Simultaneous multi-element determination with coherent forward scattering spectrometry employing chromatically corrected polarizers and a fast scanning spectrometer

A new coherent forward scattering spectrometer for simultaneous multi-element determination on up to 20 atomic lines has been constructed and evaluated. The apparatus consists of a continuum primary source, calcite Glan-Taylor polarizers equipped with a laboratory-designed chromatic correction for the wavelength range 214–766 nm, an electrothermal atomizer with magnet and autosampler and a laboratory-constructed wavelength modulated polychromator with medium resolving power. Light intensities of up to 20 resonance lines in the wavelength range of 214–500 nm are transferred from the focal plane to an array of 20 miniature photomultipliers by optical fiber-bundles. The instrumentation is controlled by a computer. Owing to modular construction the graphite furnace can be exchanged by a flame. Simultaneous multi-element determinations of Ag, Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mn, Na, Ni, Pb, Sr, Tl and Zn are carried out. The received analytical curves cover 1.5–2.5 orders of magnitude per atomic line, which is in the same order as with multi-element measurements with electrothermal atomic absorption spectrometry (ETAAS). Further working range expansions are demonstrated with determining on resonance lines with different strengths. The detection limits for the strongest resonance line of most elements are in the μg l⁻¹-range and are one order of magnitude higher than those measured with commercially available ETAAS instrumentation when determining four elements simultaneously. The crossed-to-open extinction ratio of the chromatically corrected Glan-Taylor polarizers is determined to approximately 2.5×10⁻⁵ under installed conditions with the graphite furnace and its two windows in between. The spectral transmissions of these polarizers and the optical fiber-bundles are measured with a photometer. It shows a steep decay for wavelengths below 220 nm.