Not knowing exactly what it is you're analyzing, one can only guess but your absorbance being very low, I'd guess that it's an effect of background overcorrection : too much subtraction from background and not enough sample to analyze.

Hello sir,

Titanium treated with APTES and glutaraldehyde solution. I'm getting the result in negative. Does it make any difference in calculating absorbance and transmittance for same sample? But when the number of the scan was increased it gave a plane graph in the attached file of same sample. Is it because of not having enough sample?

I'm afraid I don't know anything about functionalized Ti surfaces but you should at least see some absorption bands for Si-O moieties.

This is what I recommend for acquiring the FTIR spectrum (seeing you're equipped with a Perkin Elmer spectrometer) :

Conditions

Make sure CO2 and H2O correction are active

Work from 4000 cm-1 to the cutoff wavenumber of your ATR crystal (Beware of Germanium : don't go below 720-680 cm-1)

As your signal seems low, go for 16 accumulations (and more if useful)

Start acquiring at 4cm-1 resolution to limit noise ; go for 2cm-1 if possible

Work in transmission : everything that’s below the baseline should be an indication of absorbance (personal preference here, Absorption units are fine as well)

Procedure

Clean your crystal and acquire background in the chosen IR range on a raw Ti surface ; check energy (Egy in Perkin "talk" on the Y axis) to see if it's OK.

Acquire your sample spectrum on your APTES functionalized Ti : ATR force contact at 100 if you’re equipped with a Perkin ATR that allows you to control it.

See what happens

If in doubt, I suggest you coat/drop some APTES on a plastic film or an alu foil and see if you get a spectrum on it : this will tell you if something is wrong in your functionalization step.

Thank you, sir, for more detail. I will try to repeat the test and read the sample by changing the setting.

Hello sir,

I have some queries regarding the titanium disc. I again performed the experiment. and I came up with a different result with is not as expected. Don't know what is wrong going on?

Could you please go through the graph as the control and treated sample shows the same peaks?