Table 2.

Calculated proportion of the spiked toxin (Stx1a or Stx2a) detected in filtered human serum relative to that detected in unfiltered spiked human serum (HS). Identical amounts of Stx1a or Stx2a were spiked into human serum that was unfiltered or filtered through a 100,000 Da (100 K) or 300,000 Da (300 K) MWCO filter. The resulting samples were reduced/alkylated/trypsin digested and then analyzed by mass spectrometry.

Sample Description	Proportion
Stx1a + HS	1.00
Filtered HS (100 K) + Stx1a	0.99
Stx1a + HS, Filtered (100 K)	0.13
Filtered HS (300 K) + Stx1a	0.59
Stx1a + HS, Filtered (300 K)	0.15
Stx2a + HS	1
Filtered HS (100 K) + Stx2a	326
Stx2a + HS, Filtered (100 K)	14
Filtered HS (300 K) + Stx2a	115
Stx2a + HS, Filtered (300 K)	5