Precise determination of mass-dependent variations in the isotopic composition of molybdenum using MC-ICPMS

We present an analytical approach for the precise determination of mass-dependent differences in the isotopic composition of Mo between samples and reference standards using multiple-collector magnetic sector inductively coupled plasma mass spectrometry (MC-ICPMS). Either Zr or Ru "element spikes" are employed to correct for instrumental mass bias. Differences in Mo-95/Mo-97 can be determined to a precision of +/- 0.2%o (+/-2 sigma) using 1-10 mug of Mo. Similar precision is possible for other ratios after correction for isobaric interferences from either spike element. This approach facilitates study of mass-dependent variations in the isotopic composition of Mo in nature and in materials produced by laboratory processes; We observe fractionation of Mo isotopes of similar to1.5%o/amu during ion-exchange chromatography in the laboratory and a shift of -0.3%o/amu between natural MoS2 and a laboratory standard.