Petr Gebauer

Electromembrane extraction of heavy metal cations followed by capillary electrophoresis with capacitively coupled contactless conductivity detection

Electromembrane extraction (EME) was used as an off‐line sample pre‐treatment method for the determination of heavy metal cations in aqueous samples using CE with capacitively coupled contactless conductivity detection (CE‐C4D). A short segment of porous polypropylene hollow fibre was penetrated with 1‐octanol and 0.5% v/v bis(2‐ethylhexyl)phosphonic acid and constituted a low cost, single use, disposable supported liquid membrane, which selectively transported and pre‐concentrated heavy metal cations into the fibre lumen filled with 100 mM acetic acid acceptor solution. Donor solutions were standard solutions and real samples dissolved in deionized water at neutral pH. At optimized EME conditions (penetration time, 5 s; applied voltage, 75 V; and stirring rate, 750 rpm), 15–42% recoveries of heavy metal cations were achieved for a 5 min extraction time. Repeatability of the EME pre‐treatment was examined for six independent EME runs and ranged from 6.6 to 11.1%. Limits of detection for the EME‐CE‐C4D method ranged from 25 to 200 nM, resulting into one to two orders of magnitude improvement compared with CE‐C4D without sample treatment. The developed EME sample pre‐treatment procedure was applied to the analysis of heavy metal cations in tap water and powdered milk samples. Zinc in the real samples was identified and quantified in a background electrolyte solution consisting of 20 mM L‐histidine and 30 mM acetic acid at pH 4.95 in about 3 min.

On-line isotachophoresis–capillary zone electrophoresis versus sample self stacking capillary zone electrophoresis: Analysis of hippurate in serum

Abstract This paper is aimed at the problem of sensitive analysis of a microcomponent in a sample with a bulk macrocomponent and complex matrix by capillary electrophoresis. In such samples, the simple way to increase the sensitivity by increasing the injected sample volume is counterworked by the stacking–destacking processes due to the presence of transient isotachophoresis (ITP) and a certain maximum sample load exists which gives useful results. The important analytical task of the analysis of hippuric acid (benzoyl glycine) was selected as the model problem. The aim was to reach the highest possible sensitivity in the analysis of hippuric acid in serum of healthy persons where hippuric acid represented a microcomponent and serum was a representative of a sample matrix containing varying amounts of macrocomponents. In order to find the maximum allowable sample load (volume) that enabled maximum sensitivity, various stacking techniques in two types of instrumentation for capillary zone electrophoresis (CZE) and a commercially available instrumentation for the on-line ITP–CZE combination were compared. The systems for CZE differed in detectors and in using an open or closed capillary of different diameter and material, which resulted in different sensitivity of the analyses of model samples. In analyses of serum samples, however, comparable limits of detection were obtained using both a single ITP and CZE with the open or closed capillary (6·10−5 M hippurate). A limit of detection two-orders of magnitude lower (7·10−7 M hippurate) was reached in the instrumentation for the ITP–CZE combination even though the parameters of the capillary and the detector that were available for the CZE step were substantially worse than those of the open CZE system that was used.

Recent progress in capillary isotachophoresis.

This article is a continuation of previous reviews and summarizes the progress of analytical capillary isotachophoresis since 2000. Papers reviewed include methodological and instrumental aspects as well as analytical applications. Included are also papers using isotachophoresis and/or isotachophoretic principles as part of multidimensional separation schemes.

Contemporary sample stacking in analytical electrophoresis.

Sample stacking is of vital importance for analytical CE since it may bring the required sensitivity of analyses. A lot of new relevant papers are published every year and regular surveys seem to be very helpful for experts and practitioners. The contribution presented here is a continuation of a series of regularly published reviews on the topic and covers the last two years. It brings a survey of related literature organized, in accord with the main principle used in the procedure published, in the following mainstream sections: Kohlrausch adjustment of concentrations, pH step, micellar systems and combined techniques. Each part covers literature sorted according to the field of application as, e.g. clinical, pharmaceutical, food, environmental, etc.

Recent progress in analytical capillary isotachophoresis.

Capillary ITP is currently used as one of the most important tools for preseparation and preconcentration of trace analytes in complex or diluted samples. This contribution is a continuation of a series of regularly published reviews on the topic and covers the last 2 years. It brings a survey of related literature organized into following sections: theory and methodology, instrumentation and techniques, and applications.

Some practical aspects of utilizing the on-line combination of isotachophoresis and capillary zone electrophoresis

The on-line combination of isotachophoresis (ITP) and zone electrophoresis is a very effective tool for increasing the separation capability and sensitivity of capillary zone electrophoresis (CZE). Its most effective version is performed in column coupling instrumentation and is characterized by isotachophoresis in the first capillary serving as the efficient preseparation and concentration stage followed by on-line transfer of the sample cut into the second capillary where analytical zone electrophoresis proceeds as the second stage. The on-line transfer of the sample from the first capillary into the second is always accompanied by the segments of some additional amounts of the leader and/or terminator from the ITP step. This results in transient survival of isotachophoretic migration during the second stage. Hence the separation process during the second stage can be characterized as the destacking of analytes followed by zone electrophoretic separation. In this paper, both a theoretical and an experimental study is presented showing that destacking of analytes is a selective process, which affects strongly the most important final analytical parameters of the detected zones, namely the detection time and zone variance, and thus it makes the simple use of detection data for qualitative analysis misleading. It was shown that both the detection time and variance of a zone of an analyte depend strongly on the amount of the accompanying segments of the leader/terminator transferred and on the actual type of electrolyte system selected from the generally possible types. These types are (i) L-S-L, where the leading electrolyte (L) from ITP stage serves as the background electrolyte (BGE) during CZE (S = sample), (ii) T-S-T, where the terminating electrolyte (T) from the ITP stage serves as the BGE during CZE, and (iii) BGE-S-BGE, where L, T and BGE are mutually different. Explicit equations were derived enabling one to predict migration time and zone variance for actual working conditions, and, for model systems, the theoretical data were calculated and verified experimentally. Further, it is shown that the systems T-S-T and L-S-L are user friendly and a simple standardization procedure was proposed, allowing correct qualitative evaluation of the analytical data in these systems. Finally, a theory is presented predicting the existence of anomalous variances of zones in the record of analysis in BGE-S-BGE systems and its experimental verification is given.

Sample self‐stacking in capillary zone electrophoresis: Behavior of samples containing multiple major coionic components*

It is a frequent phenomenon in practice that a sample contains bulk levels of more than one coionic component that affect the stacking behavior of minor analytes and in this way also the sensitivity of the method. Here, attention is paid to stacking resulting from the presence of a macrocomponent of leading type that is deteriorated by the presence of another macrocomponent of like charge in the sample. Based on the isotachophoretic model of migration in the initial period of separation, a theoretical approach was elaborated both for strong and weak electrolytes which describes the separation process and finds the conditions that define whether transient isotachophoretic stacking of the analyte takes place or not. It is shown that the crucial parameter is the ratio of the concentrations of macrocomponents migrating in front and behind the analyte of interest. The destacking effect can also be expected when the coion of the background electrolyte is present in the sample. Rules how to cope with effects of destackers present in the sample are given. Theoretical considerations are illustrated by computer simulations and verified experimentally. Examples of antagonistic effects of macrocomponents are demonstrated for model serum samples.

Recent advances in CE-MS: Synergy of wet chemistry and instrumentation innovations.

CE with MS detection is a hyphenated technique which greatly improves the ability of CE to deal with real samples, especially with those coming from biology and medicine, where the target analytes are present as trace amounts in very complex matrices. CE‐MS is now almost a routine technique performed on commercially available instruments. It faces currently a tremendous development of the technique itself as well as of its wide application area. Great interest in CE‐MS is reflected in the scientific literature by many original research articles and also by numerous reviews. The review presented here has a general scope and belongs to a series of regularly published reviews on the topic. It covers the literature from the last 2 years, since January 2008 till June 2010. It brings a critical selection of related literature sorted into groups reflecting the main topics of actual scientific interest: (i) innovations in CE‐ESI‐MS, (ii) use of alternative interfaces, and (iii) ways to enhance sensitivity. Special attention is paid to novel electrolyte systems amenable to CE‐MS including nonvolatile BGEs, to advanced CE separation principles such as MEKC, MEEKC, chiral CE, and to the use of preconcentration techniques.

System peaks in capillary zone electrophoresis: I. Simple model of vacancy electrophoresis

The paper introduces the concept of vacancy electrophoresis where instead of normal electrophoretic zones, system peaks (concentration vacancies) migrate and are separated. The electrolyte set-up to achieve this requires a reversal of background electrolyte and sample with the capillary filled by the sample and the background electrolyte injected instead. A simple theory of electromigrational zone dispersion is used to describe the origin and properties of a system peak corresponding to a concentration vacancy. Model experiments confirm the theoretical considerations. The potential practical use of vacancy electrophoresis is discussed.

Recent progress in analytical capillary ITP

ITP is an electrophoretic technique that has been attracting constant attention for many years due to its pronounced capability to concentrate trace analytes by several orders of magnitude. In practice, it is used predominantly in capillary format, where the capillaries used have id ranging between 0.02 and 0.8 mm. The volumes of the samples introduced may be up to several tens of microliters and trace analytes diluted in such a volume are concentrated into zones having volumes in the range of picoliters. Moreover, it offers simultaneously efficient separation of the analytes. That is why ITP retains its important position in many current multistage and multidimensional separation schemes where it is used always as the starting step that brings preseparation and concentration of sample components. This article links up previous reviews on the topic and summarizes the progress of analytical capillary ITP since 2006; 90 reviewed papers include theory and methodological novelties as well as analytical applications. Papers using ITP as part of multistage separation schemes are also included.