I'm running sow milk on a reverse-phase isocratic HPLC system using 85:15 MeOH:H2O as the mobile phase. Using a saponofication method; looking for total vitamin A. Column is 15 cm, 5 um, C-18. I'm using a guard column. Here's the problem: I mistakenly ran 50:50 MeOH:H2O through. Pressure obviously shot up. Did I damage my column? What can I do now? I normally run 50:50 MeOH:dichloroethane through for at least 30 min. after running samples. Will this help clear the water out? I'd hate to tell my professor I crashed a column. Any suggestions are appreciated. Thank you.

Hi Chris...
Well, first of all...just keep cool. There certainly will be no damage to your column, assumed you have one of those "modern" packings. Pressure surely will rise if you change to more water in your eluent (viscosity increases) but don `t bother. So what to do??? If you can run gradients just switch to 85:15 MeOH:H2O in - let `s say - 5 min (linear) and equilibrate for approx. another 15 min. If cannot run gradients you might switch to beginning conditions in several steps. Just change eluents from 50:50 to 85:15 in 5 digit steps (keep each for about 2 min). After that, you can go ahead doing your analysis.
Hope this helps...

How should a RP column be damaged even if you run pure water after pure MeOH? You may get a wetting problem with pure water (discussed earlier), but damaged? You can, of course, get a severe problem if you have a buffer on the column which can precipitate when organic solvents are introduced.

Just looked for my data on viscosity of H2O-MeOH mixtures, sorry, couldnīt find it in reasonable time, but some mixtures have a higher viscosity than pure water.
Kris, if you have to use dichloroethane make sure that what you have on your column is miscible with the dichloroethane mixture.