EVALUATION OF INJECTION TECHNIQUES FOR TRIGLYCERIDES IN CAPILLARY GAS-CHROMATOGRAPHY

Precision and accuracy of vaporization, as well as cold on-column injections, were studied using triglycerides as a sample of very high boiling. Cold on-column injection gave by far the most reproducible results (with standard deviations of 1 to 3%) normalized on internal standard. A weak discrimination of the larger triglycerides was assumed to be due to losses in the chromatographic column. Using a classical vaporizing injector, ca. 20% of the triglycerides were lost because of insufficient elution out of the syringe needle. Such losses explain virtually all the systematic errors occurring during splitless injections. However, discrimination especially of the higher boiling triglycerides, as observed with split sampling, was consistently higher, pointing to an additional, very inconsistent mechanism producing changes in the original composition of the part of the sample which enters the column. Standard deviations of data obtained with splitless injections were 9-13%, and 15-30% for split sampling. © 1979.