GLC Retention Times Research Articles

Extracting Vapor Pressure Data from GLC Retention Times. Part 1: Analysis of Single Reference Approach

The vapor pressures of 52 compounds including n-alkanes and their monosubstituted derivatives, as well as chloro- and alkylbenzenes were determined exploring the gas chromatographic relative retention time (GLC-RT) technique in its simplest form, that is, using a single reference standard and neglecting the activity coefficient effect (GLC-RT1S). The selection of compounds was limited to those which are in the liquid state under the measurement conditions and for which high-quality vapor pressures obtained by direct methods are available at temperatures of GLC measurements. This approach should eliminate possible secondary error sources (such as data extrapolation or recalculation from supercooled liquid to solid phase or vice versa). On the basis of a thorough comparison of the GLC-RT1S-based and directly measured vapor pressures for the group of (functionalized) n-alkanes and by exploiting n-alkanes as reference solutes it is clear that deviations from direct data are significant (in many tens of percen...

The use of boronate derivatives in the characterization of cathecholamines and related beta-hydroxy-amines by gas liquid chromatography-mass spectrometry.

Abstract The gas chromatographic separation of various β-hydroxy-amines in the form of derived 1, 3, 2-oxazaborolidines is complemented by a mass-spectrometric study of cyclic boronates of natural catecholamines. These derivatives and their synthetic analogues yield characteristic mass spectra. Closely similar compounds, such as the n-butylboronates of the diastereoisomers (—)-ephedrine and (+)-ψ-ephedrine, give almost identical spectra but can be readily distinguished by their glc retention times. The same can be said for the positional isomer pairs synephrine and phenylephrine, and for octopamine and 4-deoxynoradrenaline. Mass-spectrometric fragmentation modes are postulated from a comparison of the shifts in the masses of fragment ions corresponding to various substituents in the group of biological amines studied. Additional correlations are derived from studies of methyl-, cyclohexyl- and phenyl-boronates.

Substitution pattern of 3-deoxy- d- manno-oct-2-ulosonic acid in bacterial lipopolysaccharides investigated by methylation analysis of whole LPS

3-Deoxy- d- manno-oct-2-ulosonic acid (Kdo) is a constituent of the inner core part of bacterial lipopolysaccharides (LPS). This sugar may contribute to biological activities of the LPS, the type of substitution of Kdo is thus of importance and this work is aimed at the evaluation of a method for monitoring the substitution of Kdo in LPS. The procedure consists of three steps, namely permethylation of the lipopolysaccharide, with iodomethane and sodium methylsulfinylmethanide or NaOH in Me 2SO, or with methyl triflate, then the product is methanolysed with HCl in MeOH and acetylated with acetic anhydride in pyridine. The resulting partially methylated acetates of Kdo methyl glycosides were analyzed by gas-liquid chromatography–electron impact ionization mass spectrometry (GLC–MS). For several derivatives of Kdo, specific GLC retention times and MS fragmentation patterns were determined. Lipopolysaccharides from several bacterial strains were isolated and analyzed with three different methods of methylation. The complete solubilization of the LPS in the acid form allows diminishing possible undermethylation. Sodium methylsulfinylmethanide is the most efficient agent in the permethylation of the whole LPS, of all the tested procedures. Methylation with methyl triflate allows the detection of base labile substituents on Kdo residues.

Synthesis of (3E, 5Z)-3,5-dodecadienylacetate, the sex pheromone of Phtheochroa cranaodes (Lepidoptera: Tortricidae.

(3E, 5Z)-3,5-Dodecadienyl acetate, the female sex pheromone of Phtheochroa cranaodes, was regio and stereo-selectively synthesized from 1-octyne and (E)-4bromo-3-buten-1-ol by using Pd(PPh3)4, CuI and piperidine to afford the enyne (5). Further elaboration afforded the target pheromone. The synthetic pheromone was identified with the natural product by its MS and IR, data GLC retention time and biological activity.

Chemical ecology of astigmatid mites XLIX β-Acaridial (2(E)-(4-methyl-3-pentenylidene)-butanedial), the alarm pheromone of Tyrophagus longior Gervais (Acarina : Acaridae)

Alarm pheromone activity was detected in the hexane extract of Tyrophagus longior. The GLC profile of the extract revealed six components ; α-acaridial {2(E)-(4-methyl-3-pentenyl)-butanedial}, tridecane, β-acaridial {2(E)-(4-methyl-3-pentenylidene)-butanedial}, an unknown (M+ ; m/z 166), n-hexyl linolate and n-hexyl stearate, among which β-acaridial was the major component, followed by tridecane. These compounds were each identified by GC/MS spectra and GLC retention times by comparing with those of authentic compounds. The active eluate from a SiO2 column by 50% ether in hexane consisted of a peak of β-acaridial. The compound isolated from the mite was active at 50 ng, and its activity was the same as the authentic β-acaridial derived from T. putrescentiae.

Synthesis of (R, Z)-7, 15-Hexadecadien-4-olide, the Sex Pheromone of the Yellowish Elongate Chafer (Heptophylla picea).

(R, Z)-7,15-Hexadecadien-4-olide, the sex pheromone of the yellowish elongate chafer (Heptophylla picea), was synthesized from l-malic acid in 15 steps. The synthetic pheromone was identical with the natural product in its MS, IR, GLC retention time, and biological activity.

An improved procedure for the analysis of linkage positions in 2-acetamido-2-deoxy- d-glucopyranosyl residues by the reductive-cleavage method

The conditions of the reductive-cleavage method were modified to allow simultaneous analysis of 2-acetamido-2-deoxy- d-glucopyranosyl residues and monosaccharides of other classes. Methyl 2-deoxy-3,4,6-tri- O-methyl-2-( N-methylacetamido)-β- d-glucopyranoside was found to undergo transglycosidation under reductive-cleavage conditions when the reaction was quenched withan alcohol. Transgly-cosidation proceeded via an oxazolinium-ion intermediate, which then acted as a glycosyl donor to form an anomerically pure product. Time-course studies showed that in the presence of trimethysilyl trifluoromethanesulfonate (Me 3SiOSO 2CF 3, 4 h were required for complete conversion of the substrate into this intermediate, which was then trapped with methanol- d 4. When the reaction was conducted in the presence of a mixture of trimethylsilyl methanesulfonate (Me 3SiOSO 2Me) and boron trifluoride etherate(BF 2·OEt 2)or with BF 3·OEt 2 alone, 24 h and 48 h, respectively, were required for complete conversion. The α anomer was unreactive after 24 h under all conditions, confirming earlier results. Reaction with racemic2-butanol yielded a pair ofdiastereomers, in a 1:1 ratio, which were distinguishableby their GLC retention times and their 1H NMR spectra. Reaction with ( S)-2-butanol gave only one of the diastereomeric products. These experiments demonstrated the feasibility of using the reductive-cleavage method to determine the absolute configuration of 2-acetamido sugars.

The Favored Formation of Threo-3-Pentulose in the Formose Reaction

ABSTRACT The “formose reaction” is the generic name for the base-catalyzed condensation of formaldehyde to give “formose” which is a complex mixture of sugars, alditols, organic acids, etc.2 Increasing attention has been recently given to this reaction because of its possible importance in the manufacture of edible carbohydrates from a simple material and its possible role in the prebiotic synthesis of carbohydrates.3 In our recent study4 on the reaction catalyzed by triethylamine (TEA) and thiamine HCl in N,N-dimethylformamide (DMF)-water mixed solvent, the formation of 3-pentulose (GP-11-1 corresponding to GLC peak number 11-1) was suggested. P. Decker et al.5 also reported that at the end of formaldehyde consumption the concentration of 3-pentuloses became smaller because of their higher reactivity (these carbohydrates cannot form stable furanoses or pyranoses) compared to tetroses, pentoses, and hexoses. Although the isolation of 3-pentuloses was not described in that report,5 erythro-3-pentulose and threo-3-pentulose in a formose were identified by comparison of GLC retention times and mass spectra with those of authentic samples.

Indoleacetonitriles—thermal degradation products of indole glucosinolates in commercial rapeseed (Brassica napus) meal

AbstractCommercial low‐glucosinolate rapeseed (Brassica napus L) meal (LG RSM) was extracted with dichloromethane and subjected to chromatography on Sephadex LH‐20 to isolate indole‐containing compounds which were detected using TLC. Thin layer chromatography of dichloromethane extracts of various heat‐treated preparations of defatted low‐glucosinolate rapeseed cv Westar was also used to establish the origin of the major indole derivative. One of the minor components was identified as 3‐indoleacetonitrile (IAN) based on comparisons of GLC retention times and mass spectral data with authentic IAN. The major indole derivative was identified as 4‐hydroxy‐3‐indoleacetonitrile by comparison of mass spectral data with that for IAN and by establishing its precursor as 4‐hydroxy‐3‐indolylmethylglucosinolate.

A simple method for the prediction of the GLC retention times of all the 209 PCB congeners

Besides the fact that our model allows to predict the chromatographic retention times for all the compounds under study, our approach also reveals the heuristic potency of the dummy variables to solve Quantitative Structure-Activity Relationship (QSAR) problems with PCBs. It is not surprising because the simplicity of the calculation of these variables, which are not redundant and their purely non-empirical natures, makes them preferable to all the other molecular descriptors generally used to encode physicochemical or biological properties of PCBs.

The di- and triesters of the lipids of steer and human meibomian glands.

Three groups of diesters have been isolated and identified in the lipids of steer meibomian glands. The first group, designated as alpha Type I, with the abbreviated formula FA-alpha OHFA-FAlc, consisted of alpha-hydroxy fatty acids esterified to fatty acids and fatty alcohols in the approximate molar ratio 1:1:1. The second group, designated as omega Type I-St, with the abbreviated formula FA-omega OHFA-St, consisted of omega-hydroxy fatty acids esterified to fatty acids and sterols in the approximate molar ratio 1:1:1. The third group, designated as alpha, omega Type II, with the abbreviated formula FA-alpha, omega diol-FA, consisted of alpha, omega-diols esterified to 2 moles of fatty acids. The sum of the different diesters comprised about 9% of total steer meibomian lipids. Capillary GLC of the fatty acids of alpha Type I diesters showed the fatty acids to be a family with a two-cluster profile, one at C12 to C20 and the other at C21 to C31, with anteiso chains predominating. Fatty acids from omega Type I-St and alpha, omega Type II diesters gave mainly a one-cluster profile in the short chain region with prominent anteiso and C18:1 peaks. Fatty alcohols of alpha Type I diesters were mainly long chain, C23 to C30, with anteiso chains predominating, while the alpha-hydroxy fatty acids were short chain C13 to C18 acids with C16 predominating. The sterols in diesters omega Type I-St were cholesterol (approximately 60%), delta 7 cholestenol (approximately 35%) and an unidentified compound (approximately 5%) with a GLC retention time slightly longer than delta 7 cholestenol on SE-30 phase. The omega-hydroxy fatty acids and alpha, omega-diols both were of exceedingly long chain lengths, C29-C38, and showed similar GLC profiles. Two types of triesters comprising approximately 1% of total steer meibomian lipids have been isolated but incompletely characterized. In terms of molar ratios, one group of triesters gave fatty acids:omega-hydroxy fatty acids:alpha-hydroxy fatty acids:sterols + fatty alcohols as approximately 1:1:1:1. The other contained fatty acids, alpha-hydroxy fatty acids and alpha, omega-diols in what appears to be a complex mixture of several triesters. Diesters omega Type I and alpha, omega Type II also were found in human meibum. Hitherto these two diesters have not been found in any animal tissue.

Enzymatic 7β hydroxylation of 4,4,10β-trimethyl- trans-decal-3β-ol (TMD)

4,4,10β-Trimethyl- trans-decal-3β-ol (TMD, 1), an inhibitor of 2,3-oxidosqualene cyclase, is converted by S 10 rat liver homogenate (RLH) to 4,4,10β-trimethyl- trans-decalin-3β,7β-diol (2) as its chief metabolite in 15 to 32% yield. Identification of 2 was accomplished by (a) gas-liquid chromatography/mass spectroscopy (GLC-MS) molecular-weight determination; (b) identity of GLC retention times with those of synthetic 2 and derived dione 15 on three columns; and (c) isotopic dilution and recrystallization to constant specific activity of both 3H-2 and its diacetate. Resolution of TMD was effected via formation of diastereomeric esters 18 and 19; and both d-TMD and l-TMD were found to be metabolized in RLH to 2, with d-TMD, the enantiomer having the nonsteroidal absolute configuration, being about twice as effectively hydroxylated.

Empirical determination of medium effects on the equilibrium between [formula omitted][formula omitted] and [formula omitted][formula omitted] 1,2-dibromo-4-t-butylcyclohexanes

Head space analysis, GLC retention time data, and solution calorimetry are used to determine the effect of medium on the thermodynamic parameters for the equilibrium (1) ∡ (2). It is shown that changes in ΔG° and ΔH° can be evaluated for the transfer of the equilibrium from a series of solvents to the gaseous phase which is used as the reference medium.

Attractants of male-gamete from a marine brown alga Sargassum horneri.

Octatrienes, 1, 3, 5- and 2, 4, 6-octatrienes (sarohornene) in the matured female receptacles, were first identified as attractants of male-gamete of a dioecious brown marine alga, Sargassum horneri by comparison of mass and UV spectra, and GLC retention times with those of synthetic specimens.

GLC-mass Spectral Determination of Mescaline in Plasma of Rabbits after Intravenous Injection

A GLC-mass spectral analysis with a deuterated internal standard was developed to measure plasma mescaline concentrations after intravenous administration to rabbits. The drug and the internal standard were extracted with benzene, derivatized with trifluoroacetic acid anhydride, and chromatographed on 2.5% QF-1 with mass fragmentographic detection. The detection limit is 5ng/ml of plasma. The relative standard deviation was ∼5%. The main advantage of this method is that it combines the specificity of the GLC retention time and mass spectral fragmentation pattern with the sensitivity of the mass fragmentographic detection.

Impurities in Drugs III: Trihexyphenidyl

Two lots of trihexyphenidyl hydrochloride raw material, one lot of elixir, and 10 lots of tablets were examined for impurities by TLC. Impurities found were l‐phenyl‐2‐propenone, 3‐piperidinopropiophe‐none, and 3‐aminopropiophenone. Not all impurities were present in all lots, and none exceeded 1.9% of the label drug claim. Impurities were identified by mass spectrometry and by comparison of TLC Rfvalues and GLC retention times to those of synthesized specimens of the impurities.

Gas-Liquid Chromatographic and Mass Spectrometric Identification of Chlorinated Trifluorotoluene Residues in Niagara River Fish

Several unknown halogenated compounds were detected in Niagara River fish using a method similar to the AOAC multiresidue method for chlorinated pesticides in high-moisture foods. From gas-liquid chromatographic-mass spectrometric (GLC/MS) data and GLC retention times on 3 columns, 7 of the compounds were identified as 4-chloro-alpha,alpha,alpha-trifluorotoluene (0.17--2.0 ppm), 2-chloro-alpha,alpha,alpha-trifluorotoluene (0.002--0.1 ppm), 3,4-dichloro-alpha,alpha,alpha-trifluorotoluene (0.02--0.28 ppm), 2,4-dichloro-alpha,alpha-alpha-trifluorotoluene (0.02--0.17) ppm), 2,3-dichloro-alpha,alpha,alpha-trifluorotoluene (trace-0.005 ppm), 2,6-dichlorotoluene (not quantitated), and 2,4,5-trichlorotoluene (0.31 ppm was found in the only sample quantitated). Other isomers of tri- and tetrachloro-alpha,alpha,alpha-trifluorotoluene and di-,tri-, and tetrachlorotoluene were also present in these samples. Recoveries of the specific chlorinated trifluorotoluenes identified in these samples ranged from 86 to 108%.

Relative Boiling Points and GLC Retention Times of Methyl Esters of Isomeric Monoethylenic Octadecenoic Acids, of Hexadecanoic and Hexadecenoic Acids, and of C18 Unsaturated Acids

Relative Boiling Points and GLC Retention Times of Methyl Esters of Isomeric Monoethylenic Octadecenoic Acids, of Hexadecanoic and Hexadecenoic Acids, and of C18 Unsaturated Acids

Identification of pentachlorobenzonitrile residues in field crops.

We recently received several carrot extracts from another FDA district laboratory for identification of a material present in each of the extracts which had a GLC retention time inconsistent with that of any known pesticide. The material, which was eluted from Florisil with 15% ether in petroleum ether (AOAC, par. 29.015, 1975) exhibited both electron capture and microcoulometric responses (LASKI and LEONE, 1976). This paper reports structural elucidation, GLC characteristics and recovery data for the material.

Identification of nonpolar methotrimeprazine metabolites in plasma and urine by GLC-mass spectrometry.

Two metabolites of methotrimeprazine, the sulfoxide and the demethylated analog, were identified in extracts from patient plasma by combined GLC-mass spectrometry. Methotrimeprazine and its sulfoxide had similar mass spectra but different GLC retention times. In addition to the metabolites found in plasma, two other metabolites, the didesmethyl analog and the monodesmethyl sulfoxide, were identified in a urine extract.