Determination of carbon isotope ratios in amino acids, proteins, and oligosaccharides by inductively coupled plasma-mass spectrometry.
Carbon isotope ratios ((12)C/(13)C) are measured for aqueous solutions of tryptophan, myoglobin, and beta-cyclodextrin using C(+) ions from an inductively coupled plasma (ICP) and a prototype twin quadrupole mass spectrometer (MS). (13)C/(12)C ratios can be determined with a relative standard deviation (RSD) of approximately 1%. This precision is close to the limiting value predicted by counting statistics (1.16%). Spectral interference on (13)C(+), presumably from (12)C(1)H(+), comes from the incomplete dissociation of myoglobin and/or beta-cyclodextrin, but not tryptophan. Decreasing the aerosol gas flow rate slightly from that which yields maximum signal eliminates this (12)C(1)H(+) interference. The count rate of the minor isotope ((13)C(+)) can be artificially enhanced by increasing the voltage of the (13)C(+) 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.
Luong
Elise T
ET
Department of Chemistry, Ames Laboratory, United States Department of Energy, Iowa State University, Ames 50011, USA.
Houk
R S
RS
D000596:Amino Acids / Q000737:chemistry*; D002138:Calibration; D002247:Carbon Isotopes / Q000032:analysis; D003505:Cyclodextrins / Q000737:chemistry; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D009211:Myoglobin / Q000737:chemistry; D009844:Oligosaccharides / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D012680:Sensitivity and Specificity
D000596:Amino Acids; D002247:Carbon Isotopes; D003505:Cyclodextrins; D009211:Myoglobin; D009844:Oligosaccharides; D011506:Proteins