Vol 72, No 8 (2017)

The review shows prospects of the use of subcritical water instead of organic solvents and aqueous–organic mixtures at different stages of analysis. Subcritical water was applied to the extraction of target compounds from natural samples, such as soils, sand, and plant raw materials. The use of subcritical water expands possibilities of HPLC. The use of subcritical water as an eluent in HPLC is complicated by the possible destruction of the adsorbent and the decomposition of substances to be determined at elevated temperatures. Adsorbents based on zirconium and titanium oxides, some polymeric adsorbents, and porous graphitized carbon are stable in the medium of subcritical water. Subcritical water can be used at several stages of analysis, for example, for the extraction and subsequent chromatographic separation of analytes.

A possibility of the analytical application of a low-melting extractant, antipyrinium acetylsalicylate, to the extraction of a number of ions from acid aqueous solutions is studied. The distribution of Al, As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sb, Sn, Ti, V, and Zn ions between the aqueous solution and an organic extractant is studied by atomic emission spectrometry. The efficiency of ion extraction from acid solutions with a low-melting flux of antipyrinium acetylsalicylate is calculated. It is shown that single extraction with an extractant flux ensures the efficient extraction of Fe, Mo, Sn, and Ti from the water phase of the analyzed solution to the flux. The introduction of chloride ions into the analyzed acid aqueous solution significantly increases the efficiency of the group preconcentration of ions by the ion-exchange mechanism.

A nanomaterial comprising Fe₃O₄-modified hydroxylated multi-walled carbon nanotubes (Fe₃O₄–MWCNTs–OH) was prepared by a co-precipitation method. Combined with HPLC-photodiode array detector (DAD), Fe₃O₄–MWCNTs–OH was used to determine brucine in human urine. Some important parameters that could influence extraction efficiency of brucine were optimized, including the extraction time, amounts of Fe₃O₄–MWCNTs–OH, pH of sample solutions, desorption solvent and desorption time. Under the optimal conditions, the recoveries of brucine from spiked urine samples were between 93.1 and 104.1%, and the relative standard deviations (RSDs) ranged from 3.1 to 5.7%. The correlation coefficient was 0.9997. The limits of detection and quantification were 6 and 21 ng/mL at a signal-to-noise ratio of 3 and 10, respectively. The results indicated that Fe₃O₄–MWCNTs–OH combined with HPLC–DAD is a promising solid-phase extraction material for the sample pretreatment in the determination of brucine.

Some features of the HPLC determination of two hydrophilic substances that poorly absorb in the UV spectral region (chondroitin sodium sulfate and glucosamine hydrochloride), associated with the absorption in the near UV region (195 nm) of components of buffer solutions with different pH values (1.2, 4.5, and 6.8), are considered. Such solutions are used, for example, in comparative dissolution kinetics tests in pharmaceutical practice. At some pH, the subtraction of the areas of system peaks from the total areas of analyte peaks made it possible to compensate for the negative effect of the solvent. To determine glucosamine hydrochloride in 0.1 M HCl, a procedure was developed and validated, involving the synthesis of o-phthalic derivatives. The revealed analytical features are caused by that the solvent of the samples and the eluent do not match; the effect can be most pronounced in measurements in the near UV region and in the determination of ionic compounds.

A novel method based on the coupling of membrane-supported headspace single-drop microextraction with gas chromatography‒mass spectrometry (GC–MS) is developed for the determination of chlorobenzenes in water samples. For the determination of five chlorobenzenes, a 15 μL toluene microdrop was placed inside the plastic membrane and exposed for 10 min for headspace extraction while stirring at 1000 rpm. The microdrop was then picked up by a microsyringe and directly injected into the injector block of the GC–MS instrument. Under the optimized operation conditions, the calculated calibration curves gave a high level of linearity for all targets with correlation coefficients range from 0.9945 to 0.9987. The limits of detection range from 0.01 to 0.05 μg/L and the RSDs for most of chlorobenzenes were below 7%. The method is simple, sensitive, and stable for single drop microextraction. Its applicability is demonstrated by the determination of chlorobenzenes in tap water samples.

Cholesterol has a number of important functions in a human body. The disorders of cholesterol biosynthesis increase the risk of the development of cardiovascular diseases and worsens the function of the immune system. This study is devoted to the development of a method for determining the concentration of cholesterol in blood serum using voltammetry. We selected the following working conditions for the determination of cholesterol: a phosphate buffer solution with pH 6.86 was a supporting electrolyte; potential sweep rate was W = 30 mV/s; and recording was carried out in the constant-current mode. An organomodified electrode was used as a working electrode. The peak was observed at +0.98 V. The dependence of the electrooxidation current of cholesterol on its concentration was linear in the range of 0.1–50 μM with a limit of detection of 0.01 μM. The results of the determination of cholesterol in blood serum by voltammetry were compared to those obtained by the fluorimetric method.