Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Single and multiple ion monitoring is employed to evaluate whether deuteriomethylated allobarbitone or methylated quinalbarbitone is the better internal standard for quantifying methylated allobarbitone through a g.c.m.s. system based on a quadrupole mass spectrometer. It is shown that the coefficient of variation of the single ion monitoring method is substantially lower than that of the multiple ion monitoring method. Small quantities of a compound are therefore most accurately determined by adding a labelled version of the compound solely to act as a carrier, plus an internal standard giving an ion in common with the compound being measured. By this means 40 pg and 100 pg of methylated allobarbitone could be determined with coefficients of variation of 11.5 and 2.0%, respectively. Using only the labelled compound as internal standard, the corresponding values were 19.8 and 15.3% for the same quantities.
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