that ultrasonic extraction of dry Tenneco Pond sediment with 
methanol gave easily measured quantities of DOP. Later, tetra- 
hydrofuran was found to give a higher yield. Then, a series of 
extracting solvents was tested comparatively and dichloromethane 
was found to give the highest extractive efficiency and relative¬ 
ly short times were required. The duration of the ultrasonic 
agitation was varied until it became certain that longer extrac¬ 
tion periods did not give greater extractive yield. 
The true extractive efficiency is not subject to direct 
measurement. Spiked addition of analyte produces a different 
sorbed state than the analyte in the sample matrix. To assess 
the apparent accuracy, two samples were selected for independent 
measurement as will be described. The approach was to do what 
could be done to show that re-extraction by baried methods did 
not lead to a higher yield. 
A major problem of contamination arises when measuring 
traces of plasticizers. The environment is widely contaminated 
by these substances, and the chemical laboratory is no exception. 
Their presence has been reported in bottle cap liners, solvents, 
extraction thimbles, preconcentrating resins and adsorbents, 
aluminum foil, glass, wood, air and pipet fillers (de Zeeuw 
1975, Singmaster et al. 1976, Webster and Nickless 1976). 
It is obvious that the reduced contamination can be achieved 
by deliberately minimizing the overall exposure to the sources 
of contamination by minimizing solvent volume, the number of 
manipulations, avoiding contact with any plastic materials, and 
ultracleaning of apparatus. This can be summarized in two 
statements: the sampling and processing apparatus must be un¬ 
contaminated, and the amount of methodology must be kept to an 
essential minimum. 
Although these aspects led us away from available methodo¬ 
logy (Giam et al. 1976), the end of the study showed that our 
method did come close to similar techniques by Dr. William 
Budde (EPA-Cincinnati). The procedure used by Budde (ultra- 
sonication, GCMS-selected ion monitoring) differs mainly in the 
technique used for drying the sample--direct addition of Na 2 SC >4 
to partly dried sediment. Our method uses the same desiccant 
but the drying efficiency is greater. Regardless, the two ap¬ 
proaches are appropriate for interlaboratory comparison. 
The measurement approach is based on a reported (Watson 1976) 
application of GCMS where the MS section is used in the selected 
ion monitoring mode (SIM). This provides an impressive gain in 
selectivity since only the predominant fragment ion masses are 
monitored. As a result there is a corresponding boost in 
instrumental sensitivity. The technique uses instrumental de¬ 
tection selectivity to replace the lesser certainty of multiple 
extractive and separation conditions (Giam et al. 1976). 
45 
