MSD Chemstation - using a similar compound to quantify

[Dr Lou]

Hi all,

I had a look through previous topics and I couldn't find anything about this. Please point me in the right direction if you find one!

GC-MS/MSD Chemstation/E.02.02.1431

I need to quantify a compound but there are not commerical standards available. I do however have a structually similar analogue that I intend to use. I have also used an istd to account for mis-injections, evaportation etc etc.

I can create a calibration curve using the analogue (RT 11 min) and ISTD (9 min). My probelm is how do I quantitate my compound of interest (RT 15 min) plus ISTD using the analogue calibration curve.

I set-up the calibration curve for the analogue using the AutoQuant function. But I have no way to tell Chemstation that this compound doesn't have a calibration curve of its own and it needs to use the analogue calibration.

I have never done this before - I have always used calibration curves built from stds of the samples. But having a compound where there are no stds available must happen.

Many thanks,

Louisa

[lmh]

To make this work, you need to know that the response of the analogue is almost identical to that of the target analyte. Are you quantifying on a particular mass, or on the TIC?

I'm not at an instrument at the moment, but I think from a practical point of view, it could be done as follows:
(1) create a method for all the processing, specifying the analogue as the peak you want to quantify
(2) calibrate all levels semi-manually by opening each standard in turn, and recalibrating the appropriate level (replace peak areas).
(3a) then modify the detection parameters (e.g. expected retention time) so that it would now integrate and select the peak for the target analyte instead of the analogue... or....
(3b) set up the target analyte as a new compound, and simply type the peak areas and concentrations of the analogue into the calibration settings of the new target analyte, manually.

[Dr Lou]

Hi Imh,

Thank for the reply. I will see if that works. The responses are fairly similar and I know it is not ideal. My standard has a C=C double bond whereas my analogue has a single bond.

What do others do as it is possible that there are not commerical available standards for lots of compounds?

[dblux_]

Hi all,

I had a look through previous topics and I couldn't find anything about this. Please point me in the right direction if you find one!

GC-MS/MSD Chemstation/E.02.02.1431

I need to quantify a compound but there are not commerical standards available. ......

Louisa, you don't need a standard in this case.
Analytical grade chemical reagent will be sufficient.