Detection Condition Optimization And Theoretical Analysis For Ions Based On Capillary Electrophoresis/ Indirect UV Method

Eleven metal ions and fourteen inorganic anions and small organic molecules were separated and detected, respectively, by capillary electrophoresis with indirect UV method. The developed methods were applied in natural water body, soil, beverage and honey samples to verify their applicability, which offered efficient, convenient and reliable methods to evaluate the qualities of environments, food and their safety.Most of metal ions are lack of UV absorption properties, therefore, it is necessary to choose a proper chromophore to fullfil UV detection. Thus, 5 chromophores which are used widely for indirect UV method were discussed and imidazole was finally selected as chromophore for its mobility is close to most of alkali, earth alkali, even some heavy metals. The separation conditions were optimized. Efficiency of separation was investigated by migration time, mobility, resolution, theoretical plate number and plate height. The background electrolyte contains 15 mmolL^-1 chromophore imidazole, and acetic acid (pH = 3.7), which functioned as pH adjustor and complexing reagent. K⁺, Ba²⁺, Ca²⁺, Na+, Mg²⁺, Fe²⁺, Zn²⁺, Cr³⁺, Cd²⁺, Li⁺ and Cu²⁺ can be completely separated within 8 min under hydrodynamic mode injection with a running voltage of 20 kV at 25 oC, and whose detection wavelength was set at 214 nm. The applicability of the method is shown by investigation of reproducibility, linearity of the calibration, whose limit of detection, linear range, correlation coefficient and relative standard deviation are in the range of 0.01-0.21 mg L^-1, 0.12-80 mg L^-1, 0.9995-0.9998 and 2.0-3.4%, respectively.By the analysis of honey samples, including a comparison with results of pretreatment and unpretreatment of 8 samples, beverage samples, natural water samples and soil samples, the results demonstrate that the developed method can be used conveniently in routine analysis of environmental and food inspection and evaluation.Some inorganic anions have no UV absorption as well, thus indirect UV detection was developed for separation of Cl-,SO₄^2-,ClO₃^-,SCN-,BrO₃^-,C2O₄^2-,F^-,HCOO^-,tartrate,IO₃^-,H₂PO₄^-,citrate,lactate and succinic acid. Compared with 5 chromophores and 5 reverse reagents of electroosmosis flow, potassium hydrogen phthalate (KHP) and hexadecyltrimethyl ammonium bromide (CTAB) were chosen. After optimization, the running buffer is in the constituent of 0.10 mmol L^-1 CTAB and 9.0 mmol L^-1 KHP, under which condition 14 inorganic anions and small organic molecules could be separated within 4.5 min under hydrodynamic mode injection with a running voltage of 20 kV at 25 oC, and whose detection wavelength was set at 210 nm. The limit of detection, linear range, correlation coefficient and relative standard deviation was listed as 0.45^-1.0 mg L^-1, 1.6-85.0 mg L^-1, 0.9981-0.9996 and 1.1-4.5%. The application of developed method was in the same real samples as metal ions detection. The results indicated that the developed method can be also used conveniently in routine analysis of environmental and food inspection and evaluation.