Chemistry Reference
In-Depth Information
Table 9.1
Preparation of the caffeine standard solutions for construction of
calibration graphs. Acetaminophen was added in the samples as
the injection marker to compensate for injection volume fluctua-
tions. Acetaminophen was dissolved in water at a concentration of
0.9 mg mL
-1
. The stock solution of caffeine at 1 mg mL
-1
was made
in the acetaminophen solution. The caffeine stock solution was
diluted to different concentrations in acetaminophen solution.
d
n
0
t
2
n
g
|
4
Sample
number
[caffeine]
standard
solution
(mgmL
-1
)
V
Caffeine
(1 mg
mL
-1
)(mL)
V
Acetaminophen
(0.9
mg mL
-1
)(mL)
V
Total
(mL)(V
C
+ V
A
)
1
900
900
100
1000
2
800
800
200
1000
3
700
700
300
1000
4
650
650
350
1000
5
600
600
400
1000
6
550
550
450
1000
7
500
500
500
1000
8
450
450
550
1000
9
400
400
600
1000
10
350
350
650
1000
11
300
300
700
1000
12
250
250
750
1000
13
200
200
800
1000
14
125
125
875
1000
15
100
100
900
1000
16
90
90
910
1000
17
80
80
920
1000
18
75
75
925
1000
19
70
70
930
1000
20
50
50
950
1000
21
25
25
975
1000
observed none-zero intercept, being either positive or negative, was due to
random errors. These errors could be due to random peak intensity variations,
caused by fluctuations in the UV light intensity, as well as errors in the small
volumes used to prepare the standard solutions (see Table 9.1) and adsorption
of the analytes onto the capillary wall.
The limits of detection and quantification, LOQ and LOD, respectively,
were determined to be approximately 10 and 25 mgmL
-1
. The LOQ and LOD
were determined according to the signal to noise ratio approach, where signal-
to-noise ratios of three and ten correspond to the detection and assay limits,
respectively. The determined LOQ was shown to be low enough for the
determination of caffeine in the examined dietary products.
9.5.3 Precision
Precision of the method was studied to define the degree of variation between a
series of multiple measurements from the same, as well as different samples.
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