After using the same reagents for the Lowry assay and seeing the color yield in the standard curve gradually decreasing year by year, we decided to make new reagents last year. Sure enough the color yield was restored, but in the next assay a few weeks later the blank was unusually high. after a month the blank read nearly 1 AU.
The problem was, we stored the alkaline reagent (NaOH + Na2CO3)in a polycarbonate bottle. I like polycarbonate because it is transparent and hard like glass, but lighter and less breakable. But polycarbonate is a polyester of Bis-phenol A with carbonic acid. Apparently the high pH slowly hydrolyzes the ester linkages, or the plastic retains some monomers that slowly leach out, and (duh!) bis-phenol A gives a positive reaction with the Folin-Ciocalto phenol reagent. ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
