Two different spectrophotometers are available for determining protein concentration, providing redundancy as well as increased confidence in measurements.
MacCHESS provides a GE NanoVue Plus spectrometer for determining concentrations using the A280 method. Concentrations can be measured on volumes of 3 microliters of less. You will need to know the molar extinction coefficient and the corresponding molecular mass of the monomer unit.
The accuracy of the device is regularly checked with a BSA standard calibrated against a NIST standard (https://www.thermofisher.com/us/en/home/life-science/protein-biology/protein-assays-analysis/protein-assays.html) at 2.00 +/-0.03 mg/ml. Our 09/25/2012 reading gives 1.92 +/- 0.03 on six samples (4% error).
NanoVue Plus manual can be found here.