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or a nitrogen blow-down system, may be used as long as it
provides results meeting the laboratory qualification/method
set-up requirements (absolute analyte recoveries >70% in both
evaporation steps).
(
c
)
Centrifuge
.—Capable of centrifugation of 50 mL tubes at
>1500 rcf for 10 min.
(
d
)
Furnace/oven
.—Capable of 600°C operation
.
(
e
)
Balance(s)
.—Analytical, capable of accurately measuring
weights from 1 mg to 10 g.
(
f
)
Gas chromatograph-mass spectrometer
.—Any GC/MS
instrument [single quadrupole, triple quadrupole, time-of-flight
(TOF), or ion trap] with electron ionization (EI) may be used as
long as it provides results meeting the laboratory qualification
requirements (to provide reliable results for the calibration range
specified in Table
2014.08A
).
(
g
)
GC column
.—Capillary column BPX-50 (30 m, 0.25 mm
id, 250 µm film thickness; Trajan Scientific, Austin, TX, USA) or
equivalent (USP specification G3), such as Rxi-17Sil MS (Restek
Corp., Bellefonte, PA, USA); DB-17MS, DB-17, or HP-50 (Agilent
Technologies, Santa Clara, CA, USA); or any other column that
enables adequate separation of PAHs as specified in the laboratory
qualification requirements (
see
G
).
C. Reagents and Materials
(
a
)
Hexane.—
>98.5%, mixture of isomers.
(
b
)
Isooctane.—
ACS or better grade.
(
c
)
Ethyl acetate.—
>99.5%, for GC residue analysis.
(
d
)
Dichloromethane.—
≥99.9%, for GC residue analysis.
(
e
)
Toluene.—
≥99.9%, for GC residue analysis.
(
f
)
Water.—
Purified, free of interfering compounds.
(
g
)
Anhydrous sodium sulfate (Na
2
SO
4
).—
≥99.0%, powder,
heated at 600°C for 7 h and then stored in a desiccator before use
(Na
2
SO
4
prepared and stored as indicated can be used for 1 month
from preparation).
(
h
)
Silica gel SPE column.—
Containing 1 g silica gel. Any
commercially available silica gel SPE column can be used as
long as it provides adequate fat cleanup and meets requirements
for low background contamination specified in the laboratory
qualification requirements: the concentrations of all analytes in the
reagent blanks had to be below the concentrations in the lowest
calibration level standard; for naphthalene, levels below the second
lowest calibration standard (equivalent to 5 ng/g naphthalene in the
sample) are still acceptable if the source of contamination could
not be eliminated.
Silica gel SPE columns can be prepared in-house using the
following procedure: Activate the silica gel by heating at 180°C for
5 h, and then deactivate it by adding 5% deionized water, shaking
for 3 h. Store in a desiccator for 16 h before use (silica gel prepared
and stored as indicated can be used for 14 days). Place a piece of
deactivated glass wool in a Pasteur pipet (5 mL), add 1 g activated
silica gel (Silica gel 60, 0.063–0.2 mm, 70–230 mesh or equivalent)
and top it with approximately 0.2 g muffled anhydrous Na
2
SO
4
.
(
i
)
Anhydrous magnesium sulfate (MgSO
4
).—
≥99.0%, powder,
heated (muffled) at 600°C for 7 h, and then store in a desiccator
before use (MgSO
4
prepared and stored as indicated can be used
for 1 month from preparation).
Note
: A preweighed (commercially
available) mixture of 2 g sodium chloride and 4 g anhydrous
magnesium sulfate (muffled) in pouches or tubes can be used.
(
j
)
Sodium chloride (NaCl).—
≥99.0%.
(
k
)
Helium 5.0 or better, nitrogen 4.0 or better.
(
l
)
Polypropylene centrifuge tubes.—
50 mL.
(
m
)
Glass Pasteur pipet.—
5 mL (for solvent transfers and/or in-
house preparation of silica gel minicolumns).
(
n
)
Syringes/pipets.—
Capable of accurate measurement and
transfer of appropriate volumes for standard solution preparation
and sample fortification (50–1000 μL).
(
o
)
Volumetric flasks.—
5–100 mL.
(
p
)
Glassware for evaporation steps
.
—
Depending on the
evaporation technique (e.g., small round-bottom flasks, suitable
tubes, or glassware for Kuderna-Danish evaporation). It is
recommended to heat the glassware for at least 2 h at 250°C to
remove potential contamination.
D. Reference Standards
(
a
)
PAH standards.—
High-purity reference standards of the
PAH analytes (1,7-dimethylphenanthrene, 1-methylnaphthalene,
1-methylphenanthrene,
2,6-dimethylnaphthalene,
3-methyl-
chrysene, anthracene, benz[
a
]anthracene, benzo[
a
]pyrene,
benzo[
b
]fluoranthene, benzo[
g,h,i
]perylene, benzo[
k
]fluoranthene,
chrysene,
dibenz[
a,h
]anthracene,
fluoranthene,
fluorene,
indeno[1,2,3-
cd
]pyrene, naphthalene, phenanthrene, and pyrene).
(
b
)
U.S. Environmental Protection Agency (EPA) 16 PAH
cocktail.—
(
13
C, 99%), Product No. ES-4087 (5 µg/mL, 1.2 mL
in nonane), Cambridge Isotope Labs (
Tewksbury, MA, USA
) or
equivalent.
Table 2014.08B. (
continued
)
PAH
No. of
laboratories
No. of
replicates
Mean
concn, µg/kg
Mean
recovery, % s
r
, µg/kg s
R
, µg/kg RSD
r
, % RSD
R
, % HorRat
9
18
18.4
92.1
1.1
1.9
5.7
10.5
0.36
Naph
8
16
27.7
110.7
2.8
2.8
10.3
10.3
0.37
9
18
84.1
105.1
5.6
8.8
6.7
10.5
0.45
8
16
158.7
99.2
9.7
34.2
6.1
21.6
1.02
Phe
8
16
15.1
100.5
0.5
1.2
3.3
7.8
0.26
9
18
49.7
99.4
1.5
3.0
3.1
6.0
0.24
9
18
168.0
96.0
8.6
16.6
5.1
9.9
0.47
Pyr
9
18
14.8
98.5
0.9
1.3
6.1
8.8
0.29
9
18
40.3
100.8
1.6
3.3
3.8
8.2
0.32
8
16
118.7
95.0
2.9
6.4
2.5
5.4
0.25
Candidates for 2016 Method of the Year
222