Postcolumn introduction of an internal standard for quantitative LC-MS analysis

A method for introducing internal standards by direct infusion into the LC effluent for the quantitative LC-MS analysis of environmental samples is de scribed. This postcolumn introduction method was found to be effective in c orrecting quantitative errors associated with matrix signal suppression. Ho wever, unlike surrogate or volumetric internal standards, the performance o f the postcolumn method does not depend on the selection of an internal sta ndard that shares identical elution time with the target analyte, As a resu lt, either structural analogues (target analyte derivatives) or isotopicall y labeled compounds may be applied as effective internal standards. Further more, the postcolumn introduction method allows the application of one inte rnal standard to address signal suppression effects for several analytes in a single LC-MS run. In contrast, volumetric and surrogate introduction met hods require an isotopically labeled internal standard for each analyte to be quantified.