10.0 CALIBRATION AND
11.0 PROCEDURE
STANDARDIZATION
1. A 100-mL aliquot of acetone is measured in a
10.1 PREPARATION OF STANDARDS: About
graduated cylinder and added to the 250-mL
0.2 g of solid picric acid (SARM or reagent grade)
sample bottle containing 20 g of soil. The bottle is
is dried to constant weight in a vacuum desiccator
capped and manually shaken for three minutes.
in the dark. About 0.125 g is weighed out to the
2. The soil is allowed to settle for 5 minutes.
nearest 0.1 mg, transferred to a 100-mL volumet-
3. The sample bottle cap is removed and a 60-
ric flask and diluted to volume with deionized
mL syringe is inserted into the extract. About 35
water. A stir bar is added and the solution stirred
40 mL of extract is pulled into the syringe. A Millex
overnight in the dark. The concentration of pi-
SR filter is placed on the tip of the syringe and 30
cric acid in this stock is about 1250 mg/L. A work-
mL of extract is expressed into a 100-mL gradu-
ing standard is made by diluting 10 mL of the stock
ated cylinder. Any remaining extract can be filtered
with deionized water to 100 mL in a volumetric
back into the extraction bottle. The filter is removed
flask. The concentration of the working standard
and placed in a waste container.
is about 125 mg/L.
4. The 30 mL of acetone extract is diluted in the
Calibration solutions are prepared in 125-mL
100-mL graduated cylinder to 60 mL with deion-
plastic bottles by diluting the working standard
ized water. This assures that all the picric acid and
with deionized water as described in Table A1.
ammonium picrate in the acetone extract is con-
Volumetric pipets are used to measure the work-
verted to picrate ion.
ing standard. A 100-mL graduated cylinder is used
5. A 3-mL Alumina-A solid-phase extraction
to measure the dilution water.
(SPE) tube is placed on the end on the same 60-mL
10.2 INITIAL CALIBRATION: A 30-mL aliquot
syringe with the plunger removed. The aqueous
of each aqueous calibration solution is diluted with
acetone mixture is added to the syringe and the
30 mL of acetone and processed according to the
plunger replaced. The plunger is depressed so that
PROCEDURE starting at Step 5. Absorbance read-
the mixture flows through the SPE tube at about
ings of Solutions A-E should range from 0.0 to 0.7
10 mL/minute. The picrate ions are retained in the
absorbance units. The slope of the relationship be-
SPE tube. The eluent is collected in a waste con-
tween the concentration of picric acid and absor-
tainer.
bance should be linear, with a zero intercept and a
6. The 60-mL syringe is removed from the SPE
response factor of 90 15 g/g per absorbance unit
tube and placed in a waste container.
on a wet-weight basis.
7. The SPE tube is filled with methanol from a
10.3 DAILY CALIBRATION: A 30-mL aliquot of
squirt bottle (about 3 mL) and an air-filled 10-mL
Calibration Solution D (10 g/mL, equivalent to
syringe is used to force the methanol through the
50 g/g in soil) is diluted with 30 mL of acetone
tube into the waste container. The SPE tube is then
and processed according to the method. The daily
filled with acetone from a squirt bottle (about 3
response factor is calculated:
mL) and rinsed as above into the waste container.
8. The SPE tube is prepared for elution of picric
daily response factor = (50 g/g)/
acid by placing a new Millex SR filter on the tip and
(Absorbance @ 400 nm).
placing a plungerless 10-mL syringe in the barrel.
9. A 10-ml aliquot of acetone is measured in one
10.4 DAILY BLANK AND MATRIX SPIKE: A
10-mL graduated cylinder. Four drops of concen-
blank soil is produced by adding a 100-mL aliquot
trated sulfuric acid are added to the acetone using
of acetone to 20 g of a soil known to be uncontami-
an eyedropper. The tip of the dropper should be
nated with picrate and performing the method. A
close to the surface of the acetone to prevent splash-
soil spiked at a concentration of 50 g/g is made
ing from the falling drop.
by adding 8 mL of the 125-mg/L working stan-
10. The 10-mL acidacetone mixture is poured
dard to 20 g of blank soil followed by 92 mL of
into a 10-mL syringe and the plunger replaced
acetone and performing the method.
while the tip of the extraction tubefilter assem-
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