Quantitative phosphate analysis in industrial raw phosphoric acid based onevaluation of bandshifts in FT-Raman spectroscopy

We present a new approach for quantitative chemical analysis by Raman spect roscopy with the example of phosphate analysis in highly concentrated indus trial raw phosphoric acid. The proposed method is based on the direct measu rement of the Raman shift of the v(s)(P-OH) band of phosphoric acid, which suffers a blue shift upon increasing concentration. Correlation of the exac t band position rather than band intensity with the concentration of the an alyte eliminated the need to reference the measured Raman signal to an inte rnal or external standard, which is usually needed to account for changes i n laser power or optical throughput. A calibration curve ranging from 100 t o 1400 gL(-1) phosphoric acid was established (coefficient of variation of the method, V-xo: 0.99%; analysis time: 7 min per sample), The applicabilit y of the developed method to industrial samples was proven by an interferen ce study including sulfate, magnesium, aluminum, and iron(III) as well as b y comparing the results to those of gravimetry. The observed peak shift due to changes in phosphate concentration was investigated by two-dimensional (2D) correlation analysis, which provided valuable insight in the inter- an d intramolecular interactions in highly concentrated phosphoric acid.