Mechanism of porous core electroosmotic pump flow injection system and its application to determination of chromium(VI) in waste-water

An electroosmotic pump flow injection system is introduced in this paper. According to electroosmotic theory, the pump's properties were described. A large flow range (mu l min(-1)-ml min(-1)), moderate carrier pressure (> 0.15 MPa), reduced performance voltage (< 500 V) and stable flow rate (RSD < 3.0% in 4 h) are the main properties of the pump. NH4OH (0.35 mM) was used as carrier for improving the pump's flow stability. The electroosmotic efficiency of the pump's medium, porous core, can be recovered and regenerated. A sandwich zone was used for sample and reagent introduction in order to adapt to the pump performance. Flow injection-spectrophotometry was employed for the determination of Cr(VI) in waste-water, based on the formation of the complex with 1,5-diphenylcarbazide and absorbance measurement at 540 nm. Within the calibration range of 0-7.0 mg l(-1) of Cr(VI), the RSD was 0.4% (n = 5). The recovery of 0.70 mg l(-1) Cr(VI) added to the waste-water sample was 94.5 +/- 2.0% (n = 5). (C) 2000 Elsevier Science B.V. All rights reserved.