Oxidation of polysaccharide such as dextran with oxidant resulted to breaking of C-C bound in glucose unit. This breaking concluded to formation of aldehyde group. What is the peak of carbonyl (C=O) in FTIR spectra?
The characteristic aldehyde peak in oxidized polysaccharide is very difficult to observe at degree of oxidation less than 50 %. If the degree of oxidation is higher and beyond 50 %, you can see a small peak around 1730-1740 cm-1. Intensity of this peak is poor compared to other peaks in the polysaccharide. We can identify the aldehydic C-H peak near to 2850 cm-1 which gives a clear evidence of the presence of aldehyde. You can refer the following links.