Converting A/I values (ion exchange) to D/L values (reverse phase) for amino acid geochronology |
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Institution: | 1. Department of Mining Exploitation and Prospecting, University of Oviedo, 33004 Oviedo, Spain;2. Escuela Superior Politécnica del Litoral, ESPOL, Facultad de Ciencias Naturales y Matemáticas, Campus Gustavo Galindo Km 30.5 Vía Perimetral, P.O. Box 09-01-5863, Guayaquil, Ecuador;2. Department of Oceanography, Texas A&M University, College Station, TX, USA;3. Sequoia Scientific, Inc., 2700 Richards Road, Suite 107, Bellevue, WA 98005, USA;4. University of Washington, School of Oceanography, Box 357940, Seattle, WA 98195, USA;5. National Institute of Marine Geology and Geoecology, 23-25, Dimitrie Onciul Street, RO 024053 Bucharest, Romania |
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Abstract: | Several analytical techniques have been used in amino acid geochronology to measure the relative abundances of D- and L-enantiomers. During the past two decades, reverse-phase (RP) liquid chromatography has become most common, whereas ion-exchange (IE) liquid chromatography was widely used prior to the mid-1990s. This study is based on intra-lab paired analyses of RP and IE liquid chromatography to mathematically convert A/I (allo-isoleucine:isoleucine) values determined with IE to corresponding D/L values for comparison with new RP results. Pooled results of 340 paired IE and RP analyses show that A/I values can be confidently converted to equivalent D/L values for aspartic acid, glutamic acid, alanine, valine and isoleucine, with 2σ uncertainties of ±24–41% depending on the amino acid. For specific sample types including gastropod, bivalve, eggshell and whole rock, A/I can readily be converted to D/L aspartic acid and D/L glutamic acid with 2σ uncertainties of ±20% and 26%, respectively, using sample-type-specific relations. A/I is also reliably converted to D/L valine and D/L isoleucine with 2σ uncertainties of ±31 and 35%, respectively. Regression equations are provided to convert A/I to an equivalent D/L value for five amino acids, thereby enabling the large literature base of AAR results from IE chromatography to be compared and integrated with AAR results from RP chromatography. |
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Keywords: | Amino acid racemization Isoleucine epimerization Quaternary geochronology |
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