TESTING THE LIMITS OF ICP-MS - DETERMINATION OF TRACE-ELEMENTS IN-GROUND WATER AT THE PART-PER-TRILLION LEVEL

An ICP-MS, equipped with an ultrasonic nebulizer and active-film multi plier detector, is used to attempt to determine 54 trace elements dire ctly in ground water. Lithium, arsenic, rubidium, strontium, barium, a nd antimony are found in the microgram-per-liter (part-per-billion = p pb) range. Most of the other elements are present at nanogram-per-lite r (part-per-trillion = ppt) concentrations. Ion exchange preconcentrat ion is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt fo r lutetium, thulium, and terbium. The formation of molecular species i n the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measure ment of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these inte rferences are discussed. All together, the concentrations of the 54 el ements in water from four Nevada springs span almost seven orders of m agnitude.