11 / 71
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