I am estimating the total phenolic content (TPC) of 70% ethanol plant extract using the Folin-Ciocalteu method. My samples are rich in phenolics, so I need to dilute them to proper concentration before the measurement. I observed that when I am using 70% ethanol to dilute the samples I obtain higher TPC value then when I am using water. The rest of the method remains the same. What could be a reason of this variability?
I agree with Nirmal. Enhanced solubility of phenolics in alcohol is well known and hence the variability in your experiment. Another possible, though less plausible, could be degradation of some phenolic compounds when you dissolve your extract in water alone.
Dear
Like dissolve like, alcohols such as methanol and ethanol are able to dissolve high amounts of phenolic compounds due to the affinity of formation of hydrogen bonds and polarity similarity. Nevertheless their are non polar phenolic compounds which can be extracted better with the less polar solvents, however it also can be gained with alcohols due hydrogen bonds. But the use of water in such case will not be sufficient.
Sometimes the extraction of polyphenols in particular solvents is not because of the solubility of components; it may be due to the chemical interactions. So, it is better to use the extracting solvent which had used during experiments for dilution. You can use the same solvent for dilution before going to TPC assay.
Alcohol especially methyl alcohol may be a suitable solvent for phenol. For alkyl substituted phenols, ethanol can be used. For pure, simple phenol or polyhydroxy phenol water can be a better solvent.
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