Taurine is a sulfur-containing amino acid, and sulfur has a unique effect on the isotope cluster of peptides in mass spectrometry data because 4.2% of sulfur isotopes are 34 S which contain two neutrons more than 32 S. Therefore, high resolution mass spectra of relative abundances within the isotope cluster can be used to evaluate the inclusion of sulfur. Addition of taurine to a peptide necessarily shifts the cluster in favor of the third peak in the cluster more than the addition of the same mass from some other combination of C, H, N, or O due to the presence and effect of 34 S. This effect is most noticeable for small peptides given that the isotope cluster of small peptides that do not contain sulfur is dominated by the distribution of 13 C and 2 H, which enhance the second isotopic peak much more than the third one.