0.9
y = 0.54659 0.35373 Log(x)
0.8
R2 = 0.997
0.7
0.6
0.5
0.4
0.3
0.2
1
0.1
10
Figure 9. Ohmicron: three sets of
TNT (g/L)
standards.
300
y = 0.28507 + 1.4782x
R2 = 0.999
200
100
0
Figure 10. RP-HPLC values vs.
50
150
0
100
200
Ohmicron average values.
TNT Equivalents, RP-HPLC (g/L)
TNT when the regressed comparison extended to
tive replacement for Method 8330 RP-HPLC deter-
the three samples that needed dilution to fall
mination. It includes a negative control, predilut-
within the range of the kit (Fig. 7). The RPD crite-
ed standards, and a check solution, whose value
rion was met 86% of the time. An examination of
should lie within a range of accuracy in order to
the individual values produced within the range
proceed with the test. Three calibration curves
of the kit (Fig. 8) shows a large overestimation.
based on the percent inhibition compared with the
This overestimation of concentrations produced
negative control had a relative standard deviation
two false positives. These samples did however
of slopes equal to 3.4% (Fig. 9). A comparison be-
contain several g/L of TNT transformation
tween the RP-HPLC concentrations and the aver-
products. If there are eight or more samples a day
age calculated values and all of the within-range,
to analyze, this kit is the least expensive to use;
diluted values (Fig. 10 and 11) shows that this kit
however, the cost of false positives must be care-
overestimated the level of contamination. The
fully considered.
RPD criterion was met 85% of the time. No false
positives occurred above the 2-g/L level. Three
Millipore also offers a TNT in Soil kit that uses
test tubes and a standard spectrophotometer for
of the Crane wells that required dilution to fall
quantitation. Since its detection limit is around 2
within the range of the kit were assayed at two dif-
g/L, it is not offered for sale as a water test kit. *
ferent dilutions. When the slopes of these serial
Ohmicron RaPID assay
* Personal communication, B. Furgeson, Immunosystems,
The Ohmicron kit is intended to be a quantita-
Scarboro, Maine, 1994.
11
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