A major advance in the application of mass spectrometry to macromolecules came with the development of techniques to overcome which problem?

A) Macromolecules were insoluble in the solvents used in mass spectrometry.
B) Mass spectrometric analyses of macromolecules were too complex to interpret.
C) Mass spectrometric analysis involved molecules in the gas phase.
D) Most macromolecules could not be purified to the degree required for mass spectrometric analysis.
E) The specialized instruments required were prohibitively expensive.