The Laser Ablation Microprobe (LAM) Laboratory
The laser ablation microprobe in the Inco Innovation Centre consists of the Finnigan ELEMENT XR, a high resolution double focusing magnetic sector inductively coupled plasma mass spectrometer (HR-ICPMS), and a GEOLAS 193 nm excimer laser system.The system operates by ablating material from a sample with the laser, ionizing the chemical atoms of the ablated material in an inductively coupled plasma of argon, focusing and accelerating the produced ions in a beam, and measuring the relative abundances of the ions after separating them on the basis of mass in a magnetic field.
Laser ablation of polished samples takes place in a sealed cell filled with helium. The ablated material consists of gas and particulates which are transported in a helium gas stream to the ICP. The ablation site on the sample surface is viewed through a camera, which permits precise positioning of the laser spot.
The Element XR has a incredibly large dynamic range (1012) that allows measurement of both major elements and trace elements in the same analyses. This is accomplished using a single Faraday collector with the secondary electron multiplier, allowing measurement in counting, analog and Faraday detector modes.
The instrument also has high mass resolution capabilities for resolving polyatomic interferences and the highest instrumental sensitivity of any commercial available ICPMS.
The ablation system utilizes an argon-fluorine gas laser emitting at the 193 nm wavelength. Deep-ultraviolet ablation greatly improves the coupling of laser energy to the sample surface, therefore increasing sampling efficiency. The laser system is flexible with regard to repetition rate, i.e., rate of firing, and laser beam spot size, which permits very controlled ablation rates and spatial resolution of sampling.
Sampling resolution down to about 10 micrometres can be achieved, although ablation pits on the order of 30 – 50 micrometres are usually used, when grain size allows, to provide better precision and detection limits.
For a large number of trace elements, low to sub ppb detection limits can be expected at 40 µm sampling resolution. For more information on the flexibility of the technique and particular LAM projects, please contact Mike Tubrett (firstname.lastname@example.org).