Vol 74, No Suppl 1 (2019)

The conditions for the coprecipitation of arsenic and antimony with trace amounts of tungsten and iron in the form of PbWO₄ and Na₃FeF₆ are found. The introduction of hydrofluoric acid in the deposition of macrocomponents results in the formation of precipitates with the lowest specific surface area and porosity, which contributes to the inhibition of the coprecipitation of the analytes (As and Sb). We prepared certified reference materials of ferrotungsten composition according to the developed procedure for the determination of arsenic and antimony by inductively coupled plasma atomic emission spectrometry (ICP–AES). The difference between the found and certified concentrations of analytes does not exceed the values specified by GOSTs. The method of simultaneous ICP–AES determination of arsenic and antimony with preliminary separation of the main components is applicable to the analysis of materials and alloys with high contents of iron and tungsten.

The manifestation of noticeable effects of the discrimination of sample composition upon split injection into short capillary columns with large diameters at small splitting ratios is discussed. They consist in the anomalously strong dependences of the peak areas of even volatile components on the injector temperature, the solvents used and, to a lesser extent, on the amounts of injected samples. It is proposed to consider the following criteria for assessing the degree of manifestation of these factors: (1) the dependence of the absolute peak areas of different analytes on the injector temperature and (2) the analogous dependence of the relative peak areas of the same components in different solvents. In this case, the relative peak areas of various components in the same solvents remained almost constant regardless of the injector temperature. The above effects complicate quantitative determinations based on the measurement of absolute peak areas (the method of internal normalization and the determination of distribution coefficients in partition chromatography). For these purposes, it is preferable to use standard capillary columns with split sample injection at a sufficiently high splitting ratio.

The adsorption of polychlorinated aromatic hydrocarbons on graphitized thermal carbon black was simulated by a molecular-statistical method. The results of calculations were compared with data on chromatographic retention under gas chromatography conditions. A version that took into account the conformational flexibility of molecules was used for polychlorinated biphenyls. Different computational chemistry methods (classical molecular dynamics and semiempirical quantum methods) for evaluating the internal energy of a molecule were considered. It was found that the use of a molecular-statistical method and the AM1 semiempirical method for estimating the internal energy of molecules makes it possible to correctly predict the order of elution of isomeric dichlorobiphenyls. It was demonstrated that this approach can be used to confirm the assignment of peaks in a chromatogram to particular isomers.

We propose amperometric biosensors for the determination of aflatoxin M1, based on screen-printed platinum electrodes modified by carbon nanotubes (CNT), graphene oxide (GO), gold nanoparticles (Au-NP) in chitosan, and immobilized tyrosinase. The conditions for obtaining gold nanoparticles are optimized. Aflatoxin M1 exhibits properties of a reversible tyrosinase inhibitor, which makes ensures its determination using biosensors modified by nanomaterials in the concentration range 1 × 10^–11–1 × 10^–6 M with LOD = 5 × 10^–12 M. The kinetic studies of the enzymatic conversion of phenol in the presence of aflatoxin M1 and a tyrosinase biosensor show both two-parameter mismatch inhibition (modification with a CNT/Au-NP composite) and two-parameter coordinated inhibition (modification with GO/Au-NP). Using the proposed enzyme sensors based on tyrosinase, the procedures for determining aflatoxin M1 in dairy products are tested.