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1 <br /> B Standard Curves <br /> Spectrophotometers are standardized daily with at least <br /> three concentrations for every test. Absorbances are <br /> t recorded in the bound notebook associated with each test; <br /> this step permits detection of any change in absolute per <br /> - <br /> formance. Indications of declining sensitivity or wave- <br /> length inaccuracy are corrected by having the unit <br /> i professionally serviced. <br /> Gas chromatograph and CC/MG determinations are standardized <br /> with three-point curves as described in the October 26, <br /> 1984 Federal Register. The curves are verified on a daily <br /> basis with a quality control standard. <br /> k - <br /> Standard solutions are prepared at intervals specified in <br /> the referenced methods. Where no limit is stated, they are <br /> replaced at intervals short enough to prevent detectable <br /> deterioration during the lifetime of the material, Even <br /> when no deterioration is detected, standards are replaced <br /> 1, <br /> at least once every six months. <br /> f C. Internal Standards and surrogates <br /> Internal standards are added to concentrated sample <br /> f extracts of semivolatile priority pollutants and to the <br /> purging aliquots of volatile priority pollutant samples. <br /> They serve to detect losses during capillary column <br /> injection of semivolatiles or during the purging of <br /> volatile priority pollutants. They provide a means for <br /> applying corrections to individual sample results providing <br /> that such losses are not extraordinarily large. <br /> Surrogates are typically spiked into the samples prior to <br /> extraction and thereby provide recovery data for sample <br /> workup. Although such data arQ typically derived from coin- <br /> pounds closely related to the compounds under investi- <br /> gation, they are not compound-specific and therefore cannot <br /> be used for making corrections for recovery. Since the <br /> information is provided with every sample, however, it is <br /> very useful in detecting both sample-specific and <br /> systematic racovery problems. <br /> Surrogates are occasionally useJ in trace metal analysis as <br /> a sample-specific check for recovery problems. We incor- <br /> porate surrogates into the trace metal quality assurance <br /> .. program Only if other evidence shows them to be necessary. <br /> V-2 <br />