Rj. Caimi et Jt. Brenna, DIRECT ANALYSIS OF CARBON-ISOTOPE VARIABILITY IN ALBUMINS BY LIQUID FLOW-INJECTION ISOTOPE RATIO MASS-SPECTROMETRY, Journal of the American Society for Mass Spectrometry, 7(6), 1996, pp. 605-610
We demonstrate the high precision C isotopic analysis of a series of p
urified albumins by liquid chromatography-combustion isotope ratio mas
s spectrometry (IRMS) by using direct aqueous liquid injection. Albumi
ns from 18 species and albumens from chicken and turkey egg were obtai
ned from a commercial source and shown to be of > 98% purity by capill
ary zone electrophoresis and high-performance liquid chromatography. O
ne microliter of an aqueous protein solution with a total of < 40-pmol
protein (2.5 mu g), which contained about 150-nmol C, was injected di
rectly into a flowing stream of high-performance liquid chromatography
grade water. The solution passed through a pneumatic nebulizer, was s
prayed onto a moving wire, passed through a drying oven, and was combu
sted in a furnace. After the water of combustion was removed, the resu
lting CO2 gas was directed to a high precision IRMS instrument operate
d in continuous flow mode. The average precision across the 20 samples
analyzed was SD(delta(13)C) = 0.45 parts per thousand, and the averag
e accuracy was delta(13)C < 0.4 parts per thousand compared to aliquot
s analyzed by conventional preparation by using combustion tubes and d
ual inlet analysis. The observed isotope ratio range was about -22.5 p
arts per thousand < delta(13)C(PDB) < -16 parts per thousand as expect
ed for modern materials from a natural source. These results demonstra
te rapid, high precision, and accurate C isotopic analysis of untreate
d macromolecules in an aqueous stream by Liquid source IRMS.