2,2,4,4,6,6-Hexakis[(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl)oxy]-2,2,4,4,6,6-hexahydro- 1,3,5,2,4,6-triazatriphosphorine is a component of Ultramark 1621 which is a useful calibration compound for negative and positive ion fast-atom bombardment (FAB) high-resolution mass spectrometry.