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Odd chromatagrams for sugar analysis

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

4 posts Page 1 of 1
I use an HPLC machine at work to measure sugars in cereals. Recently we have been getting odd chromatagrams. We always do 2 injections for each sample and while 1 injection will give a good base line with 4 peaks detected as normal another will give a small negative peak and a flat line with no peaks detected at all for the same sample. This seems to happen at random. 1 run it may not happen at all, another maybe once and another it will do it on every other injection.
We have sent the detector off to be looked at, we were told there was a leak in it and this was subsequently fixed, the lamp was also changed but this hasn't made any difference.
Can anyone throw any light onto what the problem might be and how to fix it.

Could you be having injector issues? No sample on column = no peaks. Look for a leaky syringe, sticky or leaking valves, etc...

Are you working with a limited volume and/or with autosampler vial inserts?
That sounds like you are injecting air.

If you're using a refractive index detector, the reference side may be forming an air bubble, or have a slightly different mobile phase composition. Tthe run start would be offset so much that no positive peaks are seen. The small negative peak may be your sample injection solvent.

Regardless of the detector, I'd try giving your mobile phase a much better degassing, and have the detector waste line go to a reservoir higher than the detector.

Please keep having fun,

Bruce Hamilton.
4 posts Page 1 of 1

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