INDUCTIVELY-COUPLED PLASMA MAGNETIC-SECTOR MASS-SPECTROMETRY METHOD FOR STABLE LEAD-ISOTOPE TRACER STUDIES

Studies in our laboratory and elsewhere require the analyses of stable lead (Pb) isotopes at sub-ppb Iel els as tracers of lead metabolism a nd therapeutic chelation treatment in animal models and humans. While analytical alternatives such as thermal ionization mass spectrometry ( TIMS) provide excellent isotope measurement sensitivity and precision, TIMS is not well-suited for rapid throughput of large numbers of biol ogical samples. Here me report the development of an inductively coupl ed plasma magnetic sector mass spectrometry (Finnigan MAT Element) met hod, possessing suitable lead isotope measurement sensitivity and prec ision for use in biologically stable lead isotope tracer studies in wh ich the natural relative abundance of one or more isotopes (i.e., Pb-2 04, Pb-206, Pb-207, or Pb-208) has been enriched by > 5%. Standard ref erence materials (SRMs) NBS 981 lead isotope standard and four differe nt NIST biological SRM materials mere spilled with bismuth-209 as an i nternal standard, and analyzed at lead concentrations of 1-10 ppb, The method consisted of 300 passes per sample for masses 201, 204, 206, 2 07, 208 and 209, with a total analysis time of about five minutes per sample. Concentrations for Pb-204, Pb-206, Pb-207, and Pb-208 were det ermined by comparison to a certified lead concentration standard that had been isotopically characterized by TIMS. Analyses of lead concentr ations in the NIST biological SRMs yielded a measurement accuracy (rec overies) of 96-101%, with a detection limit of 0.013 ppb total lead. A ccuracy of isotope abundance analyses of NBS SRM 981 (n =12) mas 99.92 -99.99% of that expected for all four isotopes, with a measurement pre cision of 0.07-0.22% RSD. Thus, this method is ideally suited for the rapid, accurate, and precise measurements of lead concentrations and s table isotope abundances in lead isotope tracer studies in animals and humans, where one or more lead isotopes are enriched above natural le vels.