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Helfman, PM, Bada JL.  1975.  Aspartic-Acid Racemization in Tooth Enamel from Living Humans. Proceedings of the National Academy of Sciences of the United States of America. 72:2891-2894.   10.1073/pnas.72.8.2891   Website
Helfman, PM, Bada JL.  1976.  Aspartic-Acid Racemization in Dentin as a Measure of Aging. Nature. 262:279-281.   10.1038/262279b0   Website
Helfman, PM, Bada JL, Shou MY.  1977.  Considerations on Role of Aspartic-Acid Racemization in Aging Process. Gerontology. 23:419-425.Website
Hoopes, EA, Peltzer ET, Bada JL.  1978.  Determination of Amino-Acid Enantiomeric Ratios by Gas-Liquid Chromatography of N-Trifluoroacetyl-L-Prolyl-Peptide Methyl-Esters. Journal of Chromatographic Science. 16:556-560.Website
Hutt, LD, Glavin DP, Bada JL, Mathies RA.  1999.  Microfabricated capillary electrophoresis amino acid chirality analyzer for extraterrestrial exploration. Analytical Chemistry. 71:4000-4006.   10.1021/ac9903959   AbstractWebsite

Chiral separations of fluorescein isothiocyanate-labeled amino acids have been performed on a microfabricated capillary electrophoresis chip to explore the feasibility of using such devices to analyze for extinct or extant life signs in extraterrestrial environments. The test system consists of a folded electrophoresis channel (19.0 cm long x 150 mu m wide x 20 mu m deep) that was photolithographically fabricated in a 10-cm-diameter glass wafer sandwich, coupled to a laser-excited confocal fluorescence detection apparatus providing subattomole sensitivity. Using a sodium dodecyl sulfate/gamma-cyclodextrin pH 10.0 carbonate electrophoresis buffer and a separation voltage of 550 V/cm at 10 degrees C, baseline resolution was observed for Val, Ala, Glu, and Asp enantiomers and Gly in only 4 min. Enantiomeric ratios were determined for amino acids extracted from the Murchison meteorite, and these values closely matched values determined by HPLC. These results demonstrate the feasibility of using microfabricated lab-on-a-chip systems to analyze extraterrestrial samples for amino acids.