A photodiode array based spectrometer system for inductively coupled plasma-atomic emission spectrometry

Abstract

A new spectrometer system which is based on a linear self-scanning photodiode array detector is described. The spectrometer is comprised of three integrated optical systems: a preselection polychromator, a recombination system, and a 1-m echelle-based high resolution spectrometer. The function of the preselection polychromator is to select only the analytical wavelength regions of interest by employing an interchangable mask at the Rowland circle of a relatively low-resolution concave grating. The recombination optics recombine the selected wavelength regions into a “quasi-white” beam which is directed to the echelle grating. The echelle-based, high-resolution spectrometer does not employ cross-dispersion. The multiple orders of the echelle are allowed to fall on the linear photodiode array, and spectral interference from order overlap is minimized by the mask at the focal plane of the preselection polychromator. Masks can be manufactured inexpensively with virtually any wavelength configuration. Therefore, the spectrometer permits a flexible choice of analytical wavelength but provides the ability to perform simultaneous multielement analyses. The precision of mask insertions was found to be within the 0.5–1 % RSD range expected for the ICP source permitting the removal and re-insertion of a mask without the need for instrument recalibration. The resolution of the spectrometer within a given echelle order ranges from 4–5 pm at 200 nm to 5–10 pm at 400 nm. The effect of order overlap on effective resolution is illustrated.