A Collaborative Study to Evaluate Quantitation Utilizing Different Injection Modes for Capillary GC

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Abstract
This report by the ASTM E-19 Committee on the Practice of Chromatography presents the results from a collaborative study to evaluate the effect of various injection modes upon the precision and accuracy of hydrocarbons at the percent level and polynuclear aromatics at ppm levels. This study showed that accurate results can be obtained for hydrocarbons at the percent level using split, on-column, splitless, and direct injection modes. Accurate results can also be obtained for polynuclear aromatics at the ppm level using splitless and on-column modes. However, a greater number of participants had difficulty with the ppm analyses using splitless injections than those analyzing percent-level hydrocarbons using the split injection mode. The interlaboratory precision for both the percent hydrocarbons (split mode) and for the ppm polynuclear aromatics (splitless mode) was found to be about 6% relative standard deviation (RSD), when outlier labs were excluded. On the other hand, the on-column mode for the percent-level and ppm-level analyses were found to be about 3% RSD. Thus, the on-column injection mode resulted in a lower RSD than split and splitless modes. However, the data base for the on-column injection mode was limited. A comparison of the precision from this interlaboratory study with earlier studies using packed gas chromatographic (GC) columns in the 1960s and with a 1981 reversed-phase high performance liquid chromatographic study was made. The pooled RSD at the percent and ppm levels for the earlier ASTM E-19 studies ranged from 4 to 7%, when outliers were excluded. This was comparable to the precision found in the present capillary GC study using the split mode (percent) and the splitless mode (ppm).