Sediment Drying by Isopiestic Dehydration 
a. The collected sediment is homogenized in the sample 
container using a clean metal spatula. 
b. A 10 g sample is spread evently onto the surface of a 
clean 12 cm watch glass using the same spatula. 
c. An organic-free desiccator is charged with 0.25 kg 
Drierite in the desiccator at 23°C for 48 hours. 
d. To complete the drying, the sediment is removed to 
repeat the drying process. The desiccant is re¬ 
dried by baking in the desiccator at 250°C for 
12 hours. The partly dried sediment is then re¬ 
turned to the cooled freshly baked desiccant for 
another 48 hours. 
e. The dry sediment is scraped into a clean glass 
mortar. It is then pulverized using a clean glass 
pestle, transferred to labeled vials, and stored 
at 4 °C. 
Two solid substances will undergo a gas phase transfer of 
water until a final equilibrium vapor pressure is reached. The 
repeated exposure of moist sediment to repeated fresh charges 
of the desiccant Na 2 SO^ causes isopiestic dehydration. The 
advantages of this approach are as follows: 
1. Water content in clay sediment is reduced from about 
60 percent to about 1 to 2 percent on a dry weight 
basis. 
2. Unlike the procedure of mixing the desiccant in with 
the sediment (Bulla, personal communication), the 
water is physically removed and there is less oppor¬ 
tunity for organic contamination from the desiccant. 
3. Unlike lyophilization, isopiestic dehydration is 
carried out at atmospheric pressure with 10 3 -fold 
shorter gas phase collision distances and a corre¬ 
sponding less likelihood for sublimative loss of 
the measured analytes (DBP or DEHP). 
Sediment Extraction 
From Karrickhoff's work (1979), it is known that organic 
pollutants in sediment are associated with the organic carbon 
content, due principally to humic and other associated polymers. 
Based on this, the sorptive structure should be modeled effec¬ 
tively by n-octanol. Accordingly, a volative extraction solvent, 
similar to polarity to octanol, was chosen as more likely to 
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