D-Amino acids indicate aging, bacterial origin, and pathogenic properties of peptides. in the environment, but the reliable assessment of D-enantiomers must account for a yet unknown formation during hydrolyses. Here, we introduce a method for the in vitro determination of the hydrolysis-induced racemization (HIR) of amino acids, in environmental samples. It involves hydrolyses with hydro-and deuteriochloric acid (6 M, 12 h, 105 degreesC), desalting, and selective detection of chiral Mass fragments of amino acid-N-pentafluoropropionyl derivatives. D-Amino acids formed in (HCl)-H-2 incorporated deuterium into their C-alpha position. This resulted in a relative signal loss of the nondeuterated fragment compared with the (HCl)-H-1 hydrolysate. Mathematically evaluating the relative target signal intensities of both hydrolysates allowed the quantification of the proportion Of D-amino acids formed during sample processing. Side-chain incorporations of deuterium were no limitations for this method as they could be estimated from that of the respective L-enantiomers. In soil and litter samples, between O (D-glutamic acid) and 85% (D-alloisoleucine) of the detected D-amino, acids were formed upon hydrolysis (standard error, 5-11%). For a given amino acid, the HIR varied by a factor, of 2-10 between samples, thereby confirming that HIR must be individually assessed for samples from different environments.