How do mass spectrometers identify the presence of sulfur in organic compounds?

In mass spectrometry, the presence of sulfur in organosulfur compounds is primarily identified through the analysis of isotope patterns. Specifically, the occurrence of sulfur-34 (${}^{34}$S) peaks serves as a diagnostic indicator, as this isotope has an abundance of 4.4 percent relative to the more common sulfur-32 (${}^{32}$S) isotope.1

Additionally, these compounds frequently produce strong molecular ions in which the positive charge is located predominantly on the sulfur atom. While mass spectrometry generally functions by ionizing molecules and separating the resulting fragments based on their mass-to-charge ratio, these specific isotopic and charge-localization characteristics allow chemists to confirm the presence of sulfur within an organic structure.12