Mihkel Koel

Ionic Liquids in Chemical Analysis

Room-temperature ionic liquids are salts with a melting point close to or below room temperature. They form liquids composed in the majority of ions. This gives these materials the potential to behave very differently when they are used as solvents compared to conventional molecular liquids. The search for their application is growing in every area of analytical chemistry—electrochemistry, chromatography, electrophoresis, and even mass spectrometry. The literature on ionic liquids is growing almost exponentially. The basis for this activity is the easy preparation of salts with different ion constituents. This ability might best be described as the “chemical tunability” of ionic liquids, a class of solvents with members possessing similar physical properties but having different chemical behavior. Their good solvating properties, together with large spectral transparency, make ionic liquids suitable solvents for spectroscopic measurements. It has been demonstrated that task-specific ionic liquids have adv...

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.

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.

Separation of polyphenolic compounds extracted from plant matrices using capillary electrophoresis.

Phenolic compounds constitute a large group of secondary plant products whose chemical structure may range from quite simple compounds to highly polymerized substances. The polyphenols content have been investigated in the alcoholic extract of the fruits of three different plants: sweet gale, sea buckthorn, hiprose. The trans-resveratrol content we have studied in roots, stems, leaves and flowers of Japanese knotweed grown in Estonia. Plant material was pre-treated in two different ways: by infusing with methanol and by supercritical fluid extraction with carbon dioxide modified with different alcohols. The relationship between variables (pressure, temperature, modifier amount) and yields are examined. The capillary zone electrophoresis methods were developed for the separation of polyphenolic anti-oxidative compounds. Using both water based borate buffer and acetonitrile based non-aqueous media it was possible to get reliable separation of several polyphenolic compounds. Based on that there has been identified such as flavone, trans-resveratrol, catechin, chlorogenic acid, quercetin and myricetin in plant extracts. Changes in the relative concentrations of trans-resveratrol in different parts of the knotweed have been established.

Thermal stability of styrene grafted and sulfonated proton conducting membranes based on poly(vinylidene fluoride)

The thermal stability of styrene grafted and sulfonated poly(vinylidene fluoride), PVDF-g-PSSA, proton conducting membranes has been studied using thermal gravimetric analysis in combination with mass spectrometry and thermochromatography. The matrix polymer, PVDF, and the non-sulfonated counterpart, PVDF-g-PS, were studied as reference materials. It was found that the degradation of the PVDF-g-PS membrane proceeds in two steps starting atca. 340 °C with the evolution of degradation products typical of polystyrene. The PVDF-g-PSSA membranes are stable to around 270 °C even in a strongly oxidising atmosphere. The degradation starts with the simultaneous evolution of water and sulfur dioxide. The polystyrene grafts start decomposing at 340 oC in the PVDF-g-PSSA membranes. Thus the membranes are suitable for tests in electrochemical applications at elevated temperatures.

Micellar electrophoresis using ionic liquids.

In this study, ionic liquid based cationic surfactants were evaluated as pseudo-stationary phases in micellar electrokinetic chromatography (MEKC). The aggregation behaviour of long-chain (C(12) and C(14)) alkylimidazolium ionic liquids in water and aqueous phosphate buffer was investigated by spectrophotometry. The critical micelle concentrations of these salts were determined and compared to those of tetradecyl- and dodecyltrimethylammonium chloride, salts commonly used in capillary electrophoresis. The practical utilization of a new type of surfactant in MEKC was evaluated by introducing an ionic liquid into the running aqueous buffer to separate neutral analytes-methylresorcinol isomers and benzene derivatives.

Analysis of Trace Amounts of Metal Ions Using Silica-Based Chelating Resins: A Green Analytical Method

This review is concerned mainly with the applications of chelating resins, based on silica gel, for the separation and preconcentration of trace metal ions from various substrates. General methods of preparations of silica-based resins have been discussed. A synthesis of various silica-based chelating resins and their applications in the extraction of trace amounts of metal ions have been reviewed critically and have also been reported in tabular form.

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.

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.