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C.
Standards
a.
L-Carnitine
, USP Reference Standard Cat. No. 1359903, store desiccated
b.
L-Carnitine-d
3
HCl (methyl-d
3
), Cambridge Isotope Laboratories Inc. DLM-1871-0.1,
store refrigerated
c.
Choline Chloride
, USP Reference Standard Cat. No. 1133547
d.
Choline Chloride-d
9
(Trimethyl-d
9
98%) DLM-549-1 Cambridge Isotope Laboratories
Inc.
D.
Solution Preparation
a.
Mobile phase.—
i.
Mobile phase A
— 10 mM ammonium acetate (95/5 water/acetonitrile v/v).
Quantitatively transfer 770 (±15) mg ammonium acetate into a 1 liter glass
bottle and dissolve with 950 mL laboratory water. Adjust pH up to 8.2 ~ 8.6 by
ammonium hydroxide (B a. iv). Record the amount of ammonium hydroxide
added. Add 50 mL acetonitrile to the bottle and mix well. Store room
temperature. Expiration: one week.
ii.
Mobile phase B
— 10 mM ammonium acetate (5/95 water/acetonitrile v/v).
Weigh 770 (±15) mg ammonium acetate into a 100 mL beaker. Dissolve with 50
mL laboratory water. Add same amount of ammonium hydroxide as added into
mobile phase A and then mix well. Transfer the 50 mL solution into a 1 liter
glass bottle quantitatively. Add 950 mL acetonitrile into the bottle and mix well.
Store room temperature. Expiration: 2 weeks.
b.
Native Stock Solutions
i.
Choline Hydroxide (approximately 3000 µg/mL)
Store at 2-8ºC.
Expiration: 1 month (currently trying to extend to 1 year).
1.
Dry approximately 200 mg of choline chloride USP reference standard
at in a vacuum oven at 65 ºC (±3 ºC ) for 4 hours
2.
Weigh 170 mg (± 17 mg) into an appropriate weighing boat.
3.
Transfer into a 50 mL volumetric flask quantitatively.
4.
Dissolve and bring to volume with laboratory water.
ii.
L-Carnitine (approximately 750 µg/mL)
Aliquot the stock solution into 2 mL
plastic vials with each vial receiving at least 1 mL and store ≤ -15ºC.
Expiration: 1 year.
1.
Weigh 150.0 mg ± 15 mg into an appropriate weighing boat as quickly
as possible
2.
Transfer into a 200 mL volumetric flask.
3.
Dissolve and bring to volume with laboratory water.
4.
Correct weight for moisture content.
c.
Internal Standard stock Solutions
i.
Choline Chloride-d
9
(approximately 20,000 µg/mL)
Aliquot the stock solution
into 2 mL plastic vials with each vial receiving about 1 mL and store ≤ -15ºC.
Expiration: 1 year.
1.
Transfer 1 gram of d
9
-choline chloride into a 50 mL volumetric flask.
2.
Dissolve and bring to volume with laboratory water
ii.
L-Carnitine Chloride-d
3
HCl (approximately 10,000 µg/mL)
Aliquot the stock
solution into 2 mL plastic vials with each vial receiving about 1 mL and store ≤ -
15ºC. Expiration: 1 year.
Candidates for 2016 Method of the Year
326