Mihkel Kaljurand

Ionic liquids as electrolytes for nonaqueous capillary electrophoresis

Acetonitrile is a well‐suited medium for nonaqueous capillary electroseparations and enables extending the range of applications of capillary electrophoresis (CE) techniques to more hydrophobic species. In this study, the dialkylimidazolium‐based low temperature melting organic salts know as “ionic liquids” (ILs) are used as electrolytes. At room temperature these liquids are miscible with acetonitrile which makes it easy to use them for adjustment of analyte mobility and separation. The anionic part as well as the concentration of an IL influence the general electrophoretic mobility of the buffer system. The separation of different analytes is achieved because they become charged in the presence of ILs in separation media. There is also a possibility for a complex formation between the solute and the electrolyte which alters the mobility of the solute. A selected application of separations of phenols and aromatic acids will be discussed.

Application of 1-alkyl-3-methylimidazolium-based ionic liquids in non-aqueous capillary electrophoresis

In many cases salts, which are liquid at room temperature show a better solubility in organic solvents, and can be used in nonaqueous capillary zone electrophoresis as ionic additives. In this study 1-alkyl-3-methylimidasolium-based ionic liquids were used as additives in separation media to assess the interactions between the analytes and the ionic additive present and to find an influence of the type and concentration of the ionic additive, also the nature of the nonaqueous medium employed. Different organic solvents (acetonitrile and methanol) contribute differently to the conversion of analytes into a charged form. Complexes with either an anionic or a cationic part of the ionic liquid additive were formed. This was the case for electrophoresis separation of Brønsted acids and polyphenolic compounds.

Capillary Electrophoresis Time-of-Flight Mass Spectrometry for Comparative Metabolomics of Transgenic versus Conventional Maize

In this work, capillary electrophoresis time-of-flight mass spectrometry (CE-TOF-MS) is proposed to identify and quantify the main metabolites in three lines of genetically modified (GM) maize and their corresponding nontransgenic parental lines grown under identical conditions. The shotgun-like approach for metabolomics developed in this work includes optimization of metabolite extraction from GM and non-GM maize, separation by CE, online electrospray-TOF-MS analysis, and data evaluation. A large number of extraction procedures and background electrolytes are tested in order to obtain a highly reproducible and informative metabolomic profile. Thus, using this approach, significant differences were systematically observed between the detected amounts of some metabolites in conventional varieties (Aristis, Tietar, and PR33P66 maize) compared with their corresponding transgenic lines (Aristis Bt, Tietar Bt, and PR33P66 Bt maize). Results point to some of these metabolites as possible biomarkers of transgenic Bt maize, although a larger number of samples needs to be analyzed in order to validate this point. It is concluded that metabolomics procedures based on CE-TOF-MS can open new perspectives in the study of transgenic organisms in order to corroborate (or not) their substantial equivalence with their conventional counterparts.

Application of the principles of green chemistry in analytical chemistry

The introduction of the dimension of green chemistry into the assessment of analytical methods should be a natural development trend in chemistry and should coincide with its general policy. Some of the principles of green chemistry - such as prevention of waste generation; safer solvents and auxiliaries; design for energy efficiency; safer chemistry to minimize the potential of chemical accidents; development of instrumental methods - are directly related to analytical chemistry. Analytical chemistry is considered to be a small-scale activity, but this is not always true in the case of controlling and monitoring laboratories whose number of runs performed is high. This makes an analytical laboratory comparable with the fine chemicals or pharmaceutical industry. The use of instrumental methods instead of wet chemistry, automation, and minimization is a new trend in analytical chemistry, making this branch of chemistry more sustainable. In this study, widespread separation methods are considered and an attempt is made to characterize them against the above-mentioned principles. Special attention is given to capillary electrophoresis (CE), which provides a very good opportunity to improve analytical chemistry by replacing many chromatographic methods that consume large volumes of solvents. The choice of different solvents and micronization in analytical chemistry is also discussed.

Capillary electrophoretic analysis of neutral carbohydrates using ionic liquids as background electrolytes

In this study, ionic liquids (ILs) as BGE additives were applied for the analysis of neutral carbohydrates in CE. The ILs served primarily as chromophores for indirect UV detection. The influence of imidazolium‐based ionic liquids on the separation, detection limits and mobility of underivatized neutral carbohydrates was investigated. BGEs consisting of 10–50 mM of ILs at pH 12.4 without other additives provided fast separation of neutral sugars. This method was used to determine sucrose, glucose and fructose in certain vegetable juices.

Evaluation of antioxidative capability of the tomato (Solanum lycopersicum) skin constituents by capillary electrophoresis and high-performance liquid chromatography.

In the current study, phenolic compounds of the tomato (Solanum lycopersicum) skin extract were separated and their composition was determined by capillary electrophoresis and tandem high‐performance liquid chromatography diode array detection‐mass spectrometry (HPLC‐DAD‐MS/MS). Both the total phenolic and flavonoid contents of the extract were determined. The antioxidative capability of the extract was measured using a stable free radical 2,2‐diphenyl‐1‐picrylhydrazyl assay. The monitoring of the radical scavenging capability of specific phenolic compounds was carried out both by capillary electrophoresis and HPLC‐MS/MS.

A portable capillary electropherograph equipped with a cross-sampler and a contactless-conductivity detector for the detection of the degradation products of chemical warfare agents in soil extracts

A fully portable CE device equipped with a capacitively coupled contactless‐conductivity detector and a cross‐injection device is put to the test in laboratory conditions. The portable device is capable of working on batteries for at least 4 h. After that, its performance is strongly affected by the drop in the high‐voltage output and analysis may be interrupted if its length exceeds a reasonable time. The concentration of the BGE affects both ionic strength and conductivity. Choosing an optimal concentration of BGE is therefore about finding a good compromise between selectivity and sensitivity. All experiments were performed using a mixture of histidine and MES with a concentration of 15 mM as BGE. The performance of the cross‐injection device is optimized by the use of internal standards. Satisfactory reproducibility is gained as the RSD of peak areas is reduced to 8% or less. LODs for different phosphonic acids are in the range of 2.5–9.7 μM. For the analysis of adsorption of phosphonic acids in sand and loamy soil samples, calibration curves are constructed. Linearity in a measured concentration range of 10–100 μM is excellent, as the squares of correlation constants are ∼1. The concentration analysis of phosphonic acids in soil extracts demonstrates that their adsorption curves in sand and loamy soil follow different adsorption isotherms.

Analysis of the stable free radical scavenging capability of artificial polyphenol mixtures and plant extracts by capillary electrophoresis and liquid chromatography–diode array detection–tandem mass spectrometry

The oxidation process of phenolic compounds of an artificial mixture consisting of six polyphenols and the extract of eggplant (Solanum melongena) skin was monitored by using capillary zone electrophoresis and liquid chromatography-diode array detection-tandem mass spectrometry. The methods developed enabled simultaneous evaluation of the antioxidative capability of each compound. The above oxidation process was carried out using two radicals, viz. the 2,2-diphenyl-1-picrylhydrazyl and hydroxyl radicals generated via the Fenton reaction. The radical scavenging effects of artificial and natural polyphenol mixtures were compared.

Recent Advancements on Greening Analytical Separation

60–80% of the analysis time for a significant number of analytical methods is taken up by the preparation, treatment, and separation of individual sample components, and most of the chemicals and solvents involved in the analysis are consumed in this step. We will demonstrate that many emerging methods of analytical separation science can meet the requirements of green chemistry by reducing the use of solvents and other reagents, lowering energy consumption by increasing the speed of analysis, and by miniaturizing and making equipment portable. Although recent efforts to make high performance liquid chromatography greener are praiseworthy, capillary electrophoresis, which comprises a group of separation methods that use narrow-bore fused-silica capillaries, is especially promising. It is highly competitive with liquid chromatography, which is the biggest consumer of organic solvents in analytical chemistry. However, capillary electrophoresis has not received the recognition it deserves as a green separation method that consumes microscopic volumes of solvent. It is a technique that is sufficiently mature to promote the greening of analytical chemistry via miniaturization—the most auspicious development in contemporary analytical chemistry. In this review, we will discuss recent developments in greening chromatography, and demonstrate the potential of electrophoresis and microfluidics in this regard.

Capillary electrophoresis with LED-induced native fluorescence detection for determination of isoquinoline alkaloids and their cytotoxicity in extracts of Chelidonium majus L.

In this study, we introduced a simple and sensitive method of capillary electrophoresis with ultraviolet light-emitting diode-induced native fluorescence (UV-LEDIF) detection for the determination of isoquinoline alkaloids in extracts of Chelidonium majus L. Samples were extracted with acidic methanol and the extracts were directly analysed by CE. Simultaneous determination of protopine, chelidonine, coptisine, sanguinarine, allocryptopine, chelerythrine and stylopine was performed in 20mM phosphate buffer (pH 3.1). The baseline separation of these alkaloids was finished within 20 min. As these alkaloids have native fluorescence, they were directly detected using the commercially available UV light emitting diode without troublesome fluorescent derivatisation. Satisfactory LOD values were obtained for the studied compounds considering their appearance in natural extracts. Lower limits of detection were 0.05 μg/mL for protopine, 0.06 μg/mL for stylopine and allocryptopine, 0.07 μg/mL for chelidonine, 0.22 μg/mL for sanguinarine, 1.7 μg/mL for chelerythrine and 5.5 μg/mL for coptisine. The developed method was successfully applied to determine the contents of seven alkaloids in the aerial parts of Chelidonium majus L, which varied from 0.025 to 0.763% (w/w). Also, to demonstrate the potential of the proposed CE method, an estimation of the cytotoxic properties of selected Celandine alkaloids in a natural extract was carried out.