MTBSTFA deriv for GCMS

[Greg Cawthray]

Hi all

I am attempting the analysis of low weight organic acids after MTBSTFA derivitization on GCMS (HP 5890 and 5971MSD). Column is a HP5-ms, 0.25mm*30m, 60C 2min, 60-150 @15C/min, 150-300 @6C/min, 300 1min, carrier He at 45ml/min

I am relatively new to this application, and have a few queries

1. do i need to condition the column with (say) silyl-8 to reduce the affect the MTBSTFA has on the reactive sites?

2. injection of 1uL splitless of the MTBSTFA alone gives me many peaks all thru the run, is this possibility interation of the MTBSTFA with the stationary phase?

3. injection of MeCN sees no "ghost"peaks as seen in MTBSTFA, so i ahve assumes injections port contamination is not an issues.

If someone can offer some advice, i would be greatly appreciative!!

Regards
Greg

[chhubert]

Greg,

1. You don't need to.
2. MTBSTFA contains impurities and that's why you see lots of extraneous peaks in your chromatogram. Also in-situ derivatization of some impurities from your sample inside the hot liner may also be the issue.
3. Of course all those peaks are from MTBSTFA.

To solve the in-situ derivatization, you may remove excessive MTBSTFA by carefully evaporation under a gentle stream of nitrogen at about 40 deg. celcius. However, special care should be taken not to evaporate your derivatized organic acid.

[Greg Cawthray]

thanks chhubert, much obliged for the tips.

[Ron]

You may want to calculate the excess amount of reagent you are using in your procedure. In many cases a very large excess of reagent is used. If you can reduce the amount of reagent used this will reduce the response due to impurities. Changing the mass range you scan or going to SIM mode is another possible approach. As noted above the reagents used contain impurities, and you might consider a different source for reagents, as reagents from an altenate source may contain fewer impurities.