Can someone help me with the mechanism of this colorimetric assay? I know that the pentose is converted to furfural by heat and presence of a mineral acid, HCl to be exact (as stated in the journal I am using as reference). However, I am confused with what the function of glacial acetic acid is. I also saw a protocol online that uses water and HCl only and it will be a whole lot easier if I can just discard the use of glacial acetic acid. But obviously, it was used because it has a function. Please help. Thanks in advance.
Take silver nitrate in Test tube add NaOH dropwise the black ppt. formed is dissolved by adding NH3 whivh is known as Tollen,s reagent . Add into it pentose solution in water & heat on burner . The silver mirror if forned along the side of test tube .
Tollens’ Test
Tollens’ test, also known as silver-mirror test, is a qualitative laboratory test used to distinguish between an aldehyde and a ketone. It exploits the fact that aldehydes are readily oxidized (see oxidation), whereas ketones are not. Tollens’ test uses a reagent known as Tollens’ reagent, which is a colorless, basic, aqueous solution containing silver ions coordinated to ammonia [Ag(NH3)2+]. Ketones are not oxidized by Tollens’ reagent, so the treatment of a ketone with Tollens’ reagent in a glass test tube does not result in a silver mirror.
The Tollen's test for pentoses is NOT the silver mirror test.
Use of glacial acetic acid is not required, but would make the system significantly more acidic and probably faster. Be sure to use a positive and a negative control, the colour change occurs fairly quickly for pentoses. Sucrose, galactose and glucuronic acid will also react given enough time.
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