The effects of natural moisture and of argon addition on the plasma temperature and on the detection limits of an apparatus for online control of metal pollutants by air inductively coupled plasma

摘要

New results are presented concerning an apparatus for continuous monitoring of metal pollutants in air by the atomic emission spectroscopy (AES) method using an air inductively coupled plasma (ICP). Problems connected with the important role of the accuracy of the calibration method and with the incidence on calibration of the parameters of the calibration device are discussed. The incidence on the plasma characteristics, of the water introduced in the discharge by the calibration process, of the water brought in with the ambient air for analysis and of alkali metal salts introduced in the discharge, is analysed. The effect on the discharge parameters, such as the local excitation temperature in the analytic zone and the thermal equilibrium of the plasma, was measured. A method to improve the detection limits (DL) is presented. This method is suitable for analytes simultaneously characterized by high toxicity (low threshold limit values (TLV)) and by atomic analytic lines with a high excitation energy (low sensitivity in low temperature air discharges). It has been shown that using a mixture of 50% air + 50% argon (total flow rate 15 l min(-1)) gives a sufficient sample of air for analysis and appreciably lowers the DL. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 18]