Tackling contamination

A new analysis method can detect the kidney-damaging chemical melamine, which was used to contaminate infant formula in China last September, at very low levels within a matter of seconds.

A research team at Purdue University created the analysis method to detect levels of melamine in the low parts-per-billion in milk and milk powder in about 25 seconds.

An estimated 50,000 Chinese children fell ill and several died after drinking the melamine-contaminated formula.

Melamine, which is used in plastics, was deliberately added to the formula to artificially bump up apparent protein levels.

The chemical also was found in the contaminated pet food produced in China responsible for the deaths of a reported 8,500 dogs and cats in the US in March 2007.

The US Food and Drug Administration issued new guidelines in November 2008, limiting melamine in dairy products to one part-per-million or less.

R. Graham Cooks, Purdue's Henry B. Hass distinguished professor of chemistry, who led the team that developed the analysis method, said:  'This situation created an immediate need for an analytical method that is highly sensitive, fast, accurate and easy to use.'

'We took it as a challenge to use simpler instrumentation and to develop a faster method that allows the testing to be done on site and does not require pretreatment of samples.'

The new method pairs mass spectrometry with a low-temperature plasma ionisation probe technique.

Mass spectrometry is a commonly used analysis method known for its sensitivity and accuracy; however, most available mass spectrometers require that a sample be pretreated and remain in the controlled environment of a vacuum for analysis, Cooks said.

The Purdue team took advantage of the recent availability of new ambient ionisation methods in which samples are examined in their native environment with little or no preparation.

Cooks said: 'Ambient ionisation methods, such as the low-temperature plasma ionisation we used, can greatly reduce the time-intensive and sometimes difficult requirements of mass spectrometers.

'The experiment can be done in a high-throughput fashion at a rate of two samples per minute.'

The method itself directs a collection of charged particles, or plasma, onto the sample using a slow stream of helium or other gas.

The plasma reacts with the sample and ionises some of the molecules, which can then be vacuumed into a mass spectrometer for analysis.

Heating the sample assists in ionisation, Cooks said.

Indianpolis-based Prosolia has commercialised Cooks's ambient ionisation technology, which is called desorption electrospray ionisation, or DESI.