GB/T 15072.20-2025 Methods for chemical analysis of precious metal alloys—Part 20: Determination of rhodium content English, Anglais, Englisch, Inglés, えいご
This is a draft translation for reference among interesting stakeholders. The finalized translation (passing through draft translation, self-check, revision and verification) will be delivered upon being ordered.
ICS 97.120.99
CCS H 57
National Standard of the People's Republic of China
GB/T 15072.20-2025
Replaces GB/T 15072.20-2008
Methods for chemical analysis of precious metal alloys - Part 20: Determination of rhodium content
Issue date: 2025-08-29 Implementation date: 2026-03-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
Introduction
1 Scope
2 Normative References
3 Terms and Definitions
4 Method 1: Cobalt Hexammonium Nitrate Gravimetric Method
5 Method 2: Potentiometric Titration with Potassium Iodide (KI)
6 Method 3: Fire Assay Gravimetry
Methods for chemical analysis of precious metal alloys - Part 20: Determination of rhodium content
Warning—Personnel using this document shall have practical experience in a standard laboratory setting. This document does not address all potential safety issues. The user is responsible for implementing appropriate safety and health measures and ensuring compliance with national regulatory requirements.
1 Scope
This document describes two methods for determining rhodium content in precious metal alloys:
Method 1: Cobalt hexammonium nitrate gravimetric method (applicable to rhodium content of 5.00%–95.00% by mass).
Method 2: Spectrophotometric method (applicable to 3.00%–<5.00% in Pt-Pd-Rh alloys).
2 Normative References
The following documents are indispensable for the application of this document. For dated references, only the edition corresponding to the date applies; for undated references, the latest edition (including all amendments) applies.
GB/T 8170 Rules for rounding off numbers and expression of limiting values.
3 Terms and Definitions
No terms or definitions require definition in this document.
4 Method 1: Cobalt Hexammonium Nitrate Gravimetric Method
4.1 Principle
The sample is digested in a PTFE digestion vessel or hard glass sealed tube with HCl-H₂O₂ under high temperature and pressure. In a slightly acidic solution of rhodium chloride complexes, cobalt hexammonium nitrate is added to form a double salt precipitate, and the rhodium content is determined by gravimetry.
4.2 Reagents and Materials
Unless otherwise specified, only analytical-grade reagents and distilled or deionized water (or equivalent purity) are used.
4.2.1 Sodium nitrite (NaNO₂).
4.2.2 Nitric acid (ρ=1.42 g/mL).
4.2.8 Cobalt hexammonium nitrate solution: Dissolve 17 g of crystalline cobalt hexammonium nitrate in 300 mL water, filter, and dilute to 1,000 mL.
4.2.9 Washing solution: Dilute 15 mL of the above solution to 500 mL with water.
4.3 Instruments and Equipment
4.3.1 Balance (sensitivity 0.01 mg).
4.3.2 Oven (≤300 °C).
4.3.3 Glass fritted crucible (No. 4).
4.3.4 PTFE digestion vessel (wall thickness 25 mm, volume 30 mL).
4.4 Sample Preparation
The sample is processed into shreds (thickness ≤ 0.2 mm, length/width ≤ 2 mm), soaked in glacial acetic acid for 10 min, rinsed with anhydrous ethanol, dried, and homogenized.
4.5 Procedure
4.5.1 Test Portion
Weigh the sample (4.4) according to Table 1 to ±0.00001 g.
Table 1 Test Portion Sizes
4.5.2 Duplicate Test
Conduct two parallel tests and report the average.
4.5.3 Blank Test
Perform a blank test alongside the sample.
4.5.4 Determination
4.5.4.1 Sample Dissolution
4.5.4.1.1 For Rhodium Content <40%
Place the test portion (4.5.1) in a PTFE digestion vessel (4.3.4).
Add 20 mL HCl (4.2.3) and 5 mL H₂O₂ (4.2.6).
Heat at 150 ± 5°C for 24 h, then cool.
4.5.4.1.2 For Rhodium Content ≥40%
Place the test portion (4.5.1) in a hard glass tube (see Appendix A).
Add 10 mL HCl (4.2.3) and 2 mL H₂O₂ (4.2.6).
Heat at 150 ± 5°C for 24 h, then cool.
4.5.4.2 Test Solution Treatment
Transfer the solution (4.5.4.1) to a 500 mL beaker, evaporate to near dryness, and dilute to 300 mL with water.
Cover with a watch glass, heat to 60°C, add 5 g NaNO₂ (4.2.1), and bring to a boil.
While stirring, add 25 mL cobalt hexammonium nitrate solution (4.2.8) until heavy precipitation occurs. Maintain gentle boiling for 10 min.
Cool in 10–20°C water for 1 h.
4.5.4.3 Filtration and Drying to Constant Mass
Filter through a pre-cleaned, dried, and pre-weighed No. 4 glass fritted crucible (4.3.3) using suction.
Use a rubber-tipped glass rod to remove any adhering precipitate from the beaker walls.
Rinse the precipitate into the crucible with cobalt hexammonium nitrate wash solution (4.2.9).
Wash with: 2 × wash solution (4.2.9). 3 × anhydrous ethanol (4.2.4). 1 × ether (4.2.5).
Dry in a glass desiccator for 30 min, weigh, and repeat until constant mass.
4.6 Data Processing
Standard
GB/T 15072.20-2025 Methods for chemical analysis of precious metal alloys—Part 20: Determination of rhodium content (English Version)
Standard No.
GB/T 15072.20-2025
Status
to be valid
Language
English
File Format
PDF
Word Count
10500 words
Price(USD)
315.0
Implemented on
2026-3-1
Delivery
via email in 1~5 business day
Detail of GB/T 15072.20-2025
Standard No.
GB/T 15072.20-2025
English Name
Methods for chemical analysis of precious metal alloys—Part 20: Determination of rhodium content
GB/T 15072.20-2025 Methods for chemical analysis of precious metal alloys—Part 20: Determination of rhodium content English, Anglais, Englisch, Inglés, えいご
This is a draft translation for reference among interesting stakeholders. The finalized translation (passing through draft translation, self-check, revision and verification) will be delivered upon being ordered.
ICS 97.120.99
CCS H 57
National Standard of the People's Republic of China
GB/T 15072.20-2025
Replaces GB/T 15072.20-2008
Methods for chemical analysis of precious metal alloys - Part 20: Determination of rhodium content
Issue date: 2025-08-29 Implementation date: 2026-03-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
Introduction
1 Scope
2 Normative References
3 Terms and Definitions
4 Method 1: Cobalt Hexammonium Nitrate Gravimetric Method
5 Method 2: Potentiometric Titration with Potassium Iodide (KI)
6 Method 3: Fire Assay Gravimetry
Methods for chemical analysis of precious metal alloys - Part 20: Determination of rhodium content
Warning—Personnel using this document shall have practical experience in a standard laboratory setting. This document does not address all potential safety issues. The user is responsible for implementing appropriate safety and health measures and ensuring compliance with national regulatory requirements.
1 Scope
This document describes two methods for determining rhodium content in precious metal alloys:
Method 1: Cobalt hexammonium nitrate gravimetric method (applicable to rhodium content of 5.00%–95.00% by mass).
Method 2: Spectrophotometric method (applicable to 3.00%–<5.00% in Pt-Pd-Rh alloys).
2 Normative References
The following documents are indispensable for the application of this document. For dated references, only the edition corresponding to the date applies; for undated references, the latest edition (including all amendments) applies.
GB/T 8170 Rules for rounding off numbers and expression of limiting values.
3 Terms and Definitions
No terms or definitions require definition in this document.
4 Method 1: Cobalt Hexammonium Nitrate Gravimetric Method
4.1 Principle
The sample is digested in a PTFE digestion vessel or hard glass sealed tube with HCl-H₂O₂ under high temperature and pressure. In a slightly acidic solution of rhodium chloride complexes, cobalt hexammonium nitrate is added to form a double salt precipitate, and the rhodium content is determined by gravimetry.
4.2 Reagents and Materials
Unless otherwise specified, only analytical-grade reagents and distilled or deionized water (or equivalent purity) are used.
4.2.1 Sodium nitrite (NaNO₂).
4.2.2 Nitric acid (ρ=1.42 g/mL).
4.2.8 Cobalt hexammonium nitrate solution: Dissolve 17 g of crystalline cobalt hexammonium nitrate in 300 mL water, filter, and dilute to 1,000 mL.
4.2.9 Washing solution: Dilute 15 mL of the above solution to 500 mL with water.
4.3 Instruments and Equipment
4.3.1 Balance (sensitivity 0.01 mg).
4.3.2 Oven (≤300 °C).
4.3.3 Glass fritted crucible (No. 4).
4.3.4 PTFE digestion vessel (wall thickness 25 mm, volume 30 mL).
4.4 Sample Preparation
The sample is processed into shreds (thickness ≤ 0.2 mm, length/width ≤ 2 mm), soaked in glacial acetic acid for 10 min, rinsed with anhydrous ethanol, dried, and homogenized.
4.5 Procedure
4.5.1 Test Portion
Weigh the sample (4.4) according to Table 1 to ±0.00001 g.
Table 1 Test Portion Sizes
4.5.2 Duplicate Test
Conduct two parallel tests and report the average.
4.5.3 Blank Test
Perform a blank test alongside the sample.
4.5.4 Determination
4.5.4.1 Sample Dissolution
4.5.4.1.1 For Rhodium Content <40%
Place the test portion (4.5.1) in a PTFE digestion vessel (4.3.4).
Add 20 mL HCl (4.2.3) and 5 mL H₂O₂ (4.2.6).
Heat at 150 ± 5°C for 24 h, then cool.
4.5.4.1.2 For Rhodium Content ≥40%
Place the test portion (4.5.1) in a hard glass tube (see Appendix A).
Add 10 mL HCl (4.2.3) and 2 mL H₂O₂ (4.2.6).
Heat at 150 ± 5°C for 24 h, then cool.
4.5.4.2 Test Solution Treatment
Transfer the solution (4.5.4.1) to a 500 mL beaker, evaporate to near dryness, and dilute to 300 mL with water.
Cover with a watch glass, heat to 60°C, add 5 g NaNO₂ (4.2.1), and bring to a boil.
While stirring, add 25 mL cobalt hexammonium nitrate solution (4.2.8) until heavy precipitation occurs. Maintain gentle boiling for 10 min.
Cool in 10–20°C water for 1 h.
4.5.4.3 Filtration and Drying to Constant Mass
Filter through a pre-cleaned, dried, and pre-weighed No. 4 glass fritted crucible (4.3.3) using suction.
Use a rubber-tipped glass rod to remove any adhering precipitate from the beaker walls.
Rinse the precipitate into the crucible with cobalt hexammonium nitrate wash solution (4.2.9).
Wash with: 2 × wash solution (4.2.9). 3 × anhydrous ethanol (4.2.4). 1 × ether (4.2.5).
Dry in a glass desiccator for 30 min, weigh, and repeat until constant mass.
4.6 Data Processing
