mates will vary widely from subsample to sub-
Table 1. White phosphorus concentrations found
sample depending on the number and size of par-
in field samples collected from an Army train-
ticles in the subsample. To prevent the introduc-
ing area (Racine 1995).
tion of subsampling error for the samples prepared
Concentration
for this project, individual spiked soil samples
range
Number of Percent of
were prepared such that the whole sample is taken
(g/g)
samples
samples
for analysis.
A standard soil was obtained from the U.S.
Not detected
1281
66
Detection limit to
0.00099
79
4
Army Environmental Center (Aberdeen Proving
0.001to
0.0099
203
11
Ground, Maryland). Aliquots (20 g) of soil were
0.01 to
0.099
185
10
weighed into 120-mL jars equipped with Teflon-
0.1 to
0.99
72
4
lined caps. Then sufficient water (10 mL) was
1.0 to
9.99
43
2
added to thoroughly saturate the soil. The jars
10
to
99.99
38
2
100
to 999.9
16
1
were capped, sealed with Parafilm, and equili-
1000
to 9,999.9
6
0.3
brated for two weeks in the dark at room tempera-
ture.
A single white phosphorus particle was added
to each wet soil sample, yielding a white phos-
phorus concentration of 182 g/g on a wet soil
weight basis [5460 g (20 g soil plus 10 g wa-
to 54C (10C higher than the melting point of
white phosphorus). Then 3-L droplets (5.46 mg)
ter)]. Samples were tightly sealed with screw caps,
sealed with Parafilm and stored at room tempera-
were obtained from the molten white phospho-
ture in the dark. Samples were taken for analysis
rus using a Gilson Microman Positive Displace-
on days 1, 14, 28, 57, 112, 209 and 288.
ment Pipet (size M25) equipped with disposable
capillaries and pistons. Each droplet was trans-
Preparation of low concentration samples
ferred under water to an individual test tube. The
Several approaches were tested for the prepa-
test tubes containing the white phosphorus drop-
lets were cooled in a refrigerator (4C). White phos-
ration of low concentration samples since lack of
stability proved to be a considerable problem.
phorus can supercool (i.e., remain liquid below the
The procedure that produced samples with rela-
melting point); thus the water had to be cooled
well below 44C to ensure solidification of the
tively stable white phosphorus concentrations was
as follows. A stock solution of white phosphorus
white phosphorus.
was prepared by dissolving 90.1 mg of WP in 250
Upon solidification, the white phosphorus par-
mL of toluene to yield a concentration of 360 mg/
ticles were spherical and translucent with a lus-
L. A spiking solution was made by mixing 1 mL
trous surface. Diameters of the particles were mea-
of the stock solution with mineral oil* in a 50.0-
sured using a SPI (Swiss Precision Instruments)
mL volumetric flask, and bringing the flask to vol-
6-in. (15.2-cm) caliper with 0.1-mm graduations.
ume with mineral oil to yield a concentration of
Based in the measurement of 127 white phospho-
7.2 mg/L. Because of the high viscosity of the min-
rus particles produced in this laboratory by the
method described above, the mean ( standard
eral oil, care was taken to thoroughly mix this so-
deviation) diameter was 1.79 0.06 mm (3.2% rela-
lution by inverting the flask numerous times. Us-
ing a positive displacement micropipet, a 25-L
tive standard deviation). Based on a density of 1.82
g/cm3, the corresponding mass for a 1.79-mm
aliquot of the spiking solution was added to a
mixture of 30-g glass microbeads (25 m) (3M
diameter particle is 5.47 mg, which agrees within
Company) wetted with 10 g of water in 120-mL
0.01 mg of the mass based on the volume of white
glass jars. (These glass beads are in the size range
phosphorus used to make the particles.
of silt, which is 3.9 to 62.6 m.) The mass of white
phosphorus added to each 40-g wet sample was
Preparation of soil/sediment samples
0.18 g, yielding a white phosphorus concentra-
Certified reference materials, which are fre-
quently used as performance evaluation samples
for most analytes, are thoroughly homogenized
and subsamples may be taken for analysis. When
*Mineral oil (also known as paraffin oil) is a mixture of
the analyte is a heterogeneously distributed par-
hydrocarbons from petroleum and may be purchased
ticle, like white phosphorus, concentration esti-
from several sources (e.g., Aldrich Chemical Co.).
2
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