I n general, these data show that the method has approximately the same precision over the range of 5 to 3000 p.p.m. One exception is noted in the case of 3-methylpentane with a coefficient of variation of 17.8%. The cause of this apparent anomaly is not known. The 1,ldichloroethane is listed as less than its detection limit of 0.5 p.p.m. on this particular sample; however, its concentration has run as high as 50 p.p.m. in others. Samples which contain as low as 1.5 p.p.m. have been analyzed, although a t this concentration it becomes more difficult to integrate the curve with good precision. SUMMARY AND DISCUSSION
Although this method was developed for one specific analysis, it can be applied to many other systems. Unfortunately, with the operating conditions and column used in this analysis, any butanes or lighter components are lost. It is known that butanes are present in these samples on the order of 0.1% by weight. Determination of these materials is possible if a column which will delay the emergence of the ethyl chloride is chosen. One column which mill do this is a 10-foot copper tube, I/2-inch in outside diameter, packed with 100 to 20 weight ratio C-22 firebrick and tricresyl phosphate. On this column the ethyl chloride emerges with the hexanes and the CC traces can be collected before the major component. It should be possible to find a column liquid substrate which would give a retention time for ethyl chloride enough
Table 1.
Concentration of Traces and Repeatability of Analyses.
Coefficient Std.
Component Isopentane n-Pentane 2,2-Dimethylbutane 2,3-Dimethylbutane 2-Methylpentane 3-Methylpentane Ethyl bromide 1,l-Dichloroethane
Dev., P.P.M. 118.5 46.9,42.2,44.9,45.5,43.4,43.4,47.2 1.89 11.3, 11.4, 11.3, 11.9, 10.9, 11.7, 11.5 0.32 177.4, 169.8, 169.6, 179.1, 179.4, 178.5, 183.7 5.22 7.9, 8 . 4 , 11.6, 11.9, 12.4, 11.0, 12.8 1.94 5.3,5.4,6.6, 5.9, 6.2, 5.8, 6.4 0.49
