I have been testing different methods for extracting phycocyanin from lake samples to get a general range in ug/L to compare with extracted Chl (in ug/L). I am using 3 freeze/thaws + sonication in phosphate buffer solution and the equation from Bennett and Bogorad (1973). I am curious what PC values others are getting in their lakes and if they use a corrected equation to estimate mg/mL (or ug/L) PC similar to below. Bottom line, how close are we to establishing a standard protocol for PC extraction and thresholds?

PC in mg/mL = OD_620 * (0.474*OD_652) / 5.34

where the OD_620 is corrected for turbidity (OD_620 - OD_750) and OD_652 is corrected for turbidity (OD_652 - OD_750).