5. AOACSPDSMethods-2018AwardsV3

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Stock standard solution, mg/L = M × P × (1 − W ) × 1000

where A is the absorbance of the sample test solution at 765 nm; b is the y -intercept of the calibration curve; m is the slope of the calibration curve; W is the weight of the test material (mg); V is the volume of the sample test solution (100 mL); D is the dilution factor (20); and 1000 is the conversion from mL to L. Note that values are expressed as gallic acid equivalents. ( f ) Total phenolic content in test material on dry weight basis. — Calculate the total phenolic content of the test material, in % w/w on a dry weight basis, as follows: Total phenols, % w/w, dry = total phenols as is/ M where M is the dry weight fraction of the test material, expressed as (100 – % moisture)/100. The % moisture of the test material can be determined by standard methods such as the Karl Fischer vacuum oven or the Halogen Moisture Analyzer (Mettler Toledo HR73) methods. Note that values are expressed as gallic acid equivalents. References: J. AOAC Int . (future issue) AOAC SMPR 2015.009 J. AOAC Int . 98 , 1109(2015) DOI: 10.5740/jaoac.int.SMPR2015.009 Posted: February 2018

where M = mass of gallic acid (g); P = purity of gallic acid (%); and W = water content of gallic acid (expressed as decimal, determined by Karl Fischer method or Loss on Drying method). ( b )  Calibration standard solutions .—Using concentration of gallic acid of stock standard solution, calculate the actual concentration of each calibration standard solution as follows: Calibration standard solution, mg/L = ( S × V )/25 mL where S is concentration of stock standard solution (mg/L) and V is volume of stock standard solution (mL). ( c )  Calibration curve .—Plot absorbance at 765 nm versus concentration of calibration standards. Using linear regression, calculate slope, y -intercept, and r 2 value of the calibration curve for gallic acid. ( d ) System suitability .—r 2 value of the calibration curve must be ≥0.990. ( e ) Total phenolic content in test material as is .—Calculate total phenolic content of the test material, in % w/w as is, as follows: Total phenols, % w/w, as is = [( A – b )/ m ] × [( V × D )/( W ×1000)] ×100

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