297 / 471
M
astovska
et al
.:
J
ournal of
AOAC I
nternational
V
ol
.
98, N
o
. 2, 2015
483
and 4 mL hexane, followed by application of the 1 mL extract in
hexane. The analytes are eluted with hexane–dichloromethane
(3 + 1, v/v) using volume determined for the given silica gel
SPE cartridges from the elution profiles of target analytes
and fat, which are dependent on the silica deactivation. The
clean extract is carefully evaporated, reconstituted in 0.5 mL
isooctane, and analyzed by GC/MS.
See
Figure
2014.08A
for
the method flow chart.
B. Apparatus
(
a
)
Homogenizer
.—WARING blender Model 38BL40
(Conair Corp., Stamford, CT) or equivalent.
(
b
)
Solvent evaporator
.—Any suitable solvent evaporator,
such as a rotary vacuum evaporator, Kuderna-Danish
evaporator, 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
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
238