Simple identification of a cross-linked hemoglobin by tandem mass spectrometry in human serum

Hemoglobin-based oxygen therapeutics are prepared by reaction of hemoglobin with cross-linking molecules and are utilized as blood substitutes. They can be used as doping agents to increase the oxygen-carrying capacity of hemoglobin. We have compared a glutaraldehyde-polymerized bovine hemoglobin (Oxyglobin, Biopure Corp.) with natural bovine hemoglobin by mass spectrometry in order to detect specific fragment ions of the cross-linked protein for further potential applications in doping control of human blood samples. HCl acid (6 N) hydrolysis was performed in parallel on both proteins. Hydrolysates were then analyzed by direct infusion electrospray mass spectrometry (ESIMS) using a triple quadrupole mass spectrometer. Confirmation and precision were obtained by LC-ESIMS(n) experiments performed on an ion trap mass spectrometer. Chromatographic and mass spectrometry data allowed detection of two potential Oxyglobin-specific ions--m/z 299 and 399--that were shown to lose a 159 u neutral fragment under collision-induced dissociation conditions. Thus, monitoring of constant neutral loss of 159 u on acid hydrolysates of human serum samples spiked with different amounts of Oxyglobin has proved to be an efficient screening method to specifically detect and identify Oxyglobin. LC-MS of the spiked serum sample hydrolysates enabled detection of Oxyglobin at a detection limit of 4 g x L(-1).