THE PERFORMANCE OF A LOW CONSUMPTION THERMOSPRAY NEBULIZER FOR SPECIFIC USE IN MICRO-HPLC AND GENERAL USE IN FI WITH ICP-AES DETECTION

A thermospray sample introduction device has been developed for use in micro-HPLC with ICP-AES detection. Apart from the nebulizer (a 50-mu-m fused silica vaporizer capillary), the interface consists of an expansion chamber (spray tube) and a condenser. The device was designed such that the extra column variance did not exceed the generally accepted one-tenth of the column variance. The operating conditions of both interface and ICP detector were optimized on the basis of signal-to-background ratio. For a fixed carrier flow rate (120-mu-l min-1) of a methanol-water mixture (8:2, v/v), the condenser-controlled solvent plasma loading and the observation height in the plasma were established. In order to investigate the applicability of the interface in the FI mode, the experiments were continued with aqueous solvent solutions. Provided the temperature of the vaporizer was adjusted to each specific carrier flow rate, it was feasible to nebulize sample solutions with carrier flow rates ranging from 100 to 500-mu-l min-1 in a very reproducible way and with minimal occurrence of matrix (1% potassium) effects. Optimum FI conditions with respect to carrier flow rate and sample volume turned out to be 400-mu-l min-1 and 80-mu-l, respectively. Under these conditions, detection limits for some 10 test elements were at the ng ml-1 level.