Resonance Rayleigh Scattering Determination of Trace Ozone Based on the Cationic Surfactant Association Particles

In the presence of pH 4.0 HAC-NaAC buffer solution, using H₃BO₃-KI (BKI) as absorption solution, O₃ oxidized KI to produce I₂, and it reacted with excess I^- to form I^- ₃ that combined with the cationic surfactant (CS) such as cetylpyridinium chloride (CPCl), tetradecyl pyridinium bromide (TPB), cetyl trimethyl ammonium bromide (CTMAB), and tetradecyl dimethylbenzyl ammonium chloride (TDMAC) to produce stable (CS-I₃) _n association particles, which exhibited a strong resonance Rayleigh scattering (RRS) peak at 470 nm. Under the chosen conditions, as the concentration of O₃ (C) increased, the concentration of I^- ₃ increased, and the RRS intensity at 470 nm (I _{470 nm}) increased due to more association particles forming. The increased RRS intensity I ₄₇₀ nm was linear with O₃ concentration. For the four CS systems, the linear range was 1550, 50100, 525 and 150 μmol·L^-1 O₃ respectively. The regression equation is ΔI=8.81c-4.01, ΔI=5.44c-3.11, ΔI=15.39c-1.55, and ΔI=16.88c+0.51. The detection limit is 4.9, 12, 2.85 and 0.56 μmol·L^-1 O₃ respectively. The influence of some foreign substances was examined on the determination of 2.5×10^-6 mol·L^-1 O₃, within ±10% relative error. Results showed that a 4.0×10^-5 mol·L^-1 Hg²⁺, 8.7×10^-5 mol·L^-1 Fe³⁺, 5.0×10^-5 mol·L^-1 Ca²⁺, 2.5×10^-5 mol·L^-1 Zn²⁺ and Cu²⁺, 2.8×10^-6 mol·L^-1 Pb²⁺ and Cr³⁺, 4.2×10^-5 mol·L^-1 Mg²⁺, Mn²⁺ and Ba²⁺ do not interfere with the RRS determination. This showed that this RRS method is of good selectivity. The TDMAC system is most sensitive, and was chosen to detect O₃ in air samples. The analytical results were in agreement with that of spectrophotometry results. Furthermore, laser scattering technique was utilized to examine the particle size distribution of (TDMAC-I₃) _n system. Results indicated that the particle size located in the range of 190531 nm, in the absence of O₃. Upon addition of O₃, the excess KI reacted with O₃ to produce I^- ₃, and I^- ₃ interacted with the TDMAC to form (TDMAC-I₃) _n associated particles with a size range of 1 1063 091 nm. This test identified that there are associated particles in the TDMAC system.