GB/T 37907-2019Reclaimed water quality—Determination of sulfide and cyanide—Ion chromatography (English PDF)

6.1 Collection and preservation of samples

6.1.1 Collect water samples in accordance with the provisions of GB/T 5750.2

After collecting the samples to a brown glass bottle, use sodium hydroxide solution (40 g/L) to adjust the pH to 9.0 ~ 10.0. The sampling bottle shall be filled with water samples, so that there are no air bubbles in the bottle. Immediately seal it; avoid direct sunlight during transportation.

6.1.2 The collected water sample shall be analyzed as soon as possible; otherwise, it shall be stored at low temperature (0°C ~ 4°C) and protected from light; the measurement shall be completed within 24 h.

6.2 Interference and sample pretreatment

6.2.1 When the water sample contains cobalt ( > 0.05 mg/L), it is necessary to add 1 mL of sulfuric acid solution to adjust the water sample to pH< 2.0; then, use an all-glass distillation device for distillation; then, use 10 mL of sodium hydroxide solution (10 g/L) to absorb; lastly, filter it through a 0.22 µm water-phase filter and test.

6.2.2 Water sample that contains oxides such as free chlorine ( > 1.0 mg/L) will interfere with the determination of cyanide. Sodium sulfite solution can be added before distillation to eliminate interference. Measure two samples of the same volume; add 1 ~ 3 piece(s) of potassium iodide-starch test paper to one of the samples; add sulfuric acid solution to acidify; drop sodium sulfite solution to the potassium iodide-starch test paper until it becomes colorless from blue; write down the amount. For another sample, do not add potassium iodide-starch test paper; only add the above-mentioned amount of sodium sulfite solution.

6.2.3 Water sample that contains nitrite ions ( > 50 mg/L) will interfere with the determination of cyanide. Sulfamic acid can be added before distillation to eliminate the interference. For 1 mg of nitrite, 2.5 mg of sulfamic acid is needed.

7.1 Setting of the ion chromatography conditions

Debug the ion chromatograph according to the best conditions that are provided in the instrument instruction manual. Set the chromatographic conditions as follows: […]