LA-ICP-MS

Laser ablation inductively coupled plasma mass spectrometry, LA-ICP-MS for short, is one of the most sensitive analytical methods in gemmology. It measures trace elements down to parts per billion and has become indispensable for many questions of origin and treatment.

The principle

A focused laser removes a tiny amount of material from an inconspicuous spot on the stone, usually the girdle. The resulting crater is only a few hundredths of a millimetre across and invisible to the eye. The removed material is carried into a plasma, ionised there, and separated and counted by mass in a mass spectrometer.

What the method is used for

• Origin: the pattern of many trace elements, for example in corundum or emerald, is compared with reference stones
• Beryllium diffusion: beryllium in sapphires can hardly be detected by other methods but reliably with LA-ICP-MS
• Paraíba tourmaline: copper, manganese and other elements help to confirm the variety and give clues to the deposit
• Synthesis: certain elements reveal growth methods and flux

Microdestructive

Because material is removed, the method is not entirely non-destructive. Reputable laboratories therefore use it only when the question justifies it, choose the measuring spot carefully and document it. The owner should consent to the measurement.

The limits

Even the most sensitive measurement only provides data. They become meaningful only through comparison with extensive reference collections and in combination with inclusions and spectroscopy. For some deposits the chemical patterns overlap, so an origin may remain open.

Effort and cost

The instruments are expensive and require specialised staff. The method is therefore used mainly for high-value stones or for specific questions.

In brief

LA-ICP-MS measures trace elements with the highest sensitivity and is often decisive for origin and beryllium diffusion. The method removes a tiny amount of material and is therefore used with justification, documentation and consent.

At NOBILITH

When a laboratory report supports an origin or rules out beryllium treatment, an LA-ICP-MS measurement often lies behind it. In the dossier we reproduce the laboratory's statement verbatim.

Sources

• GIA: Gems & Gemology, articles on LA-ICP-MS
• LMHC: Information Sheets on Paraíba tourmaline and beryllium diffusion