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Analytical and Bioanalytical Chemistry (v.365, #5)
Selectivity problems of membrane ion-selective electrodes by K. Ren (pp. 389-397).
A brief review of problems related to the determination of selectivity coefficients of ion-selective electrodes and their interpretation is given, along with a short critical description of the so far applied methods of their determination. A new method is proposed, the experimental part is similar to the mixed solution method recommended by IUPAC but avoids its drawbacks and can be used in cases when the latter cannot be applied. The method proposed permits the determination of the electrode selectivity as a function dependent on the activity of the ions studied, permitting conclusions on the mechanisms of the potential formation and selectivity. The performance of the method is illustrated for a nitrate electrode. Significant dependencies of the selectivity coefficients on concentration of the disturbing ions were interpreted as a result of the process of ion adsorption at the interface between the electrode membrane and the solution studied. The experimental evidence supports the conclusions from the studies of Pungor et al., who claimed that processes at this interface play the main role in the mechanism of generation of the potential of ion-selective electrodes.
Electromigration peak dispersion of isotachophoretic protein zones during capillary zone electrophoresis by J. Gysler; U. Jaehde; W. Schunack (pp. 398-403).
The relationships between electromigration dispersion (EMD) and on-line isotachophoresis-capillary zone electrophoresis (ITP-CZE) are described for several basic model proteins and interleukin-6 (rhIL-6). During CZE separation of the highly concentrated analyte zones which were generated during the initial ITP step EMD evolves from intrinsic differences in conductivity between the focused ITP zones and the leading electrolyte. Nearly triangular peaks with a sharp front and diffuse rear side were observed. An electromigration dispersion factor (FEMD) was introduced to measure peak asymmetry. EMD of individual peaks was shown to increase with the absolute amount of the respective analyte injected and with analyte mobility. Good linearity was observed when FEMD was plotted against protein mobility (r > 0.95). The slope of the graphs describing this relationship increased with the amount of analyte injected. The influence of EMD on the separation efficiency of neighboring peaks appeared to be less pronounced than expected. Consecutive release from the ITP-stack during transition from ITP to CZE might be an explanation for this observation.
Saturation effects in the laser ablation of stainless steel in air at atmospheric pressure by L. M. Cabalín; D. Romero; J. M. Baena; J. J. Laserna (pp. 404-408).
A pulsed Nd : YAG laser was used to generate a plasma from stainless steel targets in air at atmospheric pressure. Laser focusing was found to be an important factor in the ablation process. The influence of focal conditions on spatial profiles of plasma, emission intensity and averaged ablation rate (AAR, μm pulse–1) of stainless steel samples as a function of laser energy are discussed. At high energies and depending on laser beam focusing, ablation efficiency tends to decrease compared to that at lower energies. This effect can be due to plasma shielding and air breakdown. The averaged ablation rate was found to be dependent on the thickness of the sample. This effect results in shielding of the incoming laser beam and redeposition of removed material in the crater. By focusing the beam inside the material free expansion of plasma is allowed, resulting in more efficient erosion of the sample at larger energies. For comparative purposes, data on ablated mass per pulse are presented.
Determination of the interchangeable heavy-metal fraction in soils by isotope dilution mass spectrometry by H.-E. Gäbler; A. Bahr; B. Mieke (pp. 409-414).
An isotope dilution technique using enriched stable isotopes is applied to determine the interchangeable heavy-metal fraction in soils. Metals in two soil samples are extracted at constant pH, with water, NH4NO3, and EDTA. A spike of enriched stable isotopes is added to the suspension of sample and eluant at the beginning of the extraction. The heavy-metal fraction which exchanges with the added spike during the extraction is called the interchangeable fraction. The extractable heavy-metal fractions are obtained from the heavy-metal concentrations in the eluates. Isotope ratios and concentrations are determined by HR-ICP-MS. The isotope dilution technique described enables both the extractable and the interchangeable heavy-metal fractions to be determined in the same experiment. The combination of both results gives additional information on elemental availability under different conditions that cannot be obtained by analyzing the extractable heavy-metal fractions alone. It is demonstrated that in some cases different eluants just shift the distribution of the interchangeable fraction of an element between the solid and liquid phases (e.g., Pb and Cd in a topsoil sample) while the amount of the interchangeable fraction itself remains constant. For other elements, as Ni, Zn, and Cr, the use of different eluants (different pH, complexing agents) sometimes enlarges the interchangeable fraction.
Application of a hexapole collision and reaction cell in ICP-MS Part I: Instrumental aspects and operational optimization by I. Feldmann; N. Jakubowski; D. Stuewer (pp. 415-421).
The application of an ion-guiding buffer gas-filled hexapole collision and reaction cell in ICP-MS has been studied in order to give a preliminary performance characterization of a new instrument providing this feature for increasing the ion yield and decreasing contributions from Ar induced interfering molecular ions. As buffer gas He was used while H2 served as reaction gas. Addition of the latter can be an effective means for reduction of typical argon induced polyatomic ions (Ar+, ArO+, Ar2 +) by orders of magnitude owing to gas phase reactions. Molecular interferences generated in the cell can be suppressed by a retarding electric field established by a dc hexapole bias potential of –2 V.
Application of a hexapole collision and reaction cell in ICP-MS Part II: Analytical figures of merit and first applications by I. Feldmann; N. Jakubowski; C. Thomas; D. Stuewer (pp. 422-428).
The application of an ion-guiding gas-filled hexapole collision/reaction cell in ICP-MS has been studied to characterize the analytical figures of merit that can be achieved with this approach. For the elements investigated, application of a buffer and a reaction gas resulted in improved sensitivities which are lowest for Be with about 7 · 107 cps per μg mL–1 and highest for Ba with about ¶6 · 108 cps per μg mL–1. Relative standard deviations (RSD) < 0.1% were obtained. Application of the reaction gas H2 was used to suppress polyatomic ions caused by argon. The reduction amounted up to four orders of magnitude so that elements such as Ca, K, Cr, Fe, As and Se could be analyzed in nitric and hydrochloric acid or in methanol. Detection limits of 6 pg mL–1 for Cr in 2% methanol, 23 pg mL–1 for As and 9 pg mL–1 for Se in 0.28 M HCl were achieved. For other elements detection limits ¶< 1 pg mL–1 were realized in the medium and high mass range. Accuracy was proved using the NIST 1643d standard reference material.
Determination of trace elements in geological samples by laser ablation inductively coupled plasma mass spectrometry by J. S. Becker; H.-J. Dietze (pp. 429-434).
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for the sensitive multi-element analysis of traces and ultra-traces in geological samples. In order to prepare homogeneous targets the powdered geological samples were melted together with a lithium-borate mixture (90% Li2B4O7, 10% LiBO2) in a muffle furnace at 1050 °C. The quantification of the analysis results was carried out using the BCR-2G and BM standard reference material (SRM). The experimentally determined relative sensitivity coefficients (RSC) for both SRMs vary between 0.2 and 3 for most of the elements, whereas the relative standard deviation (RSD) of the determination (N = 3) of the concentration was 5–20%. The analysis results of LA-ICP-MS for various geological samples are in agreement with those of other methods.
Comparison of different flow-through adsorptive stripping voltammetric methods for the determination of molybdenum(VI) by Sylvia Sander (pp. 435-443).
Four different complexing reagents namely chloranilic acid, oxine, tropolone, and cupferron were applied for AdSV determinations of molybdenum. The parameters for the determination using a flow-through cell with a hanging mercury drop (HMDE) as working electrode were examined systematically for all four systems and evaluated. Cyclic voltammograms were recorded to examine the electrode reaction, alternating current (AC) voltammetry was used to determine adsorption processes. The comparison includes sensitivity, detection limit, linear concentration range, the susceptibility to interference by organic compounds or foreign ions, and the applicability to sea and tap water samples. The interpretation of the electrode reaction mechanism for the reduction of the Mo cupferron complex published from Jiao et al. [10] was improved.
Determination of the antibacterial drug sulfamethoxazole in pharmaceutical preparations containing trimethoprim by spectrofluorimetry after derivatization with fluorescamine by C. Cruces-Blanco; A. Segura Carretero; S. Fernández Peinado; M. Román Ceba; A. Fernández Gutiérrez (pp. 444-447).
An analytical method was developed for the determination of sulfamethoxazole (SMZ) in the presence of trimethoprim (TMP) by normal fluorescence. When both analytes are present a selective derivatization with fluorescamine of SMZ gives an intense fluorescent derivative with no interference from the other compound. The reaction was optimized to obtain the best analytical performance. The detection limit and the lower limit of quantitation of SMZ in the reaction medium was 5.2 ng/mL. The intra-day precision (relative standard deviation) was 1.51% for a 100 ng/mL SMZ standard solution and the inter-day precision over 7 days for a 100 ng/mL solution in the presence of 20 ng/mL TMP solution was 2.5%. The method has been applied to three pharmaceutical preparations containing both compounds, without any separation steps required.
Measurement of the peroxidation of Brji-35 in aqueous solution by hemin and horseradish peroxidase catalyzed fluorogenic reaction by J.-Y. Liu; Y.-Z. Li; W.-B. Chang (pp. 448-451).
The non-ionic surfactant Brij-35 can easily be oxidized in solution by dissolved oxygen upon light radiation during its storage. Various factors, such as light radiation, temperature, pH, ionic strength as well as dissolved oxygen influencing the stability of Brij-35 were studied. The results showed that light radiation is the most important factor inducing the oxidation by the dissolved oxygen. The oxidized product was confirmed, indirectly, to be the peroxide of Brij-35 based on a number of evidences. The extent of the oxidation can be traced by a peroxidase or hemin catalyzed fluorogenic reaction with p-hydroxyphenylacetic acid as a substrate. The concentration of the peroxide in a Brij-35 solution (0.8%, w/v) stored at room temperature for a month is in the range of 9 × 10–5 mol/L.
Detection of Escherichia coli O157:H7 DNA using two fluorescence polarization methods by Bang-Ce Ye; K. Ikebukuro; I. Karube (pp. 452-457).
Using stx 2 gene in verotoxin-producing Escherichia coli O157:H7 as a target DNA, polymerase chain reaction (PCR) amplification has been combined with fluorescence polarization (FP) by two distinct combination protocols. The first approach (PCR-probe-FP) requires that fluorescence labeled specific probes are hybridized with the asymmetric PCR product. In the second protocol (PCR-primer-FP), the fluorescence labeled primer is used in PCR amplification. In both methods, the PCR products are detected using fluorescence polarization. Hybridization (in the PCR-probe-FP method) and conversion (in the PCR-primer-FP method) of 5′-fluorescence labeled oligodeoxynucleotide to the PCR product are monitored by an increase in the anisotropy ratio. The results demonstrate the importance of asymmetric PCR (in the first method) and the selection of dye-modified primer concentration (in the second method) for designing a polarization strategy for the detection of DNA sequence. It has been found that the methods can be used for the identification of infectious agents. This system has also been applied to the determination of Escherichia coli O157:H7 strains.
Determination of chlorophenols in urine of children and suggestion of reference values by P. Bartels; E. Ebeling; B. Krämer; H. Kruse; N. Osius; K. Vowinkel; O. Wassermann; J. Witten; C. Zorn (pp. 458-464).
During the course of a human biomonitoring project (Biebesheim in Hessen, Germany) we elaborated a simple but sensitive method for the determination of tri- (TCP), tetra- (TeCP) and pentachlorophenol (PCP) in human urine. Urine samples, spiked with internal standards, were treated by acid hydrolysis. After a steam bath distillation the distillates were extracted using solid phase extraction. Derivatization of the chlorophenols was not carried out. GC/ECD system was used for detection. Detection limits of the chlorophenols were found in the range of 0.02 μg/L urine (detection limits of the ECD: 0.52 to 2.76 μg/L). By this method mono- and dichlorophenols cannot be detected. We investigated 24h-urine samples of 339 pupils (age 10 to 12 years). The children live either in the surroundings of a hazardous waste incinerator (SVA) in Biebesheim (n = 193), or controls (i.e. regions without waste incinerator) in the non polluted areas of Odenwald (n = 90) and Rheintal (n = 56). Between these three groups we did not find statistically significant differences in chlorophenol concentrations of the urine samples. The 95-percentiles of the analyzed samples are 0.74 μg/L (2,3,4-TCP), 1.24 μg/L (2,3,5-TCP), 0.70 μg/L (2,3,6–TCP), 1.10 μg/L (2,4,5–TCP), 1.74 μg/L (2,4,6–TCP), 2.84 μg/L (3,4,5–TCP), 4.78 μg/L (2,3,4,5-TeCP), 1.86 μg/L (2,3,4,6-TeCP), 2.90 μg/L (2,3,5,6-TeCP) and 4.39 μg/L (PCP).
The reaction of thiourea to dicyandiamidine sulfate on silver surfaces investigated by reflection-absorption infrared spectroscopy by D. G. Kurth (pp. 465-466).
The reaction pathway of thiourea degradation on silver surfaces was investigated with reflection-absorption infrared spectroscopy. Adsorption of thiourea from aqueous solution produces a thin stable thiourea film that is not removed by rinsing. Aging at elevated temperature results in conversion to dicyandiamidine sulfate. The same reaction product is observed on daguerreotypes that were treated with commercial thiourea based silver cleaner.
A simple and rapid visual method for the determination of ammonia nitrogen in environmental waters using thymol by M. Okumura; K. Fujinaga; Y. Seike; S. Honda (pp. 467-469).
Simple visual and spectrophotometric methods for the determination of ammonia nitrogen in water are proposed, based on the color development of indothymol blue formed between ammonia and thymol. The color development was accelerated by nitroprusside to complete in 3 min. This color development is remarkably rapid compared with that of the other conventional methods with indothymol blue and indophenol blue. The concentration range of ammonia nitrogen spectrophotometrically determined was 0.04–1.2 mg/L NH4-N. The absorbance per 1 μg NH4-N was 0.0215 (molar absorptivity = 1.51 × 104) at 690 nm. The visual method not using any instrument as an in situ method in field works was developed based on the optimum conditions for the established spectrophotometric method. This visual method was successfully applied to the determination of ammonia nitrogen in environmental waters.
Separation and preconcentration of Se(IV)/Se(VI) speciation on algae and determination by graphite furnace atomic absorption spectrometry in sediment and water by Li Shunxin; Qian Shahua; Huang Ganquan; He Fei (pp. 469-471).
A novel method for the separation and preconcentration of Se(IV)/ Se(VI) with algae and determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. The Se(VI) is extracted with algae from the solution containing Se(IV)/Se(VI) at pH 5.0, and the remaining Se(IV) is then preconcentrated pH 1.0. The detection limits (3σ, n = 11) of 0.16 μg L–1 for Se(IV) and 0.14 μg L–1 for Se(VI) are obtained using 40 mL of solution. At the 2.0 μg L–1 level the relative standard deviation is 2.6% for Se(IV) and 2.3% for Se(VI). The method has been applied to the determination of Se(IV)/Se(VI) in sediment and water samples. Analytical recoveries of Se(IV) and Se(VI) added to samples are ¶97 ± 5% and 102 ± 6% (95% confidence), respectively.
Ultrasonic/Soxhlet/supercritical fluid extraction kinetics of pyrethrins from flowers and allethrin from paper strips by A. Otterbach; B. W. Wenclawiak (pp. 472-474).
Three different extraction methods (ultrasonic extraction (USE), Soxhlet extraction (SOX) and supercritical fluid extraction (SFE)) were compared for the extraction of pyrethrins from chrysanthemic flowers and commercial insecticide powder. Allethrin was extracted from paper strips. All extracts and the kinetics were analyzed by supercritical fluid chromatography and flame ionization detector.