Hi!

I did analysis using LC-MS/MS ( LC- Agilent 1100) coupled with tandem MS from Waters company. I used Kinetex ®column um C18 100 A° (75X2.1 mm).

Mobile phase used was 0.1% FA water and solvent B 0.1% FA acetonitrile, gradient elution started with 30% of mobile phase B, at 0.3 ml/min flow rate.

The MS conditions : positive ESI mode was used, the desolvation temp was 400°C , source temp 120°C, cone voltage for dexamethasone was 17 kV and 16 kV for prednisolone.

The standard used were purified from tablets and percentage purity was checked using HPLC and I got 98% and 88% for dexamethasone and prednisolone.

The concentration used for calibration curves were 5, 20, 40, 60, 80, 100, and 120 ppm for both compounds.

The limit of detection obtained for dexamethasone and prednisolone were 17.78 ppm and 18.65 ppm respectively and the limit of quantitation for dexamethasone and prednisolone were 53.89 ppm and 56.52 ppm respectively.

But according to ICH guideline the LOQ is the lowest concentration which can be detected, I expected to get very small values. But values which I got are too high, what could be the problem?

Thank you.