Originally Posted by The Raptor,Jul 26 2006, 04:02 AM

An initial 3-point calibration was performed on July 25, 2006 by preparing a calibration solution from a pre-mixed standard supplied by Supelco, Inc. The standard contained common halogenated solvents and aromatic hydrocarbons (see Table 1). The individual compound concentrations in the standards ranged between 0.025 ng/ul and 0.25 ng/ul.

The initial three point calibrations consisted of 20, 100 and 500 ul injections of the calibration solutions. A calibration factor on each analyte was generated using a best fit line method using the HP data system. If the r2 factor generated from this line was not greater than 0.990, an additional three point calibration would have been performed. Method detection limits were calculated to be 1.0 ug/L for the individual compounds.

TABLE 1

Dichlorodifluoromethane Carbon Tetrachloride Chloroethane
Trichlorofluoromethane 1,2-Dichloroethane Benzene
1,1-Dichloroethene Trichloroethene Toluene
Methylene Chloride 1,1,2-Trichloroethane Ethylbenzene
trans-1,2-Dichloroethene Tetrachloroethene m-/p-Xylene
1,1-Dichloroethane Chloroform o-Xylene
cis-1,2-Dichloroethene 1,1,1,2-Tetrachloroethane Vinyl Chloride
1,1,1-Trichloroethane 1,1,2,2-Tetrachloroethane Freon 113
4-Methyl-2-Pentanone Cyclohexane Acetone
Chlorobenzene 2-Butanone

Sample Replicates

A replicate analysis (duplicate) is run when concentrations exceed the calibrated range of the instrument/detector being used. The duplicate sample is diluted using a smaller injection volume to assure that the instrument response falls within 50% of the calibrated range. In addition, a duplicate analysis is run a minimum of once each day to evaluate the reproducibility of the sampling system and instrument. If the difference between samples varies more than 20%, the entire system is evaluated and the inconsistency is determined and corrected, if possible.

Equipment Blanks

Blanks are run at the beginning of each workday, after calibrations and whenever sampling conditions appear to change. New vapor probes are used following each sample with positive results or when probes were damaged during installation. The blanks are collected using an ambient air sample. These blanks checked the septum, syringe, GC column, GC detector and the ambient air. Contamination was not found in any of the blanks analyzed during this investigation. Blank results are given along with the sample results.