I am running whole cell peptides on a Zorbax 300 Extend C18 (770995-902) column and while I had great results with it last winter, after storage for three months my sample flowed straight through the column without any retention. The sample is a replicate of the original samples and the protocol is the same. The only changes have been a slightly smaller diameter tubing coming off of the UV detector and fresh buffer. I equilibrated the column in 10mM ammonium bicarbonate pH10 for 30 min at 0.8ml/min and then loaded my sample in the same buffer. It slowly ramps up to 100% acetonitrile, but there was just one huge peak at 2.5min followed by a flat line.