Miniature Recoil Ion Mass Spectrometer enables correlative elemental isotopic and backscatter analysis from solid nanovolumes

Mass spectrometric measurement of elemental isotopic ratios from solids has been mostly obtained by secondary ion mass spectrometry (SIMS) which has a sensitivity for almost all elements superior to Xray fluorescence and laser desorption ICPMS- In SIMS elemental and molecular ions are liberated from the near surface of a solid by energetic micron or submicron focused ion beams and extracted with an electric field into a mass spectrometer (often a time of flight mass spectrometer)- Two problems prevent SIMS from competing successfully with XRF and ICP MS for elemental identification in plant and animal tissues: 1) Quantitative SIMS elemental analysis is almost impossible in complicated biological systems 2) Molecular ions almost always overwhelm the desired elemental ions thus requiring large high resolution imaging Mass Spectrometers for separation- In contrast, Ionwerks has invented and marketed an instrument and method for measuring forward recoiled surface elemental ions which are also created during but excluded from the SIMS analysis process- These elemental ions are created during forward keV energies in a billiard ball type collision from a glancing angle, energetic primary ion which gives the recoiled ion keV energies into the forward direction exiting the surface- Molecular information is destroyed during this violent collision leaving only the ionized elements in the spectrum which can be easily analyzed with less complex time of flight spectrometers than SIMS- Under the correct geometries these recoil intensities are a significant minority portion of all the sputtered elements and molecules created during the primary ion collision- We call this alternative technique Mass Spectrometry of Recoiled Ions (MSRI)- In Figure 1A a direct comparison of SIMS and MSRI data acquired sequentially with the same beam dose from the same surface shows similar intensities of the doped Be signal from the two techniques- The presence of complicating SIMS molecular ion signals which prohibit Cr and Fe analysis is eliminated in MSRI- In Phase I we will explore the possibility that these simple isotopically resolved elemental spectra can be acquired from a specially designed miniature time of flight detector which will simultaneously detect both positive and negative ions originating from the same surface volume (something SIMS cannot do)- In a phase II effort, this miniature bipolar MSRI spectrometer would be located within the Zeiss Orion Helium/Neon Ion microscope at Rutgers University in which the Ionwerks NanoRBS is now operational- At present the sensitivity of NanoRBS is 280,000 atoms of Pt within a 2500 nm3 volume (equivalent of one 15 nm diameter Pt nanoparticle)- Quantitation of the MSRI signals will arise by the correlative combination of NanoMSRI and NanoRBS, which can be made quantitative by standards- Thus each pixel in an elemental image map within intercellular organelles might be made quantitative by comparison the Neon backscatter signal acquired simultaneously with the MSRI ion intensities- This instrumental combination will be useful in locating either dispersed endogenous elements or toxicants as well as intact elemental Nanoparticulates which are intentionally or accidentally introduced into the organism- Moreover, if the high pressure freezers and sample preparation techniques developed for cryoTEM are ultimately implemented within the Zeiss Orion, then depth profiling of complicated fragile structures may be attempted -