128 / 363
E
llingson
et al
.:
J
ournal of
AOAC I
nternational
V
ol
.
99, N
o
.
1, 2016
207
where
R
= results expressed in mg/100 g, C = concentration of the
analyte in the injected solution in ng/mL, V = volume of the initial
extract in mL,
S
= sample weight in grams, and D = dilution factor,
the inverse of any dilution made. All results were calculated on
a RTF or reconstituted basis of 25 g diluted to 225 g with water,
except for SRM 1849a that was calculated back to powder basis.
Results and Discussion
Linearity was assessed from the percent deviation from the
theoretical concentration across the working standard range
(Table 1). The results from the validation showed an overall
repeatability for free and total choline of 1.9 and 2.3% RSD
r
,
whereas the overall intermediate precision obtained for free and
total choline was 2.4 and 2.7% RSD
INT
, respectively (Table 2).
Free and total carnitine had an overall repeatability of 2.9
and 2.7% RSD
r
, whereas the overall intermediate precision
obtained for free and total carnitine was 3.3 and 3.1% RSD
INT
,
Table 2015.10B. Compound transitions
Compound
Use/type
Transition
(Q1/Q3)
Collision
energy, V
Retention
time, min
Carnitine
Quantitation 162.0/103.0
25
1.7
Carnitine-d3 Internal
standard
165.0/103.0
25
1.7
Carnitine
Confirmation 162.0/84.4
29
1.7
Carnitine
Confirmation 162.0/59.1
27
1.7
Choline
Quantitation 104.2/60.0
25
2.1
Choline-d4
Internal
standard
108.2/60.0
25
2.1
Choline
Confirmation 104.2/45.2
25
2.1
Table 1. Linearity
a
Percent deviation from theoretical concn, ng/mL
Compound 10
20
500 2000 4000 5000 Mean
Carnitine 2.9 3.0
2.0 2.4 1.2 2.0 2.2
Choline
2.5 4.1
1.4 1.1 1.0 1.7 1.9
a
Average from three analyses of duplicates at each working standard
level.
Table 2. Choline precision summary
a
Sample
Free choline
Total choline
Mean
concn,
mg/100 g
RSD
r
,
%
RSD
INT
,
%
Mean
concn,
mg/100 g
RSD
r
,
%
RSD
INT
,
%
SRM
1849a
b,c
81.3
2.1 2.3
105 2.1 1.8
AN powder
milk protein-
based
0.364
d
1.8
d,e
2.7
d,f
4.11 2.3
g
2.8
f
IF hydrolyzed
milk-based
14.4
1.7 2.7
18.8 2.1 3.5
IF hydrolyzed
soy-based
17.8
1.7 2.7
17.8 2.0 2.9
AN powder
low fat
15.5
1.6 3.5
18.1 2.4
h
2.8
Child formula
powder
4.61
1.0 1.7
5.70 2.3 2.6
IF elemental
powder
8.11
1.1 2.2
8.68 2.2 2.8
IF powder
milk-based
13.8
2.2 2.5
17.4 2.1
i
3.3
f
IF powder
soy-based
14.9
1.1 2.1
20.2 2.6 4.0
IF RTF milk-
based
12.6 3.1
i
2.7
g
21.4 2.8 2.5
AN RTF high
protein
42.8
2.7 2.6
49.3 1.6 1.5
AN RTF
high fat
48.1
1.4 1.5
53.2 1.2 1.5
Child formula
powder
placebo
0.205
d
2.2
d
4.0
d
1.25
d
2.7
d
2.2
d
IF elemental
powder
placebo
0.118
d
6.4
d
6.4
d
0.651
d
1.8
d
3.0
d
AN RTF high
protein
placebo
0.491
d
1.7
d
1.9
d
6.03 3.4 3.2
AN RTF high
fat placebo
0.522
d
2.8
d
2.8
d
5.10 2.7 2.5
IF RTF
milk-based
placebo
5.42
1.6 2.4
13.2 2.0 2.2
Overall
1.9 2.4
2.3 2.7
a
Samples were run in triplicate across 4 days,
n
= 12. Deviation is
footnoted due to outliers by Grubbs’ test at a 95% confidence interval,
loss of sample during preparation, or failure to prepare in triplicate.
Twelve data points were still obtained for all samples.
b
Free choline information mass fraction value of 79.8 mg/100 g.
c
Total choline certified mass fraction mean and range of 109 mg/100 g
and 98.0–120 mg/100 g, respectively.
d
Results below the SMPR-required LOQ of 2.0 mg/100 g and are not
included in the calculations.
e
Three days of duplicates used for calculation.
f
Calculated across 5 days.
g
Two days of duplicates and 1 day of four replicates used for
calculation.
h
One day of duplicates and 1 day of four replicates used for calculation.
i
One day of duplicates used for calculation.
Figure 2015.10B. Extracted ion chromatogram (XIC) of carnitine.
Candidates for 2016 Method of the Year
127