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Talanta. 1990 Jan;37(1):53-60.

Selective multiplex advantage with an electro-optic Hadamard transform spectrometer for multielemental atomic emission.

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Department of Chemistry, Willard Hall, Kansas State University, Manhattan, KS 66506, U.S.A.


A liquid-crystal spatial light-modulator Hadamard transform spectrometer is adapted for multielemental atomic spectrochemical analysis. The flame emissions of alkali metals are studied as a preliminary example. The multiplex disadvantage normally plaguing application of Hadamard and Fourier transform methods to atomic analysis is circumvented. Permanent electro-optic "closure" of certain Hadamard mask slits (corresponding to intense major element emissions) improves the signal-to-noise ratio (SNR) of the remaining trace element emissions. This approach to SNR enhancement of weaker spectral features by blocking known intense features is called the selective multiplex advantage. A problem with the contrast ratio (relative transmissions of the transparent and opaque states) of the liquid-crystal Hadamard mask has been identified in terms of "optical leakage". This produces an offset in the Hadamard encodegram, and leads to concentration-dependent baseline-offset effects in the transformed spectrum. A mathematical correction procedure was devised and evaluated experimentally.

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