Analysis of nickel (II) in particulate matter by Raman microspectroscopy

A Raman microspectroscopy-based method utilizing sample derivatization is developed for determination of soluble and low solubility nickel (II) compounds in size-resolved samples of atmospheric particulate matter (PM). In this method, particles are collected in a cascade impactor on an aluminum substrate which has been pre-treated with dimethylglyoxime (dmg) to form [Ni(dmgH)2]. This Ni complex has strong characteristic Raman features at 1352 and 1510 cm−1, ascribed to contributions of normal modes ν(C−CH3)+ν(NO) and ν(CN), respectively. The method is tested using submicron-sized aerosols generated in the laboratory by atomization of solutions/suspensions of individual water-soluble NiSO4 and low-solubility NiCO3, Ni(OH)2, and NiO as model compounds. Additionally, Raman spectra of particles containing NiSO4 internally mixed with ammonium sulfate, oxalic acid, and humic acid are obtained. The presence of these atmospherically abundant inorganic and organic compounds does not interfere with the detection of Ni(II).