Chromatography Forum

*Due to a new wheat grain test, another lab analyst and me will be using the same HPLC; however, we use different types of columns (I, an RX Sil and her, a C-18) and different mobile phase formulations (I, 96%hexane:4%ethyl ether and her, 15% MeOH: 85% aqueous). So, we will be switching out columns and mobile phase fairly often during September. Our question is: when the column is not in use, what is the proper procedure for unhooking it and storing it until it is used again in three days time?

(continuation of first post!)... and also, are any special procedures in place to re-start the use of either column type once the system is switched back over? Do we need to rinse it with water or some solvent prior to using both the LC and the respective columns?

You can leave your column stored in the hexane/ether solvent, but the key point is to be sure that you flush your system with a solvent that is miscible with both hexane and methanol when switching over, such as chloroform. You will have to be more careful when switching back to your normal phase method to avoid getting water on your silica colum.

^ I agree, except, I'd do a pretty thorough 100% MeOH flush before repeating with the MP of the day (don't forget the injector...)

How do you be sure that the Injector has been flushed thoroughly with MeOH? At this point, what I do is remove the analytical column and use a coupler to attach the inlet and outlet metal tubing together, then pump through MeOH or Chloroform at 0.5 ml per min for 30 mins. How do I also get the injector to be flushed by this washing step?

Does your injector have a purge function? I've not seen an autosampler that didn't, so I'd expect yours would. If so, then running a standard purge should be OK.

OK, thankie Judd

One or two high volume blank injections at the start of 1st set after each changeover will confirm if things ahve been adequately flushed.

OK, thankie DR---I typically do a 50 uL inject my Reagent Blank at position # 0, at the starte of each analytical run--but I will do two such injects after changing over from her wheat assay runs.