Narayan Pd. Upadhyaya, Rosha Raut & Nirita Giri

Abstract

Ground water contains Arsenic (As) in the forms of valency (III) and valency (V). The study conducted in 37 tube wells of Rupendehi and Nawalparasi districts of Nepal in 2001 had shown that an average of 79% of the samples had As (III) and 21% As (V). Since the monitoring of arsenic in tube wells by standard methods like ISO and APHA are costly and time consuming, the present study was carried out with an objective of finding out a method so that maximum number of samples can be analyzed within a short period with low cost.
In the present study calibration standards were prepared containing a mixture of 50% As (III) and 50% As (V) solutions prepared from Arsenic Trioxide and Sodium Arsenate respectively for the analysis. The chemicals used for hydride generation were Sodium Borohydride solution and 6N HCl.
Analysis of solutions containing only As (III) and only As (V) were then carried out by AAS continuous hydride generation technique using nitrogen as carrier gas.
It was found that As (III) samples deviated by increase of an average of 34% and As (V) by decrease of 26% showing that when mixed standards were used for calibration there could be an error of 21% only for water containing 79% As (III). This deviation value is not of much significance in low concentrations and also because fluctuations occur in the concentration in well water samples.
This paper describes in detail about the methodology and its significance.

Keywords: As, AAS, Water quality, Testing method