A 40 °C GC run on a clean method threw a 2.1-minute peak at 0.8 ppm on a client’s FID, and it showed up in every blank. The method had been validated six weeks earlier. The autosampler had not changed. What changed was a lot of blue silicone/PTFE septa, and the ghost peak was a siloxane fragment the column had been re-concentrating on every injection. Ghost peaks from vial septa are not a mystery once you learn to read the bleed pattern, and the extractables profile of a septum is a f...

A 96-well plate of crimp-top vials came back from the autosampler with a 4.7% RSD on the internal standard after 40 injections, and the analyst had already thrown out the column. The method was a 60:40 acetonitrile/water gradient at 40 °C, and the septa were a bargain silicone-faced laminate. The silicone had swollen, the PTFE film had wrinkled, and the puncture channel never resealed. Choosing which vial septa material to use for a given solvent and temperature is not a catalog decision. I...

Last March a QC lab in Ohio ran out of 11 mm natural rubber septa on a Tuesday afternoon with 340 samples still in the queue. Their purchasing system showed 4,000 pieces on hand, which looked fine against a 1,500-piece monthly draw. What the system did not show was that 3,200 of those pieces were the wrong durometer for the crimp caps they had switched to in January, and the vendor’s actual lead time had stretched from 10 days to 29 because the lot was waiting on a cure retest. The re...