GB/T 20975.7-2020 in English

Analysis of the core content of the standard

Method	Measurement range	Principle	Key improvements
Potassium periodate spectrophotometry	0.0040%-2.00%	Potassium periodate oxidation color development under acidic conditions, absorbance measurement at 525nm	Add safety warnings and reagent requirements, and modify precision data
Na2EDTA titration	8.50%-45.00%	EDTA complexation is excessive, zinc standard solution is back titrated	New method, suitable for samples with high manganese content

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Technical points of the method

Key controls of potassium periodate spectrophotometry

Color control: Phosphoric acid (5mL) must be kept present, boiling color development time is 15-30min, and the solution volume must be constantInterference elimination: When the cerium content is greater than 0.005%, other methods must be used, and when the silicon content is high, fluoroboric acid treatment is required

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Precautions for Na2EDTA titration

Pretreatment: Dissolve and filter with NaOH first, then dissolve the precipitate with mixed acidEnd point judgment: The orange-red end point needs to be confirmed by oscillation for more than 10s, and titration needs to be slow near the end point

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Highlights of standard revision

• Added Na2EDTA titration method to extend the detection range to 45%
• Added normative reference documents (GB/T8005.2 terminology standard)
• Refine the reagent purity requirements (analytical grade + secondary water)
• Update the precision data (repeatability limit increased by 20-30%)

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Implementation Suggestions

Application scenarios	Method selection	Critical control points
Low content arbitration analysis	Spectrophotometry	Strictly control the colorimetric acidity and boiling time
High manganese aluminum alloy	Titration method	Pay attention to the completeness of the precipitate dissolution

Laboratory preparation: Platinum utensils (spectrophotometry) and a three-stage water purification system (titration) are required