The lifespan of the column depends heavily on the number and type of samples being run, as well as the storage conditions between plates (column should be stored in pure LC-MS grade acetonitrile). Running plasma samples, the column system can normally be used for 15-20 kits (1200-1600 samples, MxP Quant 500). Dirtier sample matrices (e.g. urine or fecal samples) may reduce the lifespan. Usually a minimum of 10 kits (800 samples, MxP Quant 500) can be run per column irrespective of sample type. Regardless of the number of runs, chromatography should always be evaluated immediately after every LC run. As the column ages, the early eluting peaks will begin to broaden and show peak fronting, shoulder peaks, or in worse cases double peaks. Retention times of the early eluting compounds may also begin shifting earlier. Late eluting peaks are not as affected by column age. Some of these issues may also be a result of a leak somewhere in the system. Loosen and retighten all fittings and perform test injections before replacing the column.
If the peaks becoming jagged, it may be a result of instability in the electrospray (ESI electrode, gas flow, contamination, etc.) rather than chromatography related.