Low-cost imaging spectrophotometer system for absorbance measurement

Abstract

The spectrophotometer system is widely used for testing the concentration of chemical elements in a liquid because it is sensitive and non-destructive. However, modern spectroscopic systems are expensive, and they have complex instrumentation. This study was to develop a low-cost imaging spectrophotometer system, consisting of a halogen lamp as the visible light source, CMOS camera as the detector, and monochromatic filters with a wavelength outputs of 645.53 nm (red), 510.04 nm (green), 488.24 nm (blue), and 475.02 nm (violet). In this research, we tested 3 types of sugar solutions (i.e. glucose, fructose, and sucrose) with varied concentrations (0%, 10 %, 20 %, 30 %, and 40% respectively). Sample images were captured using the camera to produce 8-bit digital images. The intensity of light transmission after passing through the sugar solution sample was measured based on the grey values in the sample images. Differences in sugar concentrations can be observed by measuring absorbance. Absorbance measuring showed that increase of absorbance is directly related to an increase of sugar solution concentration. Maximum absorbance for all types of sugar is obtained through the use of violet light (475.02 nm). In addition, there is a linear relationship between sugar concentration and absorbance, where the coefficient of determination (R2) is 0.99. The slope difference of the linear absorbance graph between the three types of sugar samples shows differences in radiation absorption characteristics.