calculations used a conventional blank subtraction step. How¬ 
ever, the use of the contaminated DMEP was not considered to be 
desirable and another standard was introduced. 
Since the method verification and environmental measurements 
were made at different times, we have been careful to note the 
internal standard for each experimental series. 
The more recent work involved the use of an excellent in¬ 
ternal standard, D-10-anthracene, C^D^o* A small amount of DBP 
and a negligible amount of DEHP were observed with the anthracene 
standard. A correction for the DBP in the average blank was used 
in the caluculations. The use of C^D-^q standard allowed more 
reliable measurements in the sub-ppm region. The basis for these 
statements, for the GCMS capability for discriminating between 
DEHP and DNOP, for the virtual absence of DNOP from sediment, and 
for the purity of the D-10-anthracene internal standard, i.e. 
illustrated in Figure 14. 
Interlaboratory Comparisons of Split Sediment Samples 
Two samples were carefully homogenized and sent to Dr. 
William Budde (EPA - Cincinnati) for interlaboratory comparison. 
The samples are the Chester River working standard "R" and a 
Tenneco Pond sample. The results are shown in Table 16, A much 
closer agreement exists between the Tenneco Pond than the poor 
results obtained on the initial "R" sample. Since this involved 
two essentially independent experiments on the two unrelated 
samples and standards, it was decided to accept the results as 
validative for Tenneco Pond and to reject the results on sample 
"R" as nonvalidative. 
The interlaboratory comparison was repeated using a fresh 
sample from our working standard "R." Samples were sent with and 
without use of our drying procedure. In addition, a spiked blank 
sample containing 200 ppm DEHP was sent for comparison measure¬ 
ments. Measurements on the split portions that were saved for 
that purpose were repeated. The results are given in Table 16. 
The results show reasonable agreement between the two labora¬ 
tories. It should be noted that the results from EPA- 
Cincinnati seem to be higher than our results, and this remaining 
problem is still under study. However, the main purpose of 
demonstrating comparability has been achieved. A chronological 
account of interactions with Dr. William Budde (EPA- 
Cincinnati) is presented in Appendix B. 
69 
