Ewa Poboży

Determination of triorganotin compounds by ion chromatography and capillary electrophoresis with preconcentration using solid-phase extraction

Procedures for the determination of triorganotins using HPLC with a cation-exchange column and capillary electrophoresis (CE) were optimized. In both cases indirect UV detection for trimethyl-, triethyl- and tributyltin and direct UV sensing of triphenyltin were applied. In CE the best separation of tributyl- and triphenyltin was obtained with the use of tartaric acid in the electrolyte. With both procedures a comparable analysis time was found, whereas a better separation of analytes and much lower detection limits were obtained for CE determination. Among five different commercial non-polar sorbents examined for solid-phase extraction of TBT and TPT, the best results were obtained with XAD-2.

On-Line Coupling of Solid Phase Extraction Sample Processing with High-Performance Liquid Chromatography

The development of hyphenated measuring systems is one of the predominant trends in modern analytical chemistry. Special coupling of a flow sample pretreatment methods to other instrumentation may lead to a substational progress in many types of analysis. High-performance liquid chromatography is a mature technique commonly used in routine analysis. However, despite the performance of modern chromatographic systems, sample preparation is still the most tedious and time-consuming step. In the determination of traces of the analytes, especially in biological fluids, macromolecular compounds (e.g., proteins) have to be removed from a sample prior to HPLC analysis, because they could precipitate by the large amounts of organic solvents. Nonspecific or irreversible bounding on the surface of the chromatographic support could also occur, resulting in a limited lifetime of the column. Moreover, because analyte concentration is usually low, some kind of preconcentration and/or derivatization is often required to improve analyte detectability. Solid-phase extraction (SPE) is an attractive approach to the preparation of environmental, food, and biological samples because it involves high enrichment factor, lower consumption of organic solvents, and better reproducibility than liquid-liquid extraction techniques. In addition, SPE could be performed on-line by direct connection to the chromatographic system; therefore, a fully automated technique could be utilized. Hyphenated on-line SPE-HPLC systems are designed to improve not only sensitivity and selectivity of determination but also the precision due to lower human participation. Thus, they represents a fast, modern, and reliable approach to trace analysis. This article reports the application of several SPE systems for automated preparation of environmental, food, and biological samples prior to chromatographic analysis. New selective phases such as restricted access matrix, molecularly imprinted polymers, and immunosorbents are described. The review concludes with a selected list of recent applications.

Flow-injection sample preconcentration for ion-pair chromatography of trace metals in waters

Selected trace transition metal ions have been determined in an FIA/HPLC hyphenated system using on-line preconcentration on cellulose functionalised sorbent Cellex P. For HPLC separation ion-pair chromatography was employed with spectrophotometric detection at 510 nm using post-column derivatisation with PAR. Favourable kinetic conditions of sorption and elution as well as optimisation of hyphenated system allowed to obtain detection limits at sub-microgL(-1) level at 25 min preconcentration time. The developed method was employed for determination of Co(II), Ni(II), Cd(II) and Mn(II) in river water with reasonable agreement of obtained results with electrothermal AAS determination.

Direct and replacement ion chromatography with potentiometric detection using a silver/silver bromide electrode

Abstract The use of Ag/AgX electrodes as potentiometric detectors in modern ion chromatography methods is re-examined. Contrary to previous reports, in both flow-injection and chromatographic experiments the Ag/AgBr electrode is shown to exhibit the greatest sensitivity to the widest range of anions tested. For direct detection in non-suppressed ion chromatography systems, use of the Ag/AgBr electrode permits the measurement of separated anions at levels lower than those obtainable by the conventional conductivity method. The Ag/AgBr electrode is further shown to be useful as a sensitive detector in replacement ion chromatography. In this case, all anions separated in a suppressed system are quantitatively replaced by bromide before the effluent passes through the electrochemical detector. Cation measurements can also be made by monitoring the exchange of bromide for co-eluting counter hydroxide ions following the replacement stage of the system.

Speciation of chromium by ion-pair chromatography with postcolumn spectrophotometric detection

Abstract High performance ion-pair chromatographic method of Cr(III) and Cr(VI) separation using phosphate buffer containing tetrabutylammonium bromide as eluent was developed. Post column derivatization based on Cr(VI) reaction with diphenylcarbazide and spectrophotometry monitoring of eluate at 560 nm was employed with Cr(III) oxidation to Cr(VI) using cerium(IV) sulphate. Detection limit was estimated as 7 ng/ml Cr(IIl) and 13 ng/ml Cr(VI).

Capillary electrophoretic determination of inorganic selenium species

The performance of pyromellitic electrolyte for capillary zone electrophoresis of inorganic selenium species in the presence of selected common anions with indirect UV detection was investigated. The separation was achieved with pyromellitic electrolyte at pH 8.8 and hexamethonium hydroxide as the electroosmotic flow modifier. Obtained detection limits of 0.17 microg ml(-1) for Se(VI) and 0.29 microg ml(-1) for Se(IV) were improved by a factor of 5-7 in comparison with chromate electrolyte, which has been mainly employed for selenium analysis. Good resolution for nitrate-Se(VI) peaks were obtained.

Comparison of three modifications of fused-silica capillaries and untreated capillaries for protein profiling of maize extracts by capillary electrophoresis.

In this work, capillary electrophoresis was applied to protein profiling of fractionated extracts of maize. A comparative study on the application of uncoated fused-silica capillaries and capillaries modified with hydroxypropylmethylcellulose, ω-iodoalkylammonium salt and a commercially available neutral capillary covalently coated with polyacrylamide is presented. The coating stability, background electrolyte composition, and separation efficiency were investigated. It was found that for zeins separation, the most stable and efficient was the capillary coated with polyacrylamide. Finally, the usefulness of these methods was studied for the differentiation of zein fraction in transgenic and nontransgenic maize. Zeins extracted from maize standards containing 0 and 5% m/m genetic modification were successfully separated, but slight differences were observed in terms of the zein content. Albumin and globulin fractions were analyzed with the use of unmodified fused-silica capillary with borate buffer pH 9 and the capillary coated with polyacrylamide with phosphate buffer pH 3. In the albumin fraction, additional peaks were found in genetically modified samples.

Flow-injection preconcentration of chloramphenicol using molecularly imprinted polymer for HPLC determination in environmental samples.

The residue of antibiotic chloramphenicol (CAP) is important issue for food quality control and also for the environmental monitoring. It is banned for use in food-producing animals and has very limited use in human medicine, because of its severe impact on human health. Determination of trace level of CAP in environmental samples requires a very sensitive analytical method and efficient preconcentration procedure. CAP can be efficiently preconcentrated in flow-injection system using flow-through reactor packed with molecularly imprinted polymer (MIP), but determination of CAP in eluate from MIP requires the application of chromatographic separation, which was made in reversed-phase HPLC system with UV detection. In optimized conditions the limit of detection for 100 mL sample in HPLC with offline preconcentration on MIP was evaluated as 0.66 mg/L. In hyphenated FIA-HPLC system with zone sampling the LOD for developed method was evaluated as 15 ng/L, which indicates the possibility of using it for analysis of environmental samples.

Enzymatic in‐capillary derivatization for glucose determination by electrophoresis with spectrophotometric detection

The following paper compares several procedures of in‐capillary bienzymatic derivatization with regard to glucose determination with the use of glucose oxidase and horseradish peroxidase. The procedures discussed below include continous contact in the capillary, plug–plug injection, and sequential injection with incubation in the capillary inlet. The reaction of hydrogen peroxide catalyzed by peroxidase was performed using two different substrates. The best results were achieved for nicotinamide adenine dinucleotide, reduced disodium salt (NADH) acting both as a chromogenic reagent and a substrate for peroxidase, while the method employed was sequential injection and incubation at the capillary inlet. The LOD was estimated to be 25 nM with a linear response up to 0.1 μM.

Selective determination of sulphide based on photoluminescence quenching of MPA-capped CdTe nanocrystals by exploiting a gas-diffusion multi-pumping flow method

In this study an automated flow-based methodology for the fluorometric determination of sulphide was reported. It relies on the utilization of CdTe nanocrystals as photoluminescent probes, which upon reaction with S2− are subject to a noteworthy concentration-related photoluminescence decrease. For lower S2− concentrations the photoluminescence quenching was based on dynamic processes while for higher concentrations the quenching mechanism was ascribed to the depassivation of the surface ligands, replaced by S2−, resulting in the aggregation of QDs. The developed approach was automated by resorting to a pulsed stream multi-pumping flow system guaranteeing a high versatility in terms of sample and reagent manipulation and reaction zone formation. The selectivity was ensured by means of the utilization of a gas-diffusion unit relying on a hydrophobic PTFE membrane that facilitated sulphide isolation from sample matrix interferences. Under optimal conditions, a good linear relationship between the photoluminescence quenching magnitude (ΔF) and the logarithmic of the S2− concentration within the range of 0.25–5.0 mmol L−1 were verified (R = 0.998, n = 5). The limit of detection (LOD) was found to be 0.19 mmol L−1. The sampling rate was of about 13 h−1.