characteristic mass for peak absorption, Math - title in electrothermal atomization

https://dx.doi.org/10.1351/goldbook.C00979
That mass of analyte which produces a defined peak absorbance of 0.0044 (or 1% absorbance).
Source:
PAC, 1992, 64, 253 (Nomenclature, symbols, units and their usage in spectrochemical analysis - XII. Terms related to electrothermal atomization (IUPAC Recommendations 1992)) on page 258