scholarly journals Unusual Regularity in GC Retention of Simple Amino Acid Derivatives

2019 ◽  
Vol 6 (1) ◽  
pp. 3-14 ◽  
Author(s):  
Igor G. Zenkevich ◽  
Nino G. Todua ◽  
Anzor I. Mikaia
Keyword(s):  
Gas Chromatography ◽  
Retention Index ◽  
Methyl Esters ◽  
Elution Order ◽  
Alkyl Esters ◽  
Methyl Group ◽  
The Difference ◽  
Direct Use ◽  
Derivatives Of

Background: Application of simple regularities and general principles along with direct use of reference gas chromatography retention index data for reliable structure determination of compounds can be enhanced by determination of new regularities that are specific to certain structural elements. Objective: Revelation and interpretation of an anomaly in the elution order of alkyl esters of alkoxycarbonyl derivatives of glycine and alanine on standard and semi-standard non-polar phases. Method: Preliminary derivatization of amino acids to alkyl esters of N-alkoxycarbonyl analogs and interpretation of their gas chromatographic characteristics. Results: Alkyl esters of N-alkoxycarbonyl derivatives of alanine (Alkyl = C2H5, n- and iso-C3H7) elute prior to the same derivatives of glycine, despite the presence of an additional methyl group at C(2) in the molecule. Elution order is reversed for methyl esters of N-methoxycarbonyl derivatives. Conclusion: It is established that the peculiar behavior of alkyl esters of N-alkoxycarbonyl derivatives of glycine and alanine agrees with the concepts of gas chromatography and the known retention index regularities of organic compounds. A decrease of retention index values is a result of an introduction of an additional methyl group to a carbon atom connected to two polar fragments in a molecule like CH2XY. The dependence of the difference of retention index values for homologs of the types of CH3-CHXY and CH2XY vs. the total mass of fragments (X + Y) is similar to those for other sub-groups of analytes.

Gas Chromatographic Determination of 2,4-D and 2,4,5-T and Their Derivatives in Commercial Formulations

1965 ◽  
Vol 48 (2) ◽  
pp. 327-333
Author(s):  
Patricia L Pursley ◽  
E D Schall
Keyword(s):  
Gas Chromatography ◽  
Chromatographic Analysis ◽  
Methyl Esters ◽  
Chromatographic Determination ◽  
Dichlorophenoxyacetic Acid ◽  
Alkyl Esters ◽  
Boron Trichloride ◽  
Acid Gas ◽  
Gas Chromatographic Analysis

Abstract A solution of boron trichloride in methanol was employed for the complete transcsterification of 2,4-D and 2,4,5-T esters to the corresponding methyl esters. Gas chromatographic analysis of the methyl esters permitted mixtures of 2,4-D and 2,4,5-T esters in commercial formidations to be analyzed both qualitatively and quantitatively with no sample cleanup. The method is highly specific and detected the presence of other contaminating isomers of dichlorophenoxyacetic acid. Gas chromatography was also used to qualitatively analyze mixtures of various alkyl esters of 2,4-D.

Quantitative Determination of Linoleic Acid in Infant Formulas by Gas Chromatography

1987 ◽  
Vol 70 (4) ◽  
pp. 702-705
Author(s):  
Theresa W Lee
Keyword(s):  
Gas Chromatography ◽  
Linoleic Acid ◽  
Methyl Linoleate ◽  
Quantitative Determination ◽  
Methyl Esters ◽  
Infant Formulas ◽  
Methyl Heptadecanoate ◽  
Glass Column ◽  
Peak Areas

Abstract A method has been developed for the quantitative determination of linoleic acid in infant formulas by gas chromatography (GC). A known amount of triheptadecanoin was spiked into the sample. Total lipid was extracted from the product by an ethyl ether-petroleum etherethanol system in a Mojonnier flask. The sample was saponified by methanolic KOH after the solvents were evaporated. Methyl esters of the fatty acids were prepared by boron trifluoride (BF3) in methanol and analyzed by gas chromatography. A glass column packed with 10% SP-2340 (75% cyanopropyl silicone) was used to separate and identify the methyl linoleate and the methyl heptadecanoate. The quantity of methyl linoleate was calculated by comparing the integrated peak areas of these 2 fatty acid methyl esters. This method was satisfactory for both milk protein-based and soy protein-based matrixes. The results obtained by this method are comparable to those obtained by the AOAC spectrophotometric method 28.082- 28.085.

scholarly journals Gas-Chromatographic Determination of the Trimethylsilyl Derivatives of Polyhydric Alcohol Humectants in Tobacco and in Tobacco Smoke

1971 ◽  
Vol 6 (2) ◽  
Author(s):  
N. Carugno ◽  
S. Rossi ◽  
G. Lionetti
Keyword(s):  
Gas Chromatography ◽  
Mass Spectra ◽  
Triethylene Glycol ◽  
Chromatographic Determination ◽  
Flame Ionization ◽  
Trimethylsilyl Derivatives ◽  
Gas Chromatographic Method ◽  
Derivatives Of ◽  
Quantitative Procedure

AbstractA qualitative and quantitative procedure has been developed for the determination of humectants in manufactured tobacco by gas-chromatographic method with a flame ionization detector. It consists of extraction with methanol, concentration of the extract and treatment with Tri-Sil reagents. The operating gas-chromatographic conditions are set forth. Samples of tobacco containing glycerine, propylene glycol, diethylene glycol, triethylene glycol, 1-3 butylene glycol and sorbitol have been analysed with recoveries, for the first five ones, in the range of 95-104 %. In order to verify that each chromatographic peak corresponded to the relative glycol, with no interference by other silylated compounds, the mass spectra were obtained through the combination of gas-chromatography with mass spectrometry. The results achieved confirm, as far as tobacco is concerned, that the procedure is accurate and precise. The same method for the determination of humectants was extended to cigarette smoke. Even though this involves morecomplicated problems, as compared to tobacco, because of the presence of silylated compounds, it was found that, for certain glycols, the gas-chromatography of the trimethyl derivatives can be also used as a method of analysis. The mass spectra of some polyhydric alcohols are shown

On the determination of the distillation curve of fatty acid methyl esters by gas chromatography

Fuel ◽  
2022 ◽  
Vol 314 ◽  
pp. 123143
Author(s):  
Rodica Niculescu ◽  
Mihaela Năstase ◽  
Adrian Clenci
Keyword(s):  
Gas Chromatography ◽  
Fatty Acid ◽  
Fatty Acid Methyl Esters ◽  
Methyl Esters ◽  
Distillation Curve ◽  
Acid Methyl

BEZIEHUNGEN ZWISCHEN SUBSTITUTION IM RING A UND ABBAU IM STOFFWECHSEL BEI VERWANDTEN DES TESTOSTERONS

1962 ◽  
Vol 41 (4) ◽  
pp. 494-506 ◽  
Author(s):  
H. Langecker
Keyword(s):  
Double Bond ◽  
Ring System ◽  
Keto Group ◽  
Hydroxyl Group ◽  
Methyl Group ◽  
Structural Peculiarities ◽  
Metabolic Degradation ◽  
The Difference ◽  
Testosterone Metabolites ◽  
Derivatives Of

ABSTRACT Judging from the metabolites found in the urine, 1-methyl-androst-1-en-17β-ol-3-one (methenolone) and testosterone are metabolized in a different manner. For further clarification, other derivatives of testosterone with modifications in Ring A were investigated with regard to the oxidation of the 17-hydroxyl group. The production of urinary 17-ketosteroids decreased in the following sequence: testosterone; 1α-methyltestosterone and androstan-17β-ol-3-one; 1β-methyl-androstan-17β-ol-3-one; 2α-methyl-androstan-17β-ol-3-one and androst-1-en-17β-ol-3-one; 1α-methyl-androstan-17β-ol-3-one; 1-methyl-androsta-1,4-dien-17β-ol-3-one; 1,17α-dimethyl-androst-1-en-17β-ol-3-one and 1 -methyl-androst-1 -en-17β-ol-3-one (methenolone). The difference in metabolic degradation is also demonstrated in the fractionation of the urinary ketones. While after the administration of testosterone practically only hydrogenated 17-ketones are observed in the urine, the unchanged compound is still traceable in remarkable quantities after the administration of methenolone, along with minor quantities of the corresponding diketone. Testosterone-metabolites here are absent, whereas they represent the major substances present after the administration of androst-1-en-17β-ol-3-on. Following the administration of 1α-methyltestosterone only hydrogenated 17-ketones are detected which are still partly methylated. The 1-methyl-group and the Δ 1-double-bond seem to be responsible for the inhibition of the oxidation of methenolone in the 17-position. In addition, the hydrogenation of the double-bond and the reduction of the 3-keto-group are inhibited, obviously on account of the same structural peculiarities. The demethylation of methenolone is also inhibited. Any change in the steroid ring system forms a new substrate, thus producing new conditions for the enzymatic attack in the metabolic degradation.

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