Pressure effects on protein mass spectra in an ion mass spectrometer (2008)
Undergraduates: Arthur Wilson, Brittany Butler
Faculty Advisor: Gary Glish
Department: Chemistry
Mass spectrometry can be used to elucidate structures of molecules. Most quadrupole ion trap mass spectrometers use a bath gas to aid in analyte detection. Helium bath gas pressure in a quadrupole ion trap affects the appearance of mass spectra for different protein samples. A study is being performed to determine the effect of bath gas pressure on charge state distribution and overall ion intensity for proteins. The proteins involved in this study include cytochrome c, lysozyme, ubiquitin, and myoglobin. The normal operating pressure of the quadrupole ion trap is approximately 4.2 x 10-5 mbar. Each protein is being studied over a pressure range of 4.0 x 10-5 mbar to 5.2 x 10-5 mbar. Changes in signal intensity are observed as the pressure is increased above the normal operating pressure. Pressure affects the signal intensity for each protein differently. These results demonstrate that the bath gas pressure is an important parameter in the appearance of protein mass spectra. Also, the optimal bath gas pressure may be protein dependant. For example, signal intensity of cytochrome c increases as pressure increases. At a pressure of 4.3 x 10-5 mbar, the maximum signal is observed. Above this pressure, the signal intensity then decreases. The overall signal intensity for all four proteins decreases as pressure approaches 5.2 x 10-5 mbar. Studying the effects of pressure on different proteins can lead to a better understanding of protein conformation.