Monte-carlo simulation of gas chromatographic separation for the prediction of retention times and peak half widths

Summary A new method for prediction of gas chromatographic retention times and peak half widths is based on the renewal theory. The only requirements are the heats of vaporization of the compounds to be separated and one calibration measurement. With this data, retention times and peak half widths can be predicted for isothermal as well as temperature-programmed gas chromatography. For the separation of non-polar substances on non-polar stationary phases the prediction error for retention times is approx. 1–2%. First simulations of polar molecules and polar stationary phases indicate that this method is also applicable in these cases but some extension will be required.     

Temperature dependence of the resolution of diastereomeric isoprenoids in capillary GC. Experiments with 50 μm, 100 μm,and 250 μm i.d. Columns

The resolution of the diastereoisomers of norpristane, pristane, and phytane was studied as a function of the column internal diameter and/or the residence time of the compounds in the column. Increasing the residence time in the column by operating the column at a lower temperature program rate enhances the resolution more than reducing the internal diameter of the column. Practical experience with ultra narrow bore columns is also presented.     

Optimum gas chromatographic conditions in wall-coated capillary columns. Extended and simplified forms of the Golay-equation

Band broadening in capillary columns is satisfactorily described by the Golay-equation extended to situations of appreciable pressure drop by Giddings. In practice, however, several simplifications are often made. The effect of these simplifications on the calculated values of the minimum plate height and optimum carrier gas velocity are treated systematically.     

Quantitative relationship and application of 3‐benzylketoimine metal dichlorides in the analysis of volatile hydrocarbons

The paper concerns the analysis of volatile hydrocarbons on newly designed and produced capillary columns. According to the type of coating used, the columns are of the PLOT type, and according to the adsorbate‐adsorbent type interactions they belong to the category of complexation GC. The adsorbent used was silica, whose surface was modified with bonded 2‐(3‐triethoxysilylpropylimino)‐3‐(benzyl)‐pentanone‐4 to change the adsorption characteristics. The presence of the ketoimine group of strongly electron‐accepting properties permitted the binding of transition metals. The metal ions are capable of interacting selectively with nucleophilic compounds including olefins. The transition metal ions used for sorbent modification were copper(II) chlorides and nickel(II) chlorides. The supported adsorbent was immobilised by bonding the modified silica to the column walls by a film of poly(dimethylsiloxane). Due to this strategy, the coating was very stable, no sorbent loss from the column was observed and the column could be washed with solvent. Besides exemplary separations, the paper quotes retention parameters of the group of compounds analysed and presents a discussion of the specific interactions between the adsorbate and adsorbent.     

Application of the “cooled needle” technique to split and splitless sampling onto capillary columns

Cooled needle sampling using syringes was applied to splitless injection and to simulated distillation analyses. Slight changes of the construction of the previous device are also described. The changes concern the temperature profile within the injector and especially the vaporization insert. Even with the low carrier gas flow through the injector during splitless injection, discrimination by component volatility can be avoided. Precision and accuracy of simulated distillation data obtained with split sampling also can be improved by the cooled needle technique.     

The theoretical basis of column chromatography in multicomponent separations. Part 1: Analytical requirements and peak resolution. Development of a high performance column system

The point of our published papers since 1957 is reviewed. The relations between the required value of peak resolution, K₁ (or R), and peak separation, K₃ (eqn 9); K₁ and relative accuracy of a peak height quantitative method, P_h (eqn. 10); K₁ and relative accuracy of a peak area method, P_a, (eqn. 12) at different concentration ratios, ?, are derived. The final result in Table 2 shows a large influence of ? on the required value of K₁. The approximately linear relation between peak width and retention value (eqn. 18) exists not only in GC. but also in HPLC. Plate height values H¹ and H^∞ for a solute with capacity ratio, k′, equal to unity or approaching infinity, respectively, are used to evaluate the column efficiency (eqn. 20). The measuring methods (eqn. 21,22,23) and parameters effecting on H¹ and H^∞ are given for GC packed column (eqn. 24), GC open tubular column (eqn. 25) and HPLC (eqn. 26). In the light of this, columns of high efficiency were developed. Some typical chromatograms for high speed analysis and separation of complex mixtures are given.     

Preparation,evaluation, and comparison of wide bore (320 μm) and narrow bore (50 μm) cyanosilicone-coated capillary columns for gas chromatography

The preparation of wide bore (320 μm) and narrow bore (50 μm) fused silica capillary columns is described for immobilized cyanopropyl substituted silicones containing 60 and 88% substitution. The effect of high temperature deactivation with cyanopropylcyclosiloxanes was studied with a special test mixture. Curing was achieved with dicumyl peroxide or azo-tert-butane. The columns were evaluated and compared in terms of efficiency, activity, polarity, and temperature stability. Different coating methods were compared for the narrow bore columns. The activity of the 60% cyanopropyl columns that had been immobilized with dicumyl peroxide was significantly larger than for azo-tert-butane immobilized columns. The polarity of polar columns appeared to depend greatly on column temperature and is completely different for wide and narrow bore columns.     

Synthesis,isolation, and chromatography of perdeuterated α-1,2,3,4,5,6-hexachlorocyclohexane

Perdeuterated α-1,2,3,4,5,6-hexachlorocyclohexane (α-PDHCH) was synthesized and isolated in pure form. α-PDHCH was baseline separated from unlabeled α-HCH by high resolution gas chromatography on different stationary phases. α-PDHCH was also resolved into its enantiomeric forms by application of a chiral GC phase. Furthermore, chiral chromatography of a mixture of labeled α-PDHDH and unlabeled α-HCH resulted in four peaks. Standard solutions of α-PDHCH are recommended both as recovery standard for sample clean-up and as internal standard for the quantitation of chlorinated hydrocarbons with GC/MS or GC/ECD in environmental samples.     

Theory of GC2 — an unusual approach

In contrast to traditional theoretical approaches by calculation of (nonexistent) theoretical plates, a unified theory of gas chromatography as given by a definition of the resolution analogue to methods in signal processing or spectroscopy using the well-known Kovacz indices as fundamental scale. A derivation of the thusly defined resolution from basic physical principles yields very practical formulae for peak width, maximum load, substance flow in peak maximum, concentration of substance in the carrier gas and other interesting parameters in dependence of capillary diameter, capillary length, film thickness, carrier gas speed, viscosities etc. Diagrams show favourite conditions for detectors responding on absolute substance flow (e.g. FID) or on concentrations.     

高惰性、低流失、高效石英毛细管色谱柱的研制及有机氯农药残留量的分析

通过过在三种不同脱活试剂中加入二丁基二月桂酸锡催化剂对石英石细管柱进行预脱活处理，屏蔽石英毛细管内表面的活性点，改善石英毛细管柱内表面与固定相的润湿性，提高色谱柱的柱效和耐温性，降低柱流失，从而制备出高质量的石英毛细管色谱柱，同时考察了不同固定相与不同脱活层的润湿性，对中药材和食品中有机氯农药残留量进行了分析，得到了满意的效果。     

6-tert-Butyldimethylsilyl-2,3-dimethyl-α-, β-, and γ-cyclodextrins,dissolved in polysiloxanes,as chiral selectors for gas chromatography. Influence of selector concentration and polysiloxane matrix polarity on enantioselectivity

The enantioselectivity of three chiral selectors, 6-t-butyldimethyl-silyl-2,3-dimethyl-α-, β- and γ-cyclodextrin (TB-α-CD, TB-β-CD, TB-γ-CD), are compared and discussed for a range of chiral test compounds. TB-β-CD in particular offers high enantioselectivity for a variety of chiral compounds and has the special property of excellent solubility in different alkylpolysiloxanes, including the weakly polar variety, because of its weak self-association. To investigate the influence of the polarity of polysiloxane matrices this selector can be used at a wide range of concentrations in the most suitable polysiloxane matrices and at low separation temperatures without impairment of resolution by peak broadening and symmetry distortion.     

Gas chromatographic indicator of the ability of five- and six-membered heterocyclic nitrogen-containing compounds for self-association in pure liquids

The retention indices of five- and six-membered nitrogen-containing heterocyclic compounds (pyrrole, pyrazole, imidazole, 1,2,4-triazole, pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, isoxazole, and oxazole) were determined on a capillary column with the OV-101 nonpolar stationary phase. The difference between the experimentally determined boiling point of the sorbate and that calculated from GC data (δT _b.p.) was proposed as a gas chromatographic indicator sensitive to the ability of substances to form self-associates in pure liquids. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 730–733, April, 1999.     

The use of glass and fused silica open tubular columns for the separation of structural,configurational, and optical isomers by selective complexation GC: Sec-alcohols and ketones

The use of glass and fused silica open tubular columns for selective separation of structural, configurational, and optical isomers (enantiomers) of underivatized aliphatic alcohols and ketones by complexation gas chromatography on optically active metal chelates is described. The method represents a powerful analytical tool for the precise determination of diastereomeric (d.e.) and enantiomeric (e.e.) excesses in asymmetric syntheses and in natural product characterization. The direct screening of the enantiomeric composition and absolute configuration of terpinene-4-ol, the aggregation phermone of Polygraphus poligraphus (L), is described.     

Characteristics and performance of gas chromatographic detectors with glass capillary columns

A comparison of the characteristics and Performance of the flame ionization, electron capture, and flame photometric detectors with capillary columns is described. Factors which may affect the limits of detection, linearity, chromatographic peak shape, and other detector performance characteristics are discussed and compared with the results of a model derived for the behavior of concentration and mass flow-rate dependent chromatographic detectors used with capillary GC systems. Examples are given of highly complex and labile mixtures such as pesticide residues and products from coal hydrogenation.     

The fabrication of poly (polyethylene glycol diacrylate) monolithic porous layer open tubular (mono‐PLOT) columns and applications in hydrophilic interaction chromatography and capillary gas chromatography for small molecules

The easy shrinkage and swelling of polymer monolithic column when exposed to mobile phase with different polarity is a problem that cannot be ignored. To overcome this drawback, a convenient aqueous two‐phase polymerization approach was used to prepare poly (polyethylene glycol diacrylate, PEGDA) monolithic porous layer open tubular (mono‐PLOT) columns (150 μm). The poly(PEGDA) mono‐PLOT column with homogeneous polymer porous layer was synthesized successfully. A maximum plate number of 41,500 plates per meter for allyl thiourea was obtained under a velocity of 1.8 mm/s. Several kinds of polar molecule were separated on the proposed mono‐PLOT column and a typical hydrophilic interaction retention mechanism was observed. High speed separation of benzoic acids was also carried out, baseline separation of five benzoic acids was successfully achieved within 5 min with a 70 cm mono‐PLOT column at 50°C. Furthermore, the resulting PLOT column was also successfully applied to separate standard analytes of three DNA oxidative damage products and RNA‐modified nucleosides and four chlorophenols. At last, the column could separate alcohols, alkanes, and aromatic isomers via GC. It had more than 20,000 plates per meter for butanol – higher than commercial coatings open tubular columns.