Good reliability of Caco-2 permeability studies requirescompetent sampling and analytical methods to ensure thecomparability of day-to-day experiments. In this work, two
n-in-one LC/MS/MS methods based on two differentionization techniques were developed and validated for agroup of reference compounds; eight of them are recommended by the Food and Drug Administration (FDA) forthe evaluation of oral drug permeability. The performanceof a new ionization technique, atmospheric pressurephotoionization (APPI), as an interface for quantitativeLC/MS analysis was evaluated in comparison to theelectrospray ionization (ESI). Generally, the validationparameters, including sensitivity, accuracy, and repeatability, were comparable for the APPI and ESI methods.The main difference was that the linear quantitative rangeof APPI was 3-4 orders of magnitude (
r2 0.998)whereas in ESI it was typically 2-3 orders of magnitude(
r2 0.990). By the APPI and ESI methods, the simultaneous analysis of nine highly heterogeneous compoundswas achieved within 5.5-7 min, which leads to significantsavings in time and cost of the analyses. The successfulvalidation data indicate the usefulness of both the methods for the rapid and sensitive (LOD values typically
5nM) testing of drug transport across the Caco-2 monolayers, and after case-specific modification, the methodsenable the permeability screening of new drug candidates.The applicability and reliability of both methods wasdemonstrated with a real batch of Caco-2 samples, eachproviding similar values of apparent permeability (
Papp).In addition, the individual permeabilities of the compounds in the cocktail experiments correlated closely tothe ones obtained from single-compound experiments.