Page 199 - Tandem Techniques

Page 182

The solvent was then removed and the steroids taken up in 10 ¬l of ethyl acetate and 100 µl of
trifluoroacetic acid anhydride, to form the acetate derivatives. The mixture was kept at 70°C for about
an hour, the reagent removed by evaporation and the residue dissolved in 15 ml of isooctane. This
solution was use for analysis by GC/MS. The GC column was a DB- 1 capillary column 30 m long, 250
µm I.D. carrying a 0.25 µm film of stationary phase. 2 µl of sample was injected directly onto the
column with no split and the column was programmed from 130°C to 250°C, at 25°C per min, and from
250°C to 300 °C at 50° per min. The ion source of the MS was held at 200°C and the transfer line at
300°C. A spectrum obtained for medroxyprogesterone acetate is shown in figure 5.12 and the
characteristic parent ion, mass 482 is clearly seen. The sensitivity of the technique can be very high and
this is clearly demonstrated by the chromatogram shown in figure 5.13. The chromatogram was
constructed by single ion monitoring using the m/z value of the molecular ion at 482.

Figure 5.13
Single Ion Monitoring of Medroxyprogesterone Acetate
Present at a Blood Plasma Level of About 6.5 ng/ml(ref.9)

The concentration of medroxyprogesterone acetate was about 6.5 ng per ml and the signal-to-noise ratio
of the steroid ester peak seems to be about