AAT Bioquest

How do you determine the concentration of PE [R-Phycoerythrin] (Cat#2258) using a NanoDrop™ 2000 Spectrophotometer?

Posted January 17, 2018

I purchased PE [R-Phycoerythrin] (Cat# 2558) to label purified antibodies. The Certificate of Analysis indicates that PE has a concentration of 20.0 mg/mL, how was the concentration calculated?


First, it is important to note that PE (Cat#2558) is preserved in 60% ammonium sulfate as precipitate. Prior to using PE make sure to purify or perform a buffer exchange.

To calculate the concentration of PE you must measure the absorbance of your stock solution at 565 nm (not 280 nm). Then calculate concentration using the following equation:

  • Molecular Weight of PE is 240,000
  • Extinction Coefficient of PE is 1,960,000 M-1 cm-1 (value located in AAT Bioquest’s Extinction Coefficient Database)
  • Dilution Factor is 1 since initial stock solution was not diluted after measuring absorbance.


Insert your recorded absorbance value in the above equation to calculate concentration.

If you are using a NanoDrop 2000 Spectrophotometer dilute PE to 0.5 ~ 1.0 mg/ml in PBS, and transfer 2 ~ 3uL to a cuvette to measure absorbance. Use this absorbance value to calculate concentration.

You can also use our Protein Concentration Calculator located under the Tools section of our website for calculating concentrations of common proteins and custom sequences.  

Additional resources

PE Product Page