We all know that the Dubois method is used to measure polysaccharides. I am wondering that if Dubois method is negative, could I consider there is no polysaccharides and even monosaccharide in this supernatant?
And also I wonder the difference between Dubois method and Orcinol sulphuric acid method in detecting saccharide.
Thank you very much!
Dear Wang,
There are several spectrophtometric methods all designed to screen and monitor sugars (polysaccharides) in samples, namely Dubois, orcinol, DNS and anthrone.
The various methods measure the absorbance at different wavelengths and have different response factors to sugars. In your case you may have to decide on the best method based on the presence (or not!) of contaminants or interfering species, like chlorophylls (plants). If that's the case, then using the anthrone or orcinol method is of limiting value.
Based on my experience measuring glycolipids in biological matrices the orcinol method was the most sensitive.
My suggestion is you conduct a preliminary study with all the spectrophotometric methods to access the best one before routinely implementing it to your samples. In the long run it will pay off to conduct this preliminary study.
Hope this helps,
Ana
Thank you Ana.
Actually I don`t know the chemical structure in this sample. First I thought it was polysaccharides because it can be oxidated by sodium periodate. So I used the Dubois method and orcinol method. But the absorbance was even below negative control (water serves as zero point).
I think that although there are difference between these methods, these methods should detect some absorbance if there is some kind of polysaccharides in this sample. So I am considering whether it is not sugar at all.
If all you want is a presence/absence result, Phenol-H2SO4 method will do.
1] Run a calibration with any sugar and determine your detection level.
2] Check your protocol. Negative values seem odd, but if you have a complex matrix, all bets are off.
Good luck!
Hi wang probably you need to have another zero not just water , in Dubois method for blank is used the mixture of phenol and h2so4 without sample, did you have a good r2 in you calibration?
Hi there D R B-D,
Good catch! I missed this point.
Correct, one should use a blank consisting of everything but the sample.
Thanks!
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