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ISE: A cost effective way to add ion selective electrodes to the general chemistry laboratory experience. Steven L Brown & Cynthia Runkel Department of.

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Presentation on theme: "ISE: A cost effective way to add ion selective electrodes to the general chemistry laboratory experience. Steven L Brown & Cynthia Runkel Department of."— Presentation transcript:

1 ISE: A cost effective way to add ion selective electrodes to the general chemistry laboratory experience. Steven L Brown & Cynthia Runkel Department of Chemistry University of Arizona

2 Why Teach ISEs? Introduction to sensor technology An affordable instrumental technique Demonstration of electrochemical measurement

3 How We Use ISEs Measurement of [Ca 2+ ]. One component of the “Water Project”. Available for Cu 2+ or Pb 2+ for the Make- your-own-ISE project.

4 History of Gen Chem ISEs at Arizona Early 80’s added an experiment using wire-coated PVC electrodes. By early 90’s, replaced with “store bought electrodes”. In 2001, commercial electrodes replaced with PVC film electrodes.

5 The Water Project Students use four techniques over three weeks to create a cation profile of water samples they provide. ISEs are used to determine [Ca 2+ ].

6 Assignment Students prepare a series of standards. Students measure standards and samples. Plot results and determine [Ca 2+ ] concentration.

7 The Electrodes Use IJ ISE Combination Ion Electrode manufactured by Ionode PTY LTD of Tennyson, Brisbane, Australia. Bodies contain a Ag/AgCl reference electrode and an open end. Tips are made by preproom staff. Open tube filled with “filling solution” and covered with a tip.

8 Manufacture Cut Tygon tips Make “cocktail” –Dissolve PVC in THF –Add plasticizers and ionophores Tips dipped and allowed to dry Re-dipped twice more. Tips inspected for bubbles. Bad tips discarded. Completed tips stored in jar (no special conditions required). Electrodes assembled as needed.

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15 Fluka http://www.sigmaaldrich.com/Brands/Fluka ___Riedel_Home/Analytical/Sensoric_Appli cations.html#iono http://www.sigmaaldrich.com/Brands/Fluka ___Riedel_Home/Analytical/Sensoric_Appli cations.html#iono Our source for the cocktails recipies and the cocktails to make them is Fluka.

16 Calcium Cocktail Contents ChemicalAmountCost per 5 mL cocktailPer tip Poly(vinyl chloride) 250g$27.80$0.20$0.01 Tetrahydrofuran 1000ml$30.10$0.15$0.01 Calcium ionophore IV 250g$678.90$0.30$0.01 2-Nitrophenyl octyl ether 25ml$120.50$2.41$0.06 Potassium tetrakis(4- chlorophenyl)borate 1.00g$134.00$0.40$0.01

17 Financial Cost Electrode Bodies$ 50 each Cocktail startup$991.30 40 electrodes$3.46

18 Manpower costs Time required to make 40 tips – xxx employee hours Pre-calibration time – 0 hours

19 Reliability 40 tips made in the Spring 30 of these are still usable in the Summer 25 are still usable in the Fall

20 A good student result

21 Student Calibration Results

22 Linearity of student plots 42 with R 2 values less than.9900 49 with R 2 values greater than.9900

23 14.50.9980 28.50.9982 26.80.9984 27.20.9987 14.00.9988 19.40.9989 27.40.9989 25.90.9993 25.20.9994 21.90.9994 26.30.9996 21.20.9996 28.50.9997 15.30.9997 27.70.9998 25.10.9998 32.50.9999

24 Average Normalized Student Calibration Plot

25 Average results from pCa 2+ 2 to 4


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