Aspartic acid enantiomer quantification using ultraperformance liquid chromatography–tandem mass spectroscopy combined with deuterium‐chloride hydrolysis to improve age estimation in Antarctic minke whale Balaenoptera bonaerensis

Abstract

AbstractAspartic acid racemization is a useful tool for estimating age in marine mammals; however, acid hydrolysis during sample preparation may increase the D‐ to L‐enantiomer ratio. To improve age estimation in Antarctic minke whale (Balaenoptera bonaerensis), we optimized the quantification of aspartic acid enantiomers in ocular lens by using ultraperformance liquid chromatography–tandem mass spectrometry combined with sample preparation by hydrolysis with deuterium chloride. Using this approach, we determined D/L in fetal and adult whale lens, examined the degree of racemization induced by acid hydrolysis, and constructed equations for age estimation. In the fetal lens, D/L obtained after hydrolysis with HCl or DCl were positively correlated with gestation age. Estimates of D/L at birth using a DCl‐hydrolysis model were much lower than those obtained using a HCl‐hydrolysis model, indicating that racemization during hydrolysis with HCl reduces the precision of subsequently derived age estimates. Furthermore, the D/L0 unaffected by Asp‐D generated during hydrolysis was estimated. The loge[(1 + D/L)/(1 − D/L)] value was exponentially increased with increasing earplug‐derived age, and the standard error of the age estimates after hydrolysis with DCl was lower than that after HCl. We conclude that our method can provide precise age estimates without methodological bias.