Determination of platinum and palladium in NIST automobile catalyst SRMs by INAA

The National Institute of Standards and Technology (NIST) has recently responded to a request by the International Precious Metals Institute (IPMI) to jointly develop two recycled automobile catalyst materials as standard reference materials (SRMs). The need for these materials was demonstrated by two IPMI round-robin analyses, which resulted in considerable variability for the three primary elements of interest: platinum, palladium, and rhodium. Two reclaimed and processed materials, one each of pellet and monolith catalysts, were donated for the project. The overall project coordination was by J. Kane of the NIST Standard Reference Materials Program (SRMP). As is the case for most NIST SRMS, at least two different in-house analytical techniques are used to certify each element to reduce the possibility of unrecognized systematic bias in the analysis. The possibility of unrecognized systematic bias is minimized if the two analytical techniques selected are very different, having few common errors. If appropriate, neutron activation analysis (NAA) is often selected for one of the techniques because, in many cases, it is able to determine the element of interest nondestructively (i.e., without errors attributed to dissolution), and also because errors based on the nuclear characteristics of the atom are very different from most other analytical techniques that are subject to errors related to the electronic characteristics of the atom of interest. Instrumental NAA (INAA) was selected as one of the NIST techniques for determination of platinum and palladium but was unable to determine rhodium in these samples. The second NIST technique was isotope dilution inductively coupled plasma mass spectrometry, Nine IPMI laboratories that participated in the second round robin also analyzed the two materials and submitted their data to the SRMP