(Sodium pyrophosphate extraction - potassium dichromate oxidation colorimetric method, this method is for reference only)

one. Reagent configuration:

1: concentrated sulfuric acid: (analytical purity 98%).

2: 0.8mol/L 1/6 potassium dichromate solution preparation: Potassium dichromate 40g dissolved in one liter of water.

3: Preparation of sodium pyrophosphate extract: 15 g of sodium pyrophosphate and 7 g of sodium hydroxide are dissolved in one liter of water.

4: 0.5% - C standard solution preparation: Weigh 1.370g glucose in a 100ml volumetric flask and make up to volume with water.

two. Steps:

1: Preparation of test solution: Weigh air-dried sample (over 0.25mm sieve) 0.5000g (accurate to 0.0002g) into a 300ml flask, add 150ml of sodium pyrophosphate soaking agent into a small funnel, Heat extraction in boiling water bath for 2 hours. Shake frequently during heating. After extraction, remove the flask and cool. Transfer all to a 200 ml volumetric flask, shake well and let stand for clarification.

2: Measurement: Aspirate 5.00 ml of extract solution in a 100 ml volumetric flask, add 0.8 mol/L potassium dichromate solution 5 ml and concentrated sulfuric acid 15 ml (add slowly), heat and oxidize in a boiling water bath for 30 minutes, remove, and cool At room temperature, add water to the mark and shake it.

3: The same standard as the above procedure is used as the standard solution and blank solution: Aspirate 5.00 ml standard solution in a 100 ml volumetric flask and add 5 ml of extractant. In another blank bottle, only 5 ml of water and 5 ml of extractant were added, both of which were added with the same oxidant as the aforementioned sample bottle, heated together with the sample bottle in a boiling water bath, cooled, and then added with water to a constant volume.

4: Colorimetric measurement on the instrument.

three. Calculation of results:

Colorimetric measurement of carbon content in the test solution / 5 × 200ml

Total humic acid (%) = ------------------―――――――――――― × 100

Sample weight (g) × 1000 × humic acid carbon content

Peat humic acid: 0.58 brown coal humic acid: 0.64

Weathered coal humic acid: 0.67

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