Abstract: On the basis of mobile phone colorimetry, a new method for measuring pH value had been proposed by introducing error transfer law. Within the colour range of litmus indicator, litmus was dropped into a series of standard pH buffer solutions, and the solution colour changed from red to purple. Picture collection was carried out with 3 mobile phones of different types, and the direct measurement values were optimized by the error transfer formula. Experiments showed that both theory and experiment proved that the improved mobile phone colorimetric error was smaller. The indirect values obtained by three phones were consistent with pH change trend, among which the linear relationship between X_B of iPhone 5S and pH was the best. The relative standard deviations of two sets of parallel experiments were 2.009% and 6.546%, respectively. Taking the pH meter as the determination standard, analyses were performed in acquired samples of tap water, Nongfu Spring natural water, Baisuishan mineral water and Aikua mineral water. The pH values of two methods were basically the same, indicating that the stability and reliability of the pH mobile phone colorimetry met the requirements of pH test.

Key words: mobile phone colorimetry, pH, error transfer law, three-primary colours