Refractometry

Gets a fast concentration or purity readout by measuring exactly how much a solution bends light passing through it, a property that shifts predictably with dissolved content.

References

• Frings, C.S., Battaglia, R.V., Kingsley, G.R. "Refractometric Determination of Serum Protein." American Journal of Clinical Pathology 49, no. 4 (1968): 474–480.