One step ahead

A team of Spanish and British scientists has developed a laser-ablation technique to detect variations in the sulphur isotopes of a single hair over time.

The information shows up changes in a person's eating habits and their movements between different countries, which could help police to undermine the alibis of international terrorists.

A group of researchers from the LGC Chemical Metrology Laboratory in the UK and the University of Oviedo in Spain, came up with the method to detect how the proportions of isotopes in a chemical element vary throughout the length of a single hair.

Their objective is to be able to use the method to track the geographical movements of people, including international crime suspects and victims.

The scientists focused on the most abundant sulphur isotopes in hair keratin - sulphur-32 (32S), which accounts for about 95 per cent, and sulphur-34 (34S), which makes up around four per cent. This proportion can change slightly in response to people's diets and if they travel from one country to another, and the technique is able to detect these small variations.

The new method is based on combining a laser-ablation system and multi-collector inductively coupled plasma mass spectrometry, according to Rebeca Santamaría-Fernández of LGC. The laser makes contact with the selected fraction of the hair, generating an aerosol, which later ionises within plasma, with the spectrometer providing the exact proportions of the sulphur isotopes.

'The advantage of this method compared with others is the high resolution resulting from use of the laser,' said Santamaría-Fernández.

The researchers believe they have overcome 'the first hurdle' - developing an effective method to measure longitudinal isotope variations in hair, with the potential to relate these changes to geographical movements.

The next objective is to demonstrate the global significance of these variations, and they are already working with hair samples from 150 volunteers with different diets and geographical origins to do just that.

In addition, the researchers will measure the isotopic variations of other elements apart from sulphur, such as carbon and nitrogen.

The scientists are confident they will be able to create databases that will one day make it possible to link the relationship between a specific isotope in hair keratin and a country or region, which would be of great help to the police in tracking down international criminals.

'Although we still cannot say that a certain isotopic variation in a person's hair shows that he or she has been in a particular country, the method can help to break down the alibis of some terrorists who claim not to have moved over recent months,' said Santamaría-Fernández.

Various British security forces, such as the London Metropolitan Police, have already expressed interest in this project. The LGC centre (previously known as the Laboratory of the Government Chemist) is working with various national and international research groups, among them the University of Oviedo.