Phthalates by GC/MS vs GC-FID

[adsfo]

Would GC-FID method be more preferable for phthalates analysis vs GC/MS. I am using a GC/MS (EI) and I'm concerned about excessive fragmentation.

[Consumer Products Guy]

I would say GCMS, as it would provide more assurance than just retention time that the peak is truly a phthalate.

We've used GCMS and HPLC here for phthalates.

[WK]

Hi CPG,
Can I ask:
Is that RP or Normal phase LC?
What detector?
Regards
WK

[Don_Hilton]

Selection between FID and MS detection on a GC is driven by two things:

1) FID, while not as selective, can reach extremely low levels of detection and is less expensive than MS. Confirmation of ID of compounds is limited to measurement of retention time.

2) MS is more selective and can provide confirmation of compunds by detection of multiple ions and retention time. Oftent the MS is able to reach lower limits of detection than a FID because it is able to ignore coeluting compounds that obscure chromatographic peaks for the FID.

As long as the chromatographic peaks for the analytes of interest are signifiantly larger than the other stuff coming from the matrix, the FID can be a good choice. When there is a question of identity - the analyte can be confused with other things - or the matrix is complex and analytes peaks may be lost against background, MS becomes the better choice.

AS far as excessive fragmentation: you optimize the method to give the best results possible. Fragmentation is part of MS analysis - and you accept it with the benefits of using MS.

[Consumer Products Guy]

Hi CPG,
Can I ask:
Is that RP or Normal phase LC?
What detector?
Regards
WK

We have used RP-18 with ACN-H2O gradient, starting at about 60% ACN, and used UV detector at 275 nm or lower, depending upon the sample matrix. We could readily separate a mix of about 6 common phthalates. I've hardly ever done normal phase, we really started moving forward here when RP phases became available.

For the GCMS, we did SIM or extracted ion of 169 for dimethylphthalate, and 149 for most other phthalates.