Alternative mass reference standards for direct analysis in real time mass spectrometry

RATIONALE: Mass spectra were acquired with the Direct Analysis in Real Time (DART (R)) ion source for an amine-terminated polyether used as positive-ion mass reference standards and for several fluorinated materials commonly used as negative-ion reference standards for mass spectrometry. METHODS: A commercial time-of-flight mass spectrometer equipped with a DART ion source was used for all measurements. Mass reference standards deposited onto the sealed end of a glass melting point tube were suspended in the DART gas stream for analysis. RESULTS: A polyetheramine (Jeffamine (R) M-600) produced intense peaks corresponding to protonated molecules. Perfluorotributylamine (PFTBA), and perfluorotripentylamine, gave useful reference spectra for different m/z ranges. DART mass spectra of Ultramark 1621 (R) resembled those previously reported for Fast Atom Bombardment (FAB) and Electrospray Ionization (ESI). Fomblin (R) Y, a fluorinated ether, was the most useful negative-ion reference standard of the materials tested. The material is commercially available, inexpensive, and provides reference peaks covering the m/z range 85 to >3000. CONCLUSIONS: Jeffamine-M600 was found to be a convenient alternative to polyethers such as polyethylene glycol (PEG) for DART positive-ion mass calibration. Fomblin Y was suitable for use as a negative-ion reference standard. Copyright (C) 2016 John Wiley & Sons, Ltd.