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© 2015 AOAC INTERNATIONAL
AOAC Official Method 2015.02
Sodium Monofluoroacetate in Dairy Powders
Liquid Chromatography-
Tandem Mass Spectrometry (LC-MS/MS)
First Action 2015
(The method has been validated in cow, goat, and sheep dairy
powders, and dairy powder formulations. It can be used for
other similar matrixes, including liquid milk, provided that it is
demonstrated that the method performance values are met.)
Specific hazards
.—
Hydrochloric acid
.—Wear personal
protective equipment (PPE) and handle in a fume cupboard.
Sulfuric acid
.—Wear PPE and handle in a fume cupboard.
Sodium fluoroacetate
.—Wear PPE, including safety glasses and
a dust mask, when weighing out the primary material.
Potassium hydroxide
.—Wear PPE and handle in a fume
cupboard; avoid inhalation of dust.
3-Nitroaniline
.—Wear PPE, including safety glasses; avoid
inhalation.
Phosphoric acid
.—Wear PPE and handle in a fume cupboard.
Sodium fluoroacetate (Figure
2015.02A
) is a rodenticide used in
New Zealand to control rats, possums, and rabbits. It is commonly
known by its original registration number as compound 1080, but
may also be known as sodium monofluoroacetate and fluoroacetic
acid sodium salt.
A. Principle
Samples are dissolved in water and extracted into acetone to
allow precipitation of proteins. After centrifugation, the solutions
are passed through an anion exchange column and eluted with acid
to give free fluoroacetic acid. This acid is converted to 2-fluoro-
3'-nitroacetanilide via a carbodiimide-mediated amide coupling
reaction. The derivative is then subjected to SPE cleanup, eluting
with
t
-butyl methyl ether
(TBME)–
n
-hexane, concentrated and
quantified by LC-MS/MS using derivatized isotopically substituted
sodium fluoroacetate as an internal standard. The method reports
the analyte as fluoroacetic acid.
B. Apparatus
Note
: Where specific equipment is listed, other brands or models
may be used provided that they have equivalent performance.
Laboratory equipment
.—
(
a
)
Air displacement pipets.—
5000 μL, with long tips.
(
b
)
Autosampler vials
.—2 mL with tapered glass inserts.
(
c
)
Balance
.—2 or 3 decimal top pan.
(
d
)
Balance
.—5 decimal place analytical.
(
e
)
Centrifuge
.—Capable of centrifuging 15 and 50 mL tubes at
4200 ×
g
RCF.
(
f
)
Centrifuge tubes
.—15 and 50 mL, tapered polypropylene.
(
g
)
Extraction cartridges
.—Oasis HLB 60 mg.
(
h
)
Glass reservoirs
.—Ground glass, 19/26 joint, approximately
20 mL.
(
i
)
Laboratory glassware
.—Measuring cylinders, volumetric
flasks, and beakers.
(
j
)
Multi-step dispenser with appropriate tips
.—Eppendorf
Stream or equivalent.
(
k
)
Nitrogen blow-down
.—Capable of maintaining a
temperature 40 ± 10°C.
(
l
)
pH meter
.
(
m
)
Polypropylene SPE reservoirs
.—10 mL, with adapters.
(
n
)
Positive displacement pipets
.—25, 100, 250, and 1000 µL,
with tips.
(
o
)
Refrigerator and freezer.
(
p
)
Resin chromatography column
.—10 mL polypropylene
(Bio-Rad).
(
q
)
Shaker
.—Reciprocating bench top.
(
r
)
Ultrasonic bath
.
(
s
)
Vacuum manifold for SPE cartridges.—
With stopcocks.
(
t
)
Vortex mixer
.
(
u
)
Water bath.—
Maintained at 40 ± 2°C.
Analytical instrumentation
.—
(
v
)
LC-MS/MS instrument
.—AB Sciex 5500 QTRAP coupled
with Agilent 1290 Series HPLC.
(
w
)
HPLC guard column
.—Phenomenex Security C18,
4 × 2 mm.
(
x
)
HPLC column
.—Agilent XDB-C18, 100 × 4.6 mm, 1.8 μm.
C. Reagents
All reagents and chemicals must be of such a grade that they do
not interfere with the analytical process.
Chemicals
.—
(
a
)
Acetone
.—Pesticide grade.
(
b
)
Acetonitrile.—
Pesticide grade.
(
c
)
AG 1-X8 resin
.—100–200 mesh chloride form, ACS reagent
grade.
(
d
)
Ammonium acetate
.—ACS reagent grade.
(
e
)
Deionized water.—
Laboratory purified, ≥18 ΩM.
(
f
)
Hydrochloric acid
.—Concentrated, ACS reagent grade; 37–
38%.
(
g
)
Methanol.—
Pesticide grade.
(
h
)
n
-
Hexane
.—Pesticide grade.
(
i
)
Phosphoric acid
.—Concentrated, ACS reagent grade.
(
j
)
Potassium dihydrogen phosphate
.—ACS reagent grade.
(
k
)
Potassium hydroxide.—
ACS reagent grade.
Figure 2015.02A. Sodium fluoroacetate.
Table 2015.02A. Fortification of recovery samples
Tube No.
Name
Volume, µL
Concn
fluoroacetic acid,
µg/kg
WS3 WS2 WS3
1
a
Matrix standard 0
a
0
a
0
a
5
a
2
Recovery 1 0
0 40
0
3
Recovery 2 25 0 40
0.1
4
Recovery 3 125 0 40
0.5
5
Recovery 4 0 25 40
1
6
Recovery 5 0 125 40
5
7
Reagent blank 0
0 40
0
a
The matrix standard is fortified at step
F
(
b
)(
9
).
Candidates for 2016 Method of the Year
20