Gas Chromatographic Properties Research Articles

Simultaneous Quantitation of Endogenous Levels of Cortisone and Cortisol in Human Nasal and Bronchoalveolar Lavage Fluids and Plasma via Gas Chromatography-Negative Ion Chemical Ionization Mass Spectrometry

Investigation of the influence of pulmonary disease upon local catabolism of cortisol in vivo is limited by the lack of availability of a selective and sensitive assay for simultaneous quantitation of cortisol and cortisone in lung and nasal lavage fluids as well as in plasma. Synthesis of bispentafluorobenzylcarboxymethoxime derivatives of cortisone and cortisol followed by trimethylsilylation yields compounds with almost ideal gas chromatographic properties. The derivatized steroids generate intense M−·-181 fragment ions in negative ion chemical ionization mass spectrometry. Monitoring of ions at m/z 829 and m/z 903, respectively, for cortisone and cortisol and corresponding fragment ions generated from multideuterated internal standards provides the analytical basis for assessment of local in vivo conversion of cortisol to cortisone in the respiratory system of human subjects. The assay method displays excellent reproducibility with variations ≤10%. Detection limits are ≤1 pg of steroid analyte per injection (S/N > 3). Endogenous levels of cortisone and cortisol, respectively, measured in human samples were as follows: nasal lavage fluid, 47 and 25 pg/ml; bronchoalveolar lavage fluid, 380 and 153 pg/ml; plasma 12.8 and 61.6 ng/ml.

One-Step Conversion of Amino Acids into N-Menthyloxycarbonyl Alkyl Ester Derivatives for Chiral Gas Chromatography

Amino acids dissolved in aqueous methanol (or ethanol) and treated with optically active menthyl chloroformate were converted into N-menthyloxycarbonyl methyl (or ethyl) ester derivatives within a few minutes at room temperature. The obtained diastereomeric derivatives, with the exception of arginine and histidine, had suitable gas chromatographic properties allowing enantiomeric analysis of a large number of proteinogenie and synthetic amino acids.

Application of gas chromatographic retention properties to the identification of environmental contaminants

Gas chromatographic retention indices ( I) were measured for congeners of commonly encountered classes of environmental contaminants, which are often reported as tentatively identified compounds. Several commonly encountered polycyclic aromatic hydrocarbons were employed as I reference standards. These indices were related to boiling points with reasonable accuracy, allowing the estimation of I for additional members of those classes.

Simultaneous analysis of 25 pesticides in crops using gas chromatography and their identification by gas chromatography-mass spectrometry

The simultaneous analysis of 25 pesticides in soy beans and rices was performed by gas chromatography with dual electron-capture detection and nitrogen-phosphorus detection. The pesticides were extracted from the samples with solvent and the Bio-Beads S-X3 clean-up procedure was used. Recovery studies were performed at the 1-ppm level of pesticides added to each crop. Their recoveries ranged between 83 and 105% with coefficient of variations of 0.5–8.2%. The gas chromatographic properties of the 25 pesticides were also investigated. Conformation analysis was achieved by the retention time and characteristic fragment ions using the technique of gas chromatography-mass spectrometry-selected-ion monitoring.

Gas chromatographic-mass spectrometric method for the assessment of oxidative damage to double-stranded DNA by quantification of thymine glycol residues

A technique for the measurement of thymine glycol at parts per million concentrations in double-stranded polymeric DNA is described. The procedure utilizes base to ring-open DNA-bound thymine glycol in the presence of monomeric [ 2H 4]thymine glycol as an internal standard, followed by reduction, solvolytic cleavage, and quantification of the characteristic methyl-2-methylglycerate released from polymeric DNA. Methyl-2-methyl-glycerate is derivatized to form the di-tert-butyldimethylsilyl [(TBDMS) 2] ether to enhance its gas chromatographic properties and electron ionization detection. This assay was tested by measuring thymine glycol levels in native, undamaged DNA (not purposefully oxidized). The measured quantities of thymine glycol are proportional to the amount of DNA analyzed. Components of DNA not containing oxidizable thymine do not contribute to the measured signal from methyl-2-methylglycerate-(TBDMS) 2. These results indicate that there is approximately one thymine glycol per 10 6 bases in undamaged DNA and that this value increases with storage of DNA in refrigerated aqueous solutions.

Gas chromatographic elution order and elution shift modelling for isomer specific analysis of halogenated dioxins

The gas chromatographic retention properties have been modelled for verification of isomer specificity in the analysis of brominated, chlorinated, and bromochlorinated dioxins. The order of elution on non-polar GC columns can be expressed as the sum of the RI of the two halves of the molecule plus the RI value of interactive effects. Retention property modelling has been extended to predicting the shifts in order of elution and relative retentions of tetra-, penta-, and hexa-chloro dibenzo-p-dioxins for polar GC columns.

Confirmation of indandione rodenticide toxicoses by mass spectrometry/mass spectrometry.

Mass spectrometry/mass spectrometry (MS/MS) with collision-activated dissociation (CAD) was utilized to unequivocally distinguish 1,3-indandione rodenticides in 2 cases of anticoagulant toxicosis. Anecdotal evidence provided by the veterinarian in a case involving feedlot cows and physical evidence at the site of occurrence in a similar case involving lambs strongly implicated diphenadione (diphacinone; DP) in both instances. However, high performance liquid chromatography indicated chlorophacinone (CP), not DP, was present in the blood samples obtained from both cows and lambs. Intact 1,3-indandiones exhibit poor gas chromatographic properties, so procedures were developed for analysis by MS/MS using a direct exposure probe for sample introduction. The EI mass spectra of DP and CP contained a base peak at m/z 173, with molecular ions (M+) at m/z 340 and m/z 374 (Cl isotope cluster), respectively. Corresponding MS/MS CAD parent ion spectra of m/z 173 showed an ion of m/z 340 for DP and 374 (Cl cluster) for CP. CAD analysis of the blood extracts showed a parent ion scan of m/z 173 identical to that of CP, with the m/z 374 (Cl cluster). (Additional evidence was obtained by MS/MS examination of the CAD daughter ion spectrum of m/z 374.) Blood extracts from the affected animals revealed CAD daughter ion spectra for m/z 374 identical to that of reference CP. Positive confirmation of CP in both cases led to identification of the source of the toxicant and prevention of further animal exposures.

Determination of aldosterone in human serum by isotope dilution gas chromatography/mass spectrometry using a new heptafluorobutyryl derivative

The formation of a new derivative of aldosterone with heptafluorobutyric anhydride for gas chromatography/mass spectrometry (GC/MS) is presented. The highest and also the most prominent ion of this derivative is observed at m/z 734. The new derivative is, under the described conditions, reproducibly formed, is stable and has good gas chromatographic properties. These characteristics make the new derivative extremely suitable for selective, sensitive, precise and accurate analysis of aldosterone in serum by GC/MS in association with isotope dilution. This is proven by the agreement between the measurement results obtained by two laboratories for samples of three batches of lyophilized control serum. The sample pretreatment procedures used in each laboratory are described.

O-(2,3,4,5,6-Pentafluorobenzyl)oxime-trimethylsilyl ester derivatives for sensitive identification and quantitation of aldehydes, ketones, and oxoacids in biological fluids

The importance of oxoacids in clinical medicine and the analytical difficulties involved in exact quantitation of low concentrations in physiological fluids (decarboxylation, dimerization and enolization) have resulted in continuing efforts to find the best suited derivative for stabilization of the oxogroup prior to gas chromatography. We have found the gas chromatographic properties of aldehydes, ketones and oxoacids in the form of their O-(2,3,4,5,6-pentafluorobenzyl)oxime-trimethylsilyl esters (0-PFBoxime-TMS esters) advantageous to the commonly used 0-ethoxime-TMS esters [l]. The formation of double peaks, corresponding to the syn and anti isomers, is less pronounced, and the higher molecular mass shift on derivatization permits the detection and quantitation of aldehydes and ketones in addition to oxoacids, compounds which elute in the solvent front with other O-substituted oxime derivatives and are therefore not detectable. We describe here some special features of the EI mass spectra of 0-PFBoxime-TMS esters providing a further increase in sensitivity and specificity.

Gas chromatographic retention properties of organoammonium exchanged montmorillonites : II. CH 3N +H 3. (CH 3) 4N +, (CH 3) 3N +CH 2C 6H 5. and 1,4-diazabicyclo[2.2.2]octane·2H +

The gas chromatographic retention properties of four organoammonium tailored montmorillonites were characterized using 68 probe molecules. The retention patterns favored a steric model in which retention was governed by three parameters: adsorbate dimensions and orientation, interlamellar plate separation distance, and inter-cation volumes in the interlamellar region. Tailored montmorillonites are limited in steric selectivity at large interlamellar plate distances by swelling and acceptance of oversized molecules.

Thermoanalytical and gas chromatographic properties of the copper(II) complexes of alkyl-substituted Schiff's bases

A study is presented of the thermoanalytical and gas chromatographic (GC) properties of the copper(II) complexes of twenty four tetradenate Schiff's bases. Variations in thermal stability, volatility and GC retention of the complexes are discussed in terms of stereo-electronic effects of the substituents. Although some complexes decomposed extensively during vaporization above 250°C all, apparently, survive chromatography intact at 200°C. Certain complexes were separated as distinct regio-isomers by GC. Fluorinated ligands still appear to be the most suitable derivatizing reagents for Cu(II).

Short columns for gas chromatography packed with plasma-modified silica gels

The development of contemporary gas chromatography is closely connected with improvements to packing materials and columns. New adsorbents obtained on the basis of treating silica gel with organic compounds in a high-frequency, low-temperature plasma give real possibilities in this direction. The influence of the time of exposure in the plasma on the gas chromatographic properties of packings such as selectivity, efficiency and retention was investigated. For this purpose modified silica gel of particle size 63–71 μm was used as a packing for short gas chromatographic columns (20 × 0.2 cm I.D.). It was found that silica gels modified in plasma, with low degrees of coverage of their surface with polymer, have good selectivity and columns packed with them show high efficiency. The results confirm the opinion that the columns under consideration could be used succesfully instead of the usual 1–2-m long packed columns.

Gas Chromatographic and Spectral Properties of Penta-fluorobenzyl Derivatives of 2,4-Dichlorophenoxyacetic Acid and Phenolic Pesticides and Metabolites

Eleven phenols and 2,4-dichlorophenoxyacetic acid, compounds that may be found in body fluids of humans exposed to pesticides, are derivatized with pentafluorobenzyl bromide and characterized by gas chromatography with electron capture detection. These derivatives are further characterized by positive and negative chemical ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and gas chromatography-Fourier transform infrared spectroscopy. Negative chemical ionization mass spectra of all derivatives have an anionic base peak derived from the parent analyte. In the positive mode the nonchlorinated derivatives have base peaks indicative of the analyte, while chlorinated derivatives are cleaved to give the pentafluorobenzyl cation as base peak. The possibility is explored that ortho-substituted phenols might be formed as byproducts in these derivatizations.

Use of Cyclic Boronates for GC/MS Screening and Quantitation of Beta-Adrenergic Blockers and Some Bronchodilators

Gas chromatographic and mass spectrometric properties of cyclic methyl and n-butyl boronates of 13 beta blockers and bronchodilators were investigated for potential use in screening and quantitation in biological materials of interest. The tested compounds included acebutolol, atenolol, labetalol, levobunolol, metoprolol, nadolol, oxprenolol, pindolol, propranolol, sotalol, albuterol, and isoproterenol. The cyclic methyl boronates were superior in gas chromatographic properties to the corresponding n-butylboronates of these compounds. Higher weights of fragments obtained with n-butyl boronation may be advantageous for analyses of complex biological matrices. Mass spectra and retention times relative to SKF-525A are provided.

Stereochemistry of leukotriene B4 metabolites formed by the reductase pathway in porcine polymorphonuclear leukocytes: inversion of stereochemistry of the 12-hydroxyl group

Leukotriene B4 (LTB4), a potent proinflammatory agent, is a major metabolite of arachidonic acid in polymorphonuclear leukocytes (PMNL). When porcine PMNL were incubated with LTB4 and the products purified by reversed-phase high-pressure liquid chromatography (HPLC), we previously identified two metabolites: 10,11-dihydro-LTB4 and 10,11-dihydro-12-oxo-LTB4 [Powell, W. S., & Gravelle, F. (1989) J. Biol. Chem. 264, 5364-5369]. Further analysis of the reaction products by normal-phase HPLC has now revealed the presence of a third major metabolite of LTB4. This product is not formed in detectable amounts in the first 5 min of the reaction but accounts for about 20-30% of the reaction products after 60 min, when LTB4 has been completely metabolized. The mass spectrum and gas chromatographic properties of the new metabolite are identical with those of 10,11-dihydro-LTB4, suggesting that it is a stereoisomer of this compound. This product was identified as 10,11-dihydro-12-epi-LTB4 [i.e., 5(S),12(R)-dihydroxy-6,8,14-eicosatrienoic acid] by comparison of its chromatographic properties with those of the authentic chemically synthesized compound. Both 10,11-dihydro-LTB4 and 10,11-dihydro-12-oxo-LTB4 were enzymatically converted to 10,11-dihydro-12-epi-LTB4 by porcine PMNL, the former compound being the better substrate. The reaction was reversible, since both 10,11-dihydro-12-epi-LTB4 and 10,11-dihydro-12-oxo-LTB4 could be converted to 10,11-dihydro-LTB4.(ABSTRACT TRUNCATED AT 250 WORDS)

Pentafluorophenyldiazoalkanes as novel derivatization reagents for the determination of sensitive carboxylic acids by gas chromatography—negative-ion mass spectrometry

A convenient access to analytically useful pentafluorobenzyl esters of sensitive carboxylic acids is described. The novel derivatization procedure takes advantage of the chemoselectivity of diazo compounds towards acids and utilizes pentafluorophenyldiazoalkanes as derivatization reagents. The superiority of the diazo reagent over pentafluorobenzyl bromide is demonstrated with the efficient derivatization of sensitive carboxylic acids which decompose extensively when subjected to the routine procedure. The α-methylpentafluorobenzyl (MPFB) esters of mono- and dicarboxylic acids thus formed exhibit excellent gas chromatographic properties. The scope and limitation of the use of diastereomeric MPFB esters is also discussed.

Vinyl chloride-induced DNA adducts I: Quantitative determination of N2,3-ethenoguanine based on electrophore labeling

A sensitive assay for quantitative determination of the vinyl chloride (VC)-induced cyclic DNA adduct N2,3-ethenoguanine (EG) was developed. The method is based on the detection of EG as its di-pentafluorobenzyl derivative (3,5-PFB2-EG). This compound exhibited good gas chromatographic properties and was detected with high sensitivity by gas chromatography with electron capture detection (limit of detection 300 amol/microliters injected solution) or with negative ion chemical ionization mass spectrometry monitoring the [M-181]-fragment ion at m/z 354 (GC-NICI-MS, limit of detection 190 amol/microliters injected solution). EG, its 13C-labeled analog [13C4]-EG and 3,5-PFB2-EG were synthesized and characterized by UV and fluorescence spectrophotometry, 1H- and 13C-NMR spectroscopy and mass spectrometry. The standards were used to optimize the isolation of EG and its derivatization with pentafluorobenzyl bromide (electrophore labeling) at fmol quantities. DNA solutions were spiked with EG, the DNA was depurinated by mild acid hydrolysis, and EG was isolated from the hydrolysates by low-pressure strong cation exchange chromatography with subsequent C18 solid-phase extraction. The extracted EG was electrophore labeled and 3,5-PFB2-EG was detected using GC-NICI-MS. [13C4]EG served as internal standard. 3,5-PFB2-EG was quantitated relative to its 13C-labeled analog by measuring the ion ratio m/z 354/358. The limit of detection for the complete method was 60 fmol EG/mumols guanine. The method was applied to liver DNA from young Sprague-Dawley rats exposed to 600 p.p.m. VC from day 10 through day 14 after birth. The EG concentration in these samples was 1.8 +/- 0.3 pmol/mumols guanine.

Analysis of bentazone herbicide by formation of the methyl derivative in the gas-liquid chromatograph using trimethylanilinium hydroxide

When bentazone herbicide is injected into the gas-liquid chromatograph together with trimethylanilinium hydroxide, it reacts to yield a methylated derivative with good gas-chromatographic properties. This derivatization technique allows a rapid qualitative and quantitative chromatography of this pesticide. Standard deviations were about ±1%.

Gas chromatography on macroporous sulfonated cation exchangers

The retention of compounds of various classes on macroporous sulfonated cation exchangers in the form of the fourth period elements in Mendeleev's table (i. e. in the K, Ca, Co, Ni, Cu, Zn-forms) has been investigated. It has been shown that these sorbents are characterized by a high specificity of molecular interaction. It has also been established that the gas-chromatographic properties of cation exchangers depend on the nature and valency of the metal ion in the ionogenic group.

Mixed silyl ether-perfluoroacyl ester derivatives for gas chromatography/mass spectrometry of oestrogens. Application to the quantitative determination of oestriol in human plasma.

The conversion of oestrogens into mixed derivatives comprising a phenolic silyl ether and one or more alcoholic perfluoroactyl ester(s) is described. They are easily formed in quantitative yield and have excellent gas chromatographic and mass spectrometric properties, making them suitable for analysis by selected ion monitoring. Reaction mechanisms are examined which propose explanations for the experimentally observed optimal reaction conditions. The 3-t-butyldimethylsilyl ether-16 alpha 17 beta-bis(pentafluoropropionate) has been used for the quantitative determination of oestriol in plasma by gas chromatography/mass spectrometry using a stable isotope internal standard. Comparison with the pertrimethylsilyl ether of oestriol indicates higher specificity and better precision for low-level (less than 0.5 ng ml-1) estimations.