The mass spectral background features of a moderate-power nitrogen microwave-induced plasma are presented. In general, the mass spectral background obtained from a nitrogen plasma is less congested at low mass than is the case with argon ICP-MS. In addition, there are no significant (less than 20 counts per second) background species above mass 60. At normal multiplier voltage, the major background species found in a dry nitrogen plasma include <sup>14</sup>N<sup>+</sup>, <sup>14</sup>NH<sup>+</sup>, <sup>14</sup>N<sub>2</sub><sup>+</sup>, <sup>14</sup>N<sub>2</sub>H<sup>+</sup>, <sup>14</sup>N<sup>16</sup>O<sup>+</sup>, <sup>14</sup>N<sup>16</sup>OH<sup>+</sup>, <sup>14</sup>N<sub>3</sub><sup>+</sup>, and <sup>14</sup>N<sub>4</sub><sup>+</sup>. This background is unchanged by the nebulization of deionized water, 5% (v/v) acids (nitric, hydrochloric, and sulfuric acids), and 5% (v/v) methanol solutions. These background species do not interfere with the determination of K, Ca, and Se at their major isotopes, which commonly have interfering background species in Ar ICP-MS. On the basis of the nebulization of 5% HCI and methanol in the nitrogen plasma, As and Cr do not have isobaric interferences at their major isotope masses 75 and 52. In addition, preliminary studies on the effect of Na as a concomitant element on analyte signals indicate severe enhancement or suppression of analyte signals.
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