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	Journal club (Metabolism/PKPD and more) Let's get synchronized! Sign up for talk! April 7th , 2008    PDF / Medline

Surrogate standard vs. Internal standard	A surrogate standard is a compound that has properties similar to the target analyte(s).The surrogate compound is not expected to be in the sample and should not interfere with the identification or quantification of the target analytes. By demonstrating that the surrogate compound can be recovered from the sample matrix with reasonable efficiency, the surrogate standard performs a quality control function on the suitability of the analytical method for the intended analyses and on the ability of the laboratory to execute that method with reasonable proficiency. If a surrogate compound is not recovered, an analyte of concern also may not be recovered. The purpose of an internal standard is to provide a reference concentration against which the responses of the target analytes are compared. By adding the internal standard to the sample just prior to instrumental analysis, the quantity present is not affected by extraction efficiencies or other sample handling procedures. The internal standard can then compensate for relatively minor fluctuations in instrument sensitivity to provide more accurate quantification of the target analytes.