A. I. Revel’skii

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%.

Gas chromatography of organic mixtures using an atomic emission detector

Specific features of the combination of gas chromatography with atomic emission detection and the prospects for the determination of components of organic mixtures are considered. Attention is mainly focused on the application of a commercial system developed in 1990 by the Hewlett-Packard Company. The scope and limitations of the method are scrutinized; methods for improving the reliability of the results of analyses are discussed.

Determination of the main component in high-purity organic substances: Current status and prospects

The current status of the determination of the purity of high-purity organic substances using direct and indirect chromatographic methods is discussed. It is shown that the results of the chromatographic determination of the main component in high-purity organic materials are generally ambiguous and unreliable. The possibility of determining the purity of organic compounds using an elemental analyzer of C, H, and N without involving standard samples of analytes is examined; the advantages and drawbacks of this approach are discussed. It is demonstrated experimentally by the example of several nitrogenated compounds that the main component can be determined with an error no worse than 0.6 rel. %, whereas the error of element (nitrogen) determination in the molecule does not exceed the permissible error of elemental analysis.

A new method for the simultaneous and highly sensitive determination of the total content of F-, Cl-, Br-, and S-organic compounds in products of oil refining

A new method for the simultaneous determination of the total content of fluorine-, chlorine-, and sulfur-containing organic compounds in products of oil refining is proposed. The method is based on the high-temperature oxidation of a sample in a flow of oxygen, the absorption of conversion products, and the analysis of the total absorbate in isocratic conditions by the ion chromatography method for the content of anions that correspond to the analytes. The detection limit for the total content of Cl-, Br-, and S-organic compounds in a sample of 1 μl is 10−5%; for F-containing compounds, it is 10−6%. The results of the analysis of samples of aviation kerosene and gasoline for the total content of F-, Cl-, Br-, and S-organic compounds are presented.

Identification of unknown compounds using data bases and computer simulation of mass spectra

The possibility of identification based on the comparison of experimental electron-ionization mass spectrum of an unknown (in our case, model) compound with the mass spectra of the candidate compounds generated by the Mass Frontier software has been demonstrated by the example of three model compounds. The structural isomers of the identified substances found in the ChemExper database have been used as the candidate compounds. The candidate substances have been ranged by the degree of similarity between their simulated mass spectra and the experimental mass spectrum of the unknown compound. The mass spectra have been compared on the basis of the algorithm used in the NIST MS Search standard search system. In all three cases, the sought-after structure has been indicated as the most probable one of all the candidate structures.

Detection of afobazole and its major metabolites using capillary gas chromatography-mass spectrometry

The possibility of detecting a target compound using Gas Chromatography-Mass Spectrometry has been demonstrated and the structure of these compounds has been confirmed. The possibility of sorption of these compounds in the chromatographic system has been analyzed. Results obtained using various sample injection modes have been compared. A highly sensitive method for detecting micromolar amounts of the compounds under investigation in samples with large volumes has been developed. The detection limits of the compounds studied equaled 5 × 10−10 g in a sample of the model solution.

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.

Analyssis of pharmaceutical substances by reaction gas chromatography/mass spectrometry

Derivatization of six pharmaceutical substances (catopril, metoclopramide, sotalol, hydrochlorothiazide, nalidixic acid, and stavudine) has been performed using five derivatizing reagents of different types; the derivatization has been followed by the GC/MS detection of the resultant products. The number of labile hydrogen atoms in the initial molecules substituted by the structural fragments of derivatizing reagents has been determined.

Determination of monosaccharides by reaction gas chromatography/mass spectrometry with reagent removal from the reaction mixture

A method for determining monosaccharides has been developed, which involves their derivatization with N,O-bis-(trimethylsilyl)trifluoracetamide in the presence of pyridine in an ultrasonic field followed by the removal of the remaining derivatizing agent and pyridine and their substitution with methyl-tert-butyl ether (MTBE). Two peaks have been obtained in the chromatogram of D-galactose and D-fructose, corresponding to different forms of trimethylsilyl derivatives of D-galactose and D-fructose, respectively. For 1-O-octyl-β-D-glucopyranozide, one intense peak has been revealed in the chromatogram, which has been attributed to the trimethylsilyl derivative of 1-O-octyl-β-D-glucopyranozide. It has been demonstrated that, under the chosen conditions, the solutions of trimethylsilyl derivatives of the considered monosaccharides in MTBE are stable in the concentration range corresponding to the amount of monosaccharide from n × 10−10 to n × 10−8 g/μL for at least three days.