Figure 1.

 Comparison of low and high trypsin digestion protocols. Recombinant HAs from A/Brisbane/59/2007 and A/Vietnam/1203/2004 were spiked into a preparation of A/Wisconsin/15/2009 at concentrations of 63·2 and 64·4 μg/ml, respectively. A trypsin to protein ratio of 1:10 or 2:1 was used for the low or high trypsin digestion protocol, respectively. For absolute quantification, a mixture of synthetic peptides was used as an internal standard. Data shown are representative of the results of three biological replicates, each of which was obtained from three technical replicates.