I do not know much about FTIR!
The material Benzethonium Chloride USP was compared to a reference standard in regards to FTIR, as per the USP testing:
Identification B. Infrared absorption (FTIR), thus complying with .
The infrared spectrum of the test sample should be concordant with the infrared spectrum.
The results for release testing are passing, see below FileA_BZT_FTIR.pdf
No peak after 3000 nm when compared to BZT Reference.
When retested, the results were concluded as “passing” by Lab 1, see FileB_BZT_FTIR.pdf
Additional peaks at 3100 – 3300 nm when compared to BZT Reference.
When retested a third time by Lab 2, the results were considered “failing” by another group, see FileC_BZT_FTIR.pdf
Additional Peak at 3100 – 3600 nm when compared to BZT Reference.
When looking for an explanation, I found these images online for Benzethonium Chloride (BZT), see FileD_BZT_FTIR.pdf
https://www.chemicalbook.com/SpectrumEN_121-54-0_IR1.htm
And also this image, see FileE_BZT_FTIR.pdf
https://www.sciencedirect.com/science/article/abs/pii/S0022286023013893
Can someone explain to me what is going on AND what does this mean for the quality of the material? It appears normal in all other quality testing requirements for BZT.
Jai Supamahitorn
To obtain benzethonium, a mixture of 32 g of p-(α, α, γ, γ-tetramethylbutyl)phenoxyethoxyethyldimethylamine and 12.7 parts of benzyl chloride is heated in 50 g of benzene for 2 hours. The benzene is then evaporated. The residual viscous mass gives a foamy soap solution in water. An additional peak in FTIR between 3100 and 3300 nm may correspond to the stretching vibration of the bonds of the anol-free ring of the remaining benzene. I use IR spectra to determine the purity of any synthetic compound.
Bands in the 3500-3100 m-1 region are usually associated with hydroxyl (OH) or amino (NH) groups. The shape of the bands in your spectra suggest amino groups. Primary amines -NH2 have two bands, secondary >NH have one. The spectrum with a strong 3462 cm-1 band is typical of an aromatic secondary amine with some structural hinderance. Amine salts show strong , broad, characteristic bands in the roughly 3000 - 2000cm-1 region. Tertiary and quaternary nitrogens have no bands in the IR spectrum.
Thank you for responding Yuri Mirgorod ! Does this mean that this "stretching vibration of the bonds" may be present post synthesis in some of the samples and may appear randomly? In addition, would this not effect the basic structure and function of the surfactant?
Thank you Geoffrey Dent for responding as well! Can you explain how the quaternary amine have no bands in the IR spectrum, I am confused. Also, do you agree with Dr. Mirgorod's answer?
Overall I am trying to understand the results and justify the quality of the QAC. Any additional info is welcome!
Jai Supamahitorn
Standards are used to prove the presence of an impurity. A new absorption band appears in the FTIR spectrum. Therefore, there is an impurity. I have indicated the probable origin of the impurity. Perhaps your competitor added an impurity. The substance is used in perfume compositions. If you ruin the face of an expensive beauty, she may sue you.
The bands in IR spectra are mainly due to vibrations from interatomic stretching, bending and/or deformation. The physical and chemical environment can affect band shape and position, e.g. hydrogen bonding, steric hinderance, physical form. The bands in the 3500-3000cm-1 region are mainly due to OH or NH stretching. Hence -NH2 has two bands, >NH has one band, >N- and N+ have no bands in this region. C-N stretches have weak bands lower in the spectrum. Dr Migorod is correct in that aromatic CH and benzene ring overtones can appear in this region but they are usually much weaker and sharper than the bands in your spectra. Yours are typical of -NH2 and >NH bands.
Hello Yuri Mirgorod and Geoffrey Dent , how can I go about determining what this "impurity" may be (as to be certain)? Since it is a quaternary ammonium compound, does this mean that the -NH2 and >NH2 bands are impurities that are found due to processing (by product) or due to breaking degradation (due to time?). The FTIR spectrums in file D and E appear to feature these shallow peaks - does this mean that this may be expected? I greatly appreciate the time taken to assist me, thank you!
Jai Supamahitorn
There is a standard spectrum that you compare with. Any deviation from the standard indicates contamination of the compound. The rest is due to the device, experimental error ...
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