Why do you use surrogates?
Surrogates are used in most organic analysis to demonstrate matrix compatibility with the chosen method of analysis. Each sample is spiked with a known concentration of surrogate compound(s) prior to the preparation and analysis of the sample. Control charts are maintained that are indicative of typical surrogate recoveries of ‘real’ samples rather than laboratory-controlled samples. Samples that fail surrogate recovery criteria are re-spiked and re-analyzed to determine if poor recovery is due to laboratory spiking error or matrix interference.
Reported surrogate recoveries are important because low recoveries indicate matrix interference in the sample resulting in suppressed recovery of analytes of interest. This becomes important when evaluating the data. For example, if TCE is an analyte of interest but the associated surrogate is only recovered at 28%, the reported value for TCE may be biased low as well and the client may want to consider the possibility that more TCE is present than is being reported.