A cholesterol benzoate RRS probe for the determination of trace ammonium ions

The measurement of NH₄⁺ has attracted considerable attention with the increase of NH₄⁺ emissions in sewage caused by human activities. So far, a variety of photometric and fluorescence methods for the detection of NH₄⁺ have been researched and summarized, but there is no report about the use of liquid crystals (LCs) cholesteryl benzoate (CB) as a resonance Rayleigh scattering (RRS) probe to determine ammonium ions. In the NaAc-HAc buffer solution with pH = 4.80, the yellow compounds 3,5 diacetyl-1,4 dihydrolutidine (DDL) generated by the reaction of NH₄⁺ with acetylacetone (AT) and formaldehyde (HCHO) act as the energy receiver and CB as the donor. Because the RRS spectrum of CB overlaps with the DDL absorption spectrum, resonance Rayleigh scattering energy transfer (RRS-ET) occurs. When the NH₄⁺ concentration increased, the generated DDL increased, and the RRS-ET also increased, so the RRS intensity of the system at 395 nm decreased. For this reason, a fast and sensitive CB RRS-ET method was established to apply to the detection of NH₄⁺ in water. The detection range was 1.00 × 10^-3 - 4.66 μg/mL, and the detection limit was 6.62 × 10^-3 μg/mL. Using this method to analyze and detect NH₄⁺ in environmental water samples, the precision and recovery rate were between 1.30-9.30% and 95.5-109.9%, respectively. Therefore, this method has the advantages of sensitivity and simplicity.