Murray, K., Boyd, R., Eberlin, M., et al. (2013). Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013). Pure and Applied Chemistry, 85(7), pp. 1515-1609. Retrieved 8 May. 2019, from doi:10.1351/PAC-REC-06-04-06
The internal standard role is the role of compounds added in accurately known amounts to a sample to be analyzed for a specified analyte. The internal standard is chemically similar to the analyte so that losses in the analytical procedure are the same for both and thus the analyte concentration can be determined relative to that of the standard. [IUPAC]
Internal standard role is the analysis role of a chemical substance that is added in a constant amount to samples, the blank and calibration standards in a chemical analysis. [Wikipedia]