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 multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram-per-liter (part-per-billion = ppb) range. Most of the other elements are present at nanogram-per-liter (part-per-trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.