Lowry Protein Assay Protocol (from Scott Hsieh)
Solution A: 4 mg/mL NaOH and 20 mg/mL Na2CO3 in water
Add 2 g of NaOH and 10 g of Na2CO3 to 400 mL water while stirring until completely dissolved,
then adjust volume to 500 mL.
Solution B: 10 mg/mL Potassium Sodium Tartrate and 5 mg/ mL CuSO4 in water
Add 100 mg Potassium Sodium Tartrate and 50 mg CuSO4 (cupric sulfate) (do not weigh on
Merchant lab balances) to 8 mL of water in a plastic falcon tube (do NOT use Merchant lab
glassware for solutions containing copper). Shake the mixture until solids are completely
dissolved, then adjust volume to 10 mL.
Mix solutions A and B and store at 4˚C this is called Lowry’s solution and should be usable for
up to six months. (50:1 mix of solutions A and B)
General comments
Before doing the assay it is important to know whether or not your samples contain interfering
species. The easiest way to do this is to prepare your samples as described in step #2 but
alongside also prepare a set of tubes containing your sample plus a known amount of protein
(BSA) to each sample. Should there be no interfering species your curves should run roughly
parallel to each other. If there is an interfering species then the curves will not run parallel.
Sample Curve to Test for Interference
(No interference)
y = 0.055x + 1E-16
R2 = 1
y = 0.055x + 0.2
R2 = 1
0
0.1
0.2
0.3
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0.5
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0.8
0246810
uL Sample added
Abs.
Standard alone
Protein + standard
Linear (Standard
alone)
Linear (Protein +
standard)
