RMs for method performance studies

This section summarises important aspects which have been described in detail in recent publications with respect to speciation studies (Quevauviller, 1998b, c). When relevant, a distinction is made between RMs and CRMs , the fundamental difference between RMs and CRMs being that some parameters in CRMs are known with great accuracy and guaranteed by the producer. 

RMs can be solutions or materials intended for testing part(s) of an analytical procedure (e.g. pure extracts or digests, raw extracts, spiked samples), or laboratory matrix RMs having a composition as close as possible to the matrix to be analysed by the laboratory in its daily practice. 

CRMs allow the user to link his results with those of internationally recognised standards, i.e. they enable the user to verify his performance at any desired moment in terms of accuracy. CRMs can be pure substances or solutions to be used for calibration and/or identification, materials of a known matrix composition for the calibration of a certain type of comparative measuring instruments, matrix RMs representing as far as possible the matrix being analysed by the user (with a certified content), or methodologically defined RMs (certified following a very strict analytical protocol), e.g. a standard (Quevauviller et al., 1995a). 

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