The specification of Cetyl trimethyl ammonium bromide CTAB (Cetrimonium bromide ), generally, according to the laws of US and European, should include following items:
Appearance: White or light yellow powder
Chain Length: Min. 95% w/w C16（C16＞95%）
Free amine: Max. 0.3% w/w（＜0.3%）
Amine salts: Max. 0.3% w/w（＜0.3%）
Assay: Min. 99% w/w（＞99%）
Solubility: Soluble in water, lower alcohols,such as methanol, ethanol and propanol
Density: 0.4 g/mL to 0.6 g/mL
Melting point: Decomposes at 245 – 250 ℃
HNMR ( Nuclear Magnetic Resonance spectroscopy) is a powerful and theoretically complex analytical tool, used not only in the determination of the structure of unknown organic compounds but also in the quantitative analysis. From a technical view, the most-concerned impurities in quaternary ammonium compounds are free amine and amine salts which can not be accurately detected or quantified by titration method, GC or LC, Ahsuperchem uses HNMR to analyze CTAB. HNMR spectra were recorded on 400 MHz spectrometerin CDCl3.
Fig.1 is one of HNMR figures of CTAB, which was produced on January 10, 2024.
Fig.1 HNMR spectrum of CTAB
Fig.2 is the HNMR spectrum of Cetyl dimethyl amine salt. From fig.2 we can see that the single at 2.75 ppm is the triple peaks at 2.92 ppm are the characteristic peaks of the Cetyl dimethyl amine salt. If there is any amine salt in CTAB, there should be a single peak at 2.78 ppm
and a triple peak at 2.92 ppm like in Fig.2. Similarly, if any free amine exists,(the characteristic peak of Cetyl dimethyl amine are with chemical shifts from 2.20 to 2.80 ppm), there should be peaks at 2.20 to 3.00 ppm in Fig.1. We can see that there is no peak from 2.00 to 3.00 ppm from Fig.1 indicating that there is no amine or amine salt in the product or the amount of amine and amine salt is lower than the detection limit of HNMR. (<0.1%)
By the same logic, there will be some other peaks if anyother organic impurities existing in production CTAB. Only five characteristic peaks of CTAB can seen, from Fig.1 we can conclude that no organic solvents remaining.
Fig.2 HNMR spectrum of Cetyl dimethyl amine salt
