Simultaneous flow injection determination of calcium and fluoride in natural and borehole water with conventional ion-selective electrodes in series

An on-line automated system for the simultaneous flow injection determinati on of calcium and fluoride in natural and borehole water with conventional calcium-selective and fluoride-selective membrane electrodes as sensors in series is described. Samples (30 mu l) are injected into a TISAB II (pH = 5 .50) carrier solution as an ionic strength adjustment buffer. The sample-bu ffer zone formed is first channeled to a fluoride-selective membrane electr ode and then via the calcium-selective membrane electrode to the reference electrodes. The system is suitable for the simultaneous on-site monitoring of calcium (linear range 10(-5)-10(-2) mol l(-1) detection limit 1.94 x 10( -6) mol l(-1) recovery 99.22%, RSD < 0.5%) and fluoride (linear range 10(-5 )-10(-2) mol l(-1) detection limit 4.83 x 10(-6) mol l(-1) recovery 98.63%, RSD = 0.3%) at a sampling rate of 60 samples h(-1). (C) 1999 Elsevier Scie nce B.V. All rights reserved.