Boltzmann constant in spectrochemical analysis

https://dx.doi.org/10.1351/goldbook.B00695
Fundamental physical constant: k = R L = 1.380 6504 24 × 10 −23 J K −1, where R is the gas constant and L the Avogadro constant.
Source:
PAC, 1996, 68, 957 (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 963