A New Technique for the Analysis of Corundum Using Laser Ablation ICP-MS

Importance of the Topic

Color-enhancement treatments for corundum significantly affect gemstone value. The introduction of beryllium diffusion at high temperature complicates routine identification, necessitating sensitive analytical approaches to safeguard market integrity and consumer trust.

Study Objectives and Overview

This research evaluates a novel beryllium-diffusion heat treatment applied to natural and synthetic corundum. The primary goal is to detect and map beryllium distribution using laser ablation ICP-MS (LA-ICP-MS) and to validate findings with secondary ion mass spectrometry (SIMS).

Methodology and Instrumentation

• Sample Set: 40 unheated or conventionally treated stones and 79 beryllium-diffused samples spanning various colors, natural and synthetic.
• LA-ICP-MS System: Merchantek UP-213 laser ablation (213 nm Nd:YAG, 5th harmonic) coupled to Agilent 7500a ICP-MS; calibrated with NIST 612 glass standard.
• SIMS System: Cameca IMS-6f magnetic sector instrument; calibrated with synthetic beryllium-doped sapphire standard.

Main Results and Discussion

• No detectable beryllium (below instrument background) in unheated or traditionally heat-treated corundum.
• All beryllium-diffused samples contained 0.3–15.7 ppm Be, confirming diffusion across stone surfaces.
• Longer heating (22 h) yielded higher Be concentrations than shorter treatment (10 h), with pronounced rim-to-core concentration gradients.
• Comparison with SIMS showed consistent distribution profiles, endorsing LA-ICP-MS as a rapid, reliable screening tool.

Benefits and Practical Applications of the Method

• LA-ICP-MS enables trace-level detection of light elements with minimal sample prep and high throughput.
• Spatial mapping of Be reveals diffusion-based treatments, aiding gemological authentication.
• Supports laboratories in verifying treatment status for quality control and market assurance.

Future Trends and Potential Applications

Emerging diffusion processes using other light-element dopants will require microanalytical methods. LA-ICP-MS can be adapted to detect diverse trace dopants in solid matrices, extending its utility to gemstone research and broader materials science.

Conclusion

LA-ICP-MS effectively identifies beryllium-diffusion treatments in corundum, distinguishing treated gems from untreated or conventionally treated stones. Its sensitivity and spatial resolution provide a robust tool for gemological authentication and understanding color-enhancement mechanisms.

Instrumentation Used

• Merchantek UP-213 laser ablation system coupled to Agilent 7500a ICP-MS
• Cameca IMS-6f SIMS instrument

References

• Giving Orange a Bad Name. Colored Stone, 2003, 16(2), p. 20.
• Mohapatra S.K., Kröger F.A. Defect Structure of α-Al2O3 Doped with Magnesium. Journal of the American Ceramic Society, 1977, 60(3–4), pp. 141–148.
• Emmett J.L., Douthit T.R. Heat Treating the Sapphires of Rock Creek, Montana. Gems & Gemology, 1993, 29(4), pp. 250–272.