SN/T 5256-2020 in English
VALIDDetermination of phosphorus content in coal microwave ashing-spectrophotometric method
- Issued on:2020-08-27
- Implemented on:2021-03-01
- File Format:PDF
- Delivery:Via email within 1~3 business days
$117.00
Introduction
Background of Standard Technology Evolution
This standard replaces SN/T 2032-2007 version. The main technical improvements are: standardization of microwave ashing procedures, optimization of acid hydrolysis process and upgrade of precision indicators. The new standard reduces the detection limit from 0.01% to 0.005%, meeting the stringent requirements of international trade on coal quality.
Core Method Principle
The sample pretreatment is completed at 815℃ using a microwave ashing furnace, and the ash is decomposed by a hydrofluoric acid-sulfuric acid system. The ammonium molybdate/ascorbic acid system is used to generate a phosphomolybdenum blue complex, which is quantitatively detected at a wavelength of 650nm using a spectrophotometer.
| Technical parameters | 2007 version | 2020 version | Improvement range |
|---|---|---|---|
| Detection range | 0.01%~0.5% | 0.005%~0.7% | ↓50% lower limit/↑40% upper limit |
| Ashing time | 120min | 45min | Efficiency improved by 62.5% |
| Repeatability limit | 15% relative value | 10% relative value | 33% improvement in accuracy |
Key operating points
Microwave ashing program control
Two-stage heating: 500℃ for 5min to decompose organic matter in the first stage, and 815℃ for 10min to complete mineralization in the second stage. Comparison data from a certain laboratory showed that this program can increase the ashing completeness of porcelain boat samples from 87% to 99.5%.
Optimization of color development system
The new version increases the concentration of ammonium molybdate from 15g/L to 17.2g/L, and uses potassium antimony tartrate as a catalyst to shorten the color development reaction time from 2h to 1h, and the color development stability RSD is <1.5%.
Implementation suggestions
- Equipment selection: The microwave ashing furnace should have a program temperature control function, and the cavity temperature uniformity should be ≤±10℃
- Quality control: Each batch of samples needs to be simultaneously measured with the GBW11104d standard substance, and the recovery rate should be controlled at 95%~105%
- Safety protection: Hydrofluoric acid treatment must be carried out in a fume hood, and the operator must wear special fluoride protective equipment
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