Understanding protein structure and function requires high-quality samples and assays performed under optimal buffer conditions. This application note uses well-characterized proteins to demonstrate how the mass photometer MyMass™ quickly assesses sample purity and homogeneity using nanograms of sample. MyMassMP measurements work across a broad mass range (55 kDa–3 MDa) and in a range of different buffers, and take just one minute. Employing mass photometry technology, MyMassMP measures the mass of single proteins in solution. With its speed, ease of use, and broad applicability, MyMassMP offers a powerful alternative to SDS-PAGE, SEC, and DLS for routine sample evaluation.