From previous articles, I have seen that Transmission mode gives downward peaks (if any) during FTIR analysis, while Absorption mode refers upward peaks.
But for my sample, it is very confusing. The graph shows Transmission mode, and showing upward peaks as well.
What shall I deduce from this? Is it %T or %A? For your convenience, I have attached the spectral analysis file.
Thanks for your time.
Negative peaks can occur on the transmission spectra, when your background or solvent subtraction is not accurate. For example, when you use a relatively concentrated solution for IR (solvent concentration ~95 % or less), subtraction of the neat solvent (100 % concentration) can give negative peaks. What do you record your IR spectra from? IR spectra without solvent for example from KBr pellets with background subtraction won't give you any negative peaks on the transmission spectra.
Dear Prof. Toth, thank you very much for this insight on negative peaks. With regard to your sample preparation or solvent concentration point, I must note that I used Bruker Alpha-e spectrophotometer, which does not require any sort of sample preparation, and any solids/powders/pastes/liquids can be analyzed with this.
In my case, the sample was Activated Carbon powders. Hence, do you suggest that the analysis was wrong?
Thank you very much, Salehin.
I agree entirely with Prof Toth. Just for clarification though, the terms you should be using are % Transmission (often referred to as Transmittance) and Absorbance (% Absorption is unlikely to be presented by any spectrometer). The instrument is not actually operating in a different mode it is just the way that the data system presents the data.
Dear Prof. Marcelo Guzman, thank you very much for your question. You are totally right!! I used an ATR accessory (equipped with ZnSe crystal). I forgot the case of saving the background (since I was standing beside the operator during the analysis), and I don't think we applied corrections as well.
Please find the attached file of the analysis and I'd be thankful to know your suggestions on this. Salehin.
Thank you very much, Sir (Dr. Farooq Wahab). I have a clear idea on this now. Salehin.
Before you start analyzing this spectrum,I do suggest that you record the sample spectra again with Absorbance Units instead of Transmission. *You can change the mode from Transmittance to Absorbance easily by mainpulating the parameters within "Measure".
When you get the Absorbance spectrum, you should see Negative peaks to confirm that the positive peaks that show up on the Transmittance spectrum are true and free of instrumental error.
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