A team of investigators from Max Planck Institute for Chemical Ecology in Jena and the Czech Academy of Sciences in Prague has developed a modified mass spectrometry device that can identify ions below 500 daltons:
Matrix-Assisted Laser Desorption/Ionization (MALDI), wherein bio-molecules (e.g. proteins) are co-crystallized with a chemical substance called a matrix subsequently irradiated with a laser leads to the formation of protein ions which can be analyzed and detected.
However, matrices used in the MALDI technique have a substantial disadvantage: the laser beam not only forms ions from the substances of interest; it also forms low-mass ions (less than 500 Da) originating from the matrix. "Because of these small interfering ions we were not able to analyze small molecules that play crucial roles in the metabolism of organisms," explains Aleš Svatoš, head of the mass spectrometry/proteomics research group at the Max Planck Institute. "The ions that originated from conventional matrices were like a haystack in which we wanted to find a few and important needles." Therefore the MALDI technique found only limited application in the field of "metabolomics".
Instead of improving the search for the "needles", i.e. metabolites such as sugars, fatty acids, amino acids, and other organic acids, the scientists began to alter the matrices with which the samples were applied so that no more interfering matrix-related ions were generated. In other words: they tried to remove the haystack to make the needles visible. The researchers succeeded with the help of physical and organic chemistry, based on the Brønsted-Lowry acid-base theory, and formulated conditions for rational selection of matrices that did not generate interfering ions but provided rich mass spectra of particular kinds of metabolites in real samples.
With the new experimental protocols they called "Matrix-Assisted Ionization/Laser Desorption – MAILD", the scientists were able to quickly and reliably determine more than 100 different analytes from single and small-sized samples.
The new MAILD method allows measurements from diverse biological and medical materials. Apart from plant and insect samples the scientists also studied a clinical sample: they were able to determine a wide range of blood-specific organic acids in one drop of human blood, smaller than a micro liter. In medical diagnostics such measurements are still conducted with intricate methods. If the scientists succeed in not only identifying, but also quantifying the metabolites, MAILD could develop into a fast method for medical and biological diagnostics.
More from the Max Planck Society for the Advancement of Science: New mass spectrometric method…
Open access article at PNAS: Acid- base-driven matrix-assisted mass spectrometry for targeted metabolomics…
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