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 pla sma mass spectrometer (He ICPMS) for the detection of metals and nonme tals. The effect of four approaches for reducing the extent of seconda ry discharge in He ICPMS is examined. These approaches include the fol lowing: (i) the use of a center-tapped load coil, (ii) modified load c oils, (iii) electrostatic shields, and (iv) application of samplers ma de from nonconductive materials and aluminum. Analytical characteristi cs 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 intensit ies, and the level of oxide and doubly charged ions are determined. Is otope ratios for Cu-63/Cu-63, Ni-58/Ni-60, and Se-80/Se-78 are measure d. The limits of detection, obtained with an analogue detector and a p rototype spectrometer, for the metals studied are in the range 0.2-9 n g/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 tha t suffer from spectral interference in Ar ICPMS.