Physical Lab - Experimental Plan - Essay Example

Physical Lab - Experimental Plan EXPERIMENTAL PLAN Introduction Ion Selective Electrode (ISE) is one of the methods used to assay fluoride. It has been successfully used to detect fluoride in water and other substances which have had cases of fluorosis (Seiler, 1994)1. The principle behind this technique is the conversion of the activity of a specific ion in a solution into an electrical potential which is then measured by a pH meter or a voltmeter. Several factors affect the function of this technique a few of which are temperature, infusion time and stirring.

One main problem experienced in this technique is the release of other ions such as oxalate which can bind to calcium making it insoluble (www.nico2000.net)2.ObjectivesThe aim of this experiment is to apply the fluoride electrode method to a practical problem by measuring fluoride in tap water and to determine whether tea infusion from several types of tea increases the level of fluoride.Materials and requirementsDigital voltmeterFluoride ISE (Ion Selective Electrode)Calcium ISECalomel reference electrode Standard Solid NaF (Sodium fluoride)Standard KCl or KNO3 ( Potassium Chloride or Potassium nitrate)UV-Visible spectrometerProcedure (Method)A number of methods exists but of preference is the Direct Method outlined below:1.

Calibration curve is prepared by measuring electrode potentials obtained from arrange of standard solutions.2. The standard solutions are prepared from stock solution e.g. 1000 parts per million (ppm) of sample can be accurately weighed and dissolved in distilled water.3. Serial dilution is done. This involves preparation of different less concentrated solutions from stock solution by dilution e.g. 10ml of 1000ppm stock solution is put in a volumetric flask and diluted with 100ml of distilled water to give 100ppm.

A given range of standard solutions is obtained.4. Ionic strength adjustment buffer (ISAB) is added so that concentration can be determined. 5. The ISE and reference electrode is then put into the least concentrated standard solution and allowed to adjust to room temperature and pressure and stirred gently after which electrode potential is measured.6. Electrodes are then rinsed with distilled water and steps 4 and 5 repeated using other concentrated standard solutions in succession.7. Same volume of sample (tea) is measured and adjusted and the electrodes placed after which it is stirred and allowed to adjust to room conditions.

Finally, electrode potential is measured. Calibration curves are then drawn. Results and ObservationsResults of electrode potential (mV) are then plotted against concentration of the sample to get the curve similar to the one shown below.DiscussionThe measured electrode potential (E) is defined by Nerst equation as :E=Eo+2.3RT/nFlog(Activity).Where, Eo is the Cell constant, RT/nF is the slope factor( shows the performance of electrode), n is ionic charge, R is the gas constant and T is the temperature in Kelvin.

This process encounters a number of problems one of which is the release of other ions such as oxalate (www.chemistry.nmsu.edu)3. Other general problems encountered are related to erroneous values obtained due to sample contamination, junction clogging, and incorrect slope of the electrode (Wroblewsk, 2012)4. Such problems are generally rectified by using pure standards and using ISAB or decomplexing to adjust the conditions so as to avoid formation of other ions. Fluoride content of tea can then be compared with that of known solutions.

Conclusion Other methods such as one point calibration, incremental techniques, multiple sample addition and titrimetric procedures may be used. ISE is applied in Agriculture to determine level of ions in the soil and in biomedical laboratories to analyze fluoride in skeletal (Noh, 2007). 5.BibliographyWroblewsk, W. (n.d.). CHEMICAL SENSORS RESEARCH GROUP. CHEMICAL SENSORS RESEARCH GROUP. Retrieved April 30, 2012, from http://csrg.ch.pw.edu.pl/tutorials/ise/Seiler, H. G. (1994). Handbook on metals in clinical and analytical chemistry .

New York: M. Dekker.Calcium Electrode, Calcium ISE, Calcium Ion Selective Electrode, Calcium. (n.d.). Ion Analysers, Ion Analyzers, Water Quality Measuring Systems, Ion Selective Electrodes, Multi-Channel Monitors, Electrochemical Sensors. Retrieved April 30, 2012, from http://www.nico2000.net/analytical/calcium.htm Noh, J. (20071207). An inter-laboratory comparative study of fluoride determination in water. Johannesburg: Water SA.Forston Labs | Fluoride Ion Selective Electrode - LabNavigator Sensors - Products . (n.d.). Forston Labs | Welcome to the Home of the LabNavigator .

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