392 / 471
P a g e
|
11
Table 6. continued
Gradient Profile
Time (min)
Flow (mL/min)
% MP A
% MP B
Curve
0.1
0.7
8
92
6
6
0.7
21
79
6
6.01
0.7
100
0
6
8
0.7
100
0
6
10
1
8
92
6
13
1
8
92
6
13.2
0.7
8
92
6
15
0.7
8
92
6
NOTES:
1.
Free choline or carnitine can be determined by weighing same sample size (as for microwave
digest procedure) into a disposable tube, skipping the microwave digestion and filtering the
sample at an equivalent dilution (neither ammonia or nitric acid to be added).
2.
Unless the sample contains milk proteins, free carnitine = total carnitine (through microwave
digestion). Thus, the method is able to determine free and total carnitine and total choline
simultaneously through microwave digestion. The non-MW prep is typically used for free
choline in products (rare) or to determine free choline/carnitine in premixes. Note that the
typical control sample, SRM 1849a, has substantially different values for carnitine depending
on whether the SRM is microwave digested.
3.
System suitability measures: the residuals must be <4% in each calibration curve; a control
sample (SRM 1849a) must be run with each set of samples and results within limits of lab
control chart.
4.
The authors acknowledge help from Jim Denison, Nick Cellar, and Wes Jacobs in completing
this work.
Candidates for 2016 Method of the Year
330