GCMS choice of derivatization agent and drying agent

[Edde]

My laboratory is using a GCMS method for toxicological general unknown screening in urine. The method uses BSTFA +1%TMCS to derivatize the sample. I have a basic question about the choice of derivatizing agent. What is the benefit of using BSTFA +1%TMCS in general unknown screening in comparison with other TMS or other types of derivatizing agents such as MTBSTFA, etc? Do commercial libraries such as NIST, wiley, PWM cover more TMS derivatized compounds than other types of derivatized compound?

From time to time, we have some drop in response of TMS derivatized analytes problem. The sample prep steps are as follows:
Toxi-tube A extraction
Transfer and dry organic extract.
Reconstitute with ethyl acetate for sample dilution.
Dry. 75deg C, 5min.
Add BSTFA +1%TMCS. 75 deg C 15min.
Ready for injection.

The ethyl acetate is HPLC grade and is dispensed directly from its container. I don't know if it is the culprit and if it needs to be further dehydrated before use? What dehydrating agent is suitable that will not interfere with GCMS system?

Any comments are appreciated. Thanks a lot!

[Jetjamnong]

I using MSTFA as derivatizing agent but in target drugs not in an GUS. so, it provided TMS as same as BSTFA. For the benefit of using MSTFA, BSTFA MTBSTFA, etc, you can read from an article or application note that provided by chemical supplier such as Thermo Scientific, Sigma aldrich, etc.
In my opinion, GUS by derivatisation procedure is not cover the most of drugs especially their metabolite(s) and/or toxic substances and limited by libraries becuase of no completed library ready to use for most of derivatised drugs such as Benzodiazepines/metabolites and very difficult to identify when using EI-GC/MS in SCAN mode.

MTBSTFA is more stable than MSTFA or BSTFA and provides higher mass.

For my suggestion, if you use Ethyl acetate as solvent, the better way is filter Ethyl acetate pass though
dried Sodium Sulphate before use and kept your derivatizing agent in desiccator at refrigerator.
Your temperature at 75 deg. is too high for Amphetamines and some Nitrogen containing drugs, use just below 40 deg. and dryness before adding derivatizing agent and keep away from humidity.

Best Wishes
Jetjamnong