Hi, I have read other threads on the same topic but I still miss my reply, if anyone can help. I have a calibration curve for the main pigments. For some of them I do not have a DHI standard, and I would like to quantify using the ratio Area(Pigmentx)/Area(IS), knowing that my IS has a final concentration of 1mg/L in the extraction solvent. To double check the accuracy of this quantification, I tested it on pigments already quantified by calibration curve. I have observed an overestimation of 10x referring to the IS area. I can understand the IS quantification might not work for Chlorophylls, but why does it not work neither for carotenoids ? How can I alternatively quantify pigments referring to the IS? Thanks