GB/T 39302-2020 in English

Analysis of the core content of the standard

This standard specifies the methylene blue spectrophotometric method for the determination of anionic surfactants in reclaimed water using a visible light spectrophotometer, with a detection limit as low as 0.05mg/L and an extended upper limit of 30mg/L. The method is based on the color reaction of the cationic dye methylene blue and anionic surfactants to form a blue salt complex.

Method principle and technological evolution

Key Operation Points

Implementation suggestions

1. Safety protection: When operating dichloromethane, it must be carried out in a fume hood, and a gas mask and chemical-resistant gloves must be worn.
2. Quality control: The absolute difference of parallel samples should meet the following requirements: ≤0.05mg/L when ≥1.00mg/L, ≤0.02mg/L when <1.00mg/L
3. Interference elimination: When emulsification occurs in the sample, <10mL of isopropanol can be added to break the emulsion.
4. Equipment calibration: The wavelength accuracy and absorbance linearity of the spectrophotometer must be verified regularly.

Application scenario expansion

This method has been verified to be applicable to matrices such as surface water and industrial wastewater. When detecting samples exceeding the limit, accurate determination can be achieved by reducing the sampling volume (to a minimum of 5mL) or dilution. For wastewater from special industries, it is recommended to conduct a spike recovery test to verify the applicability of the method.