I have seen different methods adding KOH in methanol for the extraction of Polynuclear aromatic hydrocarbons in different ways. Some researchers have added it before the Soxhlet's extraction and some after it.
What are the functions of adding KOH when extracting PAH from fish samples and what is the correct way to use it? Thank you
Adding KOH causes hydrolysis proteins and lipids, which often increases the yield of PABs
Adding KOH causes hydrolysis proteins and lipids, which often increases the yield of PABs
Hydrolysis of some reactive compounds can be done by using water only. For other compounds (such as esters or amides), the choices are : 1) Acidic hydrolysis in which water is aided by an acid catalyst or 2) Basic hydrolysis in which a base "usually hydroxide" is used besides water.
The second reaction is called saponification. Historically, an oil or fat has been treated with an aqueous solution of NaOH to produce soap. Alternatively, KOH in methanol could be used for saponification which involves the conversion the triesters of glycerol "fatty or oily material" into fatty acids "long chain carboxylic acids".
When fish or other animals take on PAHs, these compounds get accumulated mostly in the lipid part of tissues and they become held well undergoing harmful changes. Applying saponification by using KOH/MeOH eases their release.
In the attached reference (which I think is very relevant to your research project on fish), KOH is used in the 3rd step before extraction.
https://tools.thermofisher.com/content/sfs/brochures/TG-51991-Determination-PAH-Aliphatic-Hydrocarbons-Fish-TG51991-E.pdf
I have found through papers on food that the matrix especially rich in fats can be saponified or hydrolysed by the help of KOH-methanol or KOH-ethanolic solution. But, even after that there are papers which use this method for food products not necessarily very rich with fat for example fruits and vegetables. I also feel and agree that PAHs release is eased from the matrix by using this process. In general, the product needs to be refluxed with it at a specific temperature and thus may be added prior soxhlet extraction.
I have also seen, KOH:Methanolic solution to work better for tough and dirty environmental matrix example tar like products.
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