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1124
Joseph et al.
: J
ournal of
AOAC I
nternational
Vol. 98, No. 3, 2015
D. Standards
(
a
)
Primary standards
.—Primary standards are stored in a
refrigerator between 2–8°C in the dark. Subsequent solutions
should be corrected for purity, moisture, and salt (if applicable).
Wear appropriate PPE when weighing out the primary material.
(
1
)
Analytes
.—Sodium fluoroacetate (CAS No. 62-74-8).
(
2
)
Internal standard
.—
13
C
2
D
2
sodium fluoroacetate.
(
b
)
Secondary
standards
.—(
1
)
Analytes
.—
Fluoroacetic
acid (1000 mg/L)
.—Weigh approximately 12.9 mg sodium
fluoroacetate into a calibrated 10 mL volumetric flask. Add
deionized water, make to volume, and mix until solid is
completely dissolved. Transfer to a 15 mL polypropylene
screw cap test tube and cap tightly. Store in a freezer at less
than –10°C. Calculate exact concentration correcting for purity,
moisture (if applicable), and salt using Equation 1.
C
= [(
m
×
P
×
Mo
)/
V
] × [
MW
/
MW
(salt)
]
(1)
where
C
= concentration of standard solution in mg/L;
m
=
exact mass of primary standard weighed in mg;
P
= purity of
standard expressed as a decimal equal to % purity/100;
Mo
=
additional purity correction for moisture/water (if applicable).
Expressed as a decimal equal to (100 – % moisture)/100;
V
= volume of solution in L; MW = molecular weight of target
analyte; MW
(salt)
= molecular weight of analyte as salt.
(
2
)
Internal standard
.—
13
C
2
D
2
fluoroacetic acid (500
mg/L)
.—Weigh approximately 7.2 mg (corrected for chemical
and isotopic purity) of
13
C
2
D
2
labeled sodium fluoroacetate
into a calibrated 10 mL volumetric flask. Add deionized water,
make to volume, and mix until solid is completely dissolved.
Transfer to a 15 mL polypropylene screw cap test tube and cap
tightly. Store in the freezer at –10°C or below. Calculate exact
concentration correcting for purity, moisture (if applicable), and
salt using Equation 1.
(
c
)
Intermediate standards.—
(
1
)
Analyte
.—
Fluoroacetatic
acid intermediate standard (50 mg/L)
.—Dilute 2.5mL(calculate
exact volume based on concentration of secondary standard
using Equation 2) of fluoroacetic acid secondary standard (1000
mg/L) to 50 mL with deionized water in a calibrated volumetric
flask. Use a calibrated positive displacement pipet. Dispense
aliquots of the standard into 15 mL polypropylene tubes for
frozen storage. Store in the freezer at –10°C or below.
C
2
= (
C
1
×
V
1
)/
V
2
(2)
where
C
2
= concentration of required diluted solution in mg/L;
C
1
= concentration of high standard in mg/L;
V
1
= volume of
high standard required in mL;
V
2
= total volume of diluted
solution in mL.
(
2
)
Internal standard
.—
13
C
2
D
2
fluoroacetic acid standard
(50 mg/L)
.—Dilute 2.5 mL (calculate exact volume based
on concentration of secondary standard using Equation 2) of
13
C
2
D
2
fluoroacetic acid secondary standard (500 mg/L) to 25
mL with water in a calibrated volumetric flask. Use a calibrated
positive displacement pipet. Dispense aliquots of the standard
into 15 mL polypropylene tubes. Store in the freezer at –10°C
or below.
(
d
)
Working solutions (WS)
.—(
1
)
Analyte
.—(
a
)
WS1
(1.0 mg/L)
.—Dilute 1000 µL fluoroacetic acid intermediate
standard (50 mg/L) to 50 mLwith deionized water in a calibrated
volumetric flask. Dispense aliquots of the WS1 standard into
15 mL polypropylene tubes. Store in the freezer at –10°C or
below. A thawed and opened tube WS1 can be stored for up to 2
months in a refrigerator between 2–8°C provided it is resealed
and immediately refrigerated after each use.
(
b
)
WS2 (0.1 mg/L)
.—Dilute 10 mL of WS1 (1.0 mg/L)
to 100 mL with deionized water in a calibrated volumetric
flask. Dispense aliquots of the WS2 standard into 15 mL
polypropylene tubes. Store in the freezer at –10°C or below. A
thawed and opened tube WS2 can be stored for up to 2 months
in a refrigerator between 2–8°C provided it is resealed and
immediately refrigerated after each use.
(
c
)
WS3 (0.01 mg/L)
.—Dilute 500 µL of WS2 (0.1 mg/L)
to 5 mL with deionized water in a calibrated volumetric flask.
Transfer into a 15 mL polypropylene tube. Make fresh daily.
(
2
)
Internal standard
.—
Internal standard working solution
(ISWS; 0.5 mg/L)
.—Dilute 1000 µL of
13
C
2
D
2
fluoroacetic acid
intermediate standard (50 mg/L) to 100 mLwith deionized water
in a calibrated volumetric flask. Pipet aliquots of the ISWS into
15 mL polypropylene tubes. Store in the freezer at –10°C or
below. A thawed and opened tube of ISWS can be stored for
up to 2 months in a refrigerator between 2–8°C provided it is
resealed and immediately refrigerated after each use.
Table 2015.02C. HPLC solvent gradient
Time
% A
(10 mM NH
4
Ac in H
2
O)
% B
(10 mM NH
4
Ac in 97% ACN)
0
80
20
2.50
0
100
3.00
0
100
3.01
80
20
4.00
80
20
Table 2015.02D. Instrument parameters for AB Sciex
LC-MS/MS system
Parameter
Value
HPLC column
Agilent XDB-C18,
100
×
4.6 mm
×
1.8 µm
Column temperature
60°C
Autosampler temperature
10°C
Flow rate
1 mL/min
Injection volume
5 µL
Run time
4 min
Ionization mode
Electrospray
Polarity
Negative
Curtain gas (CUR)
30 psi
Source temp. (TEM)
750°C
Ion source gas 1 (GS1)
60 psi
Ion source gas 2 (GS2)
60 psi
Ion spray voltage (IS)
–4500 V
Collision gas (CAD)
Medium (8)
Entrance potential (EP)
–10 V
Candidates for 2016 Method of the Year
29