phthalates. It is also likely to exhibit physical and chemical 
properties similar to other phthalates, and it is not produced 
commercially as a plasticizer. By adding DMEP to the extracting 
solvent, methylene chloride, it is susceptible to the same sys¬ 
tematic errors during the analytical scheme as other phthalates 
being determined. 
GC/MS Autotune Procedure 
Each week "autotune" was run to adjust and to assess the 
condition of the GC/MS instrument. This procedure tunes the 
ion source and mass filter to produce a mass spectrum of per- 
fluorotributyl amine (PFTBA) to meet certain minimum specifica¬ 
tions. If these specifications, as recommended by the 
manufacturer, were not met, the problem was diagnosed and 
corrected before continuing the work. 
GC/MS-SIM Calculation 
The mass 149 chromatogram of all sediments taken from the 
Chester River show only two well-defined peaks at GC retention 
times that correspond to dibutylphthalate DBP, and dioctyl- 
phthalate. Quantitative analysis for each of these two 
compounds is based on monitoring mass 148 peak areas for DBP and 
DEHP, and mass 59 for the internal standard. Within experimen¬ 
tal error, we verified the linearity typical in GC/MS-SIM 
analysis. Defining the following terms 
C = concentration of solute in CI^C^ (mg/ml CI^C^) 
S - area under mass-chromatographic peak (area units) 
a = analyte (DEHP or DBP) 
i - internal standard (DMEP) 
k = response factor 
we have 
S = K and S. = K. c.. 
a a ill 
The ratio k a /k. was found to be constant for total analyte in¬ 
jections less than 0.3 pg providing C /C. were within a factor 
of 100 of unity. Then, it follows that * 1 
R = 
constant 
C 
a 
C 
a 
S. 
l 
55 
