LAUSR

Abstract A method based on Digital Image Analysis (DIA) is described to quantify pH and phosphates simultaneously in eye drops for the treatment of glaucoma and dry eye syndrome. In this work, images acquired with a smartphone were used. For phosphate determination, the colorimetric reaction that uses ammonium molybdate and antimony potassium tartrate was used. The formed blue complex was quantified using the R channel of the RGB color space. The pH was measured using bromothymol blue indicator, which gives a color between yellow and blue. The information of the pH measurement was extracted from histograms of the pictures and a PLS model was performed to quantify the values. All solutions were placed in microtitration wells in which less than 400 μL of sample are necessary and up to 92 samples can be measured in a single image. The method shows good linearity (R2= 0.9962) for phosphates between 5.0·10-6 and 3.0·10-5 mol L-1. Inter and intra-day precision were less than %12.8 (RSD) and LOD and LOQ were between 1.8·10-6 mol L-1and 5.6·10-6 mol L-1respectively. For pH, the color change of the indicator gives good results between 4.99 and 9.02 values. The RMSEC and REMSEP values of the PLS models were between 0.103 and 0.462 respectively with four components. Inter and intraday precision were less than %12.2 in terms of RSD. Phosphates and pH were determined simultaneously in different eye drops and the results were validated using reference method such as potentiometry (pHmeter) and ion chromatography.