One internal standard for multiple analytes: a limit and solution
Huang, L.; Wu, M.
Journal - Association of Official Analytical Chemists 87(5): 1058-1062
2004
ISSN/ISBN: 0004-5756 PMID: 15493661 Document Number: 583577
The use of a single internal standard (ephedrine-d5) as the basis for calculations of the concentrations of both the major and the minor alkaloids leads to incorrect results from variabilities in the solid-phase extraction (SPE) of the ephedra alkaloids. Because the SPE column is overloaded by ephedrine, the recovery of the internal standard, which is dependent on the dilution factor, is decreased. On the other hand, the recoveries of the minor alkaloids (methylephedrine, methylpseudoephedrine, norephedrine, and norpseudoephedrine) stay high because these compounds are less concentrated and do not overload the SPE column. Consequently, the recovery factors for the major and minor alkaloids are different, or the results are incorrect if the same recovery factor is used.