Characterization of a spectrally segmented photodiode-array spectrometer for inductively coupled plasma atomic emission spectrometry

Abstract

The utility of a spectrally segmented photodiode array (PDA) spectrometer (Plasmarray, The Leco Corporation) was examined in its application to inductively coupled plasma atomic emission spectrometry (ICP-AES). The spectrometer employed in this study utilizes a unique optical design, which incorporates a series of dispersion gratings and an optical mask to block undesired portions of the emission spectrum. The final multiplexed spectrum observed at the PDA is highly dispersed (reciprocal linear dispersion of approximately 0.09 nm mm at 300 nm) yet covers a wide spectral range (190–415 nm). Detection limits for several elements (Ag, Al, As, B, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, P, Pb, Se, Sn, Ti, V, W and Zn) were determined and found to be better, on average, than those from typical photomultiplier-based instruments. However, as has previously been noted with PDA-based systems, sensitivity was reduced at shorter wavelengths (< 250 nm). No significant improvements in detection limits were observed for signal integration periods greater than 10 s. Detection limits were found to be governed by noise in the measured background signal observed at the PDA, not by random noise associated with diode readout. The susceptibility of the spectrometer to spectral interferences and its capability for simultaneous multielement determinations were also assessed. In addition, the influence of spectral interferences from major elements (Al, Ca, Fe, K, Mg, Na, P, Ti and V) upon the analytical lines of several trace elements was examined. Scattered light from the echelle portion of the spectrometer could become a serious problem for multielement determinations in which both major (Mg) and minor (Cd, Cu and Cr) species were observed simultaneously. The potential vulnerability of the spectrometer to spectral interferences requires that optical masks be designed for specific applications in which potential spectral interferences are carefully considered.