THE PROBLEM OF OIL romwIoN OF THE SEA
14 1
sample heated to boiling. The vapour was trapped in liquid nitrogen
and then dissolved in carbon tetrachloride for analysis by mass spectrometry. Such low-boiling fractions are, however, not characteristic
of oil spilt at sea and the concentration of samples is more usually
achieved by filtering the water through a column of active charcoalsee, for example, Rosen and Middleton (1955) and Greenberg et al.
(1 965)-or
by liquid/liquid extraction with benzene, chloroform,
carbon tetrachloride or hexanes. Kirschman and Pomeroy ( 1 949)
discuss the merits of various solvents and extraction methods. Most
are unreliable where the original concentration lies below 10 p.p.m.
Merz (1959) found chloroform to be the best solvent for extracting oily
material from beach deposits. Hartung (1963) used carbon tetrachloride
to extract oil from the plumage of ducks killed in a pollution incident.
Standard laboratory methods for the sampling, determination, and
analysis of oils in water are given by the American Petroleum Institute
(1957) and the American Public Health Association ( I 960) ; techniques
for the quantitative determination of mineral oil arc briefly reviewed
by Blokker, discussing a paper by Ineson and Packham (1967). The
main problem with such determinations is that petroleum, being a
complex mixture, has no outstanding overall characteristics. Various
methods may, by their nature, exclude certain components or include
extraneous organic materials in the result : for many analytical purposes, ‘‘ oil ” and “ grease ” are terms defined on the basis of the
extraction or analysis recommended (see, for example, Ludwig et al.,
1965).
Gravimetric or volumetric methods involve the measurement of a
solvent extract after evaporation under standard conditions. The
detection limit is about 5 p.p.m. and up to 30% losses are to be expected. The extract may be purified by chromatographic separation
on alumina before evaporation and weighing, which increases the
sensitivity to 0.1 p.p.m. and also increases the accuracy. Alternatively,
the density of the extract may be obtained in a pycnometer (see, for
example, Levine et al., 1953) and compared with that of the pure
solvent ; the density of the oil, if unknown, has to be assumed. Using
carbon tetrachloride, the method is accurate only down to 10p.p.m.
but this sensitivity is increased to 0.3 p.p.m. by substituting the much
denser tetrabromoethane. Optical methods may be applied to the
partially evaporated extract, for example, measurements of infra-red
absorption at 3.3-3.5 p are sensitive to about 0.1 p.p.m. and are fairly
accurate unless there is a high proportion of low-boiling aromatics,
whose i-r absorption is weak (Simard et al., 1951). Ultra-violet light
at 2 700-4 000 A is strongly absorbed by petroleum oils, permitting a
14 1
sample heated to boiling. The vapour was trapped in liquid nitrogen
and then dissolved in carbon tetrachloride for analysis by mass spectrometry. Such low-boiling fractions are, however, not characteristic
of oil spilt at sea and the concentration of samples is more usually
achieved by filtering the water through a column of active charcoalsee, for example, Rosen and Middleton (1955) and Greenberg et al.
(1 965)-or
by liquid/liquid extraction with benzene, chloroform,
carbon tetrachloride or hexanes. Kirschman and Pomeroy ( 1 949)
discuss the merits of various solvents and extraction methods. Most
are unreliable where the original concentration lies below 10 p.p.m.
Merz (1959) found chloroform to be the best solvent for extracting oily
material from beach deposits. Hartung (1963) used carbon tetrachloride
to extract oil from the plumage of ducks killed in a pollution incident.
Standard laboratory methods for the sampling, determination, and
analysis of oils in water are given by the American Petroleum Institute
(1957) and the American Public Health Association ( I 960) ; techniques
for the quantitative determination of mineral oil arc briefly reviewed
by Blokker, discussing a paper by Ineson and Packham (1967). The
main problem with such determinations is that petroleum, being a
complex mixture, has no outstanding overall characteristics. Various
methods may, by their nature, exclude certain components or include
extraneous organic materials in the result : for many analytical purposes, ‘‘ oil ” and “ grease ” are terms defined on the basis of the
extraction or analysis recommended (see, for example, Ludwig et al.,
1965).
Gravimetric or volumetric methods involve the measurement of a
solvent extract after evaporation under standard conditions. The
detection limit is about 5 p.p.m. and up to 30% losses are to be expected. The extract may be purified by chromatographic separation
on alumina before evaporation and weighing, which increases the
sensitivity to 0.1 p.p.m. and also increases the accuracy. Alternatively,
the density of the extract may be obtained in a pycnometer (see, for
example, Levine et al., 1953) and compared with that of the pure
solvent ; the density of the oil, if unknown, has to be assumed. Using
carbon tetrachloride, the method is accurate only down to 10p.p.m.
but this sensitivity is increased to 0.3 p.p.m. by substituting the much
denser tetrabromoethane. Optical methods may be applied to the
partially evaporated extract, for example, measurements of infra-red
absorption at 3.3-3.5 p are sensitive to about 0.1 p.p.m. and are fairly
accurate unless there is a high proportion of low-boiling aromatics,
whose i-r absorption is weak (Simard et al., 1951). Ultra-violet light
at 2 700-4 000 A is strongly absorbed by petroleum oils, permitting a