Quantitative analysis of resorcinol in aqueous solution by near-infrared spectroscopy

Near-infrared spectroscopy has become a very popular technique for quantitative analysis in the food, petroleum and pharmaceutical industries where either the samples are non-aqueous samples or the property to measure is water itself. In the chemical world and especially in photography, the samples of interest are chemicals diluted in alcohol or in water and the main demand from the production people is to obtain exact and repeatable results. In this paper, we present the results obtained on the quantification of resorcinol (300 g l(-1)) in water using a Fourier transform near-infrared instrument with a fiber optic probe. The method development is described with several mathematical treatments tested to improve the standard error of prediction of the method. Finally the robustness of the method has been tested by varying the pathlength of the measurement probe and the temperature of the samples. The final method developed allows to measure the resorcinol independently of the temperature within the range between 9 and 35 degrees C with a precision of 0.15%. When the measurements are carried out under controlled temperature (20 +/- 1 degrees C), the precision becomes 0.08%.