99
98
95
90
70
50
30
10
5
2
c. Xylene (total).
0.1
1.0
10
QC
Xylenes (total)
Concentration Ratios
QA
99
98
95
90
70
50
30
10
5
d. Several VOCs in soils (benzene [seven],
2
1,2-dichloroethene [total] [five], methyl-
ethylketone [two], tetrachloroethene [eight],
0.1
1.0
10
QC
trichloroethene [eight]).
Concentration Ratios for Several VOCs
A
QA
Figure 6 (cont'd).
groundwater fell between 0.402.50. Nonetheless,
ratory subsampling for analysis. Additional vola-
we recommend that the Corps start to use vapor-
tilization loss can occur during transport and stor-
fortified secondary soil standards of the type de-
age, and biodegradation can also be a problem.
Recent articles (Siegrist and van Ee 1994, Hewitt
scribed by Hewitt (1994) and Hewitt and Grant
(1995). These fortified samples sealed in glass
et al. 1995) document losses of a factor of 1000 or
ampoules are stable for extended periods and they
more. This postulation is consistent with our ob-
can be distributed to participating laboratories.
servation in this study that samples containing
By using such secondary standards in an orga-
multiple analytes produce QC/QA ratios that are
consistently high or low for all analytes present.
nized program of performance evaluation prior
In Figure 7 we illustrate this effect by plotting
to qualification and later as periodic QC samples,
logs of total xylene QC/QA ratios vs. logs of
the laboratory portion of the analytical procedure
ethylbenzene ratios for corresponding samples.
(extraction plus analysis) can be evaluated.
We believe that the major losses are caused by
The correlation coefficient of 0.906 provides strong
volatilization during sample collection and labo-
evidence for the relationship between these re-
11
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