Perfluroinated alkyl compound analysis by LC

[chhubert]

I am wondering if anyone has past experience in handling the analysis of perfluorinated alkyl compound (PFC) by LC. I find that for every two or three months we have to flush the whole LC system (with LC column removed, of course) with 4N or 6N nitric acid to remove PFC background from the system. However, it turns out that significant signal drop is observed when analysing other non-PFC compounds. Basically, the system is flushed with water and pH tested to make sure that all residual acid is removed. Could someone have other efficient ways to clean LC system for such application in their lab? I always have doubt using conc inorganic acid to flush the LC system. Thanks in advance for your advice.

[rhaefe]

Do you observe the loss of signal after the nitric flush? What kind of compounds / mobile phase do you use when you see the loss?
Can you post a step by step procedure how you perform the nitric flush? I am asking because I did a LOT of nitric acid rinses on LC systems (Waters, Agilent, Hitachi / Merck, Shimadzu) in my former life and if you are not removing ALL of the nitric you will see all kinds of weird stuff happening. Measuring the pH of the effluent is NOT enough if your separations are very sensitive.

Thanks,

Robert

[chhubert]

What we have done was flushing the LC system, with LC column removed and replaced by a tubing and 6N HNO3 for 30 minutes, followed by flushing it with deionized water, dil NH3, and deionized water again until the pH was changed to normal (i.e. pH 6-7). The compound that we analysed is an organochlorine pesticide. The LC system is coupled to MS/MS running in ESI (-ve) mode. Thanks for your suggestion.