INVESTIGATION OF HELIUM INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY FOR THE DETECTION OF METALS AND NONMETALS IN AQUEOUS-SOLUTIONS

Aqueous solutions are introduced into a helium inductively coupled plasma mass spectrometer (He ICPMS) for the detection of metals and nonmetals. The effect of four approaches for reducing the extent of secondary discharge in He ICPMS is examined. These approaches include the following: (i) the use of a center-tapped load coil, (ii) modified load coils, (iii) electrostatic shields, and (iv) application of samplers made from nonconductive materials and aluminum. Analytical characteristics of the system such as the background mass spectrum for injection of nitric acid solution, effects of the length of the plasma confinement tube, forward power and injector gas flow rate on ion signal intensities, and the level of oxide and doubly charged ions are determined. Isotope ratios for Cu-63/Cu-63, Ni-58/Ni-60, and Se-80/Se-78 are measured. The limits of detection, obtained with an analogue detector and a prototype spectrometer, for the metals studied are in the range 0.2-9 ng/mL while those for As, Br, Se, and I are 0.2, 1, 0.2, an 0.04 ng/mL, respectively. Linear dynamic ranges of over 4 orders of magnitude are achieved. The system allows the determination of certain isotopes that suffer from spectral interference in Ar ICPMS.