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When tested individually In a clean system, NOa~a nd HNOa are shown not to be serious Inhibitors of AsH3 and H2Se evolution. The real inhibitors of AsH3 and H2Se evolution (encountered when solid samples are oxidatively dissolved In nitric acid) are shown to be correspondingly reduced nitrogen oxides (N02~, etc.) produced In sample digestion. Volatile NO, Interferants can then result upon acidic disproportionation. These volatile NO, species are found to transport with the AsH3 and H2Se analyte. The N203 species Is detected In a cryogenic trap. When dissolved In downstream H2S04 drying agents, the NO, can give rise to powerful oxidants such as NO+ which can accumulate In the H2S04 and thereby account for "memory Interferences" encountered with subsequent samples. The use of sulfamic acid Is Investigated In the preliminary removal of reduced nitrogen oxides such as N02~. Transition metal cation interferences are also studied. Several metal masking procedures previously reported to work well for AsH3 are shown here to fall for the evolution of H2Se. BH3CN" Is shown to be an effective new reductant to evolve AsH3 and H2Se from As(III,V) and Se(IV) In acid media.

Nonresonant, low-energy atomic oxygen transitions from high-energy (11 to 16 eV) singlet, triplet, and quintet states are observed in the 2 kW argon inductively coupled plasma (ICP). A table of ICP oxygen lines and relative emission intensities from 2500 to 10 000 Å is presented. The degree of molecular dissociation in the ICP is evaluated for several small, highly stable molecules as a function of rf power level over the range of 0.2 to 2.25 kW. Quantitative dissociation is achieved at power levels ≥1.95 kW. The use of these nonresonance O(I) lines for the analytical detection of oxygen is reported. The present detection limit for nonoptimized conditions is 0.5 μg. Considerable improvement is expected in the future. The response is linear, and the precision using a gas sampling loop is 0.5% RSD.

Nonresonant, low-energy (visible-near infrared) atomic nitrogen transitions from high-energy (11 to 14.4 eV) doublet and quartet excited N(I) states are observed in the 1.5 to 2.2 kW argon inductively coupled plasma (ICP) when gaseous compounds containing this element (N) are introduced as samples. A Table of ICP excited nitrogen (I) lines and relative emission intensities from 2225 to 10 950 Å is presented. A number of new nitrogen lines are observed for which transitions have not been assigned. The ICP nonresonance emission spectrum of atomic nitrogen [N(I)] is found to be especially good in the near infrared region. The use of near infrared nonresonant N(I) lines for the analytical detection of nitrogen is reported. The relative intensity of N(I) emission (derived from N2 samples) is at a maximum between the turns of the rf load coil. An “equal intensity” contour “map” of N(I) emission in the ICP is presented using N2 as the sample. The present limit of nitrogen detection in argon for nonoptimized conditions is 1.0 ppm (v/v) using continuous sample introduction (limited by photomultiplier noise). For gas sampling loop injections, the present detection limit is 0.3 μg (limited by atmospheric leakage or permeation contamination into the sampling loop system). Considerable improvement is expected in the future. The relative contributions to the baseline signal of: (1) atmospheric nitrogen entrainment in the argon plasma, (2) atmospheric permeation into the present Teflon gas sampling loop system, and (3) argon tank contaminants are evaluated. Suggestions for further improvement are given. The response is linear, and the short-term precision for repetitive introduction of samples containing 20 μg of N2 is 0.4% RSD using a 157 μl Teflon gas sampling loop.

Studies are presented describing an improved application of the NaBH4 reduction of soluble arsenite to form arsine as a preconcentration approach for ultra-trace level arsenic determination by inductively coupled plasma optical emission spectrometry. Specialized analyte introduction techniques are described for elimination of reaction by-products that would normally extinguish a medium power plasma discharge. An approach is presented to minimize the need for background correction and facilitate a superior arsenic detection limit (≤0.03 ng/ml) in a relatively inexpensive 1.2 kW inductively coupled plasma system.