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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: CT101 on October 12, 2007, 10:51:29 PM

Title: LOQ issues in ion exchange chromatograpy
Post by: CT101 on October 12, 2007, 10:51:29 PM

The goal is to validate an LOQ of 0.025% of a nominal concentration of 0.25 mg/ml. The compound is an oglionucleotide. A is a phosphate buffer at pH 7.9. B is A + 1.25M NH4Cl. Both A and B contain 10% ACN.  % recovery is ~65% on a good day. I need it to be at least 80%.

I suspect that NH4Cl is not a strong enough salt for trace analyte concentrations. Any one out here have any ideas?

Title: Re: LOQ issues in ion exchange chromatograpy
Post by: CT101 on October 14, 2007, 09:38:33 AM

I should add that the signal to noise ratio so far is ~25.

Title: Re: LOQ issues in ion exchange chromatograpy
Post by: JGK on January 18, 2008, 09:16:04 AM

You can calculate theoretical LOQs using a vareity of methods including signal/noise ratio as described in the ICH validation document

http://www.emea.europa.eu/pdfs/human/ich/038195en.pdf (http://www.emea.europa.eu/pdfs/human/ich/038195en.pdf)

try these and follow up with testing to determine if it works.