Page:Concepts for detection of extraterrestrial life.djvu/31

 CHAPTER V

Although mass spectrometry, like gas chromatography, cannot prove the existence of life, it is an experimental tool which would enable us to learn much about the organic chemistry of Mars.

The mass spectrometer approach to exobiological studies is being carried out under the supervision of Dr. Klaus Biemann at the Massachusetts Institute of Technology. Dr. Biemann has concentrated much of his experimental work on amino acids and peptides. This method accomplishes identification through the mass spectra (i.e., the distribution of the masses) of the pyrolysis products of the introduced samples. In one type of instrument an amino acid is heated near the ion source. The molecular fragments so produced vaporize off the sample and are accelerated according to their masses onto an electron multiplier. The identification of the original amino acid is based on the characterestic masses of these fragments.

The mass spectrometer is perhaps unique for the specific identification of small amounts of compounds which have been roughly classified by other methods. While not as sensitive as color reactions, ultraviolet absorption and fluorometry, mass spectrometry is an extremely versatile and powerful method for identifying organic compounds. The ability to recognize organic structures, regardless of whether they do or do not show any resemblance to the molecules with which we are familiar in terrestrial biology, could be crucially important for Martian exploration.

The sample size for mass spectroscopy ranges from a few tenths to a few millionths of a milligram. Spectral interpretation is simplified if this small sample is not too complex. Therefore, some sample preparation is required, with gas chromatography being the favored method for accomplishing this.

Mass spectrometry could also provide data on the composition of the atmosphere and the abundance of ratios of stable isotopes of the elements of low atomic number. Both of these areas are of obvious relevance to the biological exploration of celestial bodies within the solar system.

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