Selection of a ternary eluant for the determination of fat-soluble vitamins in multivitamin pharmaceutical preparations by high-performance liquid chromatography

A procedure for selecting a ternary eluant for the determination of the synthetic fat-soluble vitamins E acetate, A acetate, K₃, and D₂ in Hexavit, Undevit, and Hendevit multivitamin pharmaceutical preparations was proposed, and the composition of then-hexane-l,2-dichloroethane-n-butanol (86.42 :13.42: 0.16, vol %) eluant was optimized.     

Comparative study of three immunoassays based on monoclonal antibodies for detection of the pesticide parathion-methyl in real samples

Three immunoassay systems: indirect, direct competitive enzyme-linked immunosorbent assay (IC-ELISA and DC-ELISA), fluorescence polarization immunoassay (FPIA) based on monoclonal antibodies for the detection of parathion-methyl (PM) were developed and optimized. Several PM derivatives (haptens) were conjugated to proteins and fluoresceinthiocarbamyl ethylenediamine (EDF) to obtain immunogens and competitors. The influence of immunogen and competitor structures on the assay performance was investigated. IC-ELISA was the most sensitive of all techniques developed, with a detection limit of 0.08 ng ml⁻¹, but assay time was the longest (3.5 h per 96-well microtitre plate). DC-ELISA was easier to perform and quicker (1.5 h per 96-well microtitre plate) but less sensitive than IC-ELISA (detection limit was 0.5 ng ml⁻¹). FPIA was the fastest and simplest (7 min per 10 samples) but the least sensitive (detection limit was 15 ng ml⁻¹) technique. The methods were characterized by high specificity and reproducibility. The cross-reactivity for parathion-ethyl was around 30-40% for IC-ELISA and FPIA, but significantly higher (125%) for DC-ELISA. The immunoassays were applied to the analysis of PM residues in different food and environmental matrices. Methanol extracts of vegetable, fruit and soil samples were used for the analysis. Recoveries for most spiked samples averaged between 85 and 110%. The methods developed can be used for screening of food and environmental samples for PM residues without complicated clean-up.     

Structural Analogy Method in Studies of Adamantanes

The potential of the structural analogy method in the topological studies of adamantane derivatives and analogs is demonstrated. The topological and structural characteristics of these compounds are calculated. Chromatographic retention indices were determined experimentally. Correlations between the topological indices and the physicochemical and chromatographic characteristics are investigated.     

Investigation of several parameters influencing signal generation in flow-through membrane-based enzyme immunoassay

Rapid-response analytical tests that can be performed at the point of sampling are based on a visual detection system. The influence of different factors on the signal generation in a membrane-based enzyme immunoassay was investigated. The research was applied to a flow-through immunoassay for the detection of ochratoxin A (OTA). This assay format is a very convenient, simple and fast qualitative screening tool. Conjugates of OTA with horseradish peroxidase (HRP) and alkaline phosphatase (AP) were used as enzyme tracers. A new conjugate OTA-AP has been synthesized in our laboratory and its performance in the assay was compared with that of OTA-HRP. Different substrate systems for HRP and AP were compared. Several reagents, including polymers and surfactants, were tested for their possible effect on signal generation with the use of OTA-HRP conjugate. Polymers such as poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) 6000 exerted a favourable effect on signal amplification, whereas surfactants negatively affected assay performance. The highest signal amplification (30–70% compared to the standard assay procedure) was achieved using 0.5% PVA in tetramethylbenzidine (TMB) Colorburst substrate solution and phosphate-buffered saline (PBS) for the washing step. It allowed more reliable visual estimation of the results from OTA-HRP assay. Exclusion of the detergent (Tween 20) from the washing solution exerted a favourable effect on assay performance using both enzyme tracers. The assay using OTA-HRP was more susceptible to matrix interferences than the assay with OTA-AP. Signal development in the matrix was better for the OTA-AP assay and visual estimation of the results was easier to perform in this case. For the analysis of spiked wheat samples, OTA-AP conjugate gave a more sensitive, stable and reproducible assay with a cut-off level of 4 μg kg⁻¹ for OTA. The application of the new OTA-AP conjugate resulted in improved assay performance for the food samples.     

Synthesis of new functionalized 1,10-phenanthrolines

Styrylphenanthroline derivatives containing the fragments dithia-18-crown-6, aza-18-crown-6, and azadithia-15-crown-5 were obtained for the first time. The conditions for their synthesis were optimized.