A study of ion-molecule reactions in a dynamic reaction cell to improve elemental analysis with inductively coupled plasma-mass spectrometry

The study of ion-molecule reactions in dynamic reaction cell (DRC) has been studied for improvements in elemental analysis by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The reactions between elemental and polyatomic background ions with NH3, and 70 elemental ions and both NH 3 (ammonia) and C2H4 (ethylene) gasses were studied. Relative reaction rates were calculated in terms of the amount of ion signal lost/(mL/min increase in reaction gas flow rate in Argon equivalent units) for the elemental ions and for many background ions. It was found that when the reaction cell is pressurized with a small amount of NH3 gas, background ion signals at nearly every mass from a deionized water sample (DI H2O) are attenuated. NH3 also reduces ion signals due to argides (ArM+), oxides (MO+) and doubly charged species (M2+) from elements with low second ionization potentials. C2H4 proved to be less powerful at reducing background ion signals and was found to increase the ion signal at many masses due to the creation of product ions in the reaction cell. Signals due to product ions were attenuated by adjustment of the low mass cutoff of the reaction cell bandpass.; The loss of signal rates due to collisions and reactions between most elemental ions were moderate, with ions losing between 1 and 3 orders of magnitude per mL/min increase in NH3 flow rate (in Argon equivalent units), although loss of ion signal rates up to five orders of magnitude per (mL/min increase in NH3 flow rate) were seen. In comparison, C2H 4 reduced most elemental ion signals at a rate between less than one to 2 orders of magnitude per (mL/min increase in C2H4 flow rate) but loss of ion signal rates up to 3 orders of magnitude per (mL/min increase in C2H4 flow rate) were seen. An increase in ion signal per (mL/min increase in C2H4 flow rate) was found for a few elemental ions and was attributed to collisional focusing of the ion beam. The group of elemental ions that loose ion signal at rates faster than 3 orders of magnitude per (mL/min NH3) is nearly identical to the group of elemental ions lost ion signal at rates greater than 2 orders of magnitude per (mL/min C2H4).; The product ions from NH3 were categorized into cluster product ions and condensation product ions. Each group of product ions was analyzed for their use as analyte ions. In general, the ion signals for condensation product ions were more intense than the cluster product ions, each created from the same concentration of elemental ion in solution. Identification and categorization of C2H4 product ions from reactions with elemental ions less than 100 amu was not possible due to the numerous product ions created from reactions with background ions. The most intense product ions for monoisotopic ions above 100 amu were identified.; The effect of the Mathieu parameter q (or RPq) on elemental and product ion signals in an NH3 pressurized reaction cell was studied in detail. A strategy for developing methods with the ICP-DRC-MS is described. The pressurized, enclosed quadrupole was also found useful for improving precision of isotope ratio measurements. (Abstract shortened by UMI.)...