I am trying to determine the composition of some microbial polysaccharides I have purified. Prior to TLC and HPLC, I want to try this qualitative method known as potassium ferricyanide reducing power test, a.k.a Perkins test, which includes reacting hydrolyzed polysaccharide solutions with an alkaline solution K3[Fe(CN)6]. Briefly, reducing sugars such as glucose and fructose provide greenish-yellow color for different times in this test, so they can be distinguished.
My question is; can I use K4[Fe(CN)6] instead of K3[Fe(CN)6]?
Why not hydrolyse a sample of the polysaccharide and do a standard monosaccharide analysis using HPLC..
Color tests such as the ferricyanide will not be very helpful if your polysaccharide contains a mixture of various monosaccharides. You will simply get some blend of the various colors. I would go straight to the TLC and HPLC you mentioned. Was there some particular reason why you wanted to try the ferricyanide? There are TLC detecting reagents that will give good color differentiation of some of the different monosaccharides, which combined with their mobilities, can be very helpful. Of course, if you have uronic acids in your polysaccharide, that complicates things, and the carbazole-boric acid method may be useful there (see attached)..
Dear Prof. Cote, thank you for your answer. I just wanted to try this method out of curiosity. I could not detect any colour with K4[Fe(CN)6]. I use an alpha-naphtol solution to stain TLC plates, which gives a good color differentiation.
Since you are curious, here's one of the original papers on the alkaline ferricyanide method for reducing sugars. You should note that the reducing sugars actually cause the yellow color to disappear, so in the presence of higher levels of reducing sugars, all of the yellow color would be eliminated.
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