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, 94 HANDBOOK OF ENVIRONMENTAL ANALYSIS The reduction of standard sample size is commonly done as a measure to reduce interference and permit a determination in the presence of severe backgrounds. This effectively serves to increase the NIDL by the same degree in which the sample size is reduced. Thus decreasing the sample size by one half,doubles the MDL. Reducing the sample size by 10,multiplies the NIDL by 10. The physical characterization of solids in samples as total solids irem total dissolved solids(TDS)and total suspended solids(TSS)have an absolute requirement L a will be mum of 2.5 mg of residue detected. For 50 mL of sample processed the NIDL will be 50 filtteering ability,in0a sample mL ale the tch there will often be wide range of quite variable in A final problem with the use of NIDL as currently defined,concerns those analyses in which there is not 100%recovery of target analyte. By its very definition the NIDL is a measure of the precision of an analysis and no account is taken of accuracy Quite erratic results and misinterpretations of results are possible by data reviewers if this aspect of the NIDL is not recognized. Remember that the NIDL is determined using i be complex samplesit is not of wastewater, oil,fishg that ,etc.,etlevels ,are analyzed by cannot 1 lab. when C. Reporting Units and Common Conversions Scientific results are almost always reported in metric units such as grams,kilograms, liters,etc. SI prefixes are used to indicate variations on the basic units of grams,liters, moles and others,as indicated in the table. Table 1-33. SI prefixes IE bbv Multiplier Prefix Abbv Multiplier 10-21 exa- E 1018 10-18 peta- P 10 t5 10-15 Cera- T 1012 10.12 giga- G 109 10-9 M 108 µ 10-6 k90 k 103 m 10 3 hecta- h 102 cent!- c 10-2 deco- da 10 d 10-1 I Environmental results are often expressed in the units of parts per million(ppm), parts per billion(ppb),and parts per tnllion(ppt). These have different meanings de- aatt pending on the sample matrix. With liquids and solids the units are in terms of mass ! volume and rtlass/mass respectively,and are often interchanged based on the assumption that the density of water is 1.000 g/mL(1.000 kg/L),although this is strictly true only ei hu dr For i pe diets con wiUrna ed ppm being equal to 0.10%.are expressed as parts per en 132 Kimbrough,D.E.,and I.Wakakuwa. "Method Detection Limits in Solid Waste Analysis." Environ. Sci. Technol.27(13). 1993.pp. 2692-2699. II Genium Publishing Corporation