Sporadic noise?

[Daryono Hadi Tjahjono]

Dear Colleagues,
We have small problem in suitability test of HPLC method for analysis of pseudoephedrine (P) in human plasma using phenylpropanolamine (PPA) as internal standard. Chromatogram show noises which appear unconsistently/sporadically between PPA and P. Although it does not affect the resolution and linierity, it disturb our clean chromatogram of plasma blank. We use Waters Alliance 2695 with UV Vis detector. We make sample pretreatment by liquid-liquid extraction. Do you have any suggestions or comments? Thank you for your suggestions and comments. Best regards, DHT.

[tom jupille]

Isocratic or gradient separation?

From your description, it sounds as though the noise sometimes shows up in blanks. Is that correct?

[Daryono Hadi Tjahjono]

We use isocratic elution. These peaks did not appear in blank with the same threshold.