Question

In combustion analysis method we burn the organic compound in oxygen supply, doesn't it effects the percentage of oxygen of the organic compound while determining it?

Answer 1

It doesn’t effct the O content

This technique requires that you burn a sample of the unknown substance in a large excess of oxygen gas. The combustion products will be trapped separately from each other and the weight of each combustion product will be determined. From this, you will be able to calculate the empirical formula of the substance. This technique has been most often applied to organic compounds.

If oxygen is part of the unknown compound, then its oxygen winds up incorporated into the oxides. The mass of oxygen in the sample will almost always be determined by subtraction.