The basis for the analytical methodology can be seen in the 
following way. The upper curve in Figure 7 is a gas chromatogram 
of a dichloromethane extract of a dried sediment sample from the 
Chester River mouth. This is the working standard, sample "R," 
located in Figure 5. The omission of any cleanup procedure 
creates an unresolved bunching of chromatographic peaks due to 
the many thousands of compounds that are present in the extract. 
However, when the mass spectrometer is used as GC analyzer, an 
extraordinary boost to the selectivity of the combined instru¬ 
mentation is realized. This is shown for mass 149 as the lower 
curve in Figure 7. The integration of m/z 149 intensity to 
measure alkyl phthalates was confirmed by comparing integrated 
area ratios for confirmational fragment ion masses for DBP 
(m/z 2-5,223) and for DEHP (m/z 167,279). This was done for con- 
firmational purposes to show that no interferences were present 
at the levels being investigated. 
It has been concluded that there is no ambiguity in the pre¬ 
sent dual use of multiple ion monitoring to identify and measure 
DBP and DEHP in a single GCMS-SEM experiment. This is a result 
of the extreme molecular selectivity, and correspondingly justi¬ 
fied methodological simplication. The generic term DOP (dioctyl- 
phthalate) will be used to refer to one or both of the isomers, 
DNOP (di-n-octylphthalate) and DEHP (di-2-ethylhexylphthalte). 
Distinction between these substances was obtained later in the 
study (see Figure 14). 
Total Ion Current 
Time (minutes) 
Figure 7. GCMS of Chester River mouth sediment extract 
46 
