Control Samples: Laboratory control standards(LCSs) 

Laboratory control standards(LCSs) are certified standards  obtai n ed f rom an outside agency or commercial source to check whether thedata being generated are comparable to those obtained elsewhere. TheLCSs  provide a measure of the accuracy and can be used as audits. Asource of LCSs isstandard reference materials(SRMs), which are certifi ed standards available from the National Institute of Standards an dTesting (NIST) in the United States. NIST provides a variety of solid,liquid, and gaseous SRMs which have been prepared to be stable andhomogeneous. They are analyzed by more than one independentmethods, a nd their concentrations are certified. Certified sta  ndar dsare also available from the European Union Community Bureau ofR eference (BCR), government agencies such as the EPA, and fromvarious companies that sell standards. These can be quite expensive.Often, samples are prepared in the laboratory, compared to the certified standards, and then used as secondary reference materials fordaily use.