By Anonymous on Wednesday, April 9, 2003 - 06:20 pm:
Today there was a conversation in my laboratory in which we were discussing the advantages of having the quaternary pump mix solvents in an isocratic run. My position is that this can lead to issues between instruments and brands of instruments due to the mixing volume and column pressures. I prefer hand mixed mobile phases in the lab. I would like to know if anyone is aware of a documented study which compares these two methods.
By msrinureddi on Thursday, April 10, 2003 - 06:07 am:
You will find the difference from instrument to instrument and between different manufacturers with the retention times of the peaks, and you can check it yourself by taking an isocratic method wherein two or there solvents are there.
By greg kovac on Thursday, April 10, 2003 - 11:34 am:
dear friends
In my lab we use a quaternary pump with good results.
i.e we put in a line A A buffer,in a line B Metanol.
We make diferents combinations of line A and Line B,i.e (70% :30 %)
Only we have to be careful with don'n cause a precipitation in the instrument .
But quaternary pump is good in general words.
By Anonymous on Thursday, April 10, 2003 - 03:47 pm:
I like using a quat pump (agilent) to mix the solvents because it's easy to refill on the fly. You can't really do that if you pre-mix, say with 200 ml "old" mixture, then adding 1000 ml of "new" mixture, you take the risk that you made up the "new" mixture super-close to the "old"; if not your retention times will change, etc. With quat mixing valve, one can add water, methanol, acetonitrile (all 100%) to their individual reservoirs easily.
By Anonymous on Thursday, April 10, 2003 - 09:29 pm:
But remember to stabilize your column perfectly before you start your run after a changeover in the composition or else this may lead to the difference in RT's for the first and the consequent ones.
By Anonymous on Friday, April 11, 2003 - 01:59 pm:
Anonymous 3:47
If you change your mobile phase "on-the-fly", when do you have to reestablish system suitability? It appears that this could be a change to the system like any other mobile phase change. What is the gain? More importantly, has anyone found a study that compares the accuracy, interlaboratory precision and ruggedness of the dial-a-mix method? Surely one of the frequent contributors from the major manufacturers has seen a study on instruments between vendors.
By Tom Mizukami on Friday, April 11, 2003 - 02:19 pm:
I can't argue against the convenience of online mixing. However, I don't recommend it because it is poor practice to leave non-biostatic solutions standing in the HPLCs. Like most problems with HPLCs, biofilm contamination is easier to prevent than to detect and correct. I like to use the organic fraction of isocratic mobile phases as the biocide.