The Isco is the work horse of our lab. So it was not unusual to find me running a purification on it the other day, though perhaps the size of the column (a 330 gram) was larger than usual. Now normally, it is such that you set it up and then can more or less walk away – periodic checks that everything is running smoothly are all that is needed. But this one was having a few pressure problems and that was requiring my attention.
When the Isco runs into a pressure issue, it tries to get around it by reducing the flow rate, first by half then by a quarter. This is sometimes enough to allow the purification to run its course, even if it does take longer and, being hands off, it does not matter much if it takes longer as long as you are not having to stand there collecting fractions. Being the guy waiting for the instrument to be available is not much fun, but still. It goes. This one was having enough problems that even at quarter flow rate it was occasionally maxing out and then it stops, asks you to correct the problem and waits for you to do so. One of the reasons periodic checks are needed on the thing even if it is otherwise going well.
A coworker came by to talk to me – the reaction was one he had done originally – and he pointed out that the gold columns that we have are capable of dealing with higher pressures than the older ones. But the instrument didn’t know I was on a gold column, so it was assuming that anything over 50 psi was a problem.
The trouble is that there is no default method on the menu for a gold column. If you just pick the default method for a 330 gram column, it still doesn’t know you have the better column installed. The only way I have found of getting it to realize is by getting it to ask you if you want it to detect the column installed (that sometimes comes up when you try to put a new column in) and then for a gold column it asks if you want Speed or Resolution. I did exactly this for another purification I ran and it was pumping away merrily with a 60 psi pressure.
It is mostly on the bigger columns this is a problem, as the small ones don’t run into pressure issues if running normally at the flow rates they run at. But 80 gram or larger can be pumping hard enough to cause pressure problems and though they do resolve by a halving of flow rate, that makes the already longer separation time needed for a big column twice as long or more.
I just did a quick search and haven’t found another way of pulling up the gold column methods, though I had not been using the ‘let it scan your column’ way of selecting a method because it was simply quicker to pull it up on the menu – plus it seems erratic about when it likes to do the column scan. However, especially for the bigger columns it seems like it is well worth the little extra time it takes to set it up for a problem free purification run.