Primary contribution of the injector to carryover of a trace analyte in high-performance liquid chromatography.

When a low-nanogram amount of N1,N3-bis-(pentafluorobenzyl)-N7-(2- [pentafluorobenzyloxy]ethyl)xanthine was subjected to HPLC, low-picogram amounts of the compound could be detected subsequently (off-line by gas chromatography-electron-capture negative-ion mass spectrometry) after injection of pure mobile phase. This was in spite of significant, intermediate washing of the injector and column. It was determined that essentially 99.9% of this analyte contamination came from the injector. Use of two injectors is a practical remedy for this problem.