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Novel use of an isotope separator to determine the position of fluorine‐18 in labelled 1,1,1,2‐tetrafluoroethanes
Author(s) -
Pike Victor W.,
Waters Stephen L.,
Aigbirhio Franklin I.,
Makepeace John,
Tanner Richard J. N.
Publication year - 1994
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210290910
Subject(s) - labelling , chemistry , selectivity , ion , fluoride , fluorine , isotope , analytical chemistry (journal) , radiochemistry , separator (oil production) , ion beam , chromatography , inorganic chemistry , nuclear physics , organic chemistry , physics , biochemistry , thermodynamics , catalysis
A novel technique is described for measuring the site selectivity of methods for labelling the major CFC‐alternative, 1,1,1,2‐tetrafluoroethane (HFA 134a), with fluorine‐18 ( t 1/2 = 109.7 min). The carbon–carbon bond in radiofluorinated HFA 134a is broken in the ion source of an isotope separator. Radioactivity associated with the ion beam of the [CF 2 18 F] +. fragment ( m/z = 68) is collected, measured and divided by the integrated mass of the simultaneously collected ion beam for the [CF 3 ] +. fragment ( m/z = 69) to give the ‘specific radioactivity’ (in nCi nmol –1 ) of the radiolabel in the 1‐position. Similarly, the ‘specific radioactivity’ of the radiolabel in the 2‐position is calculated from the measured radioactivity of the ion beam from the [CH 2 18 F] +. fragment ( m/z = 32) and the integrated mass of the simultaneously collected ion beam from the [CH 2 F] +. fragment ( m/z = 33). The selectivity of the labelling procedure for a particular position is then given by the decay‐corrected ratio of specific radioactivity at that position to the sum of specific radioactivities. The labelling of HFA 134a by the reaction of [ 18 F] fluoride with trifluoroethylene was found to have 97% selectivity for the CF 3 group, whereas labelling by the reaction of [ 18 F] fluoride with 2,2,2‐trifluoroethyl p ‐toluenesulphonate was found to have 91% selectivity for the CH 2 F group. This information is of value for tracer studies of the fate of HFA 134a in man following its inhalation as a drug propellant. The described technique is of potentially wider value for determining the position of fluorine‐18 in labelled polyfluorinated molecules.