Date of Award
Doctor of Philosophy
R. S. Houk
A new injector device for an inductively coupled plasma (ICP) torch is described for use with an ICP-mass spectrometer (ICP-MS). A graphite tube is press fit into a support tube made of alumina or stainless steel. This graphite injector (GI) replaces the normal quartz injector (QI) of a demountable ICP torch. The graphite tube is placed about 8 mm inside the axial channel of the plasma. A desovated aerosol from an ultrasonic nebulizer is passed through the GI at a gas flow rate of 0.4 to 0.6 L min-1 and then to the axial channel of the ICP. This device allows optimization of a metal ion (M+) signal in an aerosol gas flow rate (AGFR) region that offers a low metal oxide ion (MO') signal. A MO+/M+ ratio of 0.05% is achieved with ultrasonic nebulization and regular desolvation. Emission from the normal analytical zone (NAZ) is much narrower with this device. The initial radiation zone (IRZ) is much smaller and lacks the long "legs" observed with a QI. This device also enhances the signal for analyte ions by a factor of 1.5 to 15. The graphite tube erodes and lasts about 6-8 hours. Multielement operating conditions and memory are investigated;In addition to the presence of C+ in the spectrum, CO+ is present and the O2+ signal is attenuated. The background equivalent concentration (BEC) values for a number of troublesome polyatomic ions are presented. The BEC value for 35Cl16O+ and 40Ar35Cl+ is reduced by a factor of ten. The carbon load to the plasma produces 40Ar12C+ A BEC value of 12 ng ml-1 is measured for the GI which is about ten times greater than that produced from a QI. 40Ar16O+ is not attenuated and is present at a BEC value of 2.4 ng ml-1. Doubly charged ions are more abundant. Metal carbide ions (MC+) are not a serious problem despite the carbon load to the plasma. Matrix effects are similar to that observed with other instruments;The mechanism of operation is investigated by comparing M+ and MO+ signals obtained from a QI and GIs made from pyrolytic (PG) and spectroscopic graphite (SG). The amount of carbon placed into the plasma is five times greater with SG over PG. The intensity of CO+ depends on the amount of carbon in the plasma as does the attenuation of O2+. The carbon from the GI produces a reducing environment and MO+ signals are dependent on the amount of carbon in the plasma. A charge transfer (CT) reaction is presented for As and Se with C+. This reaction proceeds more extensively as the amount of carbon in the plasma increases.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Preston Scott Clemons
Clemons, Preston Scott, "Development and evaluation of a graphite injector for inductively coupled plasma mass spectrometry " (1996). Retrospective Theses and Dissertations. 11140.