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vitamin B
12
peak areas of the samples are within the range of the
vitamin B
12
peak areas of the standards.
(
c
)
Calculation of standard concentrations
.
WS = S
w
× P × A/200
where WS = working standard concentration in
m
g/L; S
w
= amount
of vitamin B
12
standard weighed in mg; P = purity of USP reference
standard in
m
g cyanocobalamin (vitamin B
12
)/mg of the standard; A
= aliquot of vitamin B
12
intermediate standard used (0.5, 1, 2, 3, 4,
or 5) in mL; and 200 = dilution volume in mL.
(
d
)
Preparation of standard curves
.—At each standard
concentration, average the peak area of the standard injected at the
beginning of a set of samples with the peak area of the standard
injected at the end of the set of samples. Prepare a standard curve
by performing linear least squares (regression) on concentration
versus the average peak area of the working standards. A standard
curve must have a correlation of at least 0.999 to be considered
acceptable for sample calculations.
(
e
)
At each working standard concentration, the peak areas of
standards injected at the beginning and end of a set of samples
should not increase or decrease by more than 10%.
(
f
)
Calculation of vitamin B
12
concentrations in samples.—
The
vitamin B
12
concentration in each injected sample preparation is
extrapolated from the vitamin B
12
standard curve prepared above.
The concentration of vitamin B
12
in each product can then be
calculated.
C
p
= C
i
× D
1
÷
ss × D
2
÷
V
where C
p
= product concentration in
m
g/kg; C
i
= vitamin B
12
concentration of the injected sample preparation extrapolated from
standard curve in
m
g/L; D
1
= volume of the first dilution in mL
(100 mL); ss = sample size in g; D
2
= volume of the second (final)
dilution in mL; V = volume of filtrate loaded onto the cartridge in
mL.
For each set of samples, the control result must be within three
standard deviations of the control mean.
References:
J. AOAC Int . 95 , 313(2012)DOI: 10.5740/jaoacint.CS2011_10
AOAC SMPR 2011.005
J. AOAC Int . 95 , 293(2012)DOI: 10.5740/jaoac.int.11-0441
Posted: May 5, 2015
Candidates for 2016 Method of the Year
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