Use of equivalent isothermal retention index for identification in gas chromatography with linear temperature programming

Conclusions The equivalent isothermal index which the authors proposed earlier enables substances to be identified reliably under conditions of gas Chromatographic analysis with linear temperature programming.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 679–680, March, 1970.     

An alternative approach for the estimation of equivalent temperature in gas chromatography

The temperature at which the isothermal retention time (tRiso) is equal to the temperature-programmed retention time (tRTPGC) or the isothermal retention index (Iiso) is equal to the temperature-programmed retention index (ITPGC) is defined as the equivalent temperature (Teq). The Teq of one-, two-, three-, and four-step temperature-programmed gas chromatography (TPGC) of unsaturated fatty acid methyl esters (FAMEs) from Chinese mustard seed oil is calculated. All of the tR values obtained at the Teq (tRTeq) are very close to the tRTPGC. The highest difference for each chromatogram is less than 0.5%. The slight deviation may partly arrive from the difficulty in setting the desired carrier gas flow rate. Also, good agreement among equivalent chain length values determined by different methods is observed, including the graphical method at the Teq. Therefore, it is speculated that the proposed method may facilitate the GC identification of FAMEs as well as other organic compounds in TPGC by using the available isothermal retention index database.     

Kinetic studies of reactions connected with gas evolution under isothermal conditions in the derivatograph

Journal of Thermal Analysis and Calorimetry - A simple method has been proposed to achieve reliable thermostatic control of the oven of the Derivatograph by applying a calibrated stabilized voltage...     

Characteristics of elution profile in radial chromatography under linear conditions

Radial chromatography is one of the most efficient tools for the fast analytical and preparative separation of complex samples. Compared to conventional axial liquid chromatography, it has obvious advantage espe- cially in the preparation of biological sa…     

GC behaviour of symmetrical n-dialkyl sulphides under isothermal and temperature programming conditions

Retention indices were determined for a homologous series of n-dialkyl sulphides on three stationary phases (SE-30, OV-17 and XE-60) under isothermal and linear temperature programming conditions. Under these two different GC conditions, equations were derived for each of the three stationary phases which showed the dependence of retention index on the number of carbon atoms and the boiling points for a homologous series of n-dialkyl sulphides. The equation for the correlation isothermal retention index was shown to be applicable to the identification of n-dialkyl sulphides using linear temperature programming. It was found that the GC behaviour of n-dialkyl sulphides makes these compounds suitable for use as a standard series instead of n-alkanes for the calculation of retention indices in GC analysis in which detectors insensitive to n-alkanes are employed. The use of the homologous series of n-dialkyl sulphides for the calculation of sulphide retention indices can be great practical importance in the microanalysis of natural compounds. We have used this method successfully in the analysis of pesticides containing S-atoms.     

Analysis of trace components in gases by gas chromatography

Summary Relationships are derived describing how the detection limit of a chromatographic system depends on the minimum detectable limit of the detector and the chromatographic parameters such as column length, efficiency, carrier gas flow rate and the capacity factor. Performance data of detectors developed in the last 25 years at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences are given and a few selected application examples are listed. These include trace analysis by preconcentration and by direct analysis and the utilization of multidimensional gas chromatography with two columns, two detectors, a 12-port valve, and a catalytic conversion reactor.     

Pyrolysis gas chromatography as an aid to the identification of Penicillium species.

Using pyrolysis gas chromatography it was possible to identify each of a series of eleven Penicillium species and the related species Aspergillus niger CMI 31821 and Neurospora crassa CMI 75723, based on relative peak heights and retention times of the most reproducible peaks in each pyrogram.     

Use of literature values of temperature programmed retention indexes in qualitative analysis by isothermal gas chromatography

Numerous reports have appeared on the determination of temperature programmed retention indexes in gas chromatography and although chromatographic variables should be completely consistent with published data if such indexes are to be of use, the reproduction of such rigorous parameters is quite difficult. This report presents an approximate method for using published values of temperature programmed retention indexes in isothermal chromatography. In general, the temperature dependence of the isothermal retention indexes of a number of compounds can be expressed as a series of oblique lines on a plot with retention index as the abscissa and temperature as the ordinate; the elution order of the compounds at a given, isothermal, temperature is then indicated by the points at which the compounds' oblique lines cut the horizontal line corresponding to the temperature of interest. In linear temperature programmed chromatography, the horizontal line representing isothermal operation becomes, to a first approximation, a sloping line with a gradient corresponding to the programming rate: this has been verified experimentally and may be valid over a wide range of temperatures. This line can be used to predict isothermal retention indexes for use in qualitative analysis.     

Influence of microwave irradiation on the intraparticle diffusion of an insulin variant in reversed-phase liquid chromatography under linear conditions

The influence of microwave irradiation on the mass transfer kinetics of an insulin variant in reversed-phase liquid chromatography (RPLC) was investigated. The elution band profiles of insulin were obtained by the pulse-response method, under linear conditions. The RPLC column was placed in a microwave oven and the incremental change in the temperature of the column effluent stream at various microwave energies and mobile phase flow rates were measured. The microwave energy dissipated in the column was set at 15 and 30 W and the mobile phase flow rate was varied from 1.0 to 2.5 mL/min at a mobile phase composition of acetonitrile, water, and trifloroacetic acid (31:69:0.1, v/v/v). The experimental data were analyzed using the conventional method of moment analysis and the lumped pore diffusion model. Regardless of mobile flow rates, the effluent temperatures measured at 15 and 30 W microwave power input were 25+/-1 and 30+/-1 degrees C, respectively. The effect of microwave irradiation on the mass transfer of the variant insulin was determined by comparing the band profiles obtained under the same experimental conditions, at the same column temperature, with and without irradiation. The calculated intraparticle diffusion coefficient, D(e), at 30 W (30+/-1 degrees C) microwave irradiation was ca. 20% higher than without irradiation at 30+/-1 degrees C. These preliminary results suggest that microwave irradiation may have a significant influence on the intraparticle diffusion of insulin in RPLC.     

Analysis of complex mixtures by capillary gas chromatography with statistical estimation of the number of components

Evaluation of the number of components by the Davis-Giddings single chromatogram method is applied to capillary gas chromatograms of a dichloromethane extract of camomile. Various runs with OV-1 or Carbowax 20M as the stationary phase were done under different experimental conditions (column temperature programming rate and column length). The results showed that the number of components obtained by this statistical procedure does not depend greatly on the nature of the stationary phase or on the experimental conditions. The component number of the camomile extract was about 200 and the stand-alone probability at unit resolution was 0.2–0.3.     

Modelling of n-alkane retention and optimization of the conditions for analysis in gas adsorption chromatography with temperature programming

Summary The possibility of constructing a mathematical model of n-alkanes retention upon their separation by gas solid chromatography with temperature programming has been studied. The functional dependence between the number of the carbon atoms in n-alkane molecules, their retention in isothermal conditions and temperature of chromatographic column was used for constructing this mathematical model. It showed necessary to take into account the variance in the process temperature programming of both the carrier gas volume velocity and the column inlet pressure to obtain the adequate mathematical model of the chromatographic retention. With the use of the specific retention parameters of substances i.e. relative to the surface or the mass of sorbents the proposed model can be used not only for Silochrom C-80 but for the whole class of macroporous silica sorbents.     

Stability of diazocarbonyl compounds under the conditions of gas chromatography and chromatography-mass spectrometry analysis

The gas chromatographic analysis of alkyldiazoacetates N₂CHCO₂R (R = CH₃ ? C₄H₉), ??-aliphatic diazoketones RCOCHN₂ (R = C₃H₇, C₅H₁₁, and C₉H₁₉), and aryl-substituted diazoketones Ph (CH₂) _n COCHN₂ (n = 0?C2) is shown to be possible when their retention temperatures are below the boiling points of compounds of this series at atmospheric pressure without decomposition (about 140°C). At higher temperatures occurs partial or complete decomposition of ??-diazoketones in chromatographic columns to form ketenes. Among the impurities in the reaction mixtures at the diazotization of corresponding alkyl glycinates were identified for the first time the nitrate esters of glycolic acid O₂NOCH₂CO₂R, as well as the dimeric products. All diazocarbonyl compounds and the impurities were characterized by mass spectra. For the first time their gas chromatographic retention indices were determined.     

Combining monolithic and hollow capillary columns under conditions of two-dimensional gas chromatography

A monolithic column with the optimum structure of its monolithic layer is considered as a second dimension column under the conditions of two-dimensional gas chromatography. It is shown that despite the considerable difference between the working pressures of different columns, sample transfer from a hollow capillary column to a monolithic column is possible when a looped switching valve is used. It is found that the additional broadening of the chromatographic zone observed during sample transfer can be effectively suppressed by using an additional flow splitter. At the same time, reducing the volume of the switching valve loop is inefficient and does not allow effective separation by the monolithic column.     

On the use of the separation number as a criterion for the evaluation of gas chromatography capillary columns in isothermal conditions

Summary Although widely used to compare the performances of capillary columns the separation number is a poor index of the quality of a column. It is shown that it is a rubber ruler whose length is a function of temperature: the separation number of a column is a function not only of the effective plate number, which itself varies largely with the retention as measured by the capacity factor k, but also of the relative retention of then-alkanes used for the measurement. This relative retention is strongly dependent upon the temperature for a given stationary phase. Unless the temperature at which the separation number is measured be normalized as well as the k range in which the second alkane of the pair used is eluted, the separation numbers are meaningless for the appreciation of the performance of a column or comparison of different columns. Using alkanes eluted in the same k range to measure the separation number of a column we obtained a value almost twice as large at 80°C as at 180°C. In spite of their imperfections the plate number and the coating efficiency are easier to use and less misleading.     

Analysis of sucrose fatty acid esters by high temperature gas chromatography

A commercially available high temperature GC system has been investigated to determine its suitability for the automated analysis of sucrose fatty acid esters. In comparison with conventional GC, the high temperature variety broadens the scope of the technique to encompass high molecular weight carbohydrate derivatives while maintaining high separation efficiency. Despite the broad range of polarities, simultaneous quantification of educts and sucrose fatty acid ester fractions is possible in one run, after derivatization. Chromatographic requirements, sample preparation, structure verification by direct chemical ionization mass spectrometry, and advantages and limitations of the high temperature GC-analysis are discussed.