FIG 5.

Multiple charge states acquired by high-resolution MS for ECU. Normal human serum was spiked with ECU at 100 μg/ml and enriched for Ig with Melon Gel. After ESI, the light chains acquired multiple charge states and were detected with an Orbitrap (Thermo Fisher) instrument. (A) Mass spectrum of the +12, +11, and +10 charge states. Utilizing low-resolution scanning, the areas under the curve of one or multiple charge states are added together for quantitation of the MAb. By using a high-resolution view, the area under the curve of multiple isotopes of a given charge state can be analyzed. (B) Isotopic distribution of a +11 charge state.