Table 3. Recovery of target analytes from fortified Milli-Q water preserved with either
sodium bisulfate (pH 2), 2.5% acetonitrile at pH 3.5, or 7.5% acetonitrile without pH adjust-
ment using SOE, SPE-C, and SPE-M.
Analyte (% recovery)
Treatment/preservation
HMX
RDX
TNB
DNB
3,5-DNA
TNT
2ADNT
2,4-DNT
SOE*
control
100
112
102
102
106
107
104
100
pH 2
90
93
93
104
35
93
54
101
pH 2(neutralized)
95
103
96
96
100
95
97
93
2.5% ACN
5
103
96
95
98
96
102
98
SPE-C*
control
06
132
107
114
112
106
110
104
pH 2
05
138
104
110
112
92
106
92
2.5% ACN
03
126
101
111
126
109
120
110
SPE-M*
control
1
102
98
101
106
91
98
89
pH 2
2
106
103
107
112
96
104
94
2.5% ACN
9
76
103
108
114
96
105
96
7.5% ACN
3
3
11
14
19
40
40
45
* SOE salting-out solvent extraction
SPE-C cartridge solid-phase extraction (Porapak RDX)
SPE-M membrane solid-phase extraction (Empore-SDVB)
Table 4. Concentrations of various analytes forti-
achieve a 2.5% solution along with acidification
fied into Connecticut River water for replicate
to pH 3.5 do not cause major analytical prob-
study.
lems for Method 8330. Neutralization will be re-
quired if SOE is used for preconcentration of pH-
Fortified Connecticut River
2-preserved samples, but this is not difficult to
concentration (g/L)
achieve and the pH need only be raised to 3.5 to
X
S
Group
Analyte
enable complete recovery of the amino com-
pounds.
1
DNB
39.9
0.52
tetryl
41.2
0.58
4ADNT
57.2
0.42
Effects on the direct method
3NT
59.9
1.95
To assess the effects of acidification to pH 2
with sodium bisulfate on the direct analysis pro-
2
HMX
64.6
1.33
RDX
100.5
0.94
cedure of Method 8330, a sample of Connecticut
TNB
52.7
0.85
River water was divided into four portions and
TNT
91.4
0.37
fortified with the 15 target analytes in the four
2,4-DNT
69.7
0.38
groups indicated in Table 4. Each of these four
2NT
74.4
0.69
solutions was then divided into two aliquots; one
3
3,5-DNA
59.5
0.32
aliquot was acidified to pH 2 with sodium bisul-
2ADNT
79.5
1.03
fate and the other was left unacidified. Six repli-
4NT
178.4
0.96
cate portions of each solution were then processed
4
NB
43.6
0.48
as described in Method 8330 except that samples
2,6-DNT
99.2
1.34
were diluted 1:1 with methanol rather than ace
tonitrile and analyzed by RP-HPLC (EPA 1992).
* X = mean; S = standard deviation
The decision to use methanol rather than aceton
itrile was made to matrix-match the sample and
eluent to improve the quality of the chromato-
analyte to assess whether acidification affected the
grams near the regions where HMX and RDX elute.
analytical precision obtained for the acidified so-
The mean value and standard deviation deter-
lution relative to the unacidified control. For all
mined for each analyte in the preserved and
analytes, except TNT and 2ADNT, the variances
unpreserved solutions are presented in Table 5.
obtained were not significantly different at the
An F-test was conducted to compare the variances
95% confidence level. Thus, for these analytes, no
for acidified and unacidified portions for each
detrimental effect on analytical precision was
10
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