
Contents
14.1.09
AOAC Official Method 986.31
Nitrate in Forages: Potentiometric Method
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Published:January 2023
Cite
Nitrate in Forages: Potentiometric Method', in Dr. George W Latimer, Jr. (ed.), Official Methods of Analysis of AOAC INTERNATIONAL, 22nd Edition (
Extract
First Action 1986
Final Action 1989
Principle
Nitrate is extracted from forage into aqueous Al2(SO4)3 solution and determined potentiometrically. Lower limit of detection is 0.50% KNO3.
Apparatus
...
Reagents
Conversion factors for units of nitrate and nitrite concentrationsa
...
Preparation of Standard Curve
Determine potential of blank (use extracting solution as blank, equivalent to 70 mg KNO3/L) and each working standard solution while magnetic stirring. Plot potential against nitrate concentration (mg KNO3/L) on semilog paper with concentration on log scale. Determine standard curve per decade slope. Per decade slope specification of electrode manufacturer should be met or exceeded. (Note: Measure potential only after test solution and standards are at same temperature.)
Preparation of Test Sample
Dry test sample in 60°C forced air oven to constant weight. Grind to pass 2 mm screen and thoroughly mix. Extract 1.00 g test portion with 100 mL extracting solution by shaking 15 min. Keep extract sealed in container until potential is measured.
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