Measurement of Soil/Dust Arsenic by Gas-Phase Chemiluminescence

Maather F. Sawalha
Mrinal K. Sengupta
Shin-Ichi Ohira
Ademola D. Idowu
Thomas E. Gill
Lila Rojo
Melanie Barnes
Purnendu K. Dasgupta

A gas phase chemiluminescence (GPCL) based method for trace measurement of arsenic has been recentlydescribed for the measurement of arsenic in water. The principle is based on the reduction of inorganic As to AsH3at a controlled pH (the choice of pH governs whether only As(III) or all inorganic As is converted) and the reactionof AsH3 with O3 to produce chemiluminescence (Anal. Chem. 78 (2006) 7088-7097). The same general principlehas also been used in postcolumn reaction detection of As where As species are separated chromatographically,then converted into inorganic As by passing through a UV photochemical reactor followed by AsH3 generation andCL reaction with ozone (Anal. Chem. 79 (2007) 9197-9204). In the present paper we describe the measurement ofAs in different soil and dust samples by serial extraction with water, citric acid, sulfuric acid and nitric acid. Wealso compare parallel measurements for total As by induction coupled plasma mass spectrometry (ICP-MS).As(V) was the only species found in our samples. The ICP-MS results were highly correlated with direct GPCLand LC-GPCL results (r2 = 0.xxxx and 0.xxxx, respectively). The limit of detection (LOD) in the extracts was0.36 g/L by direct GPCL compared to 0.1 g/L by ICP-MS. In sulfuric acid based extracts, the LC-GPCLmethod provided LODs inferior to those previously observed for water based standards and were 2.6, 1.3, 6.7 ,and6.4 μg/L for As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) respectively.