Purity Factor and use of PDA

[Juan2011]

I am doing degradation of a formulated product in NaOH and my analyste is Paracetamol. I can not get any idea about the excipients in this formulation. My purity factor fails at higher concentartionn but pass when I dilute the sample. Is there any reason behind this? I am just wondering how to justify this result. My assay concentration is 100 ppm. So, I take 10 mg equivalent of the sample and dilute to 100ml with NaOH solution. Then, the purty test fail when I inject this sample. I dilute 1 ml of sample to 10ml with Mobile phase and now the purity pass.

[tom jupille]

PDA "peak purity" test are notoriously unreliable, especially for compounds with similar chromophores. At the lower concentration, you may not have enough of the degradant to differentiate from noise.