GB/T 4702.18-2020 in English

Technical background and evolution of standards

As the 18th part of the GB/T 4702 series, this standard improves the analysis system of metallic chromium. Compared with the traditional chemical analysis method, the detection limit of the method is reduced to 0.010% by using spectrophotometer combined with organic solvent extraction technology, which significantly improves the detection accuracy of trace vanadium.

Detailed explanation of the principle of the method

In the sulfuric acid-perchloric acid medium, after the chromium is volatilized and removed by chromyl chloride, pentavalent vanadium and tantalum reagent form a purple-red complex. After extraction with chloroform, the absorbance is measured at a wavelength of 530nm. Key reaction equation:

Key operating specifications

Quality Control Requirements

The laboratory allows strict classification of tolerance: when the vanadium content is 0.010%~0.050%, the tolerance is 0.004%; when it is 0.10%~0.50%, it is relaxed to 0.025%. The instrument performance needs to be verified regularly with standard substances to ensure the wavelength accuracy of the spectrophotometer is ±2nm.

Implementation suggestions

1. The perchloric acid fume phase must be completed in a fume hood to avoid the escape of chromyl chloride
2. After color development, the determination should be completed within 30 minutes to prevent the decomposition of the complex
3. When the chloroform extract is emulsified, a small amount of ethanol can be added to break the emulsion