A. S. Samokhin

A new approach to determining derivatization degree and its use for the investigation of silylation of methyltestosterone in nano-/microgram amounts

AbstractsA new approach to establishing the yield of derivatization reactions of difficult-to-derivatize steroids is proposed on the basis of the comparison of the areas of chromatographic peaks between the native form of the analyte and its derivative. The influence of material to be derivatized, i.e., methyltestosterone, in an amount of 5 and 500 ng, and the time of reaction, 5–120 min, on the degree of conversion is studied. Methyltestosterone is derivatized at 80°C in a mixture of pyridine and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane. Prior to the injection of samples into the gas chromatograph, pyridine and BSTFA are replaced with an inert organic solvent, methyl tert-butyl ether. The degree of methyltestosterone derivatization is shown statistically independent of the amount of the steroid processed. The performance of the reaction for 1 h at 80°C ensures reaction yield of around 90%.

Supercritical fluid chromatography and its application to analysis and preparation of high-purity compounds

The principles of supercritical fluid chromatography (SFC) and its application in various fields are reviewed. A comparison of high-performance liquid chromatography (HPLC) and SFC is performed. In discussing the applications, emphasis is placed on the possibility of using SFC in analysis of impurities in pharmaceuticals and biologically important substances and in preparation of high-purity substances. In describing detectors for SFC, special attention is paid to mass-spectrometric detectors.

Comparison of multidimensional impurity profiles for pharmaceuticals containing the same active compound using thermodesorption and gas chromatography coupled with mass spectrometry

The possibility of comparing pharmaceutical products containing the same active compound based on the comparison of multidimensional profiles of impurities isolated from the examined samples by thermodesorption in a carrier gas flow was studied by GC/MS with electron ionization. A substantially higher number of impurities can be detected using the analytical method based on thermodesorption of impurities and GC/MS analysis of the whole desorbate of impurities free of the active compound. The proposed approach makes it possible to compare the studied pharmaceutical products containing the same active compound taking into account information on the number of the found impurities, their retention times, and electron ionization mass spectra.

Intensity of molecular ion peak in electron ionization mass spectra

Compounds from NIST′08 and Wiley 8th databases were considered as a representative subset of the general population of organic compounds which can be analyzed using mass spectrometry with electron ionization. The percentage of organic compounds as a function of intensity of molecular ion (M+•) peak normalized to the base peak was determined for the first time. It was shown that only 26% compounds have high-intensity M+• peaks (greater than 50% of base peak). Intensity of M+• peak is less than or equal to 1 or 5% of base peak for 24 or 37% compounds respectively. It means that in case of trace-level analysis M+• peak may not be registered for quarter (or even more) of organic compounds. It is well-known that the absence of M+• peaks in electron ionization mass spectra reduces reliability of unknown compound identification based on library search. Therefore determination of molecular mass by independent technique (e.g., mass spectrometry with chemical ionization) is necessary for increasing the identification reliability.

Application of principal component analysis to the extraction of pure mass spectra in chemical analysis by gas chromatography/mass spectrometry

In this work, we investigated the possibility of the purification of mass spectra of coeluted substances containing at least one characteristic value of m/z using principal component analysis. Simulated and real gas chromatographic/mass spectrometric data were analyzed. For the simulated data, the resolution of the chromatographic peaks varied from 0.075 to 0.75, and the ratio of component concentrations ranged from 0.01 to 100. Noise-free simulated data and simulated data with randomly distributed noise were considered. It was shown that the method gave satisfactory results even when the chromatographic resolution (Rs) was less than 0.05.

Rapid screening of wines for total content of F-, Cl-, Br-, and S-organic compounds

A rapid direct method for determining the total content of heteroelement-containing organic compounds in dry white wine has been developed. The method involves the solvent extraction of these compounds, the removal of extractant outside the reactor, the oxidative conversion of the total concentrate of analytes at high temperature, and the analysis of the whole absorbate volume by ion chromatography. The detection limits for different elements ranged from 10−6 to 10−5 g/L for 1-mL wine samples and from 10−7 to 10−6 g/L for 10-mL wine samples. The possibility of identifying pesticides used in viniculture based on detecting the heteroelements present in the molecule is considered.

An improved approach to determining the yield of derivatization reaction and its application to the investigation of the silylation of some anabolic steroids

An approach to determining the yield of derivatization reaction is based on a comparison of chromatographic peak areas of the derivative and native (underivatizied) compound. In contrast to the previous publication [J. Anal. Chem., 2011, vol. 66, no. 12, pp. 1186–1189], ratio of the sensitivity coefficients of the derivative and native forms of the analyte was calculated using only experimental data obtained upon varying the derivatization conditions (solution containing equal amounts of underivatized compound and a respective derivative was analyzed previously). The approach was used to investigate the influence of the reaction time and the type of an external action on the yield of the derivatization (silylation) reaction for some anabolic steroids (methyltestosterone, methandienone, oxandrolone and oral-turinabol) containing a hindered tertiary hydroxyl group at C17. The amounts of the derivatized steroids were equal to about 20–60 ng (depending on the component). Steroids were derivatized with a mixture of pyridine and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1% trimethylchlorosilane. The derivatization reaction was carried out for 15, 30 or 45 min under conventional heating, sonication at room temperature, and sonication at elevated temperature.

A new approach to comparison of original pharmaceuticals and generics based on comparison of multidimensional impurity profiles using supercritical fluid extraction, liquid extraction, and GC-MS

This paper reports on our effort to study the possibility of comparing the original pharmaceuticals and their analogs (generics) based on comparisons of the multidimensional profiles of impurities isolated from samples by supercritical fluid extraction and liquid extraction and recorded by gas chromato-mass spectrometry (GC-MS) with electron ionization (EI) and atmospheric pressure photochemical ionization (APPhCI). Using the suggested approach makes it possible to increase the number of recorded impurities, to show that the pharmaceutical samples are authentic, and to compare the original pharmaceuticals and generics according to their quality.

Comparison of electron ionization mass spectra of some organic compounds (MW < 200 Da) recorded on mass spectrometers of various types

Low-resolution electron ionization mass spectra recorded on various types of mass spectrometers (time-of-flight, quadrupole, and three-dimensional ion trap) were compared. A model mixture of 10 organic compounds (MW < 200 Da) was analyzed by gas chromatography-mass spectrometry. Pure mass spectra of analytes were extracted using the AMDIS software. The best repeatability was achieved for the time-of-flight mass spectrometer. The mass spectra recorded by a quadrupole and a time-of-flight mass spectrometer were quite similar. In the case of these instruments, library search using a commercial mass spectral data base (NIST’05) gave satisfactory result for each analyte (rank 1 or 2 in the “hit list”; Match > 900). In some cases, the mass spectra of model compounds recorded by the ion trap mass spectrometer differed in intensity of certain mass spectral peaks (but not in the set of peaks) from the mass spectra presented in the library and from the experimental mass spectra recorded by the time-of-flight and quadrupole instruments.