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M
astovska
et al
.:
J
ournal of
AOAC I
nternational
V
ol
.
98, N
o
. 2, 2015
485
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
PAHanalytes (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.
Containing: Acenaphthene (
13
C
6
, 99%), acenaphthylene
(
13
C
6
, 99%), anthracene (
13
C
6
, 99%), benz[
a
]anthracene (
13
C
6
,
99%), benzo[
b
]fluoranthene (
13
C
6
, 99%), benzo[
k
]fluoranthene
(
13
C
6
, 99%), benzo[
g,h,i
]perylene (
13
C
12
, 99%), benzo[
a
]pyrene
(
13
C
4
, 99%), chrysene (
13
C
6
, 99%), dibenz[
a,h
]anthracene
(
13
C
6
, 99%), fluoranthene (
13
C
6
, 99%), fluorene (
13
C
6
, 99%),
indeno[1,2,3-
cd
]pyrene (
13
C
6
, 99%), naphthalene (
13
C
6
, 99%),
phenanthrene (
13
C
6
, 99%), and pyrene (
13
C
6
, 99%).
E. Preparation of Standard Solutions
(
a
)
Individual stock solutions.—
Prepare individual PAH
stock solutions at approximately 1000 or 2500 µg/mL in toluene.
(
b
)
Mixed stock standard solution.—
Use analyte individual
stock solutions to obtain a mixed solution of each PAH at
10 µg/mL (for benzo[
a
]pyrene) and other low-level PAHs)
or 25 µg/mL (for chrysene and other higher-level PAHs) or
50 µg/mL (for naphthalene) in isooctane.
See
Table
2014.08E
for analyte concentrations in the mixed stock standard solution.
(
c
)
Working PAH Solution A.—
Accurately transfer 0.5 mL of
the mixed stock standard solution into a 5 mL volumetric flask
and dilute to volume with isooctane.
(
d
)
Working PAH Solution B.—
Accurately transfer 0.5 mL of
the Working PAH Solution A into a 5 mL volumetric flask and
dilute to volume with isooctane.
(
e
)
Internal standard solution.—
Prepare 1 µg/mL solution of
13
C-PAHs in isooctane by 5-fold dilution of the 5 µg/mL EPA16
13
C-PAHs cocktail with isooctane.
(
f
)
Calibration standard solutions—
Prepare eight levels
of calibration standard solutions (1 mL each) in 2 mL amber
screw-cap vials. It is recommended to distribute small portions
(enough for a single injection) of the calibration standard
solutions into multiple crimp-top vials with 100 µL deactivated
glass inserts.
See
Table
2014.08A
for analyte concentrations in
the calibration standards and Table
2014.08F
for the dilution
scheme.
(
1
)
For level 1 calibration standard
.–Accurately transfer
50 µL of the Working PAH Solution B into the vial and add
50 µL of the 1 µg/mL
13
C-PAHs solution and 900 µL isooctane.
Cap the vial and vortex mix briefly.
(
2
)
For level 2 calibration standard
.–Accurately transfer
100 µL of the Working PAH Solution B into the vial and add
50 µL of the 1 µg/mL
13
C-PAHs solution and 850 µL isooctane.
Cap the vial and vortex mix briefly.
(
3
)
For level 3 calibration standard
.–Accurately transfer
200 µL of the Working PAH Solution B into the vial and add
50 µL of the 1 µg/mL
13
C-PAHs solution and 750 µL isooctane.
Cap the vial and vortex mix briefly.
(
4
)
For level 4 calibration standard
.–Accurately transfer
500 µL of the Working PAH Solution B into the vial and add
50 µL of the 1 µg/mL
13
C-PAHs solution and 450 µL isooctane.
Cap the vial and vortex mix briefly.
(
5
)
For level 5 calibration standard
.–Accurately transfer
100 µL of the Working PAH Solution A into the vial and add
50 µL of the 1 µg/mL
13
C-PAHs solution and 850 µL isooctane.
Cap the vial and vortex mix briefly.
(
6
)
For level 6 calibration standard
.–Accurately transfer
200 µL of the Working PAH Solution A into the vial and add
50 µL of the 1 µg/mL
13
C-PAHs solution and 750 µL isooctane.
Cap the vial and vortex mix briefly.
(
7
)
For level 7 calibration standard
.–Accurately transfer
500 µL of the Working PAH Solution A into the vial and add
50 µL of the 1 µg/mL
13
C-PAHs solution and 450 µL isooctane.
Cap the vial and vortex mix briefly.
(
8
)
For level 8 calibration standard
.–Accurately transfer
100 µL of the mixed stock standard solution into the vial and
Table 2014.08C. (
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
10
20
17.9
89.3
0.9
1.6
4.9
8.8
0.30
Naph
9
18
23.7
94.6
1.9
4.0
8.1
17.1
0.61
10
20
105.9
84.7
10.1
26.7
9.5
25.2
1.12
8
16
146.7
91.7
7.2
19.2
4.9
13.1
0.61
Phe
8
16
14.5
96.8
0.8
0.9
5.3
6.1
0.20
8
16
93.1
93.1
3.9
8.5
4.1
9.2
0.40
8
16
160.8
91.9
5.8
13.0
3.6
8.1
0.38
Pyr
10
20
14.2
94.6
0.7
1.3
5.0
9.3
0.31
10
20
71.5
95.4
2.9
7.0
4.0
9.8
0.41
10
20
116.5
93.2
4.5
9.6
3.8
8.3
0.37
Candidates for 2016 Method of the Year
240