Humic Acid Testing Methodology

Extraction Solution

In a 2l volumetric with 500ml of DI H2), add 80g NaOH, 8ml DTPA, 40ml ethanol and bring to volume.

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Standard Stock Preparation (1000 ppm):

Dry Humic Acid (Aldrich) for 4 hours @ 105^o C. Weigh out 0.1075 g of Humic Acid and dilute to 100ml with extraction solution. Shake for 1 hour.

Standard Preparation

Take 5ml of Humic Acid Standard Stock Solution and dilute to 100ml with DI H20 to make 50 ppm standard solution. Take 10ml and dilute to 100mlL to make 100 ppm standard. Take 20ml and dilute to 100ml to make 200 ppm standard.

Sample Preparation

Weigh out 2g of dry sample and add sufficient extraction solution to dissolve entire sample. Mix sample well. Centrifuge an aliquot of the sample to remove any particulates. Dilute sample as necessary so it falls within the range of the standard curve.

Test Procedure

With Spectrophotometer set at 450 nm, set up standard curve with the 50, 100 and 200 ppm standards, using water as a blank. Read your sample and calculate concentration from the standard curve.

Calculations

(ppm Humic Acid from standard curve) X (dilution factor) = ppm Humic Acid

% Humic Acid = ppm Humic Acid / 10,000

DTPA = Diethylenetriamine Penta Acetic Acid

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