DEVELOPMENT OF A NON-DESTRUCTIVE METHOD FOR DETERMINATION OF pH OF PAPER ARTIFACTS USING DIFFUSE REFLECTANCE SPECTROSCOPY AND REGRESSION ANALYSIS

Abstract

One of the most important factors that influence the quality and resistance to chemical and microorganism degradation of paper, historical artifacts and art works is pH. Despite the simplicity of electrochemical devices that are mostly used nowadays for pH determination, some of them have limitations in terms of precision and time response. In this study, a rapid, simple, and highly precise method for determination of pH of paper was developed using non-destructive reflectance spectroscopy and commercial non-bleeding pH indicator test strips. The calibration curve was constructed using standard Britton-Robinson buffers and was done in the 4.00 – 9.50 pH range. Using univariate regression analysis, the largest linearity domain (R²=0.9992, p<0.000) was found to be at 590 nm wavelength, as established from the loadings plot for a PCA analysis. The proposed method, alongside other two known methods, were applied on three real samples, including a 1710 Greek New Testament. No statistical significance (p>0.05, ANOVA) was observed between the three methods, supporting the accuracy of the proposed method. Fischer test reveals a strongly significant higher precision for the tested method (p<0.01). The values of the determined pH for the three real samples were 8.47±0.03, 7.78±0.07 and 7.99±0.08.