coupon was wiped, each cotton ball (held with clean
HMX on QA coupons (Table 1) taken from three sepa-
tweezers) was soaked in acetone (they hold approxi-
rate batches indicate that the preparation procedure was
mately 4 mL of acetone). Then, the excess solvent was
precise (relative standard deviation less than 6%) and
that analyte recovery was quantitative (100 11%, rela-
removed by pressing the ball against the side of a glass
bottle and patting it on a small paper towel (Kim wipe).
tive to the spike concentration). The results of the two
The top surface of a coupon was wiped several times,
studies of storage conditions, which appear in the same
while the coupon was held above a clean surface with
table, show that this analyte concentration remained
tweezers. Holding the coupon in the air limited, but did
stable after 7 days when held at room temperature and
not prevent, excess solvent from running onto other
after 14 days when stored in a freezer. Therefore, spiked
surfaces. After wiping, the cotton ball was transferred
coupons can be prepared ahead and stored for several
to a 20-mL VOA vial. These vials were left uncapped
days prior to being used to assess the performance of
and placed on the front edge of an exhaust hood to al-
the HGD system. As a precaution, storage in the dark
low the cotton balls to air dry before being extracted
in a freezer would be preferred, as TNT is sensitive to
with 10 mL of acetone.
light.
Lastly, a cotton ball moistened with only 1.0 mL of
Thermal treatment of spiked coupons
acetone was used to wipe the coupons. For this experi-
Following a thermal treatment of 500 20F (260
ment, each cotton ball was moistened inside a 20-mL
6.6C) for a period of 1 hour, extraction in acetone and
VOA vial by adding 1.0 mL of acetone. After wiping,
the swab was returned to the VOA vial, allowed to air
analysis by GC/TID of the QA coupons showed no de-
dry, then extracted with 7 mL of acetone. This change
tectable quantity of TNT, RDX, and HMX. This means
in procedure prevented the loss of solvent during the
that the concentrations of TNT, RDX, and HMX were
below 0.01, 0.5, and 5 g/coupon, respectively. These
wiping process.
results support the concept that moderate thermal treat-
Range scrap wiping experiment
ment can effectively degrade these explosive analytes.
Three pieces of a hand grenade that had been a low
When these QA coupons are used to assess the
order detonation were used for an initial range scrap
performance of the HGD system, Method 8095 (U.S.
wiping experiment. Before this hand grenade was tested,
EPA 1999) could also be used. This method of
several tests had shown that there were residues of
analysis has detection limits that will allow concentra-
explosives present on its interior surface. The residue-
tions for all three explosive to be measured below 0.01
g/coupon.
covered surfaces of these three hand grenade pieces (3.0
to 4.1 cm2) were each wiped with a cotton ball moist-
Recovery of explosives using different
ened with 1.0 mL of acetone. After wiping, each frag-
wiping techniques
ment was placed in small glass jar and extracted with 5
The results of the wiping experiments in Table 2
mL of acetone. The cotton ball swabs were air dried
show very different levels of analyte recovery. A cur-
then placed in a 20-mL VOA vial and extracted with 10
sory review of these four wiping techniques shows that
mL of acetone.
the cotton swabs (balls or Q-tips) achieved greater
analyte recoveries than does the filter paper. The higher
RESULTS AND DISCUSSION
recoveries seen for the Q-tips and cotton balls most
likely can be attributed to the greater amount of sol-
Analysis of samples from ATC
vent transferred to the metal surface during the wiping
process. It is estimated that the small filter papers (1.5-
Roughly half the materials sampled during the visit
cm diameter) used in these experiments hold less than
to ATC were collected after the Expray kit gave a posi-
0.1 mL of solvent, the Q-tip about 0.25 mL, while the
tive response. Most of the samples taken for off-site
cotton balls holds about 2.0 mL. Furthermore, the Q-
analysis were wipes made using solvent-wetted filter
tips and cotton balls have a more fibrous texture that
papers; however, some were small pieces of material
provides a greater surface area than does filter paper.
or particles upon which signatures of explosives were
Other general trends among these experiments were
suspected. These samples, after being extracted with
decreasing analyte recovery relative to decreasing
acetone, were analyzed by GC/TID and GC/ECD: TNT,
analyte solubility in acetone (acetone solubility TNT >
RDX, and HMX were the most prevalent explosives at
RDX > HMX), and higher recoveries of explosives from
this facility (App. B).
the aluminum as compared to the rusted steel coupon
Assessment of coupon spiking and storage
surfaces.
Table 3 shows average analyte recoveries of 74% or
The concentrations established for TNT, RDX, and
6
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