High-resolution (HR) analysis or accurate mass measurement can be obtained for samples analyzed by electrospray ionization, electron impact and chemical ionization. Samples submitted for electrospray ionization will automatically be analyzed at high resolution (at least 30,000) with a mass measuring accuracy of 5 ppm or better (up to m/z 2,500) using the LTQ-FT instrument.
EI and CI analyses are performed on a magnetic sector mass spectrometer. To obtain an accurate mass measurement, an internal standard or reference compound is added to your sample. Users will have to obtain a low-resolution (LR) spectrum of their compound before a high-resolution spectrum is requested. Students are encouraged to examine their LR spectrum before proceeding with a request for HR. If the LR spectrum indicates the presence of an impurity ion within 10 Da of the ion of interest, we may not be able to proceed with the high resolution experiment.
For EI and CI accurate mass measurements are performed at 10,000 resolution (10% valley definition). The expected mass measuring accuracy depends on the molecular weight of your compound:
• up to m/z 600: within 3 mDa
• up to m/z 1000: within 6 mDa
• up to m/z 1500: within 10 mDa
For compounds with molecular weights exceeding 1,500 Da, identifying a suitable reference compound becomes troublesome. Sometimes previously analyzed samples may be suitable as reference compounds. If the molecular weight of your compound exceeds 1,500 Da and you need accurate mass measurement, please consult with facility staff prior to submitting your sample.
Our EI/CI mass spectrometer is equipped with a gas chromatograph. Please contact facility staff, if you are interested in obtaining accurate mass measurements directly from a GC run.