Table 4. Samples containing no target analytes (<0.2 g/L) as determined by RP-HPLC.
False positives listed in bold.
Well no.
pH
RDX
TNT
Well no.
pH
RDX
TNT
766
5.7
DTECH
<5
5-15
625
--
DTECH
<5
<5
OHM
<0.07
OHM
<0.07
EG
<0.5
EG
<0.5
storedQTX
<0.05
627
--
DTECH
<5
<5
768
3.9
DTECH
<5
5-15
OHM
<0.07
EG
<0.5
OHM
<0.07
EG
<0.05
715
6.6
DTECH
<5
5-15
storedQTX
<0.05
OHM
<0.07
EG
<0.5
770
5.3
DTECH
5-15
5-15
OHM
<0.07
719
4.5
DTECH
<5
<5
EG
<0.5
OHM
<0.07
storedQTX
<0.05
EG
<0.5
772
4.7
DTECH
<5
5-15
729
6.1
DTECH
<5
5-15
OHM
<0.07
OHM
<0.07
EG
<0.5
EG
<0.5
774
--
DTECH
5-15
5-15
735
5.9
DTECH
5-15
5-15
OHM
<0.07
OHM
<0.07
EG
<0.5
EG
1.2
Lab blank
DTECH
<5
<5
739
5.8
DTECH
15-25
5-15
OHM
<0.07
OHM
<0.07
EG
<0.5
Field blank
DTECH
<5
<5
OHM
<0.07
741
3.7
DTECH
<5
5-15
EG
<0.5
OHM
<0.07
EG
0.7
BEW5
--
OHM
82
0.39
BEW6
--
OHM
852
1.36
pared with a predicted 1/ value of the RP-HPLC
wells) require two EnviroGard strips or three
100
Quantix strips. An eleventh sample would require
determination and the data regressed, the accu-
the use of an additional strip.
racy is better (Fig. 5). The scatter in the data is
These kits have other potential uses, and other
then more obvious. The RPD criterion was met
problems, that are best discussed with reference to
100% of the time. This was the only kit tested that
each kit's characteristics.
produced no false positives at its detection limit.
Quantix
EnviroGard
The Quantix kit is primarily intended as a quan-
The EnviroGard kit is also intended as a quan-
titative laboratory assay. It is the most expensive
titative laboratory assay. The EnviroGard kit
and complicated of the four kits. A strip-reader, an
requires only a strip-reader for quantitation. A
orbital plate-shaker for incubations, a plate-washer,
plate-shaker is listed as optional, as are plate-
and wash solution were recommended to achieve
washers and wash buffers other than tap water.
the best results. Five standards and a negative
One vial of TNT standard concentrate is supplied
control were supplied for calibrations. The Quan-
and must be diluted to make the suggested three
tix strip-reader has a program that calculates
standards. A negative control is supplied. The
results based on a five-point calibration. The
manufacturer recommends that absorbances be
linearity and reproducibility of four standard
normalized against the negative control and
curves was excellent, with a relative standard
expressed as a percent inhibition (%B/Bo, where
deviation of slopes equal to 4.4% (Fig. 3). How-
B = absorbance of sample and Bo = absorbance of
ever, a plot of the accuracy of the determinations
negative control). The calculation of five standard
(Fig. 4) reveals an underestimation of concentra-
curves produced a relative standard deviation of
tions compared with the RP-HPLC determinations.
slopes equal to 4.0% (Fig. 6). A negative control
Two of the samples required a 1:100 dilution with
and one standard would probably suffice for rou-
reagent-grade water to fall within the range of the
tine tests. The calculated concentrations were low
test. If the results of the diluted samples are com-
compared with the RP-HPLC concentrations of
8
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