Spot analyses of GER2B, Wil1A, and GER2B were bracketed by analyses of NIST610, SagaB, Harvard 98983, Phalaborwa and MicaMg RMs. Spot size was 65 µm at a repetition rate of 10 Hz and a fluence of 5.0 J/cm 2 . One spot analysis comprised 30 seconds of gas blank and a 30 second period to allow for complete wash-out of the aerosol. The length of the actual ablation interval was 40 s during "GER2B/Wil1A spot", and "GER2B spot" and 60 s during "homogeneity".