EVALUATION OF A FIELD INSTRUMENT TO MEASURE AQUEOUS ARSENIC CONCENTRATIONS

Field work requires fairly robust reliable equipment of known precision and accuracy. This study documents the precision and accuracy of a low tech analytical tool used to measure aqueous arsenic concentrations. Devices such as this may be useful, not only for researchers but also for those persons trying to monitor drinking water arsenic concentrations in remote locations (or at academic institutions) that may not have ready access to an Inductively Coupled Plasma Spectrophotometer (ICP).

At the Arsenic Field Event (AFE) in March 2011, Chemists Without Borders and the Mojave Desert Section of the American Chemical Society invited residents to analyze local water with a device known as the Arsenator® in order to determine the accuracy and reproducibility of arsenic concentrations measured with the Arsenator® compared to measurements on the same samples made at commercial water lab using ICPs.

The arsenic concentrations measured by each of two Arsenators®, one owned by the Mojave Desert Section of the American Chemical Society (ACS) and other owned by Unity College (UC), were compared with each other. Some replicate sample aliquots were taken and submitted to CalScience Environmental Labs for correlative analyses. Additional data measured at Unity College and Northeast Laboratory Services were also examined.

There were no statistically significant differences between the UC and ACS Arsenator® measurements. The AFE measurements were done in triplicate and the standard deviations ranged from 9 to 100% of the mean concentration. The high standard deviations generally were the result of one replicate being very different from the others. For those samples with no measurement "out of whack", the standard deviations were less than or equal to 15% of the mean. The UC Arsenator® measured concentrations were about 10% less than those measured by ICP. The linear range of the UC Arsenator® seems to be from about 4 to 95 µg arsenic L^-1.

We recommend that each Arsenator® be calibrated against an ICP to determine what the accuracy is and that field measurements be done in triplicate to protect against the possibility of an wildly imprecise measurement.