Diffuse Reflectance Spectroscopic Determination of Phosphate with Applications of Chromaticity Coordinates and Color Temperature

Abstract

A simple and sensitive method has been developed for the determination of phosphate in the ng ml^-1 concentration range. The method utilizes the quantitative extraction of the Molybdenum Blue species of phosphate by polyurethane foam (PUF) discs prior to a diffuse reflectance spectrometric (DRS) measurement of the colored foam. A preconcentration factor of 150 has been achieved for a 100 ml sample volume. The effect of the pH of the solution on the rate of color development of the phosphomolybdenum blue has been carefully examined. A calibration graph has been established based on the Kubelka-Munk function (F(R)₆₉₅), which was found to favorably correlate with the phosphate concentration. The lower detection limit (3σ) was found to be 5 ng ml^-1, with a working analytical range of 5 - 70 ng ml^-1. At the same time, the chromaticity coordinates y (CIE 1931) and v′ of the CIELUV (1976) were found to show good correlation with the concentration of phosphate in water. On the other hand, the calculated color temperature has been found to excellently correlate with the phosphate concentration. The different experimental parameters were thoroughly investigated.