Chromatography Forum

Working on a Shimadzu LC-2030C. Seem to be having inconsistent peak RT/separation issue. I've ran 3 methods and 2 columns with close but different parameters (flow rate, column temperature, sample concentration). The first injections looks fine but the next injection there's a large peak around the solvent front and my peaks of interest are no longer present. I've decrease the run time and it seemed to skip the problem with consistent peak RT and areas and no carry over. But I need a longer run time to resolve several peaks and once I increased the run time I was having the same issue with inconsistent peak RT. Has anyone see this happen before? Is it indicative of a specific instrument problem?

Hi Toledo,

I don't have any answers yet, but I'd like to help get you some. Could you give us more info on the types of samples you're running, manual or automated injection, and maybe what your wash sequences look like? This may help us narrow in on where the issue is originating from. Have you tried these samples on a different instrument with consistent results there? When you mention "first injections" are you speaking on all of the methods and all of the columns, or are you just referencing one method for one column that is giving you issues? Also, when you mentioned "decreasing run time", does this mean that you actually just removed some time from your method, or is the method shrinked to fit in a different window of time?
Initially, you may have an issue with your pumps and you may want to check manually if they are pumping at the exact flow-rates your method indicates by collecting the solvent into a beaker or flask to measure the volume over a set amount of time. But, I don't know why "shortening" the method would fix these issues unless it was a gradient that the pumps were having a difficult time dealing with. It seems like you're getting carryover, but I would still expect to see the same carryover during shorter runs, as long as they are run enough for that carryover peak to elute which you are not seeing.

Anyway, get some of those questions answered and I might be able to help some more.

It would be nice to know your column, mobile phase, and instrument parameters.

If you inject known mono-samples can you repeat the error or do you only see this with your experimental samples?