Fig. 2

Mass-resolution for NanoSIMS vs. CryoNanoSIMS. Shown are mass spectra around atomic nominal mass units 26 and 27 at which the ¹²C¹⁴N⁻ and ¹²C¹⁵N⁻ ions are routinely separated from potential mass interferences and counted in electron multiplier detectors to permit quantitative measurements of the sample ¹⁵N/¹⁴N isotope ratio. In this example, the ¹²C¹⁴N⁻ and ¹²C¹⁵N⁻ ions were derived from ¹⁵N-labeled biological tissue (Green Hydra, cf. main text), conventionally prepared (i.e., with resin embedding) in the case of NanoSIMS analysis and with the cryogenic workflow (cf. main text) in the case of CryoNanoSIMS analysis. With identical instrument settings, the mass resolution is — for all practical purposes — indistinguishable between NanoSIMS and CryoNanoSIMS analysis. The count rates shown for each analytical mode are representative of biological tissue under typical analysis conditions, i.e., with a primary Cs⁺ beam current of ca. 2 pA focused to a spot of about 150 nm and scanning a field of view 40 × 40 µm² in steps of 256 by 256 pixels; c.f. Methods. All else being equal, the count rate of ¹²C¹⁴N⁻ is generally lower from a vitrified sample than from a resin-embedded sample, but this can vary among different tissue types. Additional file 1: Figures S4 and S5 show the stability of key molecular ion species, isotope ratios, and the corresponding ion images obtained on isotopically normal biological tissue; see also Fig. 4