Abstract
Carbon isotope ratios (12C/13C) are measured for aqueous solutions of tryptophan, myoglobin, and β-cyclodextrin using C+ ions from an inductively coupled plasma (ICP) and a prototype twin quadrupole mass spectrometer (MS). 13C/12C ratios can be determined with a relative standard deviation (RSD) of ∼1%. This precision is close to the limiting value predicted by counting statistics (1.16%). Spectral interference on 13C+, presumably from 12C1H+, comes from the incomplete dissociation of myoglobin and/or β-cyclodextrin, but not tryptophan. Decreasing the aerosol gas flow rate slightly from that which yields maximum signal eliminates this 12C1H+ interference. The count rate of the minor isotope (13C+) can be artificially enhanced by increasing the voltage of the 13C+ detector, and/or by shifting the ion beam splitter offset from the central axis. Instrumental modifications to the MS that improve the sensitivity are also described.
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Published online March 10, 2003
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Luong, E.T., Houk, R.S. Determination of carbon isotope ratios in amino acids, proteins, and oligosaccharides by inductively coupled plasma-mass spectrometry. J Am Soc Mass Spectrom 14, 295–301 (2003). https://doi.org/10.1016/S1044-0305(03)00003-5
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DOI: https://doi.org/10.1016/S1044-0305(03)00003-5