DIRECT ANALYSIS OF CARBON-ISOTOPE VARIABILITY IN ALBUMINS BY LIQUID FLOW-INJECTION ISOTOPE RATIO MASS-SPECTROMETRY

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.