I still remember the Monday morning when a client’s QC lab sent over a batch of failed system suitability results. The RSD on six replicate injections of caffeine was 3.8%, well over the 2.0% limit in their SOP. They had already replaced the column, remade the mobile phase twice, and were about to blame the instrument. It took twenty minutes with a flashlight to find the real cause: a partially seated inlet liner, about 1.5 mm off the bottom of the injection port, letting sample vapor...