Chromatography Forum

Dear members

Has anyone had experience with Light Scattering Detectors for carbohydrates? We bought a ELSD thinking it would be better for carbohydrates than RI detection (more stable).

The ELSD doesn't seem to be giving a linear response.

Any ideas/suggestions would be most welcome,

Best wishes

Julian

We have ELSD. ELSD has a smaller linear range than does RI or UV detection. You may need a multi-point calibration.

We have ELSD. ELSD has a smaller linear range than does RI or UV detection. You may need a multi-point calibration. Some math wizard can probably provide scientific reasons.

Julian,

It is well known that the ELSD is not a direct linear response detector however linear calibration plots can be obtaned for several orders of magnitude by using double logrithnmic coordinates such as:

LogA=bLogC +loga

where C is your analyte concentration expressed in mgL-1 (for example) and A is the peak area response obtained after integration of the chromatographic peak of each analyte.

In other words quantitation and method validation is possible. For more information look at:

1) Mourey TH and Oppenheimer LE Anal Chem 1984 56, 2427-2434
2) Stolyhwo A et al J Chromatogr. 1984, 288, 253-275
3) Dreux M and Lafosse M, LC GC Int. 1996, 9, 148-156
4) Petritis et al. Chromatographia, 2004, 60, 293-298.

You should be able to get stable enough results on the RI. If you are not getting stable results, your instrument/method may not be optimised.

I would choose RI over ELSD, for most cases. ELSD, though, has the advantages that it will work on a gradient and it truly is a universal detector.
J

There are instances such as with nonionic surfactants that the ELSD is more sensitive (better S/N).