Determination of Myo-Inositol - AOAC International

6 Schimpf et al.: Journal of aoac international Vol. 95, no. 4, 2012
C W = W × 1/0.05 × 1/10 × A 1/V 1 × A 2/V 2
= W × 2 × A 1/V 1 × A 2/V 2
where C W is the concentration of the working standard solution
in milligrams per liter; W is the weight, in milligrams, of
myo-inositol standard weighed; 0.05 is the dilution volume of
the stock standard in liters; 1/10 is the intermediate standard
dilution (10 to 100 mL); A 1 is the aliquot of intermediate
standard used, in milliliters; V 1 is the dilution volume of the
working standard in milliliters; A 2 is the aliquot of working
standard used, in milliliters, if applicable; and V 2 is the dilution
volume of the working standard in milliliters, if applicable.
(b) Preparation of standard curve.—For each working
standard concentration, average the peak areas or heights from
each two consecutive sets of standards. Prepare a standard
curve by performing linear least squares (regression) on the
concentrations versus the averaged peak areas or heights. A
standard curve must have a correlation of at least 0.999 to be
considered acceptable for sample calculations.
At each working standard level, the peak areas or heights of
standards injected before and after a set of samples must not
increase or decrease by more than 7%.
(c) Calculation of myo-inositol in samples and controls.—
The concentration of myo-inositol in a prepared sample or
control is extrapolated from the standard curve prepared above.
From the diluted, prepared sample concentration, the product
concentration can be calculated:
C p = (C d × D 1)/S
where C p is the concentration of myo-inositol in the product
sample or control in milligrams per kilogram; C d is the
concentration of myo-inositol in the prepared sample or control
in milligrams per liter; D 1 is the dilution volume in milliliters;
and S is the sample weight in grams.
Total myo-inositol, as defined by AOAC SMPR 2011.007 (1),
can be calculated by adding the free myo-inositol and myoinositol
bound as phosphatidylinositol data.
Note: For each set of samples, the control result must be
within three standard deviations of the control mean.
Reference: J. AOAC Int. 95, (future issue)
Results and Discussion
During validation, the average repeatability was 2.0% RSD
and the intermediate precision was 2.5% RSD, as summarized
in Tables 1 and 2. Accuracy was determined by comparison to a
reference microbiological assay as detailed in Table 3 (2). The
instrument LOD and LOQ of the method were estimated to be
0.0004 and 0.0013 mg/100 mL, respectively, and correspond to
a free myo-inositol quantitation limit of 0.026 mg/100 g.
Although this method has not been fully validated for the
quantitation of myo-inositol bound as phosphatidylinositol,
some data have been generated and are summarized in Table 4.
The phosphatidylinositol quantitation limit has been estimated
to be 0.016 mg/100 g.
References
(1) AOAC SMPR 2011.007 (2012) J. AOAC Int. 95, 295. http://
dx.doi.org/10.5740/jaoac.int.11-0443
(2) Atkin, L., Schultz, A., Williams, W., & Frey, C. (1943) Ind.
Eng. Chem. Anal. Ed., 15, 141–144. http://dx.doi.org/10.1021/
i560114a022