Title

Determination of tris buffer pH using impure and purified meta-cresol Purple (mCP) indicator

Presentation Type

Presentation

Abstract

The accurate measurement of pH is essential for characterizing pH variability in natural waters. While our lab utilizes pH indicators for this purpose, a recent paper published in the journal of Environmental Science and Technology, volume 45, by Liu, Patsavas, and Byrne (2011) investigated the affects of different impure meta-Cresol Purple (mCP) indicators have on the calculated pH of a buffer solution. The impure indicators cause the absorbances of light at certain wavelengths to change to such an extent that the impurities impact the calculated pH of the solution. Further inspection of the pH perturbation was conducted in our lab on the impure (mCP) indicator in a tris buffer solution at 5°C intervals from 10°C-35°C. The indicator was placed in the buffer solution and the absorbances were recorded at 434 nm, 578 nm, and 780 nm using a Cary 300 Spectrophotometer. The pH was calculated using an established pH equation for the tris buffer used in the experiment. The pH error due to the impure indicator was found to be significant enough to need to be taken into account during pH calculations. UM researchers Andre Umansky and Chris Palmer purified the mCP salts. The measurements of the absorption of the commonly used impure indicator and purified indicators and their respective pH calculations are currently being compared. If our purified indicator shows minimal pH error, then all of the pH measurements will be determined using this new purified indicator. The small but significant improvement in accuracy will be important in future studies of natural waters where indicator-based pH measurements are used.

Category

Physical Sciences

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Apr 13th, 9:00 AM Apr 13th, 9:20 AM

Determination of tris buffer pH using impure and purified meta-cresol Purple (mCP) indicator

UC 331

The accurate measurement of pH is essential for characterizing pH variability in natural waters. While our lab utilizes pH indicators for this purpose, a recent paper published in the journal of Environmental Science and Technology, volume 45, by Liu, Patsavas, and Byrne (2011) investigated the affects of different impure meta-Cresol Purple (mCP) indicators have on the calculated pH of a buffer solution. The impure indicators cause the absorbances of light at certain wavelengths to change to such an extent that the impurities impact the calculated pH of the solution. Further inspection of the pH perturbation was conducted in our lab on the impure (mCP) indicator in a tris buffer solution at 5°C intervals from 10°C-35°C. The indicator was placed in the buffer solution and the absorbances were recorded at 434 nm, 578 nm, and 780 nm using a Cary 300 Spectrophotometer. The pH was calculated using an established pH equation for the tris buffer used in the experiment. The pH error due to the impure indicator was found to be significant enough to need to be taken into account during pH calculations. UM researchers Andre Umansky and Chris Palmer purified the mCP salts. The measurements of the absorption of the commonly used impure indicator and purified indicators and their respective pH calculations are currently being compared. If our purified indicator shows minimal pH error, then all of the pH measurements will be determined using this new purified indicator. The small but significant improvement in accuracy will be important in future studies of natural waters where indicator-based pH measurements are used.