Gold Purity Analysis: Portable XRF vs. Fire Assay

Importance of the Topic

Gold purity analysis is vital for accurate valuation, fraud detection, and quality assurance in the jewelry and precious metals industry. Portable XRF offers a non-destructive, rapid, and environmentally friendly approach compared to traditional fire assay methods.

Objectives and Study Overview

This application note evaluates the performance of Thermo Scientific™ Niton™ DXL and XL2 portable XRF analyzers against classical fire assay for determining gold purity in jewelry. The primary goals are to compare accuracy, analysis time, operational complexity, and safety requirements.

Methodology and Used Instrumentation

The comparative study involved:

• Portable XRF: Direct measurement of up to 22 elements (including Au, Ag, Ni, W) in 3–10 seconds without sample destruction or chemical reagents.
• Fire Assay: Removal of a sample fragment, fusion at 950 °C, acid digestion (hydrochloric and nitric acids), and reduction with ferrous sulfate to isolate gold.

Used Instrumentation:

• Thermo Scientific Niton DXL and XL2 Precious Metal Analyzers
• Conventional fire assay equipment: muffle furnace, digestion apparatus, and reagents

Main Results and Discussion

A high correlation (R² = 0.999) was observed between gold weight percentages measured by XRF and fire assay. Portable XRF results typically deviate by less than one-eighth of a karat from fire assay data. Additionally, XRF provides multi-element profiles that fire assay cannot deliver.

Benefits and Practical Applications

• Non-destructive testing preserves the integrity and market value of jewelry samples.
• No hazardous chemicals or extensive waste disposal required, enhancing safety and environmental compliance.
• Rapid analysis enables high throughput and immediate decision-making in field or laboratory settings.
• Portability allows on-site testing at various locations, improving customer service and operational flexibility.

Future Trends and Potential Applications

Emerging developments in portable XRF may further improve detection limits, broaden elemental coverage, and integrate with automated data management systems. There is potential to extend applications to other precious and base metal alloys, as well as to link results with digital traceability and quality-control platforms.

Conclusion

Portable XRF demonstrates accuracy comparable to fire assay while offering significant advantages in speed, simplicity, safety, and environmental impact. It represents a practical alternative for gold purity analysis in diverse industrial and commercial contexts.