Mr. Kumar,

There is great difference between isomers and enantiomers? (Basic knowledge organic chemistry, Part I, BSc grad). 

Second, is there difference between optically active compounds irradiated upon non-polarized light? (This is basic knowledge 'Instrumental analysis/Analytical instrumentation' I, BSc grad, as well)

Mr. Kumar,

There is great difference between isomers and enantiomers? (Basic knowledge organic chemistry, Part I, BSc grad). 

Second, is there difference between optically active compounds irradiated upon non-polarized light? (This is basic knowledge 'Instrumental analysis/Analytical instrumentation' I, BSc grad, as well)

Depending on the molecule, different isomers may or may not have different UV absorptions (see, for example, Luo et al, J Phys Chem Lett, 2017, 8, 1025-1030).

However, as pointed out before, isomers are a very different thing from enantiomers, which is actually the relationship between D and L glucose. When irradiated with non-polarised light, enantiomers should have the same UV absorption. 

The two samples probably differ in the amount of UV-absorbing contaminants.

D-glucose & L-glucose are stereo isomers of the enantiomeric type. Enantiomers differ only in the way they rotate plane-polarized light and the instrument, which shows that, is the (polarimeter). 

Enantiomers will have the same UV spectra. Therefore, there is something wrong with your glucose samples.

Note that the maximum absorbance of glucose is detected at 260 nm to 270 nm. 

The difference may be related to two possibilities:

1. Error in the solutions preparation. Difference in the concentrations between D and L glucose.

2. Presence of other substance(s) that cause(s) difference in absorbance between D and L glucose.

Repeat you tests taking in consideration the previous remarks.

Good luck