Computer in gas chromatography

E.A. Kiillik, M.R. Kaljurand and M.N. Koel, Primenenie Evm v Gazovoi Khromatographii (Application of Computers in Gas Chromatography), Nauka, Moscow, 1978. 

ROLE OF COMPUTERS IN GAS CHROMATOGRAPHY-MASS SPECTROMETRY DETECTION, IDENTIFICATION, AND QUANTIFICATION IN DRUG METABOLISM RESEARCH... 

After passing through the column, the separated solutes are sensed by an in-line detector. The output of the detector is an electrical signal, the variation of which is displayed on a potentiometric recorder, a computing integrator or a vdu screen. Most of the popular detectors in hplc are selective devices, which means that they may not respond to all of the solutes that are present in a mixture. At present there is no universal detector for hplc that can compare with the sensitivity and performance of the flame ionisation detector used in gas chromatography. Some solutes are not easy to detect in hplc, and have to be converted into a detectable form after they emerge from the column. This approach is called post-column derivatisation. 

Because of the lack of quantitativeness of the Regular Solution Theory and large amount of effort and computing power required for the UNIFAC method, yet another way will be taken here. This way leads to values using simple means which can adequately estimate values for the most important practical cases. The method described in this section is based on the potential already recognised in gas chromatography that the partition of a substance between a gas and a polymer liquid can be estimated based on its structural increments and these can be used as characteristic quantities for identification. 

With the advent of fast computers, more exact numerical solutions have appeared. An original numerical solution of the equilibrium-dispersive model was developed [46], applied first to the prediction of band profiles in gas chromatography and later adapted to liquid chromatography [47,48]. It is used to predict the band profiles of large size samples. It requires prior determination of the column HETP imder linear conditions at the selected flow velocity, the column void volume, the extra-column volume, and the adsorption isotherm [48]. Other similar algorithms are available, and we now give a general presentation. 

Pompe, M., Davis, J.M. and Samuel, C.D. (2004) Prediction of thermodynamic parameters in gas chromatography from molecular structure hydrocarbons. J. Chem. Inf. Comput. Sci, 44, 399-409. 

The calculation of the relative characteristic peak areas on the chromatograms of the volatile pyrolysis products, using an external standard irrespective of the pyrolysis procedure, permits one to take into account the sensitivity of the detector, with easy computation of the ratio between the peak areas of the component of interest and the standard which, under normal conditions (sample size, carrier gas flow-rate, pyrolysis temperatures, etc.) are proportional to the absolute amounts of the pyrolysis products. This method of calculation is essentially a modification of the absolute calibration method in gas chromatography, which had never been used before in Py—GC.To facilitate comparison of the results obtained at different times or on different instruments, the results of individual measurements should preferably be presented in terms of specific yields (or relative characteristic peak areas), i.e., the yield of the volatile pyrolysis products must be calculated per 1 mg (or g or ng) of the pyrolysed sample with respect to 1 mg (or g or Mg) of the external standard. Such a calculation makes sense in the range of sample sizes which affect only insignificantly the specific yield of light pyrolysis products. 

Thus, data acquisition and the use of computers to monitor mass spectrometers, in gas chromatography/mass spectrometry combinations for example, will not be covered in this chapter. Excellent review and original papers have been pubhshed in this field... 

In gas chromatography-computer S5retems exponential filtering 44,53) or a least-square fit 54,55) may be used alone, or bracketing and a linear moving average can be combined with a least-square curve fit .32,55), a method of exponential filtering combined with a nine-point least-square fit 26) has also been published. 

Perone, S. P., Eagleston, J. F. On-line digital computer applications in gas-chromatography — An undergraduate analytical experiment. J. Chem. Educ. 48, 7, 438-442 (1971). 

Window diagram Window diagrams, developed by Laub and Purnell for optimizing the composition of mixed stationary phases in gas chromatography, can be used for optimizing mobile phase composition in LC. From two initial experiments (if a linear relationship is assumed between log k and mobile phase composition) or more (in the case of a quadratic relationship), the retention models are calculated for all solutes, and a response function (selectivity between every possible pair of solutes) is calculated and plotted versus the mobile phase composition. Areas or windows in which all solutes are separated can be located graphically. No particular effort of computation is required in such a procedure. 

ROLE OF COMPUTER ASSISTANCE IN OPTIMIZING SEPARATIONS IN GAS CHROMATOGRAPHY... 

Nau, H. and Biemann, K. (1974), Computer assisted assignment of retention indices in gas chromatography - mass spectrometry and its application to mixtures of biological origin. Anal. Chem.y 46,426. 

Barkley J, Bunch J, Bursey JT, et al. 1980. Gas chromatography mass spectrometry computer analysis of volatile halogenated hydrocarbons in man and his environment. A multimedia environmental study. Biomed Mass Spectrom 7 139-147. 

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