F- Cl- Br- I- CN- S2- NO3-

Transcription

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2 Middle of the 60 s First ISE for fluoride Na+ K+ Ag+ Ca2+ NH + 4 Cu2+ Pb2+ F- Cl- Br- I- CN- S2- NO3-

3 Environment Food industry and agriculture Medecine, pharmaceutical, cosmetics Power plants

4 Fluoride Calcium Nitrates Copper water, plants, minerals, drugs water, milk, cheese, beer, wine, serum, blood ground, surface and drinking waters plants, soils, foodstuff plating bathes complex. titration of copper, nickel, cadmium

5 Economical Time saving Instrumentation simple Automation (sample changer)

6 Wide dynamic range from 10 0 to 10-7 M Measurement not disturbed by colour or turbidity, no interference from solid particles

7 Free ions only Interferences from other ions present in the sample

8 Based on Nernst equation modified by: Sensitivity factor Selectivity factor E RT nf S 100 E0 * log a x k xi a n ni

9 Parameters of the equation E = electrode potential E0 = standard electrode potential (temperature dependant) T = absolute temperature F = Faraday s constant R= gas constant n= valence of ion x ax= activity of ion x S/100% = sensitivity of electrode Kxi = selectivity constant of primary ion x to interfering ion i

10 Ionmeter Temperature sensor, ISE (with filling solution) reference electrode Standard (addition) solution Ion Strength Adjuster (ISA)

11 Concentration range ph range Response time Life time

12 Membrane resistance (high) Sensitivity deviation from the 100% (59 mv/decade) Check point : potential for a 10-2 M standard solution

13 sensitivity Check point

14 Glass Solid state Organic membrane (ion exchange) Single or combined

15 Hydrated layer around the glass membrane Surface acts as a cation exchanger H+ (ph ) electrode unique 14 decades of concentration Na+ electrode modified ph glass Strong interference from H+ Short response time

16 Inner reference element Ag/AgCl wire Inner solution Ion sensitive glass membrane

17 F - LaF3 Cl - AgCl Ag +/ S -- Ag 2 S CN -, I - AgI Solid state Electrodes Pb ++ PbS Br - AgBr Cu ++ Cu 1.8 Se

18 Ionically conducting membrane made of one or more inorganic salts Monocrystal (LaF3) or polycrystal (Ag 2 S) Inorganic salt solubility determines detection limit

19 F- electrode LaF 3 monocrystal CN- electrode AgI polycrystal F- CN- Ag+ F- TISAB ph adjuster and decomplexer of AlF 6 and MgF 4 Ag(CN) 2 - soluble, limited life in high CN- concentrations

20 Cyanide, iodide, copper Black epoxy tube Conductive rod Conductive pads Sensing polycrystal

21 Chloride, Bromide, Fluoride Silver, Lead Black epoxy tube Conductive wire Filling solution Insulating material Sensing element

22 Ammonium, Potassium, Calcium, nitrate Potassium valinomycin antibiotics Calcium Nitrate organic calcium phosphate organic ammonium nitrate Ammonium antibiotic

23 Ammonium, Potassium, Calcium, nitrate Ion exchanger dissolves in water Life stime shorter than crystaline electrodes Membrane tube is removable Spare membranes are supplied

24 Filling aperture for external reference AgAg/Cl wire external reference KCl 3M AgCl solution for ext. ref. AgAg/Cl wire internal reference Internal filling solution ( not refillable) Porous junction of external reference LaF3 Monocrystal

25 Constant potential No interference with ion in solution, no Hg/HgCl2 or Ag/AgCl with: Sodium Chloride K+ of KCl interferes Cl- of KCl contributes to measurement salt bridge or double junction reference electrode filled with relevant ISA

26 Direct potentiometry (calibration curve) Standard addition Standard subtraction Analate addition Analate subtraction

27 Sample matrix Concentration level Accuracy requested Time Convenience

28 Use of 2 or more standards Bracketing procedure Use of Ionic Strength Adjuster ph adjuster and/or decomplexing agent Temperature identical in standards and samples.

29 E E0 S 25T / T 25log( C Bl) E = measured potential E 0 = standard electrode potential (mv determined by calibration) S25 = sensitivity at 25 C (mv/pc) T = calibration temperature T25 = K C = concentration of standard Bl= blank detection limit of electrode Csmp = C meas - Bl

30 Standard potential Deviation from fitted curve for each point Blank = experimental detection limit of the electrode

31 Typically ± 2-4% for monovalent ions, ±4-8 % for divalent ions Accuracy of the meter Precision of the electrode Accuracy on sensitivity (standard solutions) Accuracy on temperature control Sample pretreatment (all ions free or not)

32 Sample Addition 1 Addition 2 9 ISE = F - Sample = F - Standard addition = F -

33 If sample matrix difficult to reproduce for standards Best accuracy if total amount of ion added is 0.5 to 2 total amount of ions in sample Valid only in linear response range Potential variation due to addition : mv for a monovalent ion 5-15 mv for a divalent ion

34 Sample Addition 1 Addition 2 9 ISE = I - Sample = I - Standard addition = Ag+ -

35 When standard of the ion is instable (I - or S 2- ) Addition volume and concentration adjusted so as not to react with all the amount of ion in the sample

36 C smp ( V smp V std C )10 std V std ( E1 E ) / S V smp For one addition/subtraction Csmp sample concentration Cstd standard concentration Vsmp sample volume Vstd standard volume E potential before 1st addition/subtraction E1 potential after addition/subtraction S sensitivity

37 Sample Analate add. 1 Analate add. 2 9 ISE = F - Standard = F - Analate (sample) = F-

38 High ion concentration in sample, avoids dilution errors When sample volume available is small

39 ISE = Pb2+ Complexing Standard = Pb(NO 3 ) 2 Analate (sample) = SO 4 2- Sample Analate add. 1 Analate add. 2 9

40 Indirect method, no ISE for the ion to determine High concentration in samples, avoids dilution CARE : the sample aliquots have to be well adjusted to avoid reacting with all reagent upon first addition.

41 C smp C std ( V std V smp )10 V smp ( E1 E )/ S C std V std For one addition/subtraction Csmp sample concentration Cstd standard concentration Vsmp sample volume Vstd standard volume E potential before 1st addition/subtraction E1 potential after addition/subtraction S sensitivity

42 When matrix is difficult to reproduce From 2 addition or analates: S calculated automatically: No need to calibrate Permanent check of electrode response Avoids dilution errors No temperature variation between measurements: volumes added are very small.

43 Only in electrode linear response range Time consuming : procedure repeated at each measurement Ion concentration in sample must be approx. known to adjust volume and concentration s of additions/analates Total volume added must be kept small to keep ionic strength/ph constant.