The analysis of inorganic anions from liquid solutions using cationic surfactants and negative secondary ion mass spectrometry

Abstract

Small inorganic anions such as nitrate, nitrite, iodate, bromate, cyanate, thiocyanate, chlorate, perchlorate, iodide, bromide, chloride, and tetrafluoroborate can be analyzed at low levels from glycerol solution using negative secondary ion mass spectrometry provided a long chain cationic surfactant such as tetradecyltrimethylammonium hydroxide is present in the solution. Sensitivities are directly related to the extent of association of the anion with the surface monolayer generated by the surfactant. Strongly interacting anions such as nitrate are detectable as intact ions at the 1 ng level (10 −5 M in glycerol, two μl of solution). The degree of interaction between the anion and the monolayer parallels the behavior of the same ions on quaternary ammonium ion exchange resins. Fluoride and hydroxide do not interact strongly and do not give signals of useful intensity. Quantification can be readily obtained using stable isotope dilution techniques. The technique has been applied to the analysis of nitrate anion in natural precipitation.