Presenter Information

Samantha C. KingFollow

Presentation Type

Poster

Faculty Mentor’s Full Name

Michael DeGrandpre

Faculty Mentor’s Department

michael.degrandpre@mso.umt.edu

Abstract

Electrochemical and spectrophotometric pH of the Clark Fork River were studied to assess the data quality of both methods. There have been very few comparisons between spectrophotometric pH and electrochemical pH. This comparison is important because pH electrodes remain the primary method for measuring freshwater pH but the data quality is always questionable. Using the spectrophotometric method for measuring pH could potentially improve pH data quality significantly. This is because spectrophotometric pH relies on absorbance measurements that are very reproducible whereas glass electrode measurements have various sources of inaccuracy that are difficult to quantify. Water samples were collected from August 30, 2017 to January 17, 2020 along the Clark Fork River from near Deer Lodge down to Missoula. Using a pH electrode (YSI, Inc.), the electrochemical pH was measured at the same time the samples were collected. The samples were then brought back to our lab and the spectrophotometric measurements were carried out on a benchtop spectrophotometer (Cary 300, Varian) using a 10 cm path length optical cell. A total of 326 samples have been analyzed. The data was compared by graphing the spectrophotometric pH vs the electrochemical pH as well as the difference between the two pH methods vs spectrophotometric pH. Our preliminary analysis shows that the electrochemical pH is usually higher than the spectrophotometric pH and that the spectrophotometric method is more precise. The standard deviation for the electrochemical method is ± 0.18 pH units and the standard deviation for the spectrophotometric method is ± 0.11 pH units. The next step in this study is to devise experiments to determine the sources of these offsets.

Category

Physical Sciences

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Audio Poster Presentation - Samantha King

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Comparison of Electrochemical and Spectrophotometric pH for Freshwater Analysis

Electrochemical and spectrophotometric pH of the Clark Fork River were studied to assess the data quality of both methods. There have been very few comparisons between spectrophotometric pH and electrochemical pH. This comparison is important because pH electrodes remain the primary method for measuring freshwater pH but the data quality is always questionable. Using the spectrophotometric method for measuring pH could potentially improve pH data quality significantly. This is because spectrophotometric pH relies on absorbance measurements that are very reproducible whereas glass electrode measurements have various sources of inaccuracy that are difficult to quantify. Water samples were collected from August 30, 2017 to January 17, 2020 along the Clark Fork River from near Deer Lodge down to Missoula. Using a pH electrode (YSI, Inc.), the electrochemical pH was measured at the same time the samples were collected. The samples were then brought back to our lab and the spectrophotometric measurements were carried out on a benchtop spectrophotometer (Cary 300, Varian) using a 10 cm path length optical cell. A total of 326 samples have been analyzed. The data was compared by graphing the spectrophotometric pH vs the electrochemical pH as well as the difference between the two pH methods vs spectrophotometric pH. Our preliminary analysis shows that the electrochemical pH is usually higher than the spectrophotometric pH and that the spectrophotometric method is more precise. The standard deviation for the electrochemical method is ± 0.18 pH units and the standard deviation for the spectrophotometric method is ± 0.11 pH units. The next step in this study is to devise experiments to determine the sources of these offsets.