Sampling and Laboratory Analysis for Solvent Stabilizers - Environmental Investigation and Remediation - page 220

900

800

700

600

8260B

500

8270ID

400

300

200

8270C

100

0

100 200 300

8270ID concentration (mg/L)

400 500 600

FIGURE 4.7 Paired comparisons of the results of EPA Methods 8260B and 8270C with 8270-Isotope
Dilution from Linton and Alonso Method Comparison Study. (From Linton, J. and Alonso, J.C. 2006,
1,4-Dioxane comparative analysis study—EPA Methods 8260B, 8270C and 8270 with isotope dilution.
Tampa, FL: Blasland Bouck and Lee Environmental Services [now Arcadis-US]. With permission.)

Results for samples from each well by Methods 8260B and 8270C were compared to
results from that well by Method 8270ID. In Figure 4.7, results from a specii c well by
Methods 8260B and 8270C ( y -axis) are plotted against the concentration obtained by
Method 8270ID ( x -axis). Regression analysis and a paired t -test showed that the results
of Method 8260B did not signii cantly differ from those of the isotope-dilution method,
and the methods correlated well. BBL recommended that the EPA consider performing
further optimization of Method 8260B to increase the sensitivity of the method. Increasing
the sample and purge volumes may decrease the MDL, and using a heated purge would
increase the purging efi ciency of 1,4-dioxane from the groundwater samples, thereby
increasing sensitivity of the method.

CAVEAT EMPTOR—DOUBLE-BLIND STANDARDS CAN
HELP TO ENSURE GOOD DATA QUALITY

The majority of contaminated site investigations rely upon laboratories' internal quality con-
trol protocols to coni rm that results are within acceptable limits of precision and accuracy.
The subject of laboratory quality control is beyond the scope of this topic; the reader is referred
to USEPA's quality pages ( http://www.epa.gov/quality/ ) for a thorough review of the funda-
mentals of laboratory quality control. Quality control tests include method blanks, initial and
continuing calibration standards, matrix spike and recovery analyses, and several others. For
emerging contaminants, unconventional analyses, analyses reported at the low end of the
method range, and analyses performed infrequently by laboratories, it is sometimes useful to
coni rm laboratory performance independently by submitting double-blind standards.
Double-blind standards are usually prepared by a third-party laboratory or provider of
analytical standards. The subject laboratory's sample container is shipped to the standards

continued