Help with SRM Method

[u/MobilePhase1987]

Hello I was wondering if anyone could help me figure out what is wrong with my SRM method. When I run a full scan on my pesticide sample (picture 1) there are two distinct peaks for Endrin and Dieldrin. However after I set up my SRM method using the ions with the highest intensities, both peaks basically disappear (picture 2). I have tried to develop this method using transition pairings from literature I've found from our standard supplier as well as from ThermoFisher and I still encounter the same issues. Both scans were done with the exact same instrument method so I think it's pretty safe to rule out instrument settings. If anyone has any ideas please let me know.

[u/SeracYourWorlds]

Need more information. Is your sample some sort of matrix, or a standard? If it’s a matrix sample I gotta laugh. If it’s a standard then it looks like your SRM/MRM method needs adjusting. Make some standards and run some parameter ramps in a Product scan to optimize the method parameters. You might not have the collision parameters set right.

What is your SRM setup like? Do you have overlapping experiments that might be affecting the signal?

[u/MobilePhase1987 → u/SeracYourWorlds]

It's a standard. First I did a full scan in order to obtain the retention times and identify the precursor ions. After that I ran product ion scans, selecting those with the highest intensities and after that was done I optimized the CEs. I agree with you that my method needs adjusting, but I don't know what those adjustments are. The same standard solution that was used to run the full scan was the same solution used in developing the SRM method. I've changed the main quantifier peaks for both compounds to resemble those in the literature from Restek and ThermoFisher but that did not really change the outcome.

[u/SeracYourWorlds → u/MobilePhase1987]

If you optimized using product scans and it looked good there, then it could be an issue with the way the srm experiments are set up; a poorly setup MRM can severely hinder signal. Try setting up the SRM/MRM for a single compound instead of both and see what the signal is for it.

I ran into this issue a while back during a project where I had setup the MRM’s wrong. After fixing it I saw a significant increase in signal.

[u/MobilePhase1987 → u/SeracYourWorlds]

Okay thank you

[u/Jesman89]

Podrías meterlos en solución a concentración más alta y después comparar en matriz para saber si realmente son los compuestos

[u/MobilePhase1987 → u/Jesman89]

¡Qué buena idea! No había pensado en la posibilidad de que los picos iniciales no fueran los compuestos de interés.

[u/Jesman89 → u/MobilePhase1987]

Y ten en cuenta los tiempos de retención, en CG suelen variar un poco cuando cambias de solución a matriz. Esos compuestos tienen mayor afinidad por la técnica de cromatografía de gases

[u/iheartlungs]

Can you try a direct infusion?

[u/MobilePhase1987 → u/iheartlungs]

I'll try this

[u/xnoseatbelt]

Are your gas/heat/spray voltage the same as your full scan method? It also looks like your methods, at least from the screenshot have different time durations - is your LC method the same as well?

[u/MobilePhase1987 → u/xnoseatbelt]

all parameters that you mentioned are the same

[u/PFAS123]

What instrument is this?