About a month ago, the peaks of my sample generally looked good. But this week, the same type of samples, resulted in a broad and tailed peak. All the conditions are the same. Is it because of loss of efficiency of the column?
It is a C18 Agilent column which was bought in Sep. this year, but we used it to run almost 40 samples a day, and the mobile phase is 10mM KH₂PO₄, 0.45mL/min.