should be chosen based on the objectives of the
10.3 Preparation of surrogate spiking solution
The analyst should monitor the performance of
analysis. A mid-range linear velocity of about 80
cm/s will be suitable for most analysis.
the extraction and analytical system, as well as the
effectiveness of the method in dealing with each
Makeup: Nitrogen (38 mL/min)
sample matrix, by spiking each sample, standard,
Oven program 100C for 2 min, 10C per min
and reagent water blank with one or two surro-
ramp to 200C, 20C/min ramp to 250C, 5 min
gates (i.e., analytes not expected to be in the sam-
hold.
ple but having properties similar to the target
analytes). Suggested surrogates are 2,5-DNT or
Detector temperature: 300C
3,4-DNT spiked at an aqueous concentration of 0.2
GC conditions for the confirmation columns
g/L. Each laboratory should generate control
are as follows:
limits and should expect recoveries of 70 to 125%.
RTX-200
a. Linear velocity 40 cm/s. Oven 100C for
10.4 Preparation of matrix spiking solutions
1.2 min, 5C/min to 140C, 1C/min to
Prepare matrix spiking solutions in acetonitrile
160C, 20C/min to 250C, hold. Injector
such that the concentration in the sample is 0.2
250C. Detector 290C.
g/L for DNB, 2,6-DNT, 2,4-DNT, TNB, TNT,
b. Linear velocity 122 cm/s (for confirma-
RDX, 4-Am-DNT, 2-Am-DNT, tetryl, and DNA, 1.0
tion of HMX). Oven 150C for 1 min,
g/L for NB, o-NT, m-NT, p-NT, NG, and PETN,
20C/min to 250C, hold. Injector 270C.
and 2.0 g/L for HMX. All target analytes should
Detector 290C.
be included. Because RDX and PETN coelute on
RTX-225
the DB-1 column, these analytes should be in sepa-
Linear velocity 108 cm/s. Oven 100C for 2
rate spiking solutions.
min, 10C/min to 220C, hold for 8 min. Injector
220C (column maximum). Detector 250C.
10.5 Preparation of materials
Prepare all materials to be used as described in
10.6.3
SW-846, Chapter 4, for semi-volatile organics.
For initial calibration, injections of each cali-
bration standard over the concentration range of
10.6 Calibration of GC
interest are made sequentially into the GC. Peak
10.6.1
heights are obtained for each analyte. Because of
The GC column should be baked at the injection-
the limited linear range of the ECD, a linear cali-
port temperature until the baseline is stable. (The
bration curve that passes through the origin is
injection-port temperature should not be set high-
not appropriate for each analyte over the entire
er than the maximum column temperature recom-
concentration range listed above. A linear cali-
mended by the column manufacturer.)
bration that passes through the origin may be
appropriate for the five lowest standards. Alter-
10.6.2
natively, a nonlinear calibration model may be
The GC conditions for the analytical column are
used as described in SW-846, Chapter 4, Method
as follows:
8000B.
GC: HP 5890 with electron capture detector (Ni63).
10.6.4
Analytical column: 6-m- 0.53-mm-i.d. fused-silica
For daily calibration, analyze the midpoint
polydimethylsiloxane (J and W DB-1 or equiva-
calibration standards from sets A and B, at a min-
lent), 1.5- or 3.0-m film thickness.
imum, at the beginning of the day, after every 10
Injection-port liner: Restek Direct Injection Uni-
samples, and after the last sample of the day. Ob-
liner (deactivated).
tain the calibration factor for each analyte from
Injection-port temperature: 250C.
the peak heights, and compare it with the re-
sponse factor obtained for the initial calibration.
Injection volume: 1 L.
The calibration factor for the daily calibration
must agree within 15% of the calibration factor
Carrier: Hydrogen (linear velocity 40 to 125 cm/s).
of the initial calibration. If this criterion is not
Note: Peak resolution is greatest at low linear ve-
met, calculate the average of the responses for all
locity, but GC response for some analytes is great-
analytes as described in SW-846, Chapter 4,
est at high linear velocity. The linear velocity
26
Previous Page
