Soil and sediments. Determination of sulfide. Methylene blue spectrophotometric method (1)

1.

This standard applies to the methylene blue spectrophotometric method for the determination of sulfide in soil and sediment

Second, the principle of the method

The sulfide in the soil and sediments is acidified to generate sulfide gas.

3.

(1) Concentrated sulfuric acid : p(H ₂ SO ₄ )=1.

(2) Hydrochloric acid : p(HCl)=1.

(3) Sodium hydroxide (NaOH)

(4) N,N-Dimethyl-p-phenylenediamine hydrochloride [NH ₂ C ₆ HN(CH ₃ ) ₂ ·2HCI]

(5) Ferric ammonium sulfate [Fe(NH ₄ )(SO ₄ ) ₂ ·12H ₂ O]

(6) Ascorbic acid (C ₆ H ₈ O ₆ )

(7) Disodium ethylenediaminetetraacetic acid (C ₁₀ H ₁₄ O ₈ N ₂ Na ₂ ·2H ₂ O)

(8) Hydrochloric acid solution

Measure 250mL premium grade pure hydrochloric acid and slowly pour into 250mL water and cool

(9) Antioxidant solution

Weigh 2.

(10) Sodium hydroxide solution: p(NaOH)=10g/L

Weigh 10.
0 g of sodium hydroxide and dissolve it in water, dilute to 1000 mL, shake well, and store in a polyethylene container
.

(11) N,N-dimethyl p-phenylenediamine solution: p[NH ₂ C ₆ H ₄ N(CH ₃ ) ₂ ·2HCl]=2g/L
.

Weigh 2.
0 g of N,N-dimethyl-p-phenylenediamine hydrochloride and dissolve it in 700 mL of water, slowly add 200 mL of concentrated sulfuric acid, dilute to 1000 ml with water after cooling, and shake well
.
This solution is stored in a sealed brown bottle at room temperature and is stable for three months
.

(12) Ferric ammonium sulfate solution: p[Fe(NH ₄ )(SO ₄ ) ₂ ]=100g/L
.

Weigh 25.
0 g of ferric ammonium sulfate and dissolve in 100 mL of water, slowly add 5.
0 mL of concentrated sulfuric acid, dilute to 250 mL with water after cooling, and shake well
.
If insoluble matter appears in the solution, it should be filtered before use
.

(13) Sulfide standard solution: p(S ^{2 -} )=100mg/L
.

Purchase certified reference materials sold by the Standard Sample Research Institute of the Ministry of Environmental Protection
.

(14) Standard solution for sulfide: p(S ^2- )=10.
0mg/L
.

Pipette 10.
00mL sulfide standard solution into a 100mL brown volumetric flask, then add 10.
0mL 10g/L sodium hydroxide solution, dilute to the mark with water, shake well, and prepare immediately before use
.

Four, instruments and equipment

(1) Analytical balance: the accuracy is 0.
01g and 0.
1mg
.

(2) Spectrophotometer: with 10mm cuvette
.

(3) Acidification-blowing-absorption device (Figure 9-1): All connecting pipes are made of silica gel
.

(4) Acidification-distillation-absorption device (Figure 9-2)
.

(5) Sampling bottle: 200mL brown glass bottle with ground top with stopper
.

(6) Absorption tube: 100mL colorimetric tube with stopper
.

(7) Commonly used instruments and equipment in general laboratories (Figure 9-1, Figure 9-2)
.

1—water bath; 2—reaction flask; 3—adding acid separatory funnel; 4—absorption tube
.

Figure 9-1 Sulfide acidification-blowing-absorption device