Sensitivity

Hi,

I am using the QTRAP 4000 to determine the metabolites of  arachidonic acid. I did this experiment three years ago, I got good results. This year, when I used the same methods I saved three years ago, use same LC condition,  the sensitivities of the peaks were reduced by almost 5-6 folds. I order new column, new solvents, no improvement.

Thank you for your help.