Perfluorotributylamine ( PFTBA ) why use tuning in Gas chromatography–mass spectrometry

PFTBA (Internal standard of Gc-MS)

Perfluorotributylamine ( PFTBA )

pftba structure
PFTBA (Perfluorotributylamine) is used to tune a mass spectrometer for several reasons:
It exhibits masses over a wide mass range (57 to 614 amu).
The masses are very separated.
The masses have zero defects.

pftba structure
The fragments created are very predictable. Our first mass that we tune on is 69. 69 is the result of CF3. Looking at the PFTBA molecule, we see that we have the potential of three (3) of these fragments for each molecule. 69 is the low mass in the tuning.

pftba structure
219 is, typically, the second mass used for tuning the mass spectrometer. This is the mid mass in the tuning. Again, you can see the potential for three fragments from each molecule. The 219 fragment is C4F9.

pftba structure
502 is, typically, the high mass used for tuning the mass spectrometer. Taking C3F7 off of the molecule, (169), will result having a mass of 502. You can see that C9F20N is mass 502. 

Why not use PFTBA? We did on older systems.

PFTBA takes a long time to pump away in NCI mode; the vapor pressure is too low.
In NCI mode, PFTBA does not have any significant ions below 302 amu. With significant ions below 302, it is easier to correctly set the lower portion of the mass axis.


PFDTD structure

PFDTD (Perfluorodimethyltrioxadodecane) is used to tune the Agilent mass spectrometer in CI mode. (For the purist: 2H-Perfluoro-5,8-dimethyl-3,6,9-trioxadodecane)

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