Room 6 at Balclutha Primary School asks :-

What is a Laser-Ablation Inductively-Coupled Plasma Mass Spectrometer?

Merilyn Manley-Harris, a chemist at Waikato University's Mass Spectrometry Facility, responded.

These are a lot of words to describe one instrument. A mass spectrometer is an instrument that measures charged particles (ions) and sorts them according to their mass (weight) and the number of charges that they carry. The mass spectrometer helps us to find out about different substances by turning the substances into ions and then sorting them out. The ions can be entire molecules (a group of atoms bonded together), fragments of molecules or single atoms. The ions can have a positive or negative charge.

This type of mass spectrometer measures only atomic ions and is mostly used to measure ions other than carbon, hydrogen and oxygen. For example, it is used to measure arsenic, sulphur, phosphorus etc, and especially in environmental samples such as lake water or rocks. Every sample that goes into the mass spectrometer has to be turned into atomic ions. Inductively-coupled plasma is a very hot gas with a temperature of thousands of degrees and any molecule that goes into the plasma is quickly broken apart into its individual atoms and ions.

The next thing to wonder about is how we get our rock into the plasma without burning our fingers off! This is where the laser ablation part comes in. Imagine throwing a football into a wet sloppy muddy puddle. What happens? Mud splatters everywhere! This is how laser ablation works. We fire a powerful laser at the rock and molecules splatter out as a fine dust which then gets sucked or blown into the plasma which turns the molecules into atoms into ions.

We purchased our instrument in 2005 at a cost of about half a million dollars. So far we have used it to look at phosphates in sediments in Lake Rotorua (the phosphates come from runoff from agricultural land around the lake) and strontium in fish ear-bones. Fish ear-bones have rings like trees and by measuring the strontium in the rings we can see how much time the fish spends in the sea (high strontium) and in freshwater (low strontium).