I use the water method to extract the anthocyanidin from Peristrophe bivalvis (L.) Merr leave, then dilute 20 times with 0.025M potassium chloride, pH1.0 and 0.4M sodium acetate buffer, pH4.5 respectively. To measure the absorbance at 510nm and 700nm.
Set into the formula:
Anthocyanin pigment concentration(mg/liter)=(A*MW*DF*1000)/(ɛ*1) \
But now I have a problem is that the result of the A=(A510-A700)pH1.0-( A510-A700)pH4.5 is a negative value that I can’t have result from this formula.
So my question is Why A would be a negative value?
Also check https://pubmed.ncbi.nlm.nih.gov/16385975/
Article Determination of total monomeric anthocyanin pigment content...
Kindly check this collaborative study conducted to determine the total monomeric anthocyanin concentration by the pH differential method, which is a rapid and simple spectrophotometric method based on the anthocyanin structural transformation that occurs with a change in pH (colored at pH 1.0 and colorless at pH 4.5). https://academic.oup.com/jaoac/article-abstract/88/5/1269/5657437
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