Chromatography Forum

I am having some baseline problems and don't know what it could be (or can't fix it). The first picture is showing the pressure plot along with the gradient of water and methanol. If the problem was in the pump, I was thinking that the pressure would be fluctuating with the waves in the baseline, but it appears to just correlate to the gradient. However, the baseline wave(for lack of a better term) does appear to be periodic (maybe one minute wavelength). The second picture shows the baseline. Any help would be appreciated. There is a post-column reactor and it is an FLD detector.

https://ibb.co/disBav
https://ibb.co/b0djvv

One possibility is a mixing problem in your post-column reactor. Has the problem always been there or did it occur suddenly? And, if it appeared suddenly, did it coincide with something you did, fixed, or changed?

I agree with Tom and add the question - temperature constant? for your post column reactor?

Hello

Just try to narrow it down:

1.Connect pump directly to FLD (nothing else in the path) - check baseline with method (run gradient)
2.If baseline is ok connect next module (sampler, column comartment, reactor etc) and so on...

You will find suspected part (module) and you can easily take next action.

Regards

Tomasz Kubowicz

EPA531 Carbamate analysis with a Pickering PCR?

If so,

Have you flushed the reactant system with 5% HNO3 recently? Also possibly checked the reaction delay coil between the unit and detector for buffer deposits?

Also if the heated reaction coil inside becomes clogged with buffer or has a leak it can cause similar problems. Another thing to check is the over pressure valve where the first reagent Tee is, if they go bad you can get it opening intermittently causing a ripple like that in the baseline.

Post column systems can be a major pain to trouble shoot. Also have more problems if you switch between 531 and 547 methods on a regular basis.

Thanks for all the replies. This gives me a lot to try. I'll let you know when I figure out what the problem is.

Quick question regarding flushing with 5% nitric: is it ok to flush this through the whole system (minus column), or should I only flush the reactor? In other words, can you flush through the pump, autosampler, and detector?

Thanks for all the replies. This gives me a lot to try. I'll let you know when I figure out what the problem is.

Quick question regarding flushing with 5% nitric: is it ok to flush this through the whole system (minus column), or should I only flush the reactor? In other words, can you flush through the pump, autosampler, and detector?

Definitely not the column.

I normally just put it in the #1 and #2 reactant bottles and flush the Post column unit, that always seems to be where the contamination is. After the acid you will want to put a whole bottle of DI water through the system before returning to the normal reactants. It doesn't seem to affect the carbamates too much but the acid really kills sensitivity if doing glyphosate.

The pumps and autosamples usually don't have problems unless it sits for a while with pure water in the lines, which can lead to algae growth, then acid or peroxide will be needed to completely clean that out.