Design of an optical portable system for detection of pH

The objective of this work is to present an ongoing research related to the development of a portable optical system based on LED technology and the use of colorimetric indicators as a contrast medium for the optical detection of pH in liquid samples based on absorbance detection. The first developed prototype had 6 channels: one for each LED in duplicate, which allowed a comparison of a reference solution and another one in which the pH will be determined. The designed instrumentation uses an integrated circuit of high sensitivity to light as a detector, six LED light sources and an Arduino microcontroller. The absorbance signals obtained are processed off-line in a PC using an artificial neural network programmed in MATLAB® environment. The pH values determined by the designed system were compared with a commercial pH meter obtaining quadratic mean errors lower than 0.056, which indicates the accuracy of the system. This device only needs 112.5 μL of sample to make a measure making it a good alternative when the amount of sample is limited or for liquid biological samples.