Detection and Quantification of Metals in Organic Materials by Laser-SNMS with Nonresonant Multiphoton Ionization

We have shown that the sensitive detection and in favorable cases the quantification of metals in organic materials by laser-SNMS with nonresonant multiphoton ionization (NRMPI) is possible. As a model system, sputter-deposited submonolayer coverages of metals on polymer surfaces (polycarbonate, poly(vinylidene chloride), polyimide) were investigated. By use of these samples, relative sensitivity factors and detection limits of several metals (Be, Cr, Mn, Fe, Co, Ni, Mo, W) were determined using laser-SNMS with NRMPI. The relative sensitivity factors for this kind of sample show a high level of agreement with those for metals sputtered from alloys. The detection limits (∼1 ppm of a monolayer) are almost the same as for inorganic matrixes such as Si or GaAs. Laser-SNMS with NRMPI was also used for the determination of the elemental composition of the active centers of metalloproteins (namely, the purple acid phosphatases extracted from sweet potatoes and from red kidney beans). These results have shown the ability of laser-SNMS to detect metal atoms bound to organic macromolecules with an atom concentration as low as 1 ppm. In comparison to TOF-SIMS, laser-SNMS is more sensitive for metal detection in organic matrixes, since the secondary ion yields observed for these matrixes are reduced compared to matrixes optimized for high secondary ion emission, such as, for example, highly oxidized surfaces.