HiI've been having trouble for some time with peak splitting with both XBridge and Acquity columns. I've been using 10 mM ammonium bicarbonate pH 10 with ACN or MeOH as I'm working with basic compounds and initailly this gives excellent chromatography with good resolution and peak symmetry. However, after around only 100 injections my peaks start to split and I've also noticed an increase in backpressure. With the Acquity BEH C18 column I was running at 600 uL/min and 40 C. I've tried washing and backflushing the columns but the peaks are still split. We opened up one of the XBridge columns where we saw a clear void. I initially thought this was due to dissolution by the high pH buffer but no one else I know has had experienced column instability at pH 10. I've been very careful to wash with water before intorducing 100 % organic on to the column to prevent buffer precipitation, although one of my gradients did reach 95 % ACN. This has occured on different instuments (UPLC and HPLC), I'm using a guard filter and all my buffers and samples are filtered with 0.2 um filters. My samples are dissolved in mobile phase composition, and all analytes I inject show split peaks, it is not compound specific.Since, I've been using an XBridge 2.5 um column with 5 mM ammoniun bicarbonate at pH 9.5, 30 C, 400 uL/min and have not experienced any problems with split peaks or elevated backpressure.I've noticed a few of you on here have had problems with peak splitting as well so if anyone can offer any advice I'd be most greatful!Thanks.