Pre-Concentration and Determination of Molybdenum in the Rouge River, Michigan, USA, with Graphite Furnace Atomic Absorption Spectrometry

Abstract

<p>Molybdenum is an essential element to humans because of its role in several enzymes, and its occurrence in natural waters is of significance from environmental and biochemical standpoints. Owing to the low concentration of molybdenum in natural waters, pre-concentration is required prior to its determination with atomic spectroscopic techniques. This paper reports on the pre-concentration and determination of molybdenum in the Rouge River, Michigan, USA with graphite furnace atomic absorption spectrometry (GFAAS). Sample preparation and pre-concentration were performed using ultra-trace analysis methodology in a class 100 clean room laboratory. The molybdenum was pre-concentrated on a Bio-Rad Chelex® 100 resin, followed by elution from the resin with ammonia solution. Subsequently, the single-point standard addition method was used, and the absorbance owing to molybdenum was measured at 313.3 nm. An overall concentration factor of ten was realized for the final pre-concentrated volume, and the results from several sampling locations on the four branches of the Rouge River yielded molybdenum concentrations ranging from 1.98 to 4.21 ug·L^-1 with an overall average of 2.94 ug L^-1. The precision of the results, based on quintuplet determinations from each sampling site, varied between 6.1 to 8.8 %relative standard deviation (%RSD). Although the concentration of molybdenum in the Rouge River is in line with the lower reported molybdenum levels in the US and world rivers, it is higher than the level that arises from natural sources only and therefore has anthropogenic causes.</p