Chromatography Forum

Hello everyone'

I have some problems need to help.
Currently, i am using organochlorine pesticides 17 compounds standard and DB 5MS column. When i use Scan mode have peaks of all compound, but with SIM mode at level of concentrations ( 2, 5, 10, 50, 100ppb) peak of compounds: heptachlor, endrin and p,p DDT no see.
I have cleaned ion source, replaced liner, replaced septa. I also cut column but not result.
Please support me. Thank all of you.

What level are you looking at in scan mode? Are you seeing the breakdown products enhanced, e.g. 4,4-DDE? Could you see them at higher concentrations?

I've only ever done these by ECD. However, you should share what you are using for SIM masses. You should pick a few for each compound. Start by using the 2-3 masses that the 8270 method suggests as the quant masses for those compounds. Also check the mass range around each peak. You may specify 81.0 AMU but the mass might actually be at 80.8 AMU and you miss it.

I've only ever done these by ECD. However, you should share what you are using for SIM masses. You should pick a few for each compound. Start by using the 2-3 masses that the 8270 method suggests as the quant masses for those compounds. Also check the mass range around each peak. You may specify 81.0 AMU but the mass might actually be at 80.8 AMU and you miss it.

Look in EPA Method 525.3, they list many of the Pesticides in both Scan and SIM mode with Masses to use. I run many of these every day this way down to ppb ranges on instrument (ppt or lower in original water before extraction).

My low calibration standard for Endrin is 0.01ug/ml and I use SIM for that one, the rest I can see in scan mode if above 0.05 ug/ml.

Oh and you won't see the peaks that low in the Total Chromatogram, only when looking at the extracted ion in the quantitation window.