SN/T 4675.22-2016 in English

Standard Overview

SN/T 4675.22-2016 specifies a colorimetric method for the determination of total sulfur dioxide in exported wines. It is applicable to all types of wines, with a detection limit of 30-60 mg/L. The method is based on the absorption of sulfur dioxide in a formaldehyde buffer solution, followed by a color reaction with pararosaniline, with absorbance measured at a wavelength of 577 nm.

Technical Principle

Sulfur dioxide is absorbed by the formaldehyde buffer solution to form a stable hydroxymethylsulfonic acid addition compound. Upon reaction with sodium hydroxide, sulfur dioxide is released, which reacts with pararosaniline and formaldehyde to form a purple compound. The color intensity of the compound is proportional to the sulfur dioxide concentration.

Operation Procedure

1. Sample pretreatment: After ultrasonic degassing, sample 0.2-0.5 mL.
2. Color development: Add 0.5 mL of formaldehyde buffer, 250 μL each of ammonium sulfamate and NaOH, and 0.5 mL of PRA solution, in that order.
3. Colorimetric determination: Develop at 20°C for 20 minutes, then measure at 577 nm.

Standard Evolution

Compared to GB/T 15038-2006, this method optimizes the stability of the colorimetric system and relaxes the reaction temperature from 25±1°C to 20±3°C, making it more suitable for large-scale testing. The 2016 version adds an MCX solid-phase extraction cleanup step to effectively eliminate interference from red wine pigments.

Implementation Recommendations

• Sulfur dioxide standard solution must be prepared freshly for use. Na₂SO₃ (CAS 7757-83-7) is recommended.
• Red wine is recommended to be cleaned up using an MCX column (60mg/3mL).
• Strictly control the colorimetric development time to 20±1 minutes.
• Laboratory temperature fluctuation should be ≤2°C/h.