Stable isotope dilution analysis of pipecolic acid in cerebrospinal fluid, plasma, urine and amniotic fluid using electron capture negative ion mass fragmentography. - Kok,R.M.; Kaster,L.; de Long,A.PJM.; Poll-The,B.T.; Saudubray,J.M.; Jakobs,C. (Clin Chim Acta, 1987)