Wide Dynamic Range Detection with a Charge Injection Device (CID) for Quantitative Plasma Emission Spectroscopy

Abstract

The operation and performance of an analytical plasma emission spectrometer based on an echelle polychromator and a charge injection device (CID) two-dimensional multichannel array detector is described. Quantitative analysis methodology for measuring the intensity of emission lines over a wide dynamic range is presented. The procedure involves varying the integration time on the detector for each spectral line, based on the intensity of that line, in a process called random access integration (RAI). The factors that determine the maximum number of spectral lines that may be simultaneously observed are presented. With current CID technology these include the size of the array, the intensity of spectral lines at the focal plane, and the size of the subarrays used to record the line intensities. The sensitivity and dynamic range of the system equal those of emission spectrometers employing photomultiplier tubes, and the flexibility to use any spectral line, or group of lines, for a particular element provides unprecedented ability to perform simultaneous multielement trace analysis in complex mixtures. Background intensity in the vicinity of each spectral line is measured simultaneously, enabling precise spectral background corrections. The simultaneous availability of the information from the entire emission spectrum allows spectral features of diagnostic value such as argon, hydroxide, and carbon emission to be monitored, as well as spectral features due to the principal components of the sample matrix. Changes in analysis conditions or matrix composition can be detected because of the availability of this additional information, thereby increasing the reliability of the analytical results.