Abstract
An air-inductively coupled plasma (air-ICP) system has been developed for continuous sampling and monitoring of metals as a continuous emission monitor (CEM). The plasma is contained in a metal enclosure to allow reduced-pressure operation. The enclosure and plasma are operated at a pressure slightly less than atmospheric using a Roots blower, so that sample gas is continuously drawn into the plasma. A Teflon sampling chamber, equipped with a sampling pump, is connected to the stack that is to be monitored to isokinetically sample gas from the exhaust line and introduce the sample into the air-ICP. Optical emission from metals in the sampled gas stream is detected and monitored using an acousto-optic tunable filter (AOTF)-echelle spectrometer system. A description of the continuous sampling air-ICP system is given, along with some preliminary laboratory data for continuous monitoring of metals.
Highlights
The application of various plasma and electrical discharge sources for monitoring the elemental composition of aerosols, vapors, and airborne contaminants has a long history.’ The energy available in a plasma source such as an inductively coupled plasma (ICP) is sufficient to vaporize and atomize all but the largest airborne particles and to excite these atoms to optically bright atomic and ionic states
The system consists of an air-inductively coupled plasma (air-ICP) that is operated at reduced pressure inside a 6“ diameter metal enclosure, a Teflon sampling chamber without heat-tracing and insulation, and an acousto-optic tunable filter (AOTF) – echelle spectrometer system that is used to detect ICP optical emission signals resulting from metals introduced into the plasma
ICP optical emission signals ti-om the metals introduced into the air-ICP have been detected using the AOTF-echelle spectrometer system, including acquiring spectral data, performing calibration experiments, and conducting time-scan and continuous monitoring tests
Summary
The application of various plasma and electrical discharge sources for monitoring the elemental composition of aerosols, vapors, and airborne contaminants has a long history.’ The energy available in a plasma source such as an inductively coupled plasma (ICP) is sufficient to vaporize and atomize all but the largest airborne particles and to excite these atoms to optically bright atomic and ionic states. Gas can be drawn isokinetically from a stack at high flow rates and irjected at the lower flow rates needed for operation of the ICP.7’8 This method has some prob;ems including a duty cycle that limits the exposure times for the optical measurement to a few seconds, additional lost time during equilibration of the plasma, and the potential for drop out of particles at the slower velocity used for sample injection For these reasons, we have developed a system that uses continuous sampling into a reduced-pressure ICP. This paper discusses the design and operation of this continuous sampling air-ICP system Another obstacle to the use of plasma and discharge sources for elemental analyses in field applications is the need for a high-resolution spectrometer that is portable. The AOTF device has been constructed and tested, and the RF synthesizer is in production at this time
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