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Analytical and Bioanalytical Chemistry (v.363, #7)
New electrochemical and optical sensing techniques for the liquid phase by Richard P. Buck; E. Lindner (pp. 607-611).
Three topics are summarized: advances in potentiometric sensors, in optical sensors, and in enzyme-based and enzyme-sensing biosensors.
Trace analysis of surfactants using chromatographic and electrophoretic techniques by C. Vogt; Katja Heinig (pp. 612-618).
Because of the widespread use, increased application of new formulations and immense impact on organisms and ecology surfactants are still in the focus of analytical chemistry. The development of methods with higher selectivity and lower detection limits is important to meet the requirements of greater responsibility for health of people and environment. Efficient separation methods, like HPLC, GC and CE, in combination with sensitive detection, like MS, are to be preferred over collective techniques which can suffer from interfering components. A review on trace analysis of ionic and neutral surfactants including sample preparation steps is presented, considering especially those methods which provide information about homologous and isomeric distribution of surfactant mixtures. Examples for the determination of linear alkylbenzene sulfonates in river water by HPLC and CE are discussed to show the capability of these methods for environmental analyses. As future trends increased applications of LC/MS (very high sensitivity) and also of CE (robustness and possibility for rapid method development) can be predicted.
Stabilization of antibodies by haptens by Michael Winklmair; Andreas J. Schuetz; M. G. Weller; Reinhard Niessner (pp. 619-624).
A new concept for the stabilization of antibodies in regenerable immunochemical sensors is described. The influence of a chemiluminescence (CL) substrate on the activity of different immobilized monoclonal antibodies (MAbs) directed to triazines has been investigated. One MAb (4A54) showed a decrease in activity of more than 50% upon incubation of the CL substrate for 2 h. It could be shown that MAb 4A54 can be stabilized by saturation with a suitable hapten. Total preservation of the antibody activity was observed by adding atrazine or simazine as stabilizing agents to the CL substrate at concentration levels of 10 μg/L and 100 μg/L. Additional amounts of hydrogen peroxide in concentration levels of 0.004% and 0.04% added to the test solutions did not increase the observed loss of activity of the antibody and also did not alter the stabilizing effect of atrazine and simazine on MAb 4A54. Loss of activity caused by low pH could not be prevented by hapten saturation under the employed experimental conditions. For practical use of this stabilization concept in immunochemical sensors, complete dissociation of the hapten used as stabilizing agent must be achieved prior to the use of the antibody in a successive sensor cycle. Therefore, the dissociation of the bound triazines was investigated. For simazine, a dissociation rate constant of 0.0052 s–1 in neutral washing buffer was determined. After a dissociation time of 10 min, no bound simazine could be detected any more. As a control experiment, ELISA calibration curves were determined for MAb 4A54 after incubating the antibody with the CL substrate. The CL substrate caused significant reduction of the ELISA signal, which could be prevented by saturation of the antibody with a hapten. Evidence was given for the full dissociation of the hapten after the stabilization step. This indicates that the proposed stabilization concept is suitable for practical applications in immunochemical sensors.
Selection of hapten structures for indirect immunosensor arrays by Andreas J. Schuetz; Michael Winklmair; M. G. Weller; Reinhard Niessner (pp. 625-631).
A multianalyte immunosensor array can be implemented by immobilization of different haptens in distinct areas of a single cavity or flow cell. In this case a mixture of different antibodies for different analytes is used in an indirect ELISA-format. The selection of the right hapten structures is very important to build up an array successfully. A system of independent hapten/antibody combinations is needed, with one immobilized hapten (coating antigen) reacting only with one antibody. If more than one antibody binds to a coating antigen no ideal calibration curves are obtained. This phenomenon is known as shared-reactivity and can lead to double-sigmoidal curves. To use monoclonal antibodies to 2,4,6-trinitrotoluene (TNT) and 2,4-dichlorophenoxyacetic acid (2,4-D), two different haptens had to be found, one only reacting with the TNT-antibody, the other only binding to the 2,4-D-antibody. 2,4-Dichlorophenoxybutyric acid was used for the 2,4-D antibody and 2,4,6-trinitrophenyl-8-aminooctanoic acid for the TNT antibody. Although 4-nitrotoluene, 2,4-dinitrotoluene and 4-amino-2,6-dinitrotoluene showed only very low cross-reactivities to the 2,4-D antibody the corresponding haptens 4-nitrophenylacetic acid, 2,4-dinitrophenyl-6-aminohexanonic acid, and 4-amino-2,6-dinitrotoluyl-(N)-glutarate are useful coating antigens for this antibody. The structure of the coating antigens had no significant influence on the midpoints (IC50) of the test for 2,4-D and even haptens with very low cross-reactivities could be used. With all haptens a test midpoint of about 0.2 μg/L for 2,4-D was achieved. For the direct assay format with immobilized antibodies the same test midpoint of 0.2 μg/L for 2,4-D was obtained. As a conclusion, the selectivity of a monoclonal antibody should not be influenced by the used tracer or coating antigen as well. It could be shown that the affinity constants of an antibody to the analytes are the main sensitivity and selectivity determining parameters for competitive immunoassays. A two-dimensional microtiter plate array was used to determine the analytes 2,4-D and TNT in parallel with a mixture of antibodies.
The preparation of a certified reference material of polar pesticides in freeze-dried water (CRM 606) by A. Martín-Esteban; P. Fernández; C. Cámara; G. N. Kramer; E. A. Maier (pp. 632-640).
The preparation of a certified reference material of polar pesticides in freeze-dried water is described. The pesticides selected were atrazine, simazine, carbaryl, propanil, linuron, fenamiphos and permethrin which were added to 6000 litres of tap water at 50–80 μg · L–1 (200–320 μg · L–1 for permethrin) level in presence of NaCl (2.5 g · L–1) prior lyophilization. After the freeze-drying process the residue was rehomogenized, filled into amber glass bottles and stored at –20 °C, +4 °C and +20 °C. All pesticides were determined by HPLC/diode array detector, except permethrin which was determined by GC/ECD. The results obtained for atrazine, simazine, carbaryl, propanil, linuron and fenamiphos showed no within- or between-bottle inhomogeneity, however the material was non-homogeneous for permethrin and therefore this was withdrawn from further studies. With respect to the stability for over one year, all pesticides were stable at –20 °C. At +4 °C all pesticides were stable for at least 9 months and at +20 °C the stability was demonstrated only during the first month of storage. The content (mass fractions) of atrazine, simazine, carbaryl, propanil and linuron in freeze-dried water (CRM 606) was certified by an interlaboratory testing and a certification campaign.
Direct determination of nickel traces on modified cellulose by diffuse reflection spectroscopy and using chromaticity characteristics by N. I. Ershova; V. M. Ivanov (pp. 641-645).
Diffuse reflection spectroscopy has been used for the direct determination of nickel traces after preconcentration on cellulose (Cel). The experimental parameters (optical characteristics, acidity of aqueous solution, shaking time, volume of aqueous solution, nickel and tartaric ion concentrations, etc.) affecting sorption of nickel species with immobilized dimethylglyoxime (DG) and benzyldioxime (BD) have been optimized. Diffuse reflection coefficient and chromaticity characteristics of the nickel sorbates indicated the same dependence on studied factors, but their sensitivity is different. The linear relations of variations of these quantities with the nickel contents were determined. Detection limits were 0.1 μg/mL and 0.2 μg/mL for BD and DG, respectively. The procedures were used for the analysis of natural and waste waters.
Determination of cobalt by catalytic-adsorptive differential pulse voltammetry in the presence of 2-aminocyclopentene-1-dithiocarboxylic acid and nitrite by A. A. Ensafi; H. Rahimi Mansour; K. Zarei (pp. 646-650).
A novel method for the determination of cobalt(II) by stripping voltammetry is described. It involves an adsorptive accumulation of the cobalt(II)-2-aminocyclopentene-1-dithiocarboxylic acid complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the complex at –1.4 V at pH = 9 (vs. Ag/AgCl). The effects of various experimental parameters on the catalytic current were investigated. An accumulation time of 60 s results in a low experimental limit of detection of 0.1 ng/mL of Co(II), and 0.50 to 40.0 ng/mL of cobalt can be determined. The relative standard deviation at 0.50 ng/mL is 2.8%. Possible interferences from co-existing ions were also investigated.
Resonance Rayleigh scattering for the determination of cationic surfactants with Eosin Y by S. Liu; Guangming Zhou; Zhongfang Liu (pp. 651-654).
Resonance Rayleigh scattering (RRS) of cationic surfactants–Eosin Y systems and their analytical application have been studied. In aqueous solution at pH 2∼3, Eosin Y reacts with a monomer of cationic surfactants (CS), such as Zephiramine (Zeph), tetradecylpyridinium bromide (TPB), cetylpyridinium bromide (CPB), cetylpyridinium chloride (CPC) and cetyltrimethylammonium bromide (CTMAB), to form an ion associate and a new RRS spectrum appears. The spectral characteristics of the five ion associates are similar and their maximum scattering wavelengths (λmax) are all at 313 nm. The intensity of RRS at λmax of the ion associate is directly proportional to the concentration of CS in the range of 0∼3.0 μg/25 mL. The technique has high sensitivity for the determination of CS; their detection limit is between 5.57 ng/mL and 7.60 ng/mL depending on the CS. In this case, most metal and non-metal ions, NH4 + and some anionic surfactants do not interfere, so that the method has a good selectivity. It can be applied to the determination of trace amounts of cationic surfactants in water samples.
Quantitative description of element concentrations in longitudinal river profiles by multiway PLS models by J. W. Einax; A. Aulinger; W. v. Tümpling; A. Prange (pp. 655-661).
Partial least squares (PLS) models were used to examine the relationships between the distributions of elements in different compartments of a river. These relationships, if existing, enabled predictions to be made of the element concentrations in one compartment by knowing the concentrations in another compartment. The subjects of the study were the element concentrations measured in the water and the sediment of the river Saale as well as in the water and the suspended matter of the river Elbe. Special emphasis was placed on a comparison between two-way and three-way PLS.
Determination of heavy metals in environmental bio-indicators by voltammetric and spectroscopic techniques by C. Locatelli; G. Torsi; T. Garai (pp. 662-666).
The determination of copper, lead, cadmium and zinc in matrices involved in the food chain as algae, species Ulva rigida, and clams, species Tapes philippinarum by differential pulse anodic stripping voltammetry (DPASV) was carried out. For the mercury determination in these matrices, a new accurate and precise method was developed employing a mixture of concentrated acids H2SO4-K2Cr2O7 for digestion and subsequent cold vapor atomic absorption spectrometry (CV-AAS) by reduction with SnCl2. The analytical procedures were verified for four reference standard materials: Ulva lactuca BCR-CRM 279, Lagarosiphon major BCR-CRM 060, Oyster tissue NBS-SRM 1566, Mussel tissue BCR-CRM 278. For all the elements the precision, expressed as relative standard deviation (sr), and the accuracy, expressed as relative error (e), were in the order of 3 to 5%, while the detection limits were in the range 0.010–0.100 μg/g. The standard addition technique improved the resolution of the voltammetric method even in the case of very high element concentration ratios. The analytical procedure was used for real matrices sampled in the Adriatic Sea south to Po river mouth, in the zone “Goro bay”, and at open sea north to the Ravenna shore.
Comparison between conventional and ultrasound accelerated Tessier sequential extraction schemes for metal fractionation in sewage sludge by B. Pérez-Cid; I. Lavilla; C. Bendicho (pp. 667-672).
Chemical sequential extraction for metal fractionation in sewage sludge using the Tessier method has been accelerated by ultrasound. The two sequential extraction schemes (conventional and ultrasound accelerated) were compared in terms of extraction efficiency, precision, treatment time and partitioning patterns of metals. Extractable contents of Cu, Cr, Ni, Pb and Zn were measured by flame atomic absorption spectrometry, and the analytical results obtained by the two procedures were statistically compared (P = 0.95). No significant differences were found in the two first fractions (i.e. exchangeable and carbonate-bound), however, in the third and fourth extracts (i.e. Fe-Mn oxides-bound and organic matter-bound) the extraction capability of the two methods differed significantly.
Determination of organophosphorus pesticides in soil by headspace solid-phase microextraction by W. F. Ng; Mui Jun Karen Teo; Hans-Åke Lakso (pp. 673-679).
Headspace solid-phase microextraction (SPME) has been developed for the analysis of common organophosphorus pesticides in soil. Factors such as adsorption-time, sampling temperature and matrix modification by addition of water were carefully considered to optimize the extraction efficiency. This technique could achieve limits of detection of 143 ng/g for Malathion and Parathion, and 28.6 ng/g for Phorate, Diazinon and Disulfoton in humic soil when the extracted sample was analyzed by gas chromatography-flame ionization detector (GC-FID). Lower limits of detection of 28.6 ng/g for Malathion and Parathion, and 14.3 ng/g for Phorate, Diazinon and Disulfoton can be achieved by analyzing the extracted sample with gas chromatography/mass spectrometric detector (GC/MS). As the extraction efficiency was generally better when analyzing sandy soil, the limits of detection are envisaged to be even better for such a matrix. The technique was found to be reliable with good precision of about 6.5% RSD for the sandy soil and about 15% for the humic material. The poorer precision of extraction from the humic material is probably related to the poorer homogeneity of this material. The linearity of extraction was good with linear calibration in the range of 0.143 to 28.6 μg/g. Finally, headspace SPME was compared to aqueous extraction of soil followed by SPME (LE-SPME). The recoveries obtained by headspace SPME were comparable to those from liquid-liquid extraction of soil followed by SPME. However, the analysis of headspace SPME has less background interference. Perhaps, the greatest advantage of this technique is its non-destructive nature so that it is possible to perform further laboratory analysis of the samples after headspace SPME has been carried out.
Determination of polar pesticides in soil by solid phase microextraction coupled to high-performance liquid chromatography-electrospray/mass spectrometry by M. Möder; P. Popp; R. Eisert; J. Pawliszyn (pp. 680-685).
The determination of carbamate and triazine pesticides from soil leachates and slurries was investigated using solid phase microextraction (SPME) coupled to high-performance liquid chromatography-electrospray/ mass spectrometry (HPLC-ESI/MS). SPME was carried out using fibres with a newly developed 50 μm Carbowax/ template coating which are suitable for relatively polar analytes. These fibers exhibit precisions better than 10% RSD, and are resistant against high contents of organic solvents during desorption. The technique shows a high sampling frequency resulting in an increasing sample throughput.
The development of an automated continuous measurement system for the monitoring of HCHO and CH3CHO in the atmosphere by using an annular diffusion scrubber coupled to HPLC by Yuichi Komazaki; Masashi Hiratsuka; Yasushi Narita; S. Tanaka; Tomio Fujita (pp. 686-695).
An automated continuous measurement system for the monitoring of formaldehyde (HCHO) and acetaldehyde (CH3CHO) in the urban atmosphere was developed by using an annular diffusion scrubber in conjunction with a high-performance liquid chromatograph (HPLC). With this technique, atmospheric HCHO and CH3CHO were effectively collected by the annular diffusion scrubber which consists of a porous polytetrafluoroethylene (PTFE) tube disposed concentrically within a Pyrex-glass tube and a scrubbing solution. 2,4-Dinitrophenylhydrazine (DNPH) was selected as the scrubbing solution for collecting HCHO and CH3CHO, which are derivatized to 2,4-dinitrophenylhydrazone-formaldehyde (DNPH-HCHO) and 2,4-dinitrophenylhydrazone-acetaldehyde (DNPH-CH3CHO), respectively. An aliquot of the sample solution was automatically injected into an HPLC equipped with a semi-micro ODS column and a UV-VIS detector for separating and determining DNPH-HCHO and DNPH-CH3CHO. All the operations are sequenced by a programmable controller, and automated continuous measurements are performed with a typical temporal resolution of 1 h. The collection efficiencies of HCHO and CH3CHO were about 97% and 93%, respectively, at an air flow rate of 0.2 L/min. The lower detection limits (3σ of the blank hydrazones) of HCHO and CH3CHO were 0.05 ppbv and 0.10 ppbv, respectively, in the case of 12-L air sample volume. Analytical response of a standard solution of DNPH-HCHO and DNPH-CH3CHO by the HPLC during a 10-day continuous measurement was unchanged and the relative standard deviation (RSD) was < 1.0%. Interferences from O3 and NO2 were insignificant in this annular diffusion scrubber method. Both for HCHO and CH3CHO measurements, concentrations from this developed system well agreed with those measured by a DNPH Silica cartridge method.
Application of solid-phase microextraction to monitoring indoor air quality by Danuta Gorlo; Bogdan Zygmunt; Marta Dudek; Anna Jaszek; Michał Pilarczyk; J. Namieśnik (pp. 696-699).
Practical application of Solid-Phase Microextraction (SPME) for the assessment of the quality of indoor air is presented. SPME was used to sample selected organic pollutants (carbon tetrachloride, benzene, toluene, chlorobenzene, p-xylene and n-decane). An SPME fiber was coated with a 100 μm film of polydimethylsiloxane. The analytes extracted were analysed with a gas chromatograph directly coupled with a mass spectrometer (GC-MS). The method was used to assess the indoor air quality in a few selected flats. The concentrations ranged from below detection limits to 6.9 mg/m3 for benzene depending on the flat; they were relatively high for newly built or freshly renovated flats.
A high performance liquid chromatographic method for the screening of 17 diuretics in human urine by H.-J. Guchelaar; L. Chandi; O. Schouten; W. A. van den Brand (pp. 700-705).
A simple and adequate HPLC method was developed for screening of human urine for the following 17 diuretic drugs: acetazolamide, bendrofluazide, bumetanide, canrenoic acid, chlorothiazide, chlorthalidone, clopamide, epitizide, etacrynic acid, furosemide, hydrochlorothiazide, indapamide, mefruside, piretanide, spironolactone, torasemide, and triamterene. The assay involves extraction from two 2 mL urine samples with ethyl acetate at pH = 5, washing with a phosphate buffer at pH = 6 and analysis by HPLC using a reversed phase C18 column and ultraviolet detection with a diode array detector for all drugs (except triamterene) using two eluents consisting of water, triethylamine, phosphoric acid and acetonitrile at different ratios and different pH values. Triamterene is determined by direct injection of diluted urine onto the column and is measured by fluorescence detection. The recoveries of the diuretic drugs were determined at two different concentrations and ranged from 43–110% (median: 87%) which is sufficient to detect abuse of these drugs. The repeatability of the assay ranged from 1–12% (median: 5.5%).
Selection of optimum pH for the iodate determination using differential pulse polarography by Jianping Lin (pp. 706-707).
The concentration of iodate in seawater samples was determined at various pH values using differential pulse polarography (DPP). The sensitivity for the iodate determination decreased rapidly below pH 7 and above pH 9. The decrease below pH 7 may be caused by conversion of iodate to iodide, followed by the successive formation of I2 and I3 –. The decrease above pH 9 is probably due to the combination of iodate and hydroxide. Theoretical calculations have demonstrated that the optimum pH for iodate determination is above pH 7.4 for Po2 = 0.101 Pa.
DNA-modified electrodes. Part 6. A new method for the determination of binding constants and binding site sizes by Yuan-Di Zhao; D.-W. Pang; M. Zhang; Jie-Ke Cheng (pp. 708-709).
A new method was developed to obtain the binding constant (K) and binding site size (n) for the interaction of DNA with other molecules using DNA-modified gold electrodes. This method is simple and microsample-consuming compared with conventional solution methods. A Q-basic program was designed to calculate K and n values. The results show that the K and n values obtained by the new method approach those obtained by conventional electrochemical methods, indicating the suitability of this method.
Determination of cadmium in Bentonite clay mineral using a carbon paste electrode by Valérie Marchal; Frédérique Barbier; Frédéric Plassard; R. Faure; Olivier Vittori (pp. 710-712).
Sodium activated Bentonite, a sodium modified Montmorillonite, was submitted to cadmium sorption from nitrate solutions in order to simulate a cadmium polluted clay mineral. The remaining cadmium concentration in solution was analyzed at equilibrium by means of Differential Pulse Polarography (DPP) in order to calculate the cadmium concentration sorbed by the clay. The cadmium distribution between clay mineral and solution was observed for different concentrations, showing a Freundlich sorption profile. The clay mineral, previously submitted to the cadmium sorption procedure, was included in a carbon paste in order to investigate the cadmium content by voltammetric determination. For cadmium detection in Bentonite, a linear response of the carbon paste electrode (CPE) was observed in the 5 · 10–5– 1.8 · 10–4 mol/g range with good reproducibility.
Simultaneous determination of propanol and butanol by a fluorometric enzymatic method based on the intrinsic fluorescence of the enzyme by José F. Sierra; Marta de Pedro; Susana de Marcos; J. Galbán; Juan R. Castillo; C. Ubide (pp. 713-715).
The application of the intrinsic fluorescence of alcohol dehydrogenase (ADH) for the simultaneous determination of propanol and butanol was investigated by using only one kinetic run. An absolute calibration method (based on a mathematical model derived from the enzymatic reaction) and a multivariate calibration method (partial least squares regression, PLSR) were tested for this purpose. Both methods were applied to synthetic samples of both alcohols with good results.