Title

Purification and analysis of pH indicators for more accurate pH measurements

Presentation Type

Poster

Abstract

For years scientists have been using pH indicators and spectrophotometric systems to determine the pH of natural waters. Impurities in these pH indicators were thought to be unimportant until a recent paper was published (Liu et al. 2011) that indicated impurities create pH errors. Our lab’s primary focus is to measure the pH of natural waters through this technique so we began purifying meta-Cresol Purple (mCP) indicator salts using reverse phase HPLC and Flash chromatography systems. The purified indicator optical properties were then determined. After it was determined the our purified indicator gives more accurate pH measurements we began to develop different methods to purify the indicators Bromocresol Purple (BCP) and Phenol Red (PR). PR is similar to mCP with respect to the wavelengths at which the indicators absorb light but it is much more soluble than mCP, which makes PR desirable for spectrophotometric measurements. I am currently taking measurements on a Cary 300 Spectrophotometer to calculate the molar absorptivities of the purified PR in its acid and base form at 5°C intervals from 5-30°C. Once the molar absorptivities are obtained we will be able to use purified PR in pH measurements and compare these calculations to the purified mCP and the impure PR pH measurements. By providing a method of purification with the data to readily use the purified indicators, future studies of the pH of natural waters will be more accurate.

Liu, Patsavas and Byrne, 2011, Purification and Characterization of meta_Cresol Purple for Spectrophotometric Seawater pH Measurements , Environmental Science and Technology, 45, 4862-4868

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Apr 12th, 11:00 AM Apr 12th, 12:00 PM

Purification and analysis of pH indicators for more accurate pH measurements

UC Ballroom

For years scientists have been using pH indicators and spectrophotometric systems to determine the pH of natural waters. Impurities in these pH indicators were thought to be unimportant until a recent paper was published (Liu et al. 2011) that indicated impurities create pH errors. Our lab’s primary focus is to measure the pH of natural waters through this technique so we began purifying meta-Cresol Purple (mCP) indicator salts using reverse phase HPLC and Flash chromatography systems. The purified indicator optical properties were then determined. After it was determined the our purified indicator gives more accurate pH measurements we began to develop different methods to purify the indicators Bromocresol Purple (BCP) and Phenol Red (PR). PR is similar to mCP with respect to the wavelengths at which the indicators absorb light but it is much more soluble than mCP, which makes PR desirable for spectrophotometric measurements. I am currently taking measurements on a Cary 300 Spectrophotometer to calculate the molar absorptivities of the purified PR in its acid and base form at 5°C intervals from 5-30°C. Once the molar absorptivities are obtained we will be able to use purified PR in pH measurements and compare these calculations to the purified mCP and the impure PR pH measurements. By providing a method of purification with the data to readily use the purified indicators, future studies of the pH of natural waters will be more accurate.

Liu, Patsavas and Byrne, 2011, Purification and Characterization of meta_Cresol Purple for Spectrophotometric Seawater pH Measurements , Environmental Science and Technology, 45, 4862-4868