GB/T 39689-2020 in English

Interpretation of the core content of the standard

This standard establishes a method system for the determination of free formaldehyde content in surfactants, and focuses on standardizing the following technical elements:

Key technical points

1. Preparation of standard solution

The formaldehyde standard solution is calibrated by iodine titration. The key reaction equation is:

HCHO + I₂ + 3NaOH → HCOONa + 2NaI + 2H₂O

When sodium thiosulfate is titrated with residual iodine, the color change point of the starch indicator is blue disappearance.

2. Spectrophotometric operation specifications

• Color development conditions: 60℃ water bath for 30 minutes, 412nm wavelength detection
• Distillation control: residual liquid volume 1-3mL, duration ≥30 minutes
• Quality control: standard curve needs to be redrawn every week

3. Special requirements for liquid chromatography

Standard implementation suggestions

1. The laboratory should establish method validation records, including recovery (recommended 85-110%) and precision (RSD≤10%)
2. For high-content samples (＞100mg/kg), it is recommended to use gradient dilution method to avoid exceeding the linear range
3. Regularly check the wavelength accuracy of the spectrophotometer and the liquid chromatography column efficiency (theoretical plate number ≥5000)

Technology Evolution Analysis

Compared with traditional methods, the innovations of this standard include:

• For the first time, liquid chromatography was included in the national standard
• Clear the arbitration priority of the two methods
• Refine the distillation operation parameters (temperature, duration, etc.)