A Note on Assessment of Radioactivity Measurements on HPLC Effluents
In establishing drug metabolite profiles, preferably with radio-labelled parent drug, HPLC is an effective approach, aided by a solvent gradient where the compounds are of widely different character . Detection results can be misleading if obtained off-line on collected fractions rather than on-line: much information is lost if the fraction size is not small enough (Fig. 1). According to Huber et al.  the ratio of the fraction size to the S.D. of the peak volume should be less than 0.5, to minimize the possible influence of collection regime. With small fractions, however, the long counting periods needed for high sensitivity and precision  delay the procurement of the chromatographic results. Off-line counting is also disadvantageous in respect of time and materials costs.
KeywordsFraction Size Background Signal Radioactivity Measurement True Sample Counting Period
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