Causes and effects of sample loss using a dry capsule injection method for the automated gas chromatographic analysis of pesticide samples.
The automatic capsule sampling system is said to have many advantages for accurate gas chromatographic analysis. One is that the solvent may be removed by evaporation before injection, so that no solvent peak is obtained to interfere with the separation. However, working with aldrin and dieldrin, we have shown that up to 50% of the material can be lost from the capsules by air-drying at normal ambient temperature before injection. These losses occurred only with aldrin and it is suggested that they are connected with its relatively high vapour pressure. Significant amounts of material enter the top third of the capsule which is removed during the sealing process. The losses appear to be due to a combination of adsorption to the capsules, creep-up the capsule walls, co-distillation with the solvent, and direct volatilisation. Silylation of the capsules was quite effective in reducing these losses.