manual of methods for determining micronutrients in fortified foods

Check the concentration of retinyl palmitate stock solution every time is used. Pipette 2 mL
stock retinyl palmitate solution into a 100-mL volumetric flask and dilute to volume with hexane.
Read the absorbance at the maximum wavelength (325-328 nm) using a 1-cm pathlength cell
and hexane as blank. Calculate the purity of retinol palmitate for the working day as:
Where w = weight to prepare the stock retinyl palmitate in hexane in mg.
Purity of stock solution when a new standard is opened:
Check purity as follows: Dissolve 50 mg (record to nearest 0.1 mg) of retinyl palmitate standard
in 2-propanol (UV-spectroscopy grade) in a 500-mL flask and dilute to volume. Dilute 10 mL
of this solution to 100 mL with 2-propanol (final concentration is approximately 10 mg per
liter). Measure maximum absorbance obtained at 325-328 nm using a 1-cm pathlength cell and
2-propanol as blank. Calculate purity of retinol palmitate as
where A max
= absorbance maximum; (5x10 6 ) = combined dilution factors, conversion to 1%
equivalent solution, and conversion to percent; 960= absorbance of pure retinyl palmitate (1%
solution in 1-cm cell), and w=weight of retinyl palmitate standard in mg.
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