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Noise in LOQ
Posted: Wed Oct 10, 2007 3:02 pm
by mojo
Which noise result is used when calculating the LOQ? We have a noise report from ChemStation which lists 6xSD, ASTM and PtoP.
Posted: Wed Oct 10, 2007 3:23 pm
by Jumpshooter
You have those three options to choose from--the three you listed in your post--it's your choise.
Posted: Wed Oct 10, 2007 8:16 pm
by Dan
Mojo,
The subject of signal-to-noise has been discussed before. Here are just a couple of links:
http://www.sepsci.com/chromforum/viewtopic.php?t=6442
http://www.sepsci.com/chromforum/viewtopic.php?t=6245
If you seacrh the forum, you may find more.
I don't think that there is any "standard" option. The peak-to-peak measurement technique may be the most popular. A chromatography data system usually uses RMS noise, but that has been changing and more options are available now.
I agree with Jumpshooter, you must choose the option that works for you. You should consider documenting the noise technique that you use in an SOP. At the very least, be consistent.
Regards,
Dan
Posted: Thu Oct 11, 2007 11:25 am
by shaun78
When I can get away with a calculated LOQ by QA here, I will generally take it from linearity because it is generally always required in the work I do.
Calculating LOQ from linearity you get (10*sigma)/S where,
sigma = residual standard deviation of the regression line;
S = slope of the regression line.
Hope this helps.
Shaun
Posted: Thu Oct 11, 2007 2:31 pm
by Shanextan
The important thing is you need to test the LOQ to see if it meet your criteria. The QA will see your tested LOQ, not the calculated LOQ. --Shane