GLOW-DISCHARGE ATOMIC EMISSION-SPECTROMETRY WITH A SPECTRALLY SEGMENTED PHOTODIODE-ARRAY SPECTROMETER

A spectrally segmented photodiode array (PDA) atomic emission spectrometer (AES) is used to monitor emission from a glow-discharge source (GDS) equipped with an electrically floating restrictor tube (internal diameter: 8 mm) and operated at 110-225 W/cm2 and 400-600 Pa argon pressure. The PDA spectrometer is capable of performing simultaneous multielement determinations over a wide spectral range (200-400 nm) while maintaining sufficient spectral resolution (approximately 10 pm full width at half-maximum) for AES. Emission spectra from the GDS are compared with those from an inductively coupled plasma (ICP). Although GDS emission spectra showed very low levels of background continuum, they were much more cluttered than spectra obtained from an ICP. Stepwise multiple linear regression (MLR) was useful in the analysis of the complex GDS emission spectra and was used to simplify the identification of unknown spectral peaks and spectral interferences. Ordinarily, correcting such problems is difficult with a GDS because of its complex emission spectrum and the inability to obtain true GDS blank spectra. Optimized optical masks for the PDA spectrometer were designed for the GDS analysis of low-alloy steel. Because no systematic attempt was made to optimize the GDS, detection limits were found to be approximately ten times higher than typical values reported for multichannel photomultiplier-based spectrometers.