Differences in graphite fumace performance characteristics require redefinition of some basic AA performance criteria. Since the magnitude of the graphite fur- nace signal observed depends on analyte mass rather than concentration, the term characteristic mass" is used as a measure ofthe sensitivity of the fumace. Char- acteristic mass is analogous to characteristic concentration for flame AA except that mass, rather than concentration, is related to absorbance. The characteristic mass of an analyte is defined as the mass ofanalyte in picograms required to pro- duce a peak height signal of 0.0044 absorbance or an integrated peak area signal of 0.0044 absorbance-seconds(A.s).