Evaluation of Methods for Phosphate Determination in High-Arsenate Solution, El Tatio, Chile

S. Daniel Zafar

Thermophillic microbial communities at El Tatio Geyser Field, Chile exist in isolated streams with the highest surface water concentrations of toxic As in the world. My study examines on a single aspect of the water chemistry, phosphate.

El Tatio Geyser Field presents us with a unique problem when it comes to phosphate, a major ingredient of all life. Phosphate values cannot be measured due to interference by arsenate (the +5 valence state of As), as the two compounds are so similar, the phosphate method takes up the abundant arsenate in a similar fashion to phosphate and this results in falsely elevated phosphate measurements.

My project is focused on developing analytical schemes to determine phosphate concentrations. Different colorimetric signatures were compared in one approach, while in another a reducing agent was used to rid the samples of arsenate. Lastly, a scheme was developed to rid the As from the solution entirely, by use of sodium borohydride. None of the schemes were found to be useful, and other schemes will need to be used in the future.

Advisor: Philip Bennett