Carbon-13 NMR spectra of hydroxylated bile acid stereoisomers

Carbon-13 NMR signals were assigned for the complete set of the 26 theoretically possible isomers of methyl 5β-cholanates having one to three hydroxy groups at positions C-3, C-7 and/or C-12 in the nucleus. Substituent effects on the ¹³C NMR shielding data serving to characterize the position and configuration of the hydroxy groups are discussed.     

Capillary gas chromatography of hydrogenation products of 1,5,9-cyclododecatriene stereoisomers

Summary The separation of the products obtained by the hydrogenation of 1,5,9-cyclododecatriene stereoisomers on fused-silica capillary columns coated with dimethylsilicone and cyanopropylmethylsilicone stationary phases was investigated. Retention indices of cyclododecatrienes, cyclododecadienes, cyclododecenes and cyclododecane were determined at three temperatures. The respective standard deviations were 0.3 and 0.6 i.u. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic hydrocarbones is discussed.     

氯代苯甲酸异构体的毛细管气相色谱分析

氯代苯甲酸是一种重要的精细化工产品,用途广泛,如用于合成临床治疗精神抑郁症的吗氯贝胺[1]及有机颜料中间体N (3 氨基 4 氯代苯甲酰基) 2 甲基 3 氯代苯胺[2]。但是氯代苯甲酸各异构体的性质差异极大,用途也不尽相同[3,4]。工业产品或多或少都会含有位置异构体,因此测定[5 7]氯代苯甲酸中各异构体含量就显得相当重要。已有报道的分析方法,或对仪器性能要求高,或操作繁琐,或分离效果不甚理想,因而在实际应用中受到一定的限制。考虑到氯代苯甲酸具有强极性、低挥发性等特点,本文采用甲酯化衍生物法对氯代苯甲酸异构体进行了气相色谱分…     

Capillary reaction gas chromatography

Summary Thermal decomposition of C₆ hydrocarbons (hexane, cyclohexane, 2-methylpentane, 2,2-dimethylbutane and trans-2-hexene) on a nickel catalyst and on alumina was studied by reaction gas chromatography. The products were analyzed on two capillary columns containing squalane and Citroflex and were identified on the basis of their retention indices. The degree of conversion of the initial substances and the relative contents of the products were determined. On the basis of the results obtained, the probable course of the catalytic decomposition is discussed.     

Capillary gas chromatographic separation of bile acid acyl glycosides without thermal decomposition and isomerization

A direct method for the capillary gas chromatographic (cGC) separation of the acyl glycosides of bile acids was successfully attained. The free acyl glycosides were derivatized to their complete trifluoroacetyl (TFA) derivatives with N-methyl-bis(trifluoroacetamide). The highly volatile TFA derivatives were chromatographed on a short-length (10 m), narrow-bore (0.1 mm) capillary column coated with a thin film (0.1 microm) of 5% phenyl polysilphenylene-siloxane at a column temperature below 280 degrees C. Each exhibited a single, well-separated peak of the theoretical shape without any accompanying peaks due to the thermal decomposition and isomerization. The bile acid 24alpha-glucosides were always eluted faster than the corresponding 24beta-glucosides, which eluted before the corresponding 24beta-galactosides. The method could be usefully applied to biosynthetic and metabolic studies of bile acid acyl glycosides in biological materials.     

Capillary gas chromatography of monosubstituted cyclopentenes and cyclohexenes

Summary Regularities in the variation of retention indices (I) and index increments (δI/°C, H, ΔI) of monosubstituted cyclopentenes and cyclohexenes with molecular structure on various liquid phases are discussed. An equation for the linear dependence of I on the carbon number is given. Differences in gas chromatographic characteristics between 1- and 3-isomers are more pronounced in the n-alkylcyclopentene series. In the n-alkylcyclohexene series extension of the side chain and increase of column temperature lead to the inversion of the elution order of 1-and 3-isomers. The temperature increments of I for cyclenes are markedly greater than those for open chain hydrocarbons (n-alkenes, n-alkynes).     

Resolution of stereoisomers of dipeptides by gas chromatography on Chirasil-Val

Several dipeptides have been separated into stereoisomers (enantiomers, diastereomers, sequential isomers) by gas chromatography on Chirasil-Val. Sufficiently volatile N-trifluoroacetyl dipeptide methyl esters were formed at ambient temperature, thus avoiding racemization (or epimerization, respectively, and cleavage of the peptide bond. This method is suitable for ascertaining the stereoisomeric composition of dipeptides in biological samples.     

Capillary gas chromatography of some metal acetylacetonates

Summary The retention and resolution of simple mixture of Al(III), Cr(III), Co(III), and Fe(III) acetylacetonates were investigated on capillary columns coated with methyl and methyl phenyl silicones (OV-1 or OV-17) used as the stationary phase, at different column temperatures and carrier gas flow rates. Successful elution and good resolution were obtained only for the Al(III) and Cr(III) complexes, both under isothermal and programmed-temperature conditions; better resolution was observed on the column coated with OV 17.     

Infrared correlations in the bile acid series

The infrared spectra of a number of esters and free acids in the cholanic acid series have been examined with the aid of a special solvent system which overcomes the problem of solubility. Eleven absorption regions in the 9–12 μ region have been correlated with specific substitution on the steroid nucleus and side chain. In certain cases, perturbations were found when di- or tri-substitution occurred in rings A, B, andJor C.     

Capillary gas chromatography of amines with ammonia as carrier gas

The use of ammonia as a carrier gas for the chromatography of aliphatic and aromatic amines has been investigated. As compared to nitrogen, ammonia gave drastically improved peak symmetry and lower capacity factors (k′) for primary and secondary amines on polar (Polyethylene glycol) and medium Polar (methylphenylcyanopropylsilicone) stationary Phases. The effect of ammonia was more Pronounced at low column temperatures. Considerably better detection limits of primary and secondary amines were obtained with ammonia as carrier gas than with nitrogen. No detrimental effects of using ammonia were observed on the gas chromatograph or on the columns over a period of about one year.     

Capillary complexation gas chromatography in analysis of halohydrocarbons

Summary Investigations were carried out on capillary columns coated with liquid stationary phases possessing cyano (3-cyanopropylmethylpolysiloxane) and thiol (3-mercaptopropylmethylpolysiloxane) groups. These phases were modified by bonding CuCl₂ and CoCl₂ to cyano groups or NiCl₂ and CoCl₂ to thiol groups. The modified phases were examined in order to assess their usefulness for the analysis of aliphatic and aromatic halohydrocarbons. A number of retention parameters (I, ΔMe, Vg), which allow characterisation of the specific interactions between the bonded metal and the halohydrocarbon molecule, were determined for the columns both with and without the metal. The separations performed show that the columns with bonded metals are applicable for the practical analysis of the halohydrocarbons.     

Capillary gas chromatography of aromatic bicyclic and tricyclic spiro ketones

Summary The separation of some aromatic bicyclic and tricyclic spiro ketones on fused silica capillary columns coated with polydimethylsiloxane, cyanopropylmethylsiloxane and poly(ethylene glycol) stationary phases was investigated. Retention indices were determined at two temperatures in order to enable understanding of the compounds’ chromatographic behaviour. The respective standard deviation values were 0.8, 0.5 and 0.3 index units. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic spiro ketones is discussed.     

Capillary gas chromatography/negative ion chemical ionization mass spectrometry for the quantification of bile acids including 1 beta-hydroxylated and unsaturated bile acids in serum and urine

12 bile acids, including 1 beta-hydroxylated and unsaturated bile acids, have been quantified by capillary gas chromatography/negative ion chemical ionization mass spectrometry, using the trimethylsilyl(TMS) ether derivatives of bile acid pentafluorobenzyl(PFB) esters. The analysis time is 12 min and the minimum measurable amount is 100 fg for each bile acid. Bile acids in 200 microL of serum and 50 microL of urine from healthy human adults were measured. These small sample sizes enhance the practicality of using this method as a screening test for bile acids in the serum and urine of human infants, where small sample size is a major problem.     

Capillary gas chromatography of plant tissues and soil phenolic acids

Summary A method for the separation of phenolic acids along with shikimic and quinic acids by means of capillary gas chromatography is described and discussed. The method involves the previous derivatization of the acids to trimethylsilyl derivatives and it has been applied to the separation of acids extracted from olive leaves and roots, elm leaves and a soil A horizon. Quite good results were achieved both from qualitative and quantitative points of view. Qualitative differences have been pointed out in the phenolic acid composition of two olive cultivars and between leaves and roots of the same cultivar; also two elm species can be discriminated on the basis of the phenolic acid content.