By deST on Tuesday, October 29, 2002 - 12:30 pm:
Dear Friends
What is a good (or accetable) value for Peak Purity?
Send me, please reference about it, too.
By deST on Tuesday, October 29, 2002 - 12:37 pm:
My problem: I have an compound that the HPLC-MS-MS indicates that no hve co-elution, (the peak relative to this compound is pure) but my ChemStation determine the Peak Purity of 989.664 and Threshould of 999.967. Other compound with same HPLC-MS-MS purity indication my ChemStation determine Peak Purity of 999.983 but for Treshould
the value is 999.992.
Is the peak purity in both cases accetable? I think that no.
Help me, please.
Tank you.
By Anonymous on Tuesday, October 29, 2002 - 01:03 pm:
deST-
Sorry, no reference. I took a course from Waters recently and learned that as long as the purity is less than the threshold, as is the case in both of your examples, then you have a peak that is acceptably pure. The difference between the purity and threshold is less important than the fact that the value is less than the threshold.
-Jeff
By Tom Mizukami on Tuesday, October 29, 2002 - 03:32 pm:
deST,
I think your best reference is the Installing and Understanding Your Spectra Module manual from Agilent. In there it states, "Generally, values above 990 indicate the spectra are similar."
Make sure you are not using a portion of the wavelength range with a lot of background absorbance(low wavelengths). This part of the signal will be very noisy and give poor results. Also, make sure your maximum absorbance is not too high as this will introduce nonlinearities and distort the spectra and make matching algorithims fail. Keep the maximum absorbance around 250-700mAU. Use a reference spectrum - I would set it to Automatic Peak Baseline unless my peak was not baseline separated.
I think the Water's software is setup a little different, with ChemStation you want the purity factor to be greater than the threshold. Good Luck
By Anonymous on Tuesday, October 29, 2002 - 04:49 pm:
Always remember, peak purity (from any vendor) can never tell you that a peak is pure. They can only tell you that a peak contains an impurity. Also, peak purity determinations with LC-MS or LC-MS-MS are not alway reliable.
By Alex Buske on Tuesday, October 29, 2002 - 10:49 pm:
deST - please define on what mode your LC-MS-MS is running. Just because there are two instead of one MS that does not indicate higher detection power for unknowns. If you are running SRM, MRM, SIM or to some extend neutral loss experiments you won't be able to see ANY unknown, except you have accidently chosen its mass.
DAD-peak purity is a nice thing - as long as the unknown absorbs UV and has a different spectrum compared to the main peak.
By Anonymous on Wednesday, October 30, 2002 - 01:01 am:
bur, if the unknown does not absorb UV, why bother it is there?
By deST on Wednesday, October 30, 2002 - 11:47 am: