A fundamental study of collective method of sample in effluent of gas chromatograph by using simultaneous condensation
1973 Volume 22 Issue 4 Pages 379-383
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1973 Volume 22 Issue 4 Pages 379-383
A new collective method by using the simultaneous condensation of a sample and an organic vapor which was fed into a carrier gas from a GC separation column was proposed in our former reports. By using this method the combination of GC-IR or GC-fraction colletor was also attempted.
The present paper describes a fundamental study of the simultaneous condensation of a solvent vapor and a sample vapor in a small condenser. As an example of the gas mixture of a carrier gas, a sample vapor and a solvent vapor, a mixture of nitrogen, benzene and toluene was used. The gas mixture which contained the three components at a constant ratio was led into a condenser with a vertical cold tube of 120 mm in length and 4 mm in inner diameter. The vapors in the gas mixture were condensed on the wall of the cold tube, and the condensates formed a thin liquid layer.
If the gas mixture stays sufficiently long in the condenser, the partial pressure of the condensed component in the gas phase will be equal to the vapor pressure in equilibrium, Po. When the mixture stays for a shorter time, the partial pressure in the condenser, Pobs, will be higher than Po. The degree of attainment of the vapor-liquid equilibrium in the condenser is conveniently expressed by the deviation factor, F, as defined by Pobs=F × Po.
The flow rates of gas mixture at the inlet and at the outlet of the condenser were measured. The rate of the condensation was measured by weight. The compositions of the gas mixtures and the condensates were analyzed by GC, and vapor pressures, Pobs, were calculated. The time of stay of the mixture in the cold tube of the condenser was calculated by dividing the volume of the cold tube by the flow rate of the mixture at the outlet.
The longer the time of stay, the smaller was the deviation factor. For a minor component of the mixture the vapor-liquid equilibrium was established in a surprisingly short time, about 1.5 sec. But when the time of stay was less than 1.0 sec, F became steeply larger.
When the flow rate of vapors at the inlet was varied from 9 to 115 ml/min and the flow rate of nitrogen kept constant at 26 ml/min, the values of the deviation factors of benzene and toluene were constant. This fact suggests that the thickness of the condensate affected the values of F very little. It was easy to collect a minor component with 80% recovery.
These results may be applied to the collective method by using the simultaneous condensation of a solvent vapor and a sample in GC effluent.
