palintest Macro 900 Operation Manual

Contents

palintest Macro 900 Operation Manual Manual pdf 93 page image

Macro 900 Operation Manual V3© 2013 Palintest Ltd. www.palintest.com Page 93 of 14716. Optional ISE Electrodes Calibration and Maintenance16.1. ISE Electrode LimitationsAll ion selective electrodes suffer from interference from ions which are similarin nature to the target ion. For this reason, ISE Electrodes are notrecommended for use in brackish or salt water due to the high level ofinterfering ions.In order to achieve accurate readings with ISE electrodes, the Probe needs tobe either placed in flowing water, or needs to be stirred or raised and loweredcontinuously to ensure a minimum flow rate of 0.3m/s over the electrode. Ifthere is no water flow across the ISE electrode, the ions in theimmediate area of the electrode will be depleted and the reading willstart to fall. This also applies to calibration, where the probe should bestirred at all times.16.2. Calibration PointsAll ISE electrodes have three calibration points. Careful calibration is essentialin order to ensure consistent and reliable results. Prior to initial calibration, allISE Electrodes should be soaked in their relevant Point 1 calibration solution for20 – 30 minutes.When an ISE electrode is first installed, it MUST be calibrated at threepoints in order to establish the electrode's slope and thermal characteristics.Two of the calibration points must be at the same temperature whilst the thirdmust be at least 10ºC cooler. Subsequently, a two-point calibration should becarried out weekly and a single point calibration should be carried out daily. TheISE electrode should be replaced every 6-12 months.16.3. Special Notes Concerning ISE Electrodes during pH CalibrationThe high ionic concentration of pHcalibration solutions (buffers), includingMacroCal, can cause significant offsets inISE electrodes.These offsets are temporary, but bestavoided because they can causesignificant errors during both calibrationand normal operation. For this reason allISE electrodes are supplied with a redrubber sealing cap.The caps should be fitted to all ISEElectrodes during pH calibration orwhen using MacroCal in order toprotect the ISE electrodes from the effects of the buffer solution.At all other times, the ISE electrodes should be left uncovered.