Making Mass Spectroscopy Mobile

By Chuck Seegert, Ph.D.

Using a new sampling technique combined with a portable mass spectrometer, Purdue University researchers have created a miniaturized lab. A long list of tests can now be run rapidly without conventional sample preparation methods.

Isolating analytes or drug specimens from a biological sample is sometimes done using a method called solvent extraction. Using the sample, which is generally water-based, and mixing it with another solvent that doesn’t dissolve in water, like ethyl acetate, leads to an interface between the two. This interface resembles oil and water, another pair of solvents that don’t mix together. At the interface, molecules contained in the biological sample that are soluble in the ethyl acetate solvent are extracted or transferred from the sample to the ethyl acetate. One can then analyze these molecules using a mass spectrometer.

While solvent extraction isn’t new, a variant of the method designed by Purdue University researcher Zheng Ouyang and his team goes beyond conventional solvent extraction, according to a recent press release.

"We've converted a series of operations into a single extraction process requiring only a pinprick's worth of blood," said Ouyang, an associate professor in Purdue University's Weldon School of Biomedical Engineering, in the press release.

The new extraction method has been termed “slug flow microextraction” by the team, and it is based on traditional solvent extraction methods — but on a very small scale. Small amounts of agitation allow the biomarkers to be transferred to the solvent, isolating them and preventing impurities.

Slug flow microextraction is a single-step method that eliminates the extensive preparation normally required in the laboratory. It has high sensitivity and precise quantitation that allows the use of samples as small as 5 microliters. Enzyme functions like cholinesterase can also be followed using reactions in blood. Real-time derivatization for urine analysis of anabolic steroids has also been demonstrated, according to the study.

"The sampling ionization technologies like slug flow microextraction could make the miniature mass spectrometers perform the actual testing without requiring other equipment for sample treatment," Ouyang said in the press release. "This will bring a new class of compact medical instruments."

The new method works in conjunction with another Purdue University innovation — a miniature mass spectrometer that uses nano-electrospray ionization, according to a study published by the team in Angewandte Chemie.. While current models of mass spectrometers are cumbersome and generally weigh over 300 lbs., the latest version of the researchers’ miniature mass spectrometer is 12.5” by 16” and weighs only 40 lbs.

"The overall goal is to use this technology for developing disposable sample cartridges to work with our mini mass spectrometry system in clinical and especially the point-of-care applications in a doctor's office," Ouyang said in the press release.

Rapid and sensitive methods of detecting biomarkers continue to gain momentum in the medical diagnostics space. Recently in an article published on Med Device Online, a method of detecting cancer biomarkers was discussed that was based on a graphene microfabrication.

Image Credit: Purdue University/Weldon School of Biomedical Engineering