Interlaboratory Comparison of Amino Acid Enantiomeric Ratios in Fossil Pleistocene Mollusks

Abstract

Enantiomeric (d/l) ratios of eight amino acids in three homogeneous powdered fossil Pleistocene mollusk samples have been compared. Eleven laboratories have contributed results to this effort. Three gas chromatographic methods and one ion-exchange chromatographic method were used. In general, the coefficients of variation (c.v.) are best for alanine, glutamic acid, and aspartic acid (3–8%). For leucine and phenylalanine, the c.v.'s are between 5 and 10%. For isoleucine, proline, and valine the c.v.'s range from 10 to 18%. Individual laboratories usually report analytical precision of between 2 and 5%, but it is clear that significant differences between laboratories' results are often encountered, and that these analytical differences could, in some cases, lead to very significant differences (25% or more) in age estimates based upon enantiomeric ratios. Multiple analyses of desalted hydrolyzates of these powder samples suggest that interlaboratory differences are often caused by instrumental and/or derivatization procedures rather than the wet-chemical sample preparative steps. It is proposed that the powder samples described here be used in all future publications of fossil amino acid enantiomeric ratio data.

Climatic cycles inferred from the aminostratigraphy and aminochronology of Quaternary dunes and palaeosols from the eastern islands of the Canary Archipelago

“…This is based on the analysis of samples from an inter-laboratory comparison exercise (cf. Wehmiller, 1984;Torres et al, 1997). The isoleucine epimerisation (D-aIle/L-Ile) values ranging between 0.45 and 1.1 obtained by IE-LC are approximately 0.10 lower than those obtained by GC in our laboratory, i.e.…”

Foraminiferal isoleucine epimerization determinations from the Nar Valley Clay, Norfolk, UK: implications for Quaternary correlations in the southern North Sea basin

“…The Interlaboratory Calibration Standards (Wehmiller, 1984) analysed at BAL in January 1991 gave the following results (total fraction): 81 ILC A 0.150 ± 0.006 (n = 5), 81 ILC B 0.430 ± 0.007 (n = 4), 81 ILC C 0.974 ± 0.020 (n = 3). …”

Amino acid geochronology: its impact on our understanding of the Quaternary stratigraphy of the British Isles

“…Foraminifera were analysed from deep-sea cores (Bada et al, 1970), while the development of shell aminostratigraphies from the Atlantic coast formed the first tests of the ability for amino acids to be used for correlation over large distances, along with the effect of temperature on the observed extent of racemization (Mitterer, 1975). Interlaboratory calibration samples were sent to amino acid labs around the world in an attempt to identify and quantify systematic offsets between different methods of analysis and labs (Bada et al, 1979;Kvenvolden, 1980;Wehmiller, 1984). Recommendations for protocols were published, underpinning the fast-developing field, and a meeting in 1978 on 'Advances in the Biogeochemistry of Amino Acids' led to a useful publication of the state of the art .…”