ISSN:
0030-493X
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 (t1/2 = 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 [CF2 18F]+. fragment (m/z = 68) is collected, measured and divided by the integrated mass of the simultaneously collected ion beam for the [CF3]+. 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 [CH2 18F]+. fragment (m/z = 32) and the integrated mass of the simultaneously collected ion beam from the [CH2F]+. 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 [18F] fluoride with trifluoroethylene was found to have 97% selectivity for the CF3 group, whereas labelling by the reaction of [18F] fluoride with 2,2,2-trifluoroethyl p-toluenesulphonate was found to have 91% selectivity for the CH2F 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.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/oms.1210290910
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