Abstrakt
The capillary electrophoresis is one of the advantageous methods for the analysis of samples with complex matrices considering its simplicity, separation efficiency, and cost efficiency. We developed a method for separation of a broad spectrum of triazoles (i.e. penconazole (Pen), tebuconazole (Teb), and two cyproconazole (Cyp) diastereoisomers A and B) fungicides with CD-MEKC.
All three of them have very low pKa i.e. 1.76. 1.57, and 1.57, for Cyp, Pen, and Teb respectively. Considering low pKa values, we expected low mobility of selected fungicides, therefore, we have chosen micellar electrokinetic capillary electrophoresis mediated with CD for separation.
The instrument for analysis was the CE apparatus (Agilent Technologies 7100 CE), equipped with a diode array detection (DAD) system. All measurements were performed at 200 nm with a constant cassette temperature of 15 °C.
The separation was conducted in internally uncoated fused silica capillary with outer polyimide coating (Polymicro Technologies, Phoenix, AR, USA) of 500/425 mm (total/effective) length and 50 x 375 um (I.D. x O.D.). The separation voltage was -15 kV (with an electric current in the range from 34.4 to 35.2 uA), electric input power range from 0.5-0.6 W per 1 m capillary length.
To improve the solubility of fungicides and separation the buffer was a hydrodynamic mixture of 20% of methanol as an organic modifier. The best separation and instrument sensitivity observed in BGE consisted of 50 mM phosphoric acid, 50 mM TRIS with 20% v/v of methanol as an organic modifier with pH 4.8.
The BGE consisted of sulfated g-cyclodextrin as a selector in concentration 17.5 mg/mL and 15 mM SDS as an anionic surfactant. Due to the presence of methanol, the constant of dissociation for the constituents of BGE was modified and pH was simulated in PeakMaster software and confirmed with a pH meter.
With this methodology achieved LOD values were: 0.73; 1.88; 0.60; and 1.18 (umol/L) for Pen, Teb, Cyp A and B, respectively. While LOQ values were 2.18; 5.66; 1.80; and 3.55 (umol/L) for Pen, Teb, Cyp A and B, respectively.
The linear regression ranged from the lowest for the standard of Cyp A with value 0.9991 to the best value for Pen standard 0.9998. The separation methodology is applicable for the determination of triazole fungicides from tomato peel.