Converting A/I values (ion exchange) to D/L values (reverse phase) for amino acid geochronology

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• 作者：Katherine E. Whitacre^a ; Darrell S. Kaufman^a ; ^{darrell.kaufman@nau.edu} ; Matthew A. Kosnik^b ; Paul J. Hearty^c
• 关键词：Amino acid racemization ; Isoleucine epimerization ; Quaternary geochronology
• 刊名：Quaternary Geochronology
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：37
• 期：Complete
• 页码：1-6
• 全文大小：708 K
• 卷排序：37

文摘

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.