Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) is the state of the art technique for chemical micro-analysis of solid materials. It has a wide range of applications in many different fields of science and industry. In the past couple of years LA-ICPMS has become more and more important in gemmology as standard analytical techniques are facing their limits in many cases.

Our LA-ICPMS system consists of the CETAC LSX-213 solid state Nd:YAG UV laser and the Perkin Elmer ELAN DRCe quadrupole ICP mass spectrometer. The laser has a wavelength of 213 nanometers (nm), which combined with a laser pulse repetition rate of 10 Hertz allows for precise ablation without cracking or splintering of the sample. During the laser ablation process the laser pulses release small amounts of the sample from the surface in the form of particles, ions, atoms and molecules. Ablated material is caught by a He gas current and transported into the Argon plasma of the mass spectrometer. In the plasma the 60-150 nm sized particles are disintegrated at ~6000° Celsius and ions are created, which can be selectively detected. The mass spectrometer is capable of quasi simultaneous detection of almost all natural elements, including very light elements such as Li, Be, B and Na, which are difficult or impossible to analyse by more traditional chemical analyses such as the X-Ray Fluorescence method. Most elements can be detected at very low concentrations down to sub-ppb (parts per billion) levels, which makes this method unchallenged by any other standard analytical instrumentation.

Standard testing of gemstones by LA-ICPMS commonly includes four individual spot analyses placed on the girdle of faceted stones or anywhere according to the client’s wish, e.g. on a facet that will be repolished. The laser beam diameter, and therefore the size of the sample pit, is ideally 50 Micrometers – half the diameter of a human hair. If placed on a reflective (polished) surface the sample pits are barely visible by the naked eye. The weight loss for each set of analyses (= 4 laser pits) is between 0.000004 ct and 0.000008 ct and therefore negligible. Thus, the appearance, quality and value of the stone will not be affected.

We are applying LA-ICPMS to determine beryllium-treatment of corundum and to support origin determination of emeralds. We are currently working on the development of methods for origin determination of rubies, sapphires, spinels, alexandrites, and paraiba tourmalines.