5520 A. Introduction
In the determination of oil and grease, an absolute quantity of
aspecific substance is not measured. Rather, groups of substances
with similar physical characteristics are determinedquantitatively on the basis of their common solubility in an
organic extracting solvent. “Oil and grease” is defined asany
material recovered as a substance soluble in the solvent. It
includes other material extracted by the solventfrom an acidified
sample (such as sulfur compounds, certain organic dyes, and
chlorophyll) and not volatilized duringthe test. The 12th edition
of Standard Methods prescribed the use of petroleum ether as the
solvent for natural andtreated waters and n-hexane for polluted
waters. The 13th edition added trichlorotrifluoroethane as an
optionalsolvent for all sample types. In the 14th through the 17th
editions, only trichlorotrifluoroethane was specified. However,because of environmental problems associated with chlorofluorocarbons,
an alternative solvent (80% n-hexane and 20%methyl-
tert-butyl ether) was included for gravimetric methods in the
19th edition. In the 20th edition, [continua]
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