AOACSPIFANMethods-2017Awards

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M c M ahon : J ournal of AOAC I nternational V ol . 99, N o . 1, 2016  227

Figure 2012.10B. HPLC chromatogram of vitaminA palmitate test sample. Peak 1, 13 cis -isomer; peak 2, cis - isomer; peak 3, trans -isomer.

Figure 2012.10A. HPLC chromatogramof vitaminA palmitate calibration standard. Peak 1, 13 cis -isomer; peak 2, trans -isomer.

( 3 ) Calculate the average absorbance reading. Calculate the spectrometric purity as a decimal, SP AA , of retinyl acetate using Equation 2: SP AA = 01 1 100 05 560 1 × × × ts AA m A r (2) where A = average absorbance reading, determined above; 1560 = extinction coefficient of retinyl acetate at 325 nm; and m st = mass of the reference standard in mg. ( c )  Spectrometric purity of α-tocopherol acetate stock solution.— ( 1 ) Pipet 3 mL α-tocopherol acetate stock standard solution into a l00 mL volumetric flask and make up to volume with ethanol. ( 2 ) Determine the absorption at 284 nm, zeroed against ethanol, in a 1 cm quartz cell. Repeat the reading twice, rinsing the sample cuvet with the solution before each reading. Calculate the average absorbance reading. ( 3 ) Calculate the spectrometric purity as a decimal, SP TA , of α-tocopherol acetate using Equation 3: SP TA = 01 3 100 05 6.34 × × × ts m A r (3) where A = average absorbance reading, determined above; 43.6 = extinction coefficient of tocopherol acetate at 284 nm; and m st = mass of the reference standard in mg. ( d )  Spectrometric purity of α-tocopherol stock solution .— ( 1 ) Pipet 3 mL α-tocopherol stock standard solution into a l00 mL volumetric flask and make up to volume with ethanol. ( 2 ) Determine the absorption at 292 nm, zeroed against ethanol in a 1 cmquartz cell. Repeat the reading twice, rinsing the sample cuvet with the solution before each reading.

Figure 2012.10C. HPLC chromatogram of vitaminA acetate calibration standard. Peak 1, 13 cis- isomer; peak 3, trans -isomer.

( 3 ) Calculate the average absorbance reading. Calculate the spectrometric purity as a decimal, SP T , of α-tocopherol using Equation 4:

A

3 100 05

01 × × × = (4)

SP T T r

=

m

8.57

ts

where A = average absorbance reading, determined above; 75.8 = extinction coefficient of tocopherol at 292 nm; and m st = mass of the reference standard in mg.