Vol 74, No 5 (2019)

Hydrophilic interaction liquid chromatography (HILIC), which includes the distribution, adsorption, ion exchange, and exclusion of analytes, has gained active development recently. The review covers the principles of the method, types of stationary and mobile phases, mechanisms of retention of highly polar compounds under HILIC conditions, implementation of 2D chromatography, and also fields of application of the method. Keywords: hydrophilic chromatography, retention mechanism, reverse phase HPLC, normal phase mode, HILIC stationary phases, zwitterionic phases, high polar analytes

A cloud point extraction method has been developed for preconcentration of Cu²⁺ ions. Tergitol 15-s-7 and Tergitol 15-s-9 are nonionic surfactants used to form micellar media. Taguchi method was used to optimize cloud point extraction conditions. Effects of foreign ions on the analyte recovery were also examined. Certified reference material (CRM 1640a) was used to demonstrate accuracy of results. All results showed a good agreement with the certified values. The proposed method was successfully applied for separation and preconcentration of Cu²⁺ ions from river water samples. The detection limits obtained were 10 and 14 ng/mL in case of using Tergitol 15-s-7 and Tergitol 15-s-9, respectively.

To assess a possibility of the measurement of the relative concentration of main gasoline components under varied conditions, we studied the absorption of electromagnetic radiation by these components in the mid-IR region. The results for the absorbance of gasoline with varying concentrations of components, obtained using Fourier-transform IR spectroscopy are presented. The use of multidimensional difference spectra of gasoline is the most effective and informative way to perform measurements. The high sensitivity of the difference spectra to changes in the composition and concentrations of the main gasoline components is demonstrated.

A simple, sensitive, rapid, precise and accurate method has been developed for simultaneous estimation of tazarotene and hydroquinone in their pharmaceutical dosage form (gel preparation). The chromatographic separation was carried out on a reversed-phase Inertsil C18 (4.6 mm I.D. × 250 mm, 5 μm) column using a mobile phase consisting of 0.02 M KH₂PO₄‒acetonitrile (80 : 20, v/v) at a flow rate of 1.0 mL/min and UV detection at λ_max = 254 nm. The method showed linearity with the correlation coefficient of 0.999 for both tazarotene and hydroquinone over the concentration range of 5‒25 and 1‒5 µg/mL, respectively. The mean recoveries were found to be in the range of 98‒101% for both components. The method was validated as per International Conference on Harmonization guidelines for linearity, limit of detection, limit of quantification, specificity, accuracy, precision and robustness. As a result, this method can be successfully applied for routine quantification of tazarotene and hydroquinone in pharmaceutical dosage form (gel preparation).

Mass spectrometry and chromatography are used to study the decomposition products of Teflon mixtures of the “Fluralite-4” brand with magnesium, tungsten, and titanium, activated by mechanochemistry. The temperature and energy parameters of water and carbon dioxide release are determined, volatile products of Teflon depolymerization are detected and identified, i.e., tetrafluoroethylene, trifluoromethylene, trifluoroethylene. It is shown that the introduction of metal mixtures in the composition significantly affects the decomposition processes of Teflon.

A simple electrochemical method for detecting glutathione reductase was developed in this work. It was observed that the impedance of electrode increased obviously after the electrode modification by glutathione, and the value of impedance was closely related to the reduced glutathione (GSH) concentration. Based on the fact that glutathione reductase (GR) could catalyze oxidized glutathione (GSSG) to GSH rapidly in the presence of NADPH (β-nicotinamide adenine dinucleotide 2'-phosphate reduced), and as GSH was immobilized on the gold electrode surface, the impedance increased drastically. Meanwhile, it was found that the impedance was correlated with the activity of GR, and a chemical equation was obtained based on the relationship between the impedance and enzymatic activity. The range of enzymatic activity that could be measured at 0.005‒0.5 U by using this assay, and the detection limit was 0.005 U (1 U means reduction of 1.0 μmol GSSG per min at pH 7.2 at 25°C). The enzymatic activity of GR obtained by this method was compared with those obtained by colorimetric detection, and the results showed that the new method is reliable. Therefore, the new method is highly sensitive with convenience consuming time within 20 min to complete a test, thus showing a promising potential of being applied in medicine.