TY - JOUR
T1 - Converting A/I values (ion exchange) to D/L values (reverse phase) for amino acid geochronology
AU - Whitacre, Katherine E.
AU - Kaufman, Darrell S.
AU - Kosnik, Matthew A.
AU - Hearty, Paul J.
N1 - Funding Information:
The Amino Acid Geochronology Laboratory (AAGL) at Northern Arizona University is funded by the National Science Foundation ( EAR-1234413 ). We thank Jordon Bright for analyzing many of the samples, AAGL collaborating scientists for allowing us to use their samples for this study, and Kirsty Penkman and an anonymous reviewer for their helpful suggestions.
Publisher Copyright:
© 2016 Elsevier B.V.
PY - 2017/2/1
Y1 - 2017/2/1
N2 - 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.
AB - 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.
KW - Amino acid racemization
KW - Isoleucine epimerization
KW - Quaternary geochronology
UR - http://www.scopus.com/inward/record.url?scp=84992708792&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84992708792&partnerID=8YFLogxK
U2 - 10.1016/j.quageo.2016.10.004
DO - 10.1016/j.quageo.2016.10.004
M3 - Article
AN - SCOPUS:84992708792
SN - 1871-1014
VL - 37
SP - 1
EP - 6
JO - Quaternary Geochronology
JF - Quaternary Geochronology
ER -