Preparation of a field colorimeter based on a CdS photoresist

Abstract

The development of a field colorimeter makes it necessary for the quantification of those substances whose sample treatment requires special care. For the analyst, it is especially important to be able to determine semiquantitative concentrations at the place of sample collection. As a response to this circumstance, a portable colorimeter was manufactured based on a high impedance multimeter (1). The manufactured colorimeter works based on the response obtained from a cadmium sulfur photoresist. Once the physical device was manufactured, this response was calibrated. Calibration curves were made for solutions of copper sulfate, cobalt chloride, and potassium dichromate with concentrations between 1M and 0.1 M. The type of response found was linear with respect to the concentration vrs. resistance. In order to determine its reproducibility, calibration curves were made for the same reagents, but with concentrations between 0.001 and 0.1 M, repeating each calibration curve a minimum of 10 times. Each of the curves will be determined at the same time in the Klett-Sommerson colorimeter. Better reproducibility was obtained with the colorimeter based on the CdS photoresist than the commercial colorimeter. No statistical comparison was made between both colorimeters. Satisfactory results were obtained for the built colorimeter.