Simultaneous determination of C1−C8 n-alkyl acetates and corresponding mono-, di- and trichloroacetates on glass capillary columns with programmed temperature rise

Summary Gas chromatography of mixtures of aliphaticn-alkyl acetates (CH₃–COOR), chloroacetates (CHCl₂–COOR), dichloroacetates (CHCl₂–COOR) and trichloroacetates (CCl₃–COOR), where the alcohol chain length (R) varied between 1 and 8, has been studied on SE-30, Carbowax 20M and OV-351 glass capillary columns with programmed temperatures from 50°C at 2, 4, 6, 8 and 10°C/min. Compounds in the homologous series are eluted in the direct order from methyl ton-octyl acetate. The isomeric chloro esters are eluted on SE-30 according to their boiling points in the order: mono-, di- and trichloro isomer, whereas on polar columns di- and trichloro esters are eluted in the reverse order. The complete separation of all 32 individual components from the mixture could not be reached by any single column, the best separation occurred on SE-30. The mixture can, however, be separated by using columns with polar and non-polar stationary phases. The relative retention times for the compounds are given and the retention order discussed.     

Glass-capillary gas chromatography of chlorobenzenes on SE-30 and Carbowax 20M columns. Simultaneous determination of chlorobenzenes and chlorophenols

Summary Gas chromatography of benzene and all chlorobenzenes has been studied on SE-30 and Carbowax 20M glasscapillary columns under various operating conditions. The benzene isomers are eluted on both columns according to their boiling points. Separation of all components in a mixture is achieved on Carbowax 20M, whereas on SE-30 the peaks of closely related isomers overlapped. Also one partial overlapping is observed on a non-polar phase. The relative retention times for compounds are given and the retention order is discussed. The retention behaviour of chlorobenzenes and chlorophenols is compared. By using an SE-30 quartz-capillary column a mixture of 33 individual components gives 29 resolved peaks the analysis time being less than 26 minutes. A polar column proved to be unsuitable for the separation of polychlorophenols.     

Gas chromatographic study of acetyl derivates of chlorinated guaiacols

Summary The gas chromatography of acetyl derivatives of guaiacol and all chlorinated guaiacols has been studied on SE-30, OV-351 and Carbowax 20M capillary columns. The retention order and relative retention times under isotermal and temperature-programmed conditions are discussed. Different retention times for all mono- and dichloro compounds have been observed on the SE-30 column. However, all trichloroguaiacol isomers were separated only on polar columns. The best overall temperature-programmed separations have been achieved on an SE-30 capillary column.     

Gas chromatographic retention indices for C6 alkanols on OV-101 and Carbowax 20M capillary columns

Summary Gas chromatographic retention indices for 16 C₆ alkanols measured on capillary columns coated with OV-101 methylsilicone and Carbowax 20M propylethyleneglycol liquid phases at 80° and 90°C were determined. The respective standard deviation values were 0.5 and 0.8 i.u. The correlation between the retention indices measured on non-polar and polar stationary phases and the boiling points of the alkanols was studied.     

Influence of elution temperature and polarity of different stationary liquids on the resolution of the diastereomers of norpristane, pristane and phytane

It is shown that glass capillaries of high separation efficiency and optimized selectivity are necessary to resolve the diastereomers of the C₁₈---C₂₀ acyclic isoprenoid alkanes. In accordance with theory, relatively low column temperatures favour maximum selectivities (relative net retention times). Therefore high phase ratios of tailor-made glass capillaries are one of the prerequisites. In addition, the resolution can be more easily achieved with Carbowax 20M or even more polar stationary liquids than with non-polar ones.     

Capillary supercritical fluid chromatography of aliphatic amines. Studies on the selectivity and symmetry with three different columns using carbon dioxide or nitrous oxide as mobile phase

The supercritical fluid chromatography of intact aliphatic amines with different columns is described. One group of amines was based on N,N-dimethyl-n-octylamine and related primary and secondary amines, and the other on the amino alcohol metoprolol and several of its analogues. Columns with three different phases were investigated, one non-polar coated with 5% phenyl methyl polysiloxane and two more polar with 25% cyanopropyl methylphenyl polysiloxane and Carbowax 20M. Generally, equal molar amounts were injected under splitless conditions and the peak symmetry was recorded. The system with the non-polar silicone phase was more inert, followed by the wax-phase column. The cyanopropyl column gave severe peak tailing although it was loaded with five times more of the amines than the other columns. The selectivity was investigated and was found higher with the two polar columns. Both showed a marked increase in the retention of amines with free hydrogens. With nitrous oxide the selectivity was almost the same as that with carbon dioxide as mobile phase. The nature of the flame ionization detector changed, however, giving a negative baseline drift on pressure programming. An interesting conclusion is that the amines are chromatographed as such with carbon dioxide as the mobile phase.     

Capillary gas chromatography of esters correlations between structure and retention index

Summary The retention index of twenty different homologous series of esters have been determined experimentally on polar (Carbowax 1540) and non-polar (squalane) columns. General equations to calculate retention index have been established by statistical methods. The influence of the length and inductive effect of acid and alcohol chains and the relative position of the carboxylic group are discussed.     

Gas-liquid chromatographic analyses : IV. Glass capillary gas chromatography of methyl and chloromethyl monochloro esters of aliphatic C5-carboxylic acids

The gas chromatography of methyl and chloromethyl esters of pivalic, 2-methylbutyric, isovaleric and valeric acid and certain of their monochloro derivatives was studied. Separation of the combined mixtures of methyl and chloromethyl esters was better on Carbowax 20M than on SE-30. The retention times of esters with subtituents adjacent (i.e. at C-2) to the carboxyl group appear to be sensitive to column polarity, particularly in the case of the chloromethyl esters. The retention order and relative retention times of compounds are discussed.     

Fatty acids. VII. The gas-liquid chromatographic properties of all dimethylene interrupted methyl cis,cis-octadecadienoates.

The gas-liquid chromatographic behaviour of all the dimethylene interrupted methyl cis,cis-octadecadienoates was studied on polar (Carbowax 20M, FFAP, DEGA, DEGS and Silar 10C), semi-polar (XE-60) and non-polar (SE-30, OV-101 and Apiezon L) stationary phases. The equivalent chain length of each isomer is recorded; the possibility of separation and the retention pattern of these isomers are discussed.     

Determination of volatiles in spirits using combined stationary phases in capillary GC

Summary The analysis of spirits with a single stationary phase is still an unsolved problem; the two amyl alcohols, ethyl acetate and acetal are not separated on a polar column, methanol and acetaldehyde coelute from an apolar column. Trials with coupled columns of different polarities showed that optimum results were obtained with a 40 m capillary column, comprising 6 m of Carbowax 20 M, 12 m of 1:1 Carbowax 20M:OV1 mixture and 30 m of PS 264. Best results were achieved when a 1 m retention gap was used, injecting a small amount of sample and using a 7 cm syringe needle.     

The selectivity and polarity of carbon layer open tubular capillary columns modified with a polar liquid phase

The polarity of carbon layer open tubular (CLOT) columns coated with a layer of non-porous graphitized carbon black (Carbopack B) modified with an appropriate amount of polar polyglycol liquid phase has been evaluated and compared with that of standard polar (Supelcowax-10) and non-polar (SPB-1) bonded phase open tubular columns. The efficiency and selectivity were measured at various temperatures and the polarity of the columns was evaluated by use of McReynolds' constants and the difference in apparent carbon number, ΔC of linear alkanes and alcohols. The polarity of the CLOT column was found to depend on temperature, and changing the analytical conditions therefore enabled the separation of compounds of different polarity whose reciprocal position and resolution were affected by temperature. The application of calculation methods which enable programmed temperature retention times to be predicted from isothermal data was also found to be possible when the polarity of the CLOT column changes with temperature.     

多壁碳纳米管作为气相色谱固定相的性能研究

将甲烷催化裂解法生产的经过纯化的多壁碳纳米管(PMWCNTs)、活性炭、石墨 化碳黑(Carbopack B)分别填装成气相色谱填充柱,比较它们分离烷烃、芳香烃、 卤代烃、醇、酮、醚、酯类的性能。分别在PMWCNTs和Carbopack B上涂清5%(w/w) 的Carbowax 20M,填装成气相色谱填充柱后,比较它们分离醇、酮、醚、酯、有机 酸类的性能。结果表明,PMWCNTs是一种性能优异的气相色谱固定相。与相同比表 面积的Carbopack B石墨化碳黑相比较,它有更强的保留能力,适合于分析沸点相 对较低的化合物;具有更均匀的表面,表现为极性化合物亦可得到对称的峰形;理 论塔板数较小。此外,和Carbopack B一样,PMWCNTs涂清5% (w/w) Carbowax 20M 后可用来分离极性化合物,甚至是强极性的小分子有机酸。     

氮杂冠醚聚硅氧烷固定液的色谱保留机理

氨杂冠醚聚硅氧烷是一类呈中等极性的新颖气相色谱固定液．本文通过测定醇、酯、卤代烃和苯系列化合物的色谱保留值和相应势力学参数，研究它对上述不同化合物的保留机理及其分子识别的热力学性质     

Fatty acids. IV. Synthesis of all the dimethylene-interrupted methyl octadecadiynoates and a study of their gas-liquid chromatographic properties.

All the dimethylene-interrupted methyl octadecadiynoates have been synthesised and the gas-liquid chromatographic behaviour of these isomers was studied on polar [Carbowax 20M, FFAP, DEGA, DEGS and Silar 10C (recently renamed as Apolar 10C)], semi-polar (XE-60) and non-polar (SE-30, OV-101 and Apiezon L) stationary phases. The possibility of identification and separation of these isomers is discussed. The delta3a,7a isomer was found to decompose on most polar phases and the delta2a,6a isomer could not be eluted from the Carbowax 20M phase.     

Comparison of column properties in reversed-phase chromatography: monolithic, cholesterolic and mixed bonded stationary phases

A commercial Chromolith C18 column and two new stationary phases with mixed ligands bonded on the Kromasil silica gel support, SG-MIX and SG-Chol, were characterized using simple tests based on the retention of non-polar, basic and acidic compounds. Polar and methylene selectivity tests in acetonitrile-water and methanol-water mobile phases revealed lower hydrophobicities of the SG-MIX and SG-Chol columns in comparison to the Chromolith column. The columns were further characterized using new test criteria - gradient oligomer capacity and isomeric selectivity and peak symmetry of naphthalene di-sulphonic acids in aqueous mobile phases. The cholesterolic column shows greater gradient oligomer selectivity for the separation of oligoethylene glycol samples than the SG-MIX and the Chromolith columns. Increased retention and peak tailing, but decreased isomeric selectivity for naphthalene-di-sulphonic acids was observed with the SG-MIX column, because of interactions with various polar bonded groups.     

Prediction of the separation number of capillary columns in programmed temperature gas chromatographic analysis

The efficiency of capillary columns in programmed temperature analysis can be evaluated by calculation of the separation number (“Trennzahl”). A procedure for the prediction of this parameter at various initial temperatures, carrier gas pressures and heating rates, by using as the starting data the retention times and the peak widths obtained in some isobaric and isothermal runs is described. An equation is proposed that permits to obtain the values of the peak width at half height in any isothermal and linearly programmed temperature gas chromatographic run and therefore to calculate the separation number value. The effect on this parameter of the column polarity was investigated by using polar and non-polar compounds (n-alkanes and 1-alcohols).     

HPLC retention behaviors of poly-aromatic-hydrocarbones on Cu(II)-octabromotetrakis(4-carboxyphenyl)porphine derivatives-immobilized aminopropyl silica gels in polar and non-polar eluents

As one of approaches of developing novel HPLC stationary phases, we prepared Cu-octabromotetrakis(4-carboxyphenyl)porphine derivative-immobilized silica gels (Cu-OBTCPP(D)), and evaluated the availability of the resultant Cu-OBTCPP(D) as a stationary phase for separation of poly-aromatic-hydrocarbons (PAHs) and their related compounds. A Cu-OBTCPP(D) column was revealed to have an ability to separate simple PAHs and be useful as a stationary phase in both polar and non-polar eluents. The retention property of the Cu-OBTCPP(D) column was evaluated in various comparative experiments using commercially available columns. In comparison with 2-(1-pyrenyl)ethyl dimetylsilyl silica gel column (PYE column) regarding the retention behavior for PAHs etc., the Cu-OBTCPP(D) column showed stronger interactions involving pi electron in non-polar eluent than PYE column. In comparison with a pentabromobenzyloxy propylsilyl silica gel column (PBB column) regarding the influence of bromination, the Cu-OBTCPP(D) column was affected differently from the PBB column. In comparison with nitrophenylethyl silica gel column (NPE column) regarding the retention behavior for compounds having a dipole in a non-polar eluent, the Cu-OBTCPP(D) column showed electrostatic interactions such as dipole-dipole interaction equivalent to or larger than the NPE column.     

Wide-bore capillary column for the direct analysis of ethanolamines and ethylene glycols

Summary The GC separation of a mixture of three ethanolamines and four ethylene glycols without any preliminary derivatization, on a wide-bore capillary column coated with Carbowax 20M is described. These high-boiling and polar compounds elute giving simmetrical peaks and show good resolution. The analysis is completed in less than 14 minutes.     

Evaluation of New Stationary Phases for the Separation of Fatty Acid Methyl Esters

In the analysis of fatty acids, one of the most commonly used tools is a GC separation of the fatty acid methyl esters (FAME). Many researchers perform this separation using a non-polar phase such the ubiquitous 5% phenyl / 95% methyl capillary columns found in most every chromatography laboratory. Numerous laboratories have also turned recently to polar phases such as 70% cyanopropyl columns, as this type of chemistry provides increased selectivity for unsaturated compounds, and thus improved separation of cis/trans and ω³/ω⁶ FAME isomers. Here, a series of columns nominally having 60, 70, 80, and 90% bis-cyanopropyl content have been tested for the separation of FAME isomers. Trends in retention and the influence of increasing phase polarity on effective and fractional chain lengths are highlighted to provide the FAME chromatographer with insight into which of these novel stationary phases might be best suited to their particular application. In addition, the elution temperatures (T_e) of the FAME and linear alkane standards are presented, as this information will be of value to comprehensive two-dimensional multidimensional GC (GC × GC) users who wish to use these columns in the primary dimension separation.     

Hydrophilic interaction chromatography using amino and silica columns for the determination of polar pharmaceuticals and impurities

Hydrophilic interaction chromatography (HILIC) is described as a useful alternative to reversed-phase chromatography for applications involving polar compounds. In the HILIC mode, an aqueous-organic mobile phase is used with a polar stationary phase to provide normal-phase retention behavior. Silica and amino columns with aqueous-acetonitrile mobile phases offer potential for use in the HILIC mode. An examination of the retention and separation of several pyrimidines, purines, and amides on silica and amino columns from three manufacturers revealed that mobile phases should contain a buffer or acid for pH control to achieve similar and reproducible results among columns from different sources. Amino columns may also be used in an anion-exchange mode, which provides an advantage for some applications. In some cases, silica can provide different selectivity and better separation than an amino column. Example applications include: low-molecular-mass organic acids and amides as impurities in non-polar drug substances, 5-fluorouracil in 5-fluorocytosine, guanine in acyclovir, and different selectivity for polar basic compounds compared to an ion-pairing system.