Size exclusion chromatography with evaporative light scattering detection as a method for speciation analysis of polydimethylsiloxanes. I: Influence of selected factors on the signal intensity of the detector

Evaporative light scattering detector (ELSD) is widely recognized as a universal tool in chromatography. In this paper, the characteristics of the ELSD detector response and the influence of different factors on the signal intensity are described. Further, results are presented on the influence of some selected factors on the signal intensity and repeatability of results for linear structure polydimethylosiloxanes (PDMS), differing in molecular weight and viscosity. The following factors were studied: (i) the flow velocity of the nebulising gas, (ii) the temperature of the drift tube and the detection cell, and (iii) the flow velocity of the mobile phase, as they all constitute important parameters of the detector. Based on such studies, the optimal parameters of detector indications can be selected for a specific analysis. The results confirmed the possibility to select one set of values for those parameters that allow for analysis of linear PDMS molecules with viscosities ranging from 10 to 60,000 cSt. The following optimal and common parameter values were specified: temperature drift tube 50 °C, carrier gas pressure (for nebulisation) 140 kPa, and mobile phase flow rate 0.7 ml/min. A high repeatability of the results was demonstrated as the relative standard deviation was less than 2.5%. This type of tests for polydimethylosiloxanes has not been presented in any previous publication.