COMPARISON OF ONLINE ENRICHMENT BASED ON ION-PAIR AND CATION-EXCHANGE LIQUID-CHROMATOGRAPHY FOR THE TRACE-LEVEL DETERMINATION OF 3-AMINO-1,2,4-TRIAZOLE (AMINOTRIAZOLE) IN WATER

Aminotriazole is a polar and water-soluble organic pesticide and its preconcentration cannot be performed using either liquid-liquid extraction or solid-phase extraction with reversed-phase sorbents such as C-18 Silica, apolar copolymers or porous graphitic carbon. Aminotriazole can be ionised and its ionisation constants have been measured in order to select the best conditions for both the chromatographic analysis using ion-pair chromatography and the extraction from water in its cationic form. On-line preconcentration based on cation-exchange and ion-pair chromatography have been investigated. Breakthrough volumes measured on small precolumns were higher than 50 mi with spiked deionised LC-grade water and detection limits as low as 0.1 mu g l(-1) have been obtained. In real samples, a competition with inorganic cations occurs lowering the cation-exchange capacity. A chemical pretreatment consisting of oxalate precipitation and EDTA complexation was applied in order to remove inorganic cations, but the sample volume that could be handled without breakthrough was lower and quantitative determination was obtained at the 0.5 mu g l(-1) level. The same competition occurred when carrying out preconcentration based on ion-pair chromatography with a precolumn packed with an apolar copolymer that has been preloaded with a sodium dodecylsulfate solution.