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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

243