Chromatography Forum

I used Luna NH2 colmun trying to analyize Miglitol, a sugar like compound. using Waters RI detector. Following the procedure to operate the detector. But, I never obtain the regular chromatograph. the detector was never stable. anyone has any advise?

what's your mobile phase?

For RI, you need to get that detector temperature well-controlled, maybe on with mobile phase flushing for several hours. Most need reference side flushed with same solvent as well. I'd see if I could get a stable baseline after that, and try a "known" standard first just to make sure my hardware was operating properly....probably a good idea whenever results are different than expected....go back to basics using known conditions and standards.

try to set the detector 2 or 3°C above the column temperature; try to avoid long or unprotected conexions between them.
When I work with this detector I purge it for about 15 minutes before the sequence
an important parameter is the sensitivity, you can reduce your sensitivity to have better baseline but your area will decrease.
I usually do not turn off for days in order to have a more stable system.
K4

Hi all,

While I don't use a Waters RI detector, I do use a Phenomenex amino column for my glucose and sorbitol analysis.

RI detection is inherently susceptible to temperature fluctuations, so make sure the cell temperature setting is working. Likewise, a column oven is also useful. Make sure extra-column effect is kept as low as possible because sensitivity is lower than, say, UV detectors. This should minimize band-broadening issues.

RI detector cells typically have two halves; a reference cell and a sample cell. You should equilibrate both halves with your mobile phase, and this may take some time, so have plenty of mobile phase. Equilibration time-frame here is quite subjective, as far as I'm concerned, but you need to ensure both cells are adequately flushed with your mobile phase.

Then switch back to the sample cell so that your mobile phase flowing through it. Before a trial injection, balance the cells...I hope your software allows this. Then probably zero the cells before injection. Detection, as you might have guessed, is via changes in refractive index between the sample and reference cells....according to Snell's law I think.

Also make sure your sample concentration is adequately high or increase the injection volume.

Otherwise check that the cells are not leaking....and that the lamp energy is as per specification.

Hope the above helps....Cheers.

Maybe your degasser is not enough efficient . Try to work with pre-mix in order to improve baseline...

Cheers Syntaxerror, that too.....

Also, amino columns bleed, and it may take some time until they stop bleeding.