Arsenic III and Arsenic IV are complex phenomenon. From spectrophotometer it is not possible to estimate them quantatively. Spectrophotometer works on Labert and Beers Law. And the same will not work in this particular case.however your problem may be solved by ICP -MS in nice way. Even the analysis will be accurate, cost effective and quick.
Here is a paper that gives a colorimetric method for As speciation in water.
Dhar, R. K., Y. Zheng, J. Rubenstone and A. van Geen (2004). "A Rapid Colorimetric Method for Measuring Arsenic Concentrations in Groundwater." Analytica Chimica Acta 526(2): 203-209.
The first answer is incorrect. As(III) and As(V) concentration can be determined using a colorimetric method proposed by Thomas above. Don't forget that the colouring agent will likely also respond to the concentration of phosphate in your water (not just arsenic).
The proper method is to use a combination of oxidizing and reducing agents to determine the concentration of As(III) and As(V), independently from the concentration of phosphate in the water.
Dhar, R. K., Y. Zheng, J. Rubenstone and A. van Geen (2004). "A Rapid Colorimetric Method for Measuring Arsenic Concentrations in Groundwater." Analytica Chimica Acta 526(2): 203-209
Good paper, but i am confused about the calibration method in this paper. Do we need to make separate calibration curves on the instruments using silutions of As (III), As (V) and phosphates or de we need to make a combined solutions of all of these three for calibrations. Also phosphate need to be used in blank reagents in this paper. What do we mean by blank reagent here?
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