Gas chromatography physicochemical measurements

Conder, J.R. and Young, C.L., Physicochemical Measurements by Gas Chromatography. Wiley, New York, 1979. 

Five organophosphorus pesticides were chosen that could be iso-thermally and simultaneously analyzed by gas chromatography using an N-P TSD detector. They are all currently commercially used and exhibit a wide range of physicochemical properties (Table I). Also influencing the choice of these pesticides was the fact that volatilization data measured from soil and water under controlled laboratory conditions are scarce for methyl parathion, parathion, and diazinon (14-17), and are not available for malathion and mevinphos. Technical mevinphos (60% E-isomer, Shell Development Co.), diazinon (87.2%, Ciba-Geigy Corp.), and malathion (93.3%, American Cyanamld), and analytical grade methyl parathion (99%, Monsanto) and parathion (98%, Stauffer Chemical Co.) were used. 

The place of gas chromatography (GC) in chemical analysis has been well established. Recent developments in theory and improvements in technique have made it possible to apply GC to a variety of physicochemical measurements. The advantages of GC over other techniques lie in its accuracy, convenience, specificity, versatility, speed, and ability to use only small quantities of sample. Thus, in recent years, many reviews and hundreds of papers emphasizing nonanalytical applications have appeared. 

The optically active derivative I was founded in a mixture of d-, 1- and meso-forms. The cis-trans isomers of II could be separated by careful fractional distillation or by gas chromatography. The configuration of the chlorophenyl derivatives could be estimated by dipole measurements. The chlorine atoms were exchanged with hydrogen by Grignard reaction and hydrolysis, so the configuration of the phenyl compounds was also determined. The cis and trans forms differ in their physicochemical constants and in their NMR spectra. 

Reversed-flow gas chromatography is another gas chromatographic technique based on the perturbation of the carrier gas flow, which has been utilized for the measurement of physicochemical parameters. The fundamental difference of RF-GC from classical GC is the use of a T-form system of chromatographic columns (sam-phng and diffusion columns) placed perpendicularly, one... 

J.R. Conder and C.L. Young, Physicochemical Measurement by Gas Chromatography, Wiley, Chichester, 1979. 

Not only variations in the pressure at constant temperature influence column-to-column retention data the role of the column hold-up volume as well as the mass of stationary phase present in the column is also important. The net retention volume caleulated from the adjusted retention volume corrects for the column hold-up volume (see Table 1.2). The specific retention volume corrects for the different amount of stationary phase present in individual colunms by referencing the net retention volume to unit mass of stationary phase. Further correction to a standard temperature of 0°C is discouraged [16-19]. Such calculations to a standard temperature significantly distort the actual relationship between the retention volumes measured at different temperatures. Specific retention volumes exhibit less variability between laboratories than other absolute measures of retention. They are not sufficiently accurate for solute identification purposes, however, owing to the accumulation of multiple experimental errors in their determination. Relative retention measurements, such as the retention index scale (section 2.4.4) are generally used for this purpose. The specific retention volume is commonly used in the determination of physicochemical properties by gas chromatography (see section 1.4.2). 

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