A new analytical method for the determination of ele- ments in filtered aqueous matrices using inductively coupled plasma-mass spectrometry (ICP-MS) has been implemented at the U.S. Geological Survey National Water Quality Labo- ratory that uses collision/reaction cell technology to reduce molecular ion interferences. The updated method can be used to determine elements in filtered natural-water and other filtered aqueous matrices, including whole-water, biota, sediment, and soil digestates. Helium or hydrogen is used as the collision or reaction gas, respectively, to eliminate or substantially reduce interferences commonly resulting from sample-matrix composition. Helium is used for molecular ion interferences associated with the determination of As, Co, Cr, Cu, K, Mg, Na, Ni, V, W and Zn, whereas hydrogen is used for Ca, Fe, Se, and Si. Other elements that are not affected by molecular ion interference also can be determined simply by not introducing a collision/reaction gas into the cell. Analy- sis time is increased by about a factor of 2 over the previous method because of the additional data acquisition time in the hydrogen and helium modes.