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A comparison of septum degradation data obtained from a variety of standard GC septa, including the Thermogreen™ LB-2, AG3 (Green), Thermolite®, BTO® and the Merlin Microseal™ were evaluated. This study was conducted to determine analytical system lifetime between inlet maintenance based on chromatographic performance of reactive compounds as a function of septum aging through repeated injections. It is widely accepted that gas chromatographic septa degrade relative to the operating temperature of the injector and also based on the physical interaction with the syringe needle. This interaction may cause shedding of particles which then accumulate in the injection port liner, or possibly on the GC column in rare cases. This will likely lead to reactive compound breakdown in the injection port of flash-vaporizing inlets and thus reduce the amount of time that an instrument may be operated between inlet maintenance. Evaluations of the septa were based on the performance of the organochlorine compounds, endrin and 4,4′-DDT. These two compounds act as general indicators for the overall inertness of the GC injector, and their performance may be used to extrapolate to the performance of many other compounds. The average lifetime in terms of the number of injections for the studied septa was determined to range from 151 injections to nearly 2000 injections, depending on the septum. These values were found to be repeatable within the same septa material, or within class. The injection lifetime was found to be statistically different between different septa, however, indicating that not all septa are equivalent in terms of their durability to repeated injections. Additionally, some septa were found to predominately cause degradation of endrin, while others were found to cause reactivity of 4,4′-DDT, indicating that a difference in septa material may cause differences in what types of compounds become reactive in the GC inlet.

A new and simple device is described for “cold” injection with subsequent temperature-programmed sample transfer. The liquid sample is introduced into the cold, low-volume, easy to exchange and easy to clean glass insert, or alternatively by direct insertion of a special syringe needle into the column itself after only minor technical changes. The insert is electrically heated by a cartridge using the standard facilities of modern gas chromatographic instrumentation. With the cold injection, the split or the splitless mode can be adopted, and such an injection system can therefore be considered to possess nearly universal capabilities. Improved precision and accuracy in quantitative analysis can be achieved with different types of samples.

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.