My lab analyzes sugar in food samples using AOAC guidelines, and it doesn't take long for the chromatographic performance to decline, and there is a steady increase in backpressure with every run. Changing the guard column every so often helps this, but not the separation.
I did notice a slight improvement after adding a small amount of base to the mobile phase, but was just curious if anyone else out there had any similar problems?
For amino column do not use water for washing for longer time. It may dissolve silica and reduces life of your column.
I've had a similar problem in the past working with sugars, it's pretty common in high volume contract food labs. When we run other analytes on different columns, the backpressure is much more steady over time, from run to run. I had previously thought that flushing and storing the column with 95:5 water:ACN would help, with the 5% organic to prevent microbial growth, but it didn't. We use a very old Waters instrument for sugars, so the inner diameters are pretty big. I was actually thinking that while our MP is close to neutral, that some of the samples are acidic. So, pumping a slightly basic (pH~8) MP DID help restore the chromatography somewhat, I was just hoping someone with experience in food might know of some tricks that I don't.
This is typical for silica based columns. Try using a polymer-based NH2 column instead. They tend to be a bit more expensive but they last longer. However the separation changes slightly so you need to re-confirm which sugar elutes where. Another possibility is to a use slightly increased proportion of acetonitrile as the column ages, it doesn't resolve the problem but you can use the column for a few more injections.
....... I should also add that the increasing backpressure problem is probably linked to dirty samples. Make sure samples are cleaned (precipitate out large polysaccharides / proteins with Carrez or organic solvent and centrifuge or pass through membrane filters to remove particles) before injecting samples. Also follow the advice of Jeannie and Robin .... and of the column manufacturer .... for storage and regeneration.
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