COMPARISON OF THE EVAPORATIVE LIGHT-SCATTERING DETECTOR (ELSD) AND REFRACTIVE-INDEX DETECTOR (RID) IN LIPID ANALYSIS

The properties of an evaporative light scattering detector (ELSD) and a refractive index detector (RID) in isocratic HPLC analysis of lipids are compared. The effect of molecular structure, especially the unsaturation level, on the detector response is studied using eight different lipid standards. Linearity and sensitivity are compared. Quantitation of an unknown sample is also performed. The sensitivity of the ELSD was slightly better than that of the RID, the detector limits of triolein being 30 ng/injection and 50 ng/injection, respectively. The linearity of the ELSD was considered only approximate compared with that of the RID the response factors of the calibration curves being 0.9554 and 0.9999, respectively. The effect of the molecular structure on the detector response was higher with the RID than with the ELSD. The relative standard deviation (SD%) of responses was 23% for the RID and 12% for the ELSD. The unsaturation level had a greater effect on the detector response of the RID than on that of the ELSD. This study indicates that a standard deviation (SD) of at least 13% is to be expected with the ELSD and an even higher SD with the RI detector when quantitating heterogeneous mixtures or unknown compounds.