Analysis of Arsenic in High Purity Metallic Copper by Hydride Generation-Atomic Absorption Spectrometry (HG-AAS)

Significance of the Topic

Arsenic at trace levels in high-purity metallic copper presents a critical quality and safety concern in refining and industrial applications. Accurate determination of sub-ppb arsenic concentrations ensures compliance with stringent purity standards and protects downstream processes and products from contamination.

Objectives and Overview of the Study

This study evaluates a hydride generation–atomic absorption spectrometry (HG-AAS) approach for quantifying trace arsenic in high-purity copper. Key goals include achieving a low limit of quantitation, verifying recovery performance via spiked samples, and demonstrating method robustness in routine laboratory practice.

Methodology and Sample Preparation

Sample preparation combines acid digestion, prereduction, and precipitation steps to remove copper matrix interference prior to hydride generation:

• Digestion: 0.5 g copper sample treated with aqua regia under heat (~120 °C) until solids dissolve (~1 h).
• Spiking: 5 mL of 100 ppb As(V) standard added for recovery tests.
• Prereduction: 5 mL digested solution mixed with concentrated HCl, KI, and L-ascorbic acid to form CuI precipitate.
• Separation: Precipitate filtered off; filtrate collected and diluted to 50 mL for analysis.
• Hydride Generation: In situ conversion of As to arsine gas using NaBH4 in HCl matrix.

Used Instrumentation

The analytical setup consists of:

• Shimadzu AA-7000F atomic absorption spectrophotometer.
• HVG-1 hydride vapor generator for on-line arsine production.
• SARF-16C electric cell heater (atomic muffle furnace) as the absorption cell, offering enhanced sensitivity over flame heating.

Main Results and Discussion

Calibration and performance metrics:

• Linear calibration from 0.5 to 2 ppb As, with correlation indicative of reliable quantitation.
• Limit of quantitation (LOQ): 0.12 ppb As, based on 10σ of blank absorbance.
• Recovery: 106 % for 1 ppb equivalent spike (1.06 µg/g in copper), demonstrating accuracy.
• Blank sample (unspiked) showed arsenic below LOQ, confirming low background.

Benefits and Practical Applications

The HG-AAS method delivers:

• Ultra-high sensitivity (≈1,000× conventional flame methods) for sub-ppb arsenic detection.
• Flameless operation, eliminating need for acetylene and gas compressors.
• Robust cell life and stable signal via electric cell heating.
• Simplicity and adaptability for QA/QC in copper refining, semiconductor materials, and high-purity metal production.

Future Trends and Applications

Potential developments include:

• Extension to other hydride-forming elements (e.g., selenium, bismuth) using the same platform.
• Integration with graphite furnace atomization (GFA) or dedicated furnace units for multi-element trace analysis.
• Automation and inline process monitoring to enable real-time purity control in metal refining.
• Miniaturized or portable HG-AAS systems for field applications and environmental surveillance.

Conclusion

This study confirms that HG-AAS, combined with selective copper precipitation and electric cell heating, provides a sensitive, accurate, and practical solution for trace arsenic determination in high-purity copper. The method meets the demands of industrial QA/QC with minimal gas requirements and straightforward sample preparation.

Reference

• Shimadzu Application Note A633: Analysis of Arsenic in High-Purity Metallic Copper by HG-AAS, First Edition Sep. 2020.