Skip to Content
Merck

One internal standard for multiple analytes: a limit and solution.

Journal of AOAC International (2004-10-21)
Li Huang, Mary Wu
ABSTRACT

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.

MATERIALS
Product Number
Brand
Product Description

Supelco
(±)-Phenylpropanolamine hydrochloride solution, 1.0 mg/mL in methanol (as free base), ampule of 1 mL, certified reference material, Cerilliant®
Supelco
(+)-Norpseudoephedrine hydrochloride solution, 100 μg/mL in methanol (as free base), ampule of 1 mL, certified reference material, Cerilliant®
Sigma-Aldrich
Cathine hydrochloride
Sigma-Aldrich
(1S,2R)-(+)-Norephedrine, 98%