420 / 670
(k)
Reference Internal Standard
.
–
Choline-1,1,2,2-d4 Chloride (CDN Isotopes) or equivalent.
Note
: All use of water in this method must be high purity MS grade water. It is recommended
that all preparation steps with nitric acid be performed within a fume hood, and the necessary
personal protective equipment used when handling.
C. Mobile Phase Preparation
Mobile phase A (5 mM ammonium formate in 50:50 (v/v) water:acetonitrile with 0.2%
formic acid) was prepared by weighing 0.63 g of ammonium formate into a 1 L graduated
cylinder. Water was added along with a stir bar and mixed to dissolve before diluting to volume
with water. The solution was transferred to a 2 L mobile phase container along with 1 L of
acetonitrile, 4 mL of formic acid, stir bar, and then thoroughly mixed. Mobile phase B (30 mM
ammonium formate in 50:50 (v/v) water:acetonitrile with 0.2% formic acid) was prepared by
weighing 3.78 g of ammonium formate into a 1 L graduated cylinder. Water was added along
with a stir bar and mixed to dissolve before diluting to volume with water. The solution was
transferred to a 2 L mobile phase container along with 1 L of acetonitrile, 4 mL of formic acid,
stir bar, and then thoroughly mixed. Mobile phase B was also used for the rinse solutions in the
autosampler.
D. Preparation of Standard Solutions
The carnitine stock standard was prepared at a concentration of 25 mg/mL by weighing
0.25 g of L-carnitine into a 20 mL polypropylene tube followed by 10 mL of water to dissolve.
The purity of L-carnitine from the Certificate of Analysis (CoA) and moisture determined by
Karl Fisher immediately at the time of weighing was used to calculate the final concentration of
carnitine. The choline stock standard was prepared at a concentration of 25 mg/mL choline by
weighing 0.62 g of choline bitartrate into a 20 mL polypropylene tube followed by 10 mL of
Chol-08/Carn-07 (February 2016)
FOR ERP USE ONLY
DO NOT DISTRIBUTE