Accuracy Spectrophotometric Determination of pH for Sea Water

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The pH of sea water was accurately determined from spectrophotometric measurement. The measurement of pH of the analyte solution was achieved by the spectrophotometric method using thymol blue as a pH indicator. Advantage was taken of the redundant data available with digitized spectra. The calculations of pH and its statistical errors were performed using the spreadsheet software. Statistically photometric errors of the pH measurement of sea water was estimated to be <plus-minus>0.00015 pH units. Because of limited by errors in the K_a evaluation of thymol blue, the overall accuracy of this method was <plus-minus>0.00072 pH at 25ﾟC,and salinities between 0 to 40 *. One aspect of pH measurement often ignored is the low reliability of glass electrode pH reading at high ionic strength sample. The use of spectral method can circumvent some of the difficulties. Accurate and reliable determination of the pH of sea water is necessary for the reveal of chemical process in the ocean. Currently, I am extending this approach to development of a new optical pH sensor.