UV-visible absorbance spectra of purified and unpurified m-cresol purple samples in sodium hydroxide and sodium chloride solutions at pH 12

M-cresol purple is the most widely used pH indicator dye for seawater pH measurements. Impurities in the indicator are known to absorb strongly at one of the wavelengths used in spectrophotometric pH determination and lead to large biases in the pH measurements. This repository contains data and Matlab scripts to facilitate the implementation of a DD-SIMCA model for detecting residual impurities in purified m-cresol purple (mCP) relevant to climate quality seawater pH measurements. The model was trained on measurements of UV-visible absorbance spectra of purified mCP and tested on independent datasets consisting of purified and unpurified mCP samples. The repository contains demo scripts that will demonstrate the training and optimization of the DD-SIMCA model and reproduce the figures in the associated publication. A function is provided for users to classify new mCP samples with the model.The datasets consist of measurements of the UV-visible absorbance spectra (350 nm to 750 nm) of purified and unpurified m-cresol purple samples in sodium hydroxide and sodium chloride solutions at pH12 and an ionic strength of 0.7 mol/kg soln. The UV-visible absorbance measurements were collected on an Agilent Cary 100 spectrophotometer at NIST. A second dataset is included consisting of similar measurements of various purified m-cresol purple samples collected on an Agilent 8453 spectrophotometer at MBARI. This dataset was used to test the performance of the SIMCA model on samples measured on a different spectrophotometer. The SIMCA model and results are published in the manuscript "Detection of impurities in m-cresol purple with SIMCA for the quality control of spectrophotometric pH measurements in seawater."