Physico-chemical properties and phase behavior of the ionic liquid-β-cyclodextrin complexes

Electroanalytical performance of a β-cyclodextrin and ionic liquid modified carbon paste electrode for the determination of verapamil in urine and pharmaceutical formulation

The analytical performance of sensitive and cost-effective electrochemical sensors based on ionic liquids (ILs) with the bis(trifluoromethylsulfonyl)imide anion, [NTf2]-, and the imidazolium cation with different alkyl chain lengths for electrochemical oxidation of verapamil (VER) was investigated. 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf2]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf2]) were studied as possible materials for modification of a carbon paste electrode (CPE) for trace-level determination of VER. The experimental parameters including selection of the working electrode, the pH of working media, and the amount of CPE modifiers were investigated. Among them, the [EMIM][NTf2]-CPE with 4.3 wt% of IL was selected as the most appropriate for the square wave voltammetric (SWV) determination of VER at pH 5.0. Cyclic voltammetric studies showed that the electrochemical oxidation of VER was adsorption controlled. Consequently, the square wave adsorptive stripping voltammetric (SW-AdSV) parameters were optimized with Eacc = -0.4 V and tacc = 180 s as the most suitable for accumulation of VER on the electrode surface. The electroanalytical performance of the [EMIM][NTf2]-CPE was further improved by its in situ electrochemical modification with β-cyclodextrin (β-CD) and the linear concentration range of VER was from 0.006 to 0.129 μg mL-1; the relative standard deviation did not exceed 0.7%, and the evaluated limit of detection in model solution was 0.002 μg mL-1. The β-CD/[EMIM][NTf2]-CPE showed adequate selectivity towards VER in the presence of inorganic ions and interferents usually found in human urine. The proposed sensor was successfully applied for VER determination in a spiked human urine sample and pharmaceutical formulation with good repeatability and recovery.

Inverse gas chromatography applications: a review

Inverse gas chromatography (IGC) is a versatile, powerful, sensitive and relatively fast technique for characterizing the physicochemical properties of materials. Due to its applicability in determining surface properties of solids in any form such as films, fibres and powders of both crystalline and amorphous structures, IGC became a popular technique for surface characterization, used extensively soon after its development. One of the most appealing features of IGC that led to its popularity among analytical scientists in early years was its similarity in principle to analytical gas chromatography (GC). The main aspect which distinguishes IGC experiments from conventional GC is the role of mobile and stationary phases. Contrary to conventional GC, the material under investigation is placed in the chromatographic column and a known probe vapour is used to provide information on the surface. In this review, information concerning the history, instrumentation and applications is discussed. Examples of the many experiments developed for IGC method are selected and described. Materials that have been analysed include polymers, pharmaceuticals, minerals, surfactants, and nanomaterials. The properties that can be determined using the IGC technique include enthalpy and entropy of sorption, surface energy (dispersive and specific components), work of co/adhesion, miscibility and solubility parameters, surface heterogeneity, glass transition temperature, and specific surface area.