally the method was successfully used for the simultaneous determination of two-target analytes of simazine and atrazine in a sample solution with severely convoluted mass chromatographic profiles.
Keywords: Second-order data; Generalized rank annihilation method; Triazines; Gas chromatography–SIM spectrometry;
Prediction of retention time of a variety of volatile organic compounds based on the heuristic method and support vector machine by Feng Luan; Chunxia Xue; Ruisheng Zhang; Chunyan Zhao; Mancang Liu; Zhide Hu; Botao Fan (101-110).
The support vector machine (SVM) and the heuristic method (HM) were used to develop the non-linear and linear models between the retention time (RT) and five molecular descriptors of 149 volatile organic compounds (VOCs). Descriptors calculated from the molecular structures alone were used to represent the characteristics of compounds. The five molecular descriptors selected by the heuristic method in CODESSA were used as inputs for SVM. The results obtained by SVM were compared with those obtained by the heuristic method. The mean squared errors (MSE) in RT predictions for the whole data set given by HM and SVM were 1.270 and 0.844, respectively, which shows the performance of SVM model is better than that of the HM model. The prediction results are in very good agreement with the experimental values. This paper provided a new and effective method for predicting the chromatography retention index.
Keywords: QSRR; SVM; VOCs; Retention time;
Post-PCR detection of nucleic acids using metalloporphyrin labels and time-resolved fluorescence by Desmond J. O'Shea; Paul J. O'Sullivan; Gelii V. Ponomarev; Dmitri B. Papkovsky (111-117).
Phosphorescent platinum(II)-coproporphyrin label (PtCP) was evaluated in post-PCR detection of nucleic acids by time-resolved fluorescence (TR-F) using three common formats. PtCP-labelled oligonucleotide primers and PtCP-dUTP were incorporated in a PCR to produce labelled amplified target −173 or 305 bp DNA. Alternatively, aminoallyl-dUTP was incorporated in a PCR and the product was subsequently labelled with PtCP. The resulting PCR mixtures containing labelled dsDNA were separated on 1.5% agarose gels and then analysed by ethidium bromide staining and by direct detection of PtCP label on a commercial TR-F plate reader Victor2 (Perkin Elmer Life Sciences) used in scanning mode. In all cases label incorporation and high yields of amplified DNA were observed. Direct TR-F detection of PtCP-labelled DNA from a gel provided high sensitivity and signal to noise ratio, with limits of detection in the range of 9–22 pg for all three formats. The sensitivity achieved with PtCP label was considerably better than that achieved with ethidium bromide staining (∼1 ng of dsDNA) or with conventional fluorescent label FITC. Neither the FITC label nor ethidium bromide staining interfered with PtCP detection, thus allowing multiplexed detection.
Keywords: Post-PCR detection; Metalloporphyrin labels; Time-resolved fluorescence; Phosphorescence;
Electrochemiluminescence polymerase chain reaction detection of genetically modified organisms by Jinfeng Liu; Da Xing; Xingyan Shen; Debin Zhu (119-123).
With the development of biotechnology, more and more genetically modified organisms (GMOs) have entered commercial market. Because of the safety concerns, detection and characterization of GMOs have attracted much attention recently. Electrochemiluminescence (ECL) method is a chemiluminescent (CL) reaction of species generated electrochemically on an electrode surface. It is a highly efficient and accurate detection method. In this paper, ECL polymerase chain reaction (PCR) combined with two types of nucleic acid probes hybridization was applied to detect GMOs for the first time. Whether the organisms contain GM components was discriminated by detecting the cauliflower mosaic virus 35S (CaMV35S) promoter and nopaline synthase (NOS) terminator. The experiment results show that the detection limit is 100 fmol of PCR products. The promoter and the terminator can be clearly detected in GMOs. The method may provide a new means for the detection of GMOs due to its simplicity and high efficiency.
Keywords: ECL; GMOs; CaMV35S promoter; NOS terminator;
Interferences in Fluo-3 based ion-flux assays for ligand-gated-ion channels by Travis R. Besanger; Hitesh Bhanabhai; John D. Brennan (125-134).
1-[2-Amino-5-(2,7-dicholoro-6-hydoxy-3-oxo-3H-xanthen-9-yl)phenoxy]-2-(2′-amino-5′methylphenoxylethane)-N,N,N′,N′-tetraacetic acid (Fluo-3), a highly sensitive calcium indicator dye, is commonly used for measuring changes in intracellular Ca2+ concentrations in response to cellular ion-channel function. In particular, Fluo-3 has been used extensively for in vivo monitoring of the response of ligand-gated-ion-channels (LGIC), such as the nicotinic acetylcholine receptor (nAChR), to the presence of agonists and antagonists. Our initial goal was to use Fluo-3 for in vitro measurement of Ca2+ influx across artificial liposomes containing reconstituted nAChR. However, it became apparent during initial control experiments that agonist and antagonist-like responses could be obtained for several known nAChR effectors in the presence of the dye alone. Steady-state and time-resolved fluorescence measurements of Fluo-3 in the presence of various nAChR agonists and antagonists revealed that Fluo-3 formed a ground state complex with the antagonist d-tubocurarine, leading to a decrease in emission intensity similar to that expected upon blockage of the ion-channel. More surprisingly, it was found that nicotine, an agonist of nAChR, could disrupt the formation of this complex with a concomitant reversal of the static quenching effects, leading to increased emission which was consistent with the expected changes in intensity for a channel opening event. These results demonstrate that interactions of agonists and antagonists with Fluo-3 could lead to false positives in screens of ligand-gated-ion-channels such as nAChR.
Keywords: Fluo-3; Fluorescence; Quenching; Acetylcholine receptor; Nicotine; d-Tubocurarine;
Microsphere optical ion sensors based on doped silica gel templates by Chao Xu; Katarzyna Wygladacz; Yu Qin; Robert Retter; Michael Bell; Eric Bakker (135-143).
A simple method for doping ion-sensing ingredients into silanized silica particles (∼3.5 μm) was developed to fabricate carrier-based ion-selective microsphere optical ion sensors. These ion sensors operate according to established bulk optode principles. Na+-selective microsphere optical sensors were prepared with the ionophore tert-butylcalixarene tetraacetic acid tetraethylester, the H+-chromoionophore 9-(diethylamino)-5-octadecanoylimino-5H-benzo[a]phenoxazine (ETH 5294), the ion exchanger sodium tetrakis[3,5-bis(tri-fluoromethyl)phenyl]borate (NaTFPB), PVC and the plasticizer bis(2-ethylhexyl)sebacate (DOS). For Ca2+ sensing, the grafted Ca2+ ionophore AU-1 in poly(n-BA) was applied with ETH 5294, NaTFPB and DOS. Fluorescence microscopy and flow cytometry were used for characterization. The resulting microsphere optical ion sensors were found to obey bulk optode theory with reliable response, high selectivities, dynamic ranges suitable for physiological measurements and a shelf time of over 6 months. The measuring ranges (logarithmic molar concentrations) at pH 7.4 were −3.5 to −1.5 for the fabricated Na+-selective optical-sensing microspheres, and −4.5 to −1.5 for Ca2+-selective optical-sensing microspheres. Corresponding thin optode films and regular PVC/DOS-based microspheres were prepared for comparison and showed similar response characteristics. The fabricated microsphere optical ion sensors were also deposited on an optical fiber bundle, and reproducible fluorescence signals were observed.
Keywords: Microsphere; Optical ion sensors; Silica gel; Optode films;
Overoxidized polypyrrole film directed DNA immobilization for construction of electrochemical micro-biosensors and simultaneous determination of serotonin and dopamine by Xiaohua Jiang; Xiangqin Lin (145-151).
A promising electrochemical microsensor was fabricated by electrochemical immobilization of calf-thymus DNA on a carbon fiber electrode (CFE) through an overoxidized polypyrrole (PPyox) template for simultaneous determination of serotonin (5-HT) and dopamine (DA). Such a DNA–PPyox biocomposite modification layer of nano-thickness exhibited superior selectivity and sensitivity towards these neuronal amines comparing with a simple PPyox or DNA coating. This microsensor gave three separated differential pulse voltammetric (DPV) peaks at 0.38, 0.20 and −0.02 V for 5-HT, DA and 25,000-fold excess of ascorbic acid (AA). The linear response was obtained in the range of 1.0 × 10−8 to 1.0 × 10−6 M with a detection limit of 7.0 × 10−9 M for 5-HT, and in the range of 3.0 × 10−7 to 1.0 × 10−5 M with a detection limit (s/n = 3.0) of 5.0 × 10−8 M for DA. A stronger interaction of 5-HT with the modification layer was observed, which led to a higher detection sensitivity for 5-HT than for DA. The utility of this modified electrode was demonstrated by the determination of 5-HT and DA in human blood serum.
Keywords: DNA-based biosensor; Serotonin; Dopamine; Overoxidized polypyrrole; Carbon fiber microelectrode;
Tissue implanted glucose needle electrodes: early sensor stabilisation and achievement of tissue-blood correlation during the run in period by S. Ahmed; C. Dack; G. Farace; G. Rigby; P. Vadgama (153-161).
In this study, two approaches were utilised to reduce surface fouling and enhance operational reliability of tissue implanted glucose sensors. The first, Open Microflow, used an open cannula incorporated needle electrode. Here, the sensor surface was subjected to slow flow of protein-free fluid (chelate containing isotonic buffer or saline) directly at the implant site. Positive outcomes of this included reduced stabilisation time (≤90 min), accelerated ‘pick up’ of tissue glucose changes after intravenous injections of glucose or insulin without the usual reported lag, and high correlation between tissue and blood glucose values under dynamic conditions avoiding the need for in vivo calibration and a reduced surface fouling. Open Microflow fluid composition was important for performance. A range of isotonic solutions were tested; NaCl alone, 4 mM KCl and NaCl, 0.74% (w/v) Na2HPO4 with NaCl or insulin (2 U/1 ml) gave partial correlation with blood glucose, while best agreement was seen with EDTA/phosphate buffer. A second approach evaluated an outer membrane barrier comprising polyurethane precursor (Trixene SC762®) and non-ionic surfactant (2% (v/v) Triton X100). This modified polyurethane conferred good haemo- and tissue biocompatibility with exposure to whole blood confirming low fouling, and for tissue no evident drift during acute monitoring.
Keywords: Haemocompatibility; Biocompatibility; Polyurethane; Surfactant; Glucose sensor; In vivo;
Label-free and reversible immunosensor based upon an ac impedance interrogation protocol by Sarah Grant; Frank Davis; Karen A. Law; Andrew C. Barton; Stuart D. Collyer; Seamus P.J. Higson; Timothy D. Gibson (163-168).
We report the fabrication of a label-free and reagentless immunosensor based on the direct incorporation of antibodies into conducting polymer films along with a subsequent ac impedimetric electrochemical interrogation. Model sensors of this type were prepared by electrochemically polymerising conducting polypyrrole films containing anti-BSA at the surface of screen-printed carbon electrodes. Films containing chloride or anti-human IgG as counter-ions were used as controls. An ac measurement protocol was used to determine the impedance of the electrodes when immersed in water or analyte solutions. A selective and reversible binding of analyte to the electrode could be monitored electrochemically and studies are reported in detail relating analyte concentrations to bulk impedimetric measurements, the real component, the imaginary component and the phase angle of the responses. The results of this study showed detectable and reversible antibody–antigen interactions could be measured and mainly affected the Faradaic behaviour of the electrode. BSA could be detected with a linear response from 0 to 75 ppm.
Keywords: Immunosensor; ac Impedance; Bovine serum albumin; Polypyrrole; Detection;
Flow injection analysis of carbofuran in foods using air stable lipid film based acetylcholinesterase biosensor by Dimitrios P. Nikolelis; Maria G. Simantiraki; Christina G. Siontorou; Klara Toth (169-177).
This work describes a technique for the rapid, selective and sensitive electrochemical flow injection analysis of carbofuran in foods using air stable lipid films in which acetylcholinesterase was incorporated. These lipid films were supported on a methylacrylate polymer (i.e., methacrylic acid was the functional monomer for the polymerization, ethylene glycol dimethacrylate was used as the crosslinker and 2,2′-azobis-2-methylpropionitrile as an initiator). The substrate was injected into flowing streams of a carrier electrolyte solution. Hydronium ions produced by the enzymatic reaction at the lipid film surface caused dynamic alterations of the electrostatic fields and phase structure of membranes and as a result ion current transients were obtained; the magnitude of these signals was correlated to the substrate concentration, which could be determined at the micromolar level. The response times were ca. 10 s. These lipid membranes were used for the flow injection analysis of pesticides. The principle of the method is based on the degree of inhibition of the enzyme by the pesticide. Carbofuran was chosen as a typical pesticide. The novelty of the method is based on the fact that an “air segmented” flow injection technique can be used as compared to previous systems that are based on lipid film technology but are not stable in air. This allows determination of the pesticide using the degree of inhibition and reactivation of enzyme by injections of substrate. Carbofuran was determined at concentration levels of 10−7 to 10−9 M. The investigation of the effect of potent interferences included a wide range of compounds usually found in foods and also proteins and lipids. The technique was applied in 50 different real samples of fruits, vegetables and dairy products. The recovery ranged between ca. 96 and 106% which shows no interferences from the matrix effects.
Keywords: Air stable lipid film; Acetylcholinesterase; Carbofuran; Foods;
Amperometric glucose biosensor based on sol–gel-derived metal oxide/Nafion composite films by Han Nim Choi; Min Ah Kim; Won-Yong Lee (179-187).
Amperometric glucose biosensors have been developed based on the encapsulation of glucose oxidase in the nanoporous composite films of sol–gel-derived metal oxide (titania and silica) and perfluorosulfonated ionomer, Nafion, on a platinized glassy carbon electrode. The presence of Nafion polymer in the sol–gel-derived metal oxide not only prevents the cracking of the pure sol–gel-derived metal oxide film but also improves the sensitivity and long-term stability of the biosensor. Analytical performance of the glucose biosensor based on the titania/Nafion composite is superior to that of the biosensor based on the silica/Nafion composite in terms of response time, sensitivity, and long-term stability. The glucose biosensor based on the titania/Nafion composite film can reach 95% of steady-state current less than 2 s. The biosensor responds to glucose linearly up to 7 mM with a sensitivity of 15 μA/mM. The biosensor retained 80% of its initial activity after 4 months of storage in 0.05 M phosphate buffer at pH 7. Sol–gel-derived titania/Nafion composite can also be used for the preparation of second-generation (mediator-based) biosensor by immobilizing the positively charged mediator such as N,N′-dimethylaminomethyl ferrocene in the composite film via electrostatic and hydrophobic interactions.
Keywords: Glucose; Biosensor; Sol–gel technique; Titania/Nafion composite; Silica/Nafion composite;
Determination of some estrogens by flow injection analysis with acidic potassium permanganate–formaldehyde chemiluminescence detection by Sulan Liao; Xiaoping Wu; Zenghong Xie (189-195).
A novel flow injection chemiluminescence (CL) method for the fast, simple and sensitive determination of three estrogens, namely dienestrol, diethylstilbestrol and hexestrol, has been investigated. It is based upon the CL reaction of the studied estrogens with formaldehyde (HCHO) and potassium permanganate (KMnO4) in sulfuric acid (H2SO4) medium. Under the optimum conditions, the linear range for the determination of estrogens were 8.00 × 10−9 to 8.00 × 10−6 g ml−1 for dienestrol, 5.00 × 10−9 to 4.75 × 10−6 g ml−1 for diethylstilbestrol, and 2.00 × 10−8 to 5.00 × 10−6 g ml−1 for hexestrol. The detection limits (S/N = 3) were 2.61 × 10−9 g ml−1 for dienestrol, 1.08 × 10−9 g ml−1 for diethylstilbestrol and 6.28 × 10−9 g ml−1 for hexestrol. The proposed method has been successfully applied to the determination of the studied estrogens in tablets and tap water. Furthermore, the possible reaction mechanism was also discussed in this paper.
Keywords: Dienestrol; Diethylstilbestrol; Hexestrol; Chemiluminescence; Flow injection analysis;
Development of flow injection spectrophotometric methods for the determination of free available chlorine and total available chlorine: comparative study by Bahruddin Saad; Wan Tatt Wai; Md. Sariff Jab; Wan Saime Wan Ngah; Muhammad Idiris Saleh; Jonathan M. Slater (197-206).
A comparative study on the development of flow-injection (FI) spectrophotometric methods for the determination of free available chlorine (FAC) and total available chlorine (TAC) is described. The use of o-dianisidine (ODS), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonate (ABTS), 4-nitrophenylhydrazine (4-NPH), methyl orange (MO), syringaldazine (SYR) and a new reagent, indigo carmine (IC), in a flow-injection set-up was optimized for common FI operating parameters such as carrier composition, flow-rate, pH, length of reaction coil and injection volume. The FI conditions were designed by the choice of acid at suitable concentration in the carrier stream such that response from FAC is maximized while at the same time minimally interfered by combined available chlorine (CAC). Analytical characteristics of the FI method using these reagents such as detection limits, linear range, selectivity and their relative stability were compared and contrasted. The reagent that yielded the most sensitive signal is ABTS and is least interfered by Mn2+, Zn2+ and Cu2+ but interference from CAC was the most severe, while SYR and 4-NPH were least affected by CAC. IC exhibited the best selectivity characteristics amongst all the reagents studied. TAC can be conveniently determined by adding NaBr to the carrier stream. Finally, some of the promising reagents were applied to the analysis of a few commercial disinfecting formulations. Good agreement on the TAC (FAC + CAC) content was found between the proposed FIA and the manual iodimetric methods.
Keywords: Free available chlorine; Total available chlorine; Spectrophotometric reagents; Flow injection analysis;
Sample introduction in multi-syringe flow injection systems: comparison between time-based and volume-based strategies by Marcela A. Segundo; Hugo M. Oliveira; José L.F.C. Lima; M. Inês G.S. Almeida; António O.S.S. Rangel (207-214).
In multi-syringe flow injection analysis (MSFIA), devices as selection, injection or commutation valves must be incorporated to the manifold to provide access to sample and standard solutions. Therefore, the definition of sample amount can be either volume or time-based. In the present work, four configurations for sample introduction (two for each approach) were tested in order to establish if the different strategies affect the analytical signal in MSFIA systems. The mean absorbance value from ten consecutive injections of a bromothymol blue solution obtained for the time-based strategy was lower than that provided by the volume-based approach as the exact volume delivered by each configuration was different from the “theoretical” volume. For time-based configurations, the exact volume delivered is 2–5% lower than the theoretical value while for volume-based configurations, the volume delivered was between 6 and 46% larger than the theoretical volume. Moreover, for time-based sampling, the order of steps in the analytical cycle was of utmost importance since any alteration in the flow direction affected the volume delivered in the subsequent step in the analytical cycle. The influence of the two sampling approaches was also evaluated in the MSFIA systems for the spectrophotometric determination of phenolic compounds and the potentiometric determination of chloride. There was no evidence that the use of either volume or time-based sampling would improve the analytical features of these determinations when real samples were tested.
Keywords: Multi-syringe; Flow injection; Sampling strategy; Time-based sampling; Volume-based sampling;
Comparison of trimethoprim molecularly imprinted polymers in bulk and in sphere as the sorbent for solid-phase extraction and extraction of trimethoprim from human urine and pharmaceutical tablet and their determination by high-performance liquid chromatography by Shu-Guo Hu; Li Li; Xi-Wen He (215-222).
Two types of trimethoprim molecularly imprinted polymers in bulk and sphere (by suspension polymerisation) were prepared and used as sorbents for solid-phase extraction. By comparing adsorption of trimethoprim in different solvents, desorption with ratio of ethanol and N,N-dimethylformamide, acetic acid and ratio of methanol and trifluoroacetic acid, we find that molecularly imprinted polymers in bulk are better at selectivity and adsorptive capacity than in sphere. Moreover specific surface area and pore volume of molecularly imprinted polymers in bulk are about twice than in sphere. But these two types of polymers may both enrich and separate trimethoprim from the human urine and the pharmaceutical tablet successfully. The linear range of trimethoprim is 1–100 nmol ml−1 and the limited detection is 0.1 nmol ml−1.
Keywords: Molecularly imprinted polymers; Solid-phase extraction; Trimethoprim; Compound sulfamethoxazole tablet;
Development and validation strategies for qualitative spot tests: application to nitrite control in waters by Maria R. Plata; Noelia Pérez-Cejuela; Juana Rodríguez; Ángel Ríos (223-230).
A general and systematic approach is proposed for the development, optimisation and validation of qualitative spot tests. A simple spot test to control water contamination by nitrite has been developed and was taken as the basis for this purpose. The qualitative information, based on a binary yes/no response, was directly obtained through the visual identification of the colour. Legislation requirements for this parameter in tap waters were selected as the threshold for classifying the samples as positive or negative. The qualitative information provided by this type of test was used for both the optimisation of the test to give a reliable response with respect the threshold and for the validation of the test.
Keywords: Qualitative analysis; Spot test; Optimization; Validation; Nitrite control; Waters;
Fast assay of angiotensin 1 from whole blood by cation-exchange restricted-access solid-phase microextraction by Florin Marcel Musteata; Markus Walles; Janusz Pawliszyn (231-237).
A novel restricted-access material with cation-exchange properties was evaluated for the extraction of the peptides angiotensin 1 (Ang1) and angiotensin 2 (Ang2) from whole blood. The ion exchange diol silica (XDS) material revealed enhanced efficiency for extraction of peptides when compared with the conventional alkyl diol silica (ADS) with reversed phase extraction centers. The outer surface of XDS particles contains diol groups while the internal surface has sulphonic acid moieties with strong cation-exchange properties toward compounds with low molecular weight. This new coating for solid-phase microextraction (SPME) offers the possibility to combine all initial sample preparation steps into a single one, even for complex biological samples such as whole blood or plasma. The XDS material was immobilized on a stainless steel wire with a binding agent; the reproducibility of the procedure was determined to be 5.56%. Compounds extracted from whole blood were separated by narrow-bore liquid chromatography (LC) and Ang1 was quantified by electrospray mass spectrometry, with good linearity over the range of 25–500 pM. Total analysis time was less than 90 min. The detection limit for Ang1 from whole blood was determined to be 8.5 pM. A single fiber could be used more than 150 times before a noticeable decrease in extraction capacity was observed. Although the limit of quantification is not as low as that of radioimmunoassay techniques, this method is much faster, less expensive and still provides enough sensitivity at physiological levels of Ang1.
Keywords: Solid-phase microextraction; Restricted-access materials; Angiotensin; Liquid chromatography; Mass spectrometry;
Single-step coacervate-mediated preconcentration of metals and metal-chelates in supramolecular vesicular surfactant assemblies and determination by flame atomic absorption spectrometry by George Z. Tsogas; Dimosthenis L. Giokas; Evangelos K. Paleologos; Athanasios G. Vlessidis; Nicholaos P. Evmiridis (239-248).
The use of ionic surfactant supramolecular aggregates is described, as means for accomplishing the concentration of analytes with different polarities using the same extraction pattern. The proposed method is based on the phase separation of an anionic surfactant through the formation of perplexed lamellar phases, allowing for the extraction of hydrated metal cations by complexation and metal-chelates by hydrophobic interactions. The data suggest that both extraction and phase separation are controlled by the presence of ionic surfactant as a function of the degree of phase divergence from the lamellar to bilayer phase. This again is determined by the composition of the phase-forming parameters, these are the surfactant concentration, the kind and amount of metallic counterparts and ionic strength. On the basis of these findings, the proposed method was successfully applied to the determination of metal species in natural waters. The limits of detection were easily brought down to the low microgram per liter levels by simply preconcentrating 10 mL of sample volume in the presence of at least 0.45% (w/v) of anionic surfactant. The method provided extraction recoveries higher than 94.0% with standard deviations well below 7.0%.
Keywords: Metals; Liquid coacervate extraction; Vesicles; Flame atomic absorption spectrometry; Natural waters;
Optimization of a multi-elemental preconcentration procedure for the monitoring survey of dissolved metal species in natural waters by Dimosthenis L. Giokas; Evangelos K. Paleologos; Miltiades I. Karayannis (249-257).
The monitoring of dissolved metal species in natural waters is pursued through the development, optimization and verification of a multi-elemental extraction procedure based on the cloud point phenomenon. More specifically, six metal species were extracted from water samples as their pyrrolidinedithiocarbamate complexes and subsequently isolated from the aqueous matrix in the micelles of a non-ionic surfactant upon increase of the solution temperature. The optimum experimental conditions that ensure the efficiency of the procedure have been investigated and are presented in detail. As an analytical demonstration, the method was applied to the monitoring survey of two natural ecosystems in Northwestern Greece in an annual monitoring study. The measured concentrations of dissolved metal species were deployed to estimate the pollution status of the ecosystems and unravel the mechanisms that contribute to the metal load.
Keywords: Dissolved metal ions; Cloud point extraction; Flame atomic absorption spectrometry; Natural waters; Monitoring survey;
On-fibre silylation following solid-phase microextraction for the determination of acidic herbicides in water samples by gas chromatography by I. Rodríguez; E. Rubí; R. González; J.B. Quintana; R. Cela (259-266).
In this work a solid-phase microextraction (SPME) method for the determination of eight phenoxy acid herbicides and dicamba in water samples has been developed. Analytes are concentrated on a SPME fibre, on-fibre silylated using N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA), and determined by gas chromatography with mass spectrometry detection (GC–MS). Influence of microextraction and derivatization conditions on the performance of the developed method are systematically evaluated. The highest enrichment factors were achieved using a polar polyacrylate (PA) fibre directly exposed to the stirred sample. Sample acidification and addition of sodium chloride improved the yield of the extraction step; however, the last factor increased the variability of the method. After the microextraction step, derivatization was carried out by exposing the SPME fibre to the headspace of a vial containing 50 μl of MTBSTFA. The on-fibre silylation reaction was completed in 10 min without need of temperature control. Quantification limits from 0.004 to 0.030 ng/ml were obtained for all compounds using an extraction step of 40 min. The proposed method showed and excellent linearity in the concentration range from 0.1 to 10 ng/ml. Repeatability was evaluated using spiked samples at different concentration levels, relative standard deviations from 4 to 12% were achieved. The yield of the whole procedure was scarcely affected by the type of water sample and the presence of relatively high levels of humic acids.
Keywords: SPME; Derivatization; Phenoxy acids; GC–MS;
Determination of Cr(VI) in potable water samples after selective preconcentration on oxalate form of Dowex-1 and electro thermal atomic absorption spectrometric determination by A.C. Sahayam; G. Venkateswarlu; S.C. Chaurasia (267-270).
A method for preconcentration of Cr(VI) from potable water samples was developed using oxalate form of Dowex-1. The resin was found to adsorb Cr(VI) selectively in presence of Cr(III). The percentage recovery (adsorption and elution) of Cr(VI) from water samples was 98.0 ± 1.0. The leaching of adsorbed Cr due to the reduction of Cr(VI) to Cr(III) reported earlier, on chloride form of Dowex-1, as a result of oxidation property of Cr(VI) on organic resins has not been observed. The method has been applied for the separation and preconcentration of Cr(VI) from Cr(III) in potable water samples. The adsorbed Cr(VI) was eluted using 0.8 M HNO3. The measurements were carried out using ET-AAS. The method has been applied for the determination of Cr(VI) in two synthetic water samples, and four real samples. The R.S.D. of the procedure was ∼3% at 10 ng mL−1 and ∼25% at 0.3 ng mL−1. The limit of detection of the method was 0.027 ng mL−1 based on signal corresponding to 0.0044 AU with a 25-fold preconcentration.
Keywords: Speciation; Cr(III); Cr(VI); Potable water; ET-AAS; Dowex-1; Oxalate;
On-line emulsion formation and multi-element analysis of edible oils by inductively coupled plasma atomic emission spectrometry by A.N. Anthemidis; V. Arvanitidis; J.A. Stratis (271-278).
A novel simple on-line emulsion formation system for multi-element analysis by inductively coupled plasma atomic emission spectrometry (ICP-AES) was developed. A laboratory made magnetic-stirring micro-chamber was used for continuous edible emulsification with Triton X-100 and for subsequent introduction of the emulsion into ICP-AES. The optimum concentration of oil in emulsion for maximum sensitivity was 50% (v/v). The performance of the system was demonstrated for Ag, Al, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, In, Mg, Mn, Ni, Pb, Tl and Zn determination in olive, sunflower and corn oil. Good agreement was found between calibration curves for oil emulsion and aqueous ones for the most of the investigated spectral lines. The calibration curves for each element were linear at least up to 1.0 mg l−1 and the correlation coefficients were ranged between 0.991 and 0.999. The proposed method was applied to the analysis of olive oil sample and compared with ETAAS-wet digestion method. No significant differences were observed between the two methods.
Keywords: Inductively coupled plasma atomic emission spectrometry; On-line; Emulsion; Edible oil; Multi-element analysis;
A phase transfer identification of core–shell structures in Au–Ru nanoparticles by J. Yang; Jim Yang Lee; Heng-Phon Too (279-284).
The difference between the transfer of citrate-stabilized Au and Ru nanoparticles from the aqueous phase to toluene was used to develop a simple experimental procedure that can positively identify the formation of bimetallic Au–Ru nanoparticles with the core–shell structure formed in the seed-mediated growth process. The procedure was independently verified by UV–vis spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The experimental results clearly showed that core–shell nanoparticles of Au–Ru were formed by the seed mediated growth method using Au nanoparticle seeds. The reverse order of using Ru nanoparticles as the seeds, on the contrary, could only produce a physical mixture of isolated nanoparticles of Ru and Au under the same experimental conditions.
Keywords: Phase transfer; Seed-mediated growth; Core–shell; Gold nanoparticle; Ruthenium nanoparticle;
Ex situ preparation of bismuth film microelectrode for use in electrochemical stripping microanalysis by Emily A. Hutton; Samo B. Hočevar; Božidar Ogorevc (285-292).
A study on the preparation and characterisation of ex situ formed bismuth film microelectrodes (BiFMEs) is presented, focusing in particular on their stable and reliable stripping electroanalytical performance. The potentiostatic pre-plating of the bismuth film onto a single carbon fibre substrate microelectrode was investigated and optimised with the aim of achieving long-term electrochemical and mechanical film stability. Several important film preparation parameters, such as plating agent, potential and time, and composition of the plating solution were examined with respect to the current signals of 40 consecutive adsorptive cathodic stripping voltammetry (AdCSV) measurements of trace Co(II) as model analyte. A comparison, also presented, of the stripping performance between bismuth and mercury film microelectrodes revealed a distinct practical advantage of the BiFME. The resulting optimised BiFME exhibited, besides excellent long-term film functional stability, attractive stripping analytical performance. Employing AdCSV with square-wave voltammetric detection, highly linear behaviour was obtained in the examined concentration range, with limits of detection of 70 and 90 ng/l and excellent reproducibility with 2.4 and 2.9% relative standard deviation at the 1 μg/l level (n = 10), for Co(II) and Ni(II), respectively, achieved using only 2 min preconcentration time in the presence of dissolved oxygen. In addition, the performance of the proposed ex situ prepared BiFME in both anodic stripping voltammetry (ASV) of Cd(II) and Pb(II) and in AdCSV of Co(II) and Ni(II) from the same test solution is demonstrated. The ex situ prepared BiFME represents a promising non-toxic, environmentally friendly microsensor for detection at microlocations and in microvolumes, in particular where in situ bismuth film electrode preparation is inappropriate, inconvenient or impossible.
Keywords: Bismuth film electrode; Carbon fibre; Microelectrode; Cadmium(II); Cobalt(II); Nickel(II); Lead(II); Adsorptive stripping analysis; Voltammetry;
Determination of free chlorine based on anodic voltammetry using platinum, gold, and glassy carbon electrodes by Fumihiro Kodera; Minoru Umeda; Akifumi Yamada (293-298).
The oxidation of free chlorine on platinum, gold, and glassy carbon disk electrodes has been investigated by using anodic voltammetry to determine the free-chlorine concentration. The voltammetric curves exhibited well-defined anodic peaks. The influences of pH, free-chlorine concentration, and potential sweep rate on the electrode response were investigated. The results show that the measurement of the oxidation peak current can be used as the basis for a simple, accurate, and rapid method for the determination of ClO−, within a concentration range of 4–400 mg Cl l−1. The results of this method were in good agreement with those obtained by iodometric titration. Differential pulse voltammetry has also been examined, resulting in an improved sensitivity at a concentration of 1.0 mg Cl l−1.
Keywords: Anodic voltammetry; Free chlorine; Glassy carbon electrode; Platinum;
Identifying the n = 2 reaction mechanism of FAD through voltammetric simulations by Morgan Cable; Eugene T. Smith (299-306).
In a previous study [E.T. Smith, C.A. Davis, M.J. Barber, Anal. Biochem. 323 (2003) 114–121], cyclic voltammograms were simulated using DigiSim software for reaction mechanisms involving multiple electron transfer steps coupled to proton transfer. Specifically, the overall reaction mechanism of the form: FAD + 2e− + 2H+ ⇌ FADH2 was used to simulate experimental reduction potentials as a function of pH. Experimental observations for free FAD were simulated based on selected reduction potentials and acid dissociation constants for three different reaction mechanisms. In this study, these three reaction mechanisms were examined further using simulations of concentration profiles to identify species that are present in significant concentrations during the electron transfer process. These concentration profiles can then be used as working curves to identify reaction mechanisms and equilibrium constants. For example, two of the three reaction mechanisms, both of which involve a redox reaction coupled to a single proton, indicate significant formation of the semiquinone species at the electrode surface at high pH and low potentials. Previous spectroscopic studies of flavoproteins with an n = 2 reaction mechanism have been unable to detect the formation of a semiquinone under any experimental conditions. Thus, the most reasonable pathway for a proton-coupled n = 2 reaction mechanism is likely to involve two protons.
Keywords: Voltammetry; Simulations; pH-dependent redox reactions; Flavoproteins; Bioelectrochemistry;
Electrochemical studies of ganciclovir at glassy carbon electrodes and its direct determination in serum and pharmaceutics by square wave and differential pulse voltammetry by Bengi Uslu; Burcu Doğan; Sibel A. Özkan (307-313).
A simple and rapid electrochemical method for the determination of ganciclovir in human serum and pharmaceutics was developed. The anodic peak at +1.15 V obtained in a buffer on glassy carbon electrode was used for analysis. The peak current and peak potential depends on pH, scan rate and initial potential. Decrease of the anodic peak with increasing pH, as well as deviations from linear plots of i p = f(C) and i p = k v 1 / 2 indicate that this peak at higher concentrations is affected by adsorption–desorption phenomena. At concentrations lower than about 1 × 10−4 M the peak current obtained by differential pulse and square wave voltammetry is practically a linear function of concentration and is suitable for quantitative determination in pharmaceutical dosage forms and human serum. The linear response was obtained in the ranges of 1 × 10−6–1 × 10−4 M give detection limit on one decimal point: 8.1 × 10−8 M for DPV and 4.52 × 10−8 M for SWV techniques. The similarly repeatability of the methods was within 1.40–1.05% for peak currents and 0.19–0.11% for peak potentials for DPV and SWV, respectively. Precision and accuracy of the developed method was checked by recovery studies.
Keywords: Ganciclovir; Determination; Pharmaceutical dosage forms; Serum analysis; Validation;
Flow analysis of p-aminophenyl phosphate with a gold nanoelectrode ensemble based detector by Tsung-Huang Hsia; Kuo-Tang Liao; Hsuan-Jung Huang (315-319).
An alkaline phosphatase (AP) immobilized gold nanoelectrode ensemble (GNEE) was fabricated by electroless deposition of Au3+ onto the nanopores (d = 50 nm) of polycarbonate membranes and modifying the surface of GNEE successively with a self-assembled monolayer (SAM) of 2-aminoethanethiol, an alkaline phosphatase (AP) layer and a porous film of poly(4-vinylpyridine-co-styrene) (PVP). Performance of the AP–GNEE was studied by monitoring the current responses from the injection of p-aminophenyl phosphate (p-APP) into a flow injection analysis (FIA) system. Optimal conditions such as concentration of AP for immobilization, pH of carrier solution, potential applied for the analysis of p-APP were studied. Calibration graph over a broad dynamic concentration range (0.1 μM to 1.0 mM) gave satisfactory linearity (R 2 = 0.986) and a very low detection limit (0.1 μM) confirming the applicability and superiority of the AP–GNEE for p-APP analysis.
Keywords: Gold nanoelectrode; Electroless deposition; Alkaline phosphatase; Flow analysis;
Simultaneous voltammetric determination of four carbamate pesticides with the use of chemometrics by Yongnian Ni; Ping Qiu; Serge Kokot (321-330).
Voltammetric behaviour of four carbamate pesticides, propoxur, isoprocarb, carbaryl and carbofuran, was investigated, and a method was developed for the simultaneous determination of these compounds. This was based on their anodic voltammetric behaviour observed following their alkaline hydrolysis, which produced electroactive phenol derivatives. It was found that by applying the differential pulse voltammertric (DPV) method in the presence of perchloric acid, the four compounds have well defined voltammetric oxidation waves with peak potentials at 712, 888, 664, and 688 mV, respectively. For each compound, a linear calibration was obtained in the concentration range of 1.0–30 mg l−1. Serious overlapping of individual voltammetric peaks was observed for the mixtures of these four compounds, and to facilitate the resolution of these complex voltammograms, different calibration models were investigated based on four different chemometrics methods, viz., classical least squares (CLS), principal component regression (PCR), partial least squares (PLS) and radial basis function-artificial neural networks (RBF-ANN). The prediction ability of these models were tested with the use of a data set constructed from synthetic solutions of the four pesticides. The analytical performance of the prediction models was characterized with the use of various figures of merit, and the best results were obtained with the PC-RBF-ANN method (%RPET = 5.6 and %Recovery (average) = 100). This method was then applied for the determination of the four pesticides in different water samples.
Keywords: Voltammetry; Carbamate pesticides; Chemometrics; Artificial neural networks;
Comparing radial basis function and feed-forward neural networks assisted by linear discriminant or principal component analysis for simultaneous spectrophotometric quantification of mercury and copper by Y. Akhlaghi; M. Kompany-Zareh (331-338).
Copper(II) and mercury(II) were analyzed simultaneously employing a spectrophotometric method based on application of murexide solution as a chromogenic reagent. A full factorial six level design was used for the construction of calibration and prediction data sets consisting of absorption spectra recorded in 350–700 nm range from solution mixtures. A control data set, from a random design, was applied for validation of the calibration models. The presence of non-linearities was confirmed by a recently discussed methodology based on augmented partial residual plots (APaRPs). Combinations of principal component analysis (PCA) or linear discriminant analysis (LDA) with radial basis function networks (RBFNs) or feed-forward neural networks (FFNNs) were built and investigated, as four calibration models. Number of inputs and hidden nodes for each of the networks were optimized. Performances of methods were tested with relative standard error of prediction (RSEP%), using synthetic solutions of two metal ions as prediction set. Linear discriminant analysis assisted networks (LDRBNN) resulted in preferred models, using only one latent variable for each of the analytes. All of the methods were applied for the analysis of a number of synthetic samples and a dental alloy sample and satisfactory results were obtained.
Keywords: Artificial neural networks; PCA; Linear discriminant analysis; Metal ions; Spectrophotometry;
Improved kinetic data from analysis of complex hydrocarbon mixtures by using SIMCA by D. Kubička; M. Rönnholm; S.-P. Reinikainen; T. Salmi; D.Yu. Murzin (339-348).
A SIMCA model was developed for classification of C10-bicycloalkanes to assist evaluation of kinetic experiments involving complex mixture of C10-hydrocarbons. The influence of different pre-processing methods, such as square root and cubic root scaling, and transformation methods, including autocorrelation transform and spectral features, on the classification of C10-bicycloalkanes was investigated. While the transformation of mass spectra into spectral features was found essential for modeling of spectra of C10-bicycloalkanes, the intensities scaling was only of little importance for the quality of the SIMCA models. The best SIMCA model was successfully applied in detailed analysis of C10-bicycloalkanes originating from decalin isomerization and contributed to identification of the decalin isomerization mechanism.
Keywords: SIMCA; Pattern recognition; Mass spectra transformation; C10-bicycloalkanes;
First order Rayleigh scatter as a separate component in the decomposition of fluorescence landscapes by Åsmund Rinnan; Karl S. Booksh; Rasmus Bro (349-358).
The application of chemometric tools to analyze multi-way data has become popular, especially for excitation–emission matrix (EEM) fluorescence spectroscopy where PARAFAC often is employed to resolve the pure component profiles of mixtures of fluorophores. There are, however, some features in a typical EEM that do not follow the required low-rank tri-linear structure required for PARAFAC to work optimally. The most significant of these features is the light scatter effects that form diagonal lines in the landscapes. These cannot be modeled by one (or a few) factor(s) in the decomposition step, and has so far been removed by subtracting a standard, inserting missing values, or weighting these areas down. This paper suggests a novel method, which models the first order Rayleigh scatter as a separate set of factor(s) in the decomposition step by shifting the Rayleigh scatter into becoming low-rank bi-linear. This method is easier to implement than current methods and provides good results; both requirements for increasing the use of fluorescence spectroscopy by the non-expert user.
Keywords: EEM; Scatter model; Multi-way; Fluorescence spectroscopy; PARAFAC; PCA;
Archaeometric characterisation of ancient pottery belonging to the archaeological site of Novalesa Abbey (Piedmont, Italy) by ICP–MS and spectroscopic techniques coupled to multivariate statistical tools by Emilio Marengo; Maurizio Aceto; Elisa Robotti; Maria Cristina Liparota; Marco Bobba; Gabriella Pantò (359-375).
This work presents the archaeometric characterisation of a group of ancient pottery remains discovered during the restoring of the Novalesa Abbey (Susa Valley, Turin, Italy) performed in 2000. The characterisation focuses on the achievement of information about provenance and production process of the samples. Firstly, the data concerning the multi-element characterisation of the samples by inductively coupled plasma–mass spectrometry (ICP–MS) were analysed by chemometric tools (principal component analysis and cluster analysis) in order to obtain information about their similarity and clustering. These information, integrated with the results of micro-Raman spectroscopy analysis of the inclusions shed light on differences in the production process of the samples.
Keywords: Principal component analysis; ICP–MS; Raman spectroscopy; Archaeometry;
Rapid determination of alcoholic strength of egg liqueur using steam distillation and oscillation-type densimetry with peristaltic pumping by Dirk W. Lachenmeier; Peter A. Burri; Tina Fauser; Willi Frank; Stephan G. Walch (377-384).
This paper introduces a new method of determining alcoholic strength in highly viscous samples like egg liqueurs. The method relies on fully automated steam distillation in combination with oscillation-type densimetry and peristaltic pumping. The procedure is much faster (taking less than 8 min per sample) and easier than the conventional reference method (distillation, pycnometry). This makes it possible to determine alcohol content efficiently and economically, both in official food control and in spirit production. In addition, the total dry extract of the liqueur can be indirectly calculated from the density of the sample and the density of the alcoholic distillate.The parameters for the automatic steam distillation were optimised for the analysis of egg liqueur samples (100% steam power, sample weight 25 g, 130 s distillation time, 50 ml receiver). Validation has proved the method robust and precise. The relative standard deviation was below 0.56% in all cases. By analysing spirit samples under routine conditions, a high correlation (R = 0.999) with the reference method was achieved.
Keywords: Ethanol; Alcoholic strength; Steam distillation; Pycnometry; Oscillation-type densimetry; Peristaltic pumping; Egg liqueur;
α-Cyclodextrin-modified infrared chemical sensing system that utilizes enzymatic reactions for the determination of glucose by Jyisy Yang; Shou-Chueh Liang (385-392).
A new infrared (IR) sensing system based on attenuated total reflection (ATR) to determine the levels of glucose in aqueous solutions was developed in this work. To increase the selectivity of the system, we employed glucose oxidase (GOx) to convert glucose into gluconic acid, which was the actual species detected by the IR-ATR sensor. Because gluconic acid is highly polar and was produced generally in low concentrations, the surface of the IR-ATR sensor was modified with cyclodextrin to increase the sensitivity of its detection. As a result, the sensitivity increased roughly by 100 times relative to that of the unmodified ATR. To simplify the detection system, we immobilized GOx onto the surfaces of glass beads and packed them into a column to function as an enzyme reactor. For comparison, GOx was also immobilized onto the internal surface of fused silica tubing. Glucose can be converted to gluconic acid effectively when passed through a flow system and using either packed or open tubular columns. To optimize the performance of the developed system, we investigated the effects of the pH of the sample solutions and the flow rate used to pump glucose through the system. Our results indicate that the optimal pH for the system was ca. 5; a low pH was required for high-efficiency detection of gluconic acid by the CD phase, but it lowered the efficiency of the enzymatic reactions. The flow rate exerted a small influence on the analytical signals over the examined range of flow rates because of the limited rates of the enzymatic reactions. Under the optimal conditions, the linear regression coefficients in the standard curve can be >0.99 for a concentration range of 1–50 mM and a detection time of 2 min. In addition, our developed system can be regenerated effectively using aqueous solutions at high pH.
Keywords: Infrared sensor; FT-IR spectroscopy; Glucose; Enzymatic reaction; GOx;
An ammonia and isocyanic acid measuring method for soot containing exhaust gases by Oliver Kröcher; Martin Elsener; Manfred Koebel (393-400).
The set-up and operating principle of an analyzer, which can be used without any filter for the continuous measurement of ammonia (NH3) and isocyanic acid (HNCO) in soot containing exhaust gases is described. Ammonia and isocyanic acid are dissolved in a buffer solution, in which ammonia is measured directly with an ammonia-sensitive electrode. The sum of ammonia and isocyanic acid is measured with the same method after hydrolysis of HNCO to NH3 and CO2. Ammonia and isocyanic acid concentrations of up to ∼500 ppm can be measured with a mean relative error of 3.6% at a standard deviation of 4.0%. The investigation of the urea thermohydrolysis, which is an important step in the selective catalytic reduction (SCR) of nitrogen oxides in Diesel exhaust gases, revealed the emission of toxic isocyanic acid besides ammonia from the SCR catalyst.
Keywords: Ammonia; HNCO; Isocyanic acid; Analyzer; Sensor; Flue gas; Exhaust gas; SCR; Catalyst; Selective catalytic reduction;
Performance of diffusive gradients in thin films for measurement of the isotopic composition of soluble Zn by Dmitry Malinovsky; Ralf Dahlqvist; Douglas C. Baxter; Johan Ingri; Ilia Rodushkin (401-405).
The application of diffusive gradients in thin films (DGT) samplers for measurements of the isotopic composition of soluble Zn by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) was tested under laboratory conditions. The effect of diffusion in hydrogels as a possible source of fractionation was investigated by measuring Zn isotope ratios for different fractions of Zn accumulated by DGT and comparing with the bulk isotope composition of the solution. An important finding of this study is that, provided quantitative elution is obtained, no fractionation of Zn isotopes due to the diffusion process is detectable within the reported precision of MC-ICPMS measurements. Consequently, DGT samplers are suitable for studies of the Zn isotopic composition in natural waters.
Keywords: Zn isotopes; MC-ICPMS; Diffusion; Diffusive gradients in thin films; Elution efficiency;
Author Index (407-409).