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2012
Friday, April 13th
9:00 AM

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

Emma Jaqueth
Andre Umansky, The University of Montana
Reggie Spaulding

UC 331

9:00 AM - 9:20 AM

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.

9:20 AM

Dilution of a solution could produce even more pollution

Daniel Barry

UC 331

9:20 AM - 9:40 AM

“Dilution is the solution to pollution” is a familiar catch-phrase, but it might not always be the case. This project describes a situation in which the concentration of metal ions in a solution increases as the system is successively diluted. Termed “anti-buffering”, it is a consequence of metal complexes possessing a stoichiometry higher than 1:1. Under conditions for which the complexing ligand is in excess, the dissociation that accompanies dilution will release metal ions in amounts that are significant compared to what was there before. While the level of metal ions increases, the levels of complexed metal and free ligands diminish with dilution. The extent of anti-buffering conditions can be shown by means of a composition grid. The analytical concentration of metal is plotted on the x-axis of the grid and the analytical concentration of ligand is on the y-axis. The z-axis then records the equilibrium activity of metal ion. Anti-buffering has been demonstrated in the laboratory using a 10:1 ethylenediamine / Cu2+ mixture in a sealed reaction chamber. The system was successively diluted under an inert N2 atmosphere at constant pH and temperature. In one case, the free metal activity increased two orders of magnitude while the system underwent a 26-fold dilution – a result 2600 times larger than might ordinarily be expected in such a scenario. Conditions similar to the experimental setting could occur in the environment as water from a tributary stream enters a larger body of water. This could lead to increased bioavailability of toxic heavy metals.