I have a ethanol-water 50% extract of mango peel. I purified mangiferin from the extract with filtration and precipitation. so i obtained a low concentrated extract which i want to se the IR spectrum and compare with the mangiferin IR spectrum. however, I would like to know what concentration should i achived to obtain a good IR spectrum from liquid samples (Standard and Extract), Also how many sample should I need in mL. Any advise would be really usefull. PD: I have not enough standard or extract to make a solid sample lecture with KBr.
You want to match the extract with standard, it is qualitative, it not needs specific concentration. Use one of these methods:
1- Nujel ( the sample with paraffin ), few mg in paraffin and use NaCl cell.
2- Thin film, dissolve few mg in volatile solvent with NO functional groups like chloroform, put drops on the NaCl cell, shake and wait to evaporate the solvent and run .
Mr. Maya,
First, there should be used CaF2 cuvettes transparent to IR irradiation within 4000-1200 cm-1. Therefore, the analyte should exhibit characteristic IR-bands within the latter region of the electromagnetic spectrum.
Second, there should be acumulated a large number of spectra (at about 250-300) in order to improve the S/N ratio, due to low concentration of the analyte.
Finally, there can be used KBr-cuvettes within the framework of a smaller number of scans (at about 100-150,) but operating with a higher concentration of the analyte.
An additional comment on: The concentration LODs, respectively, LOQs of the IR-spectroscopic quantitative analysis depends on the intensity of the characteristic IR-bands of the analyte. Therefore, there is needed an additional information about the molecular structure of the analyte, in order to, answer to your question of the amount of sample required for a reliable analysis by means of IR-spectroscopy.
Do you have access to an Attenuated Total Reflectance (ATR) accessory? In this case a drop of the solution on the crystal should be sufficient. It the concentration is too low, you can continue to measure as the droplet dries.
Dear Marcelo Maya
To prepare a liquid sample to IR analysis, firstly place a drop of the liquid on the face of a highly polished salt plate (such as NaCl, AgCl or KBr), then place a second plate on top of the first plate so as to spread the liquid in a thin layer between the plates, and clamps the plates together. Finally wipe off the liquid out of the edge of plate. You can mount the sandwich plate onto the sample holder. After finishing your experiment, clean the plates with isopropanol (No water!) and return them to the desiccators.
In addition to the above answers in the case, you do not have a CaF2 or KBr cuvettes/cells but you do have an ATR attachment, you can try to place a 1.5-2 uL drop on top of the ATR crystal and allow it to dry in order to produce a dry film and then measure. However, this technic is less sensitive than a ¨traditional¨ transmittance technic, so I would advise concentrating your sample if that is possible.
Best of lucks!
Guz
Bojidarka B. Ivanova,
I am so glad for your recommendations, I will use the CaF2 cuvettes and make the reading as you recommended, thank you.
About your last recommendation, I found some infrared spectrum made with KBr plates.
https://www.researchgate.net/publication/228480119_Studies_on_the_anti-diabetic_and_hypolipidemic_potentials_of_mangiferin_Xanthone_Glucoside_in_streptozotocin-induced_Type_1_and_Type_2_diabetic_model_rats/figures?lo=1
As I understand, the carbonyl group absorbs strongly in a characteristic band. I couldn’t found a liquid sample spectrum or an example calculus to transform transmittance to concentration. I am reading about some software but I didn’t found any tool to handle solutions. What do you think about running a standard curve with some known dilutions?, also I would like to ask if changing the solvent from ethanol-water to water will help in the lecture?
Best regards
Marcelo
Dear Marcelo,
Regarding quantification with IR, you may want to look a look at this paper: Article Direct Quantification of Drug Loading Content in Polymeric N...
It is open access.
There is also some free information on TMO website: https://www.thermofisher.com/es/es/home/industrial/spectroscopy-elemental-isotope-analysis/spectroscopy-elemental-isotope-analysis-learning-center/spectroscopy-elemental-isotope-analysis-resource-library/omnic-ftir-software-training-videos.html
check the "Working with the Cursor Tools" video
Best regards,
Guz
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