Pharmaceutical Instrumental Analysis. Prof.Dr.Joumaa Al- Zehouri Damascus university Faculty of Pharmacy

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1 Pharmaceutical Instrumental Analysis Prof.Dr.Joumaa Al- Zehouri Damascus university Faculty of Pharmacy

2 An Introduction to Electroanalytical Chemistry ( Potentiometry) Reference Indicator

3 Electroanalytical chemistry Potentiometry Coulometry Voltammetry ( Polarography) Prof. J.Al-Zehouri

4 Potentiometry Potentiometric methods of analysis are based upon measurements of the potential of electrochemical cells in the absence of appreciable currents. Since the beginning of the twentieth century,potentiometric techniques have been used for the location of end points in titrimetric methods of analysis. Prof. J.Al-Zehouri

5 Potentiometric Titration (Ph. Eur. method ) In a potentiometric titration the end-point of the titration is determined by following the variation of the potential difference between 2 electrodes (either one indicator electrode and one reference electrode or 2 indicator electrodes) immersed in the solution to be examined as a function of the quantity of titrant added. The potential is usually measured at zero or practically zero current.

6 Titration Titration is a process in which a standard reagent (solution) is added to a solution of an analyte until the reaction between the analyte and reagent is judged to be complete Prof.J. Al-Zehouri

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8 Principle of volumetric titration A + B C + D B A A C D C D C D B Equivalent Point Prof. J. Al-Zehouri

9 Anhydrous Citric Acid C 6 H 8 O ASSAY Dissolve g in 50 ml of water R. Titrate with 1M sodium hydroxide, using 0.5 ml of phenolphthalein solution R as indicator. 1 ml of 1Msodium hydroxide is equivalent to mg of C6H8O7. Prof. J. Al-Zehouri

10 Compound Sodium Chloride Mouthwash Assay For sodium chloride : To 10 ml add 10 ml of water and carry out the method for ion-selective Potentiometry, Appendix VIII E, using 0.1M silver nitrate VS. Each ml of 0.1M silver nitrate VS is equivalent to mg of NaCl. Prof. J.Al-Zehouri

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12 I- Strong acid titrated with strong base Example : Titrate of 20 ml HCl 0.1 N with 0.1 N of NaOH. Prof. J. Al-Zehouri

13 1- Determine the Initial ph value Initial ph = the ph of HCl solution before the begin of titration. ph = - log C = - log 0.1 =1 So the x and y values for the Initial Point= ph = 1, V = 0 ml Prof. J. Al-Zehouri

14 2- Determine The Equivalent Point HCl + NaOH NaCl + H 2 O After the Consume of 20 ml of NaOH NaCl = Neutral ph = 7 So the x and y values for Equivalent Point= ph = 7, V = 20 ml Prof. J. Al-Zehouri

15 Determine the Intermediate Points Prior to equivalence point ( HCl+NaCl) We will determine only the points due to the correct ph value. At ph=2 ph=2 =-log [HCl] = -log 0.01N = - log 10-2 The Concentration of acid decreased 9 time( = 0.09) 90 % consumed (18 ml), remained 10%(2ml) The x and y values for the 1. intermediate point = ph = 2, V = 18 ml Prof. J. Al-Zehouri

16 At ph = 3 ph = 3 3 = - log [HCl] = - log = - log 10-3 The HCl concentration decrease 9 times ( = 0.009) ( 2 /10 x 9 = 1.8 ml ) = 19.8 ml (99%) Remain 2x0.1 = 0.2 ml The x and y values for 2. intermediate point: ph = 3, V = 19.8 ml Prof. J. Al-Zehouri

17 At ph = ml ph= 4 = - log[hcl] =- log0.000 = - log 10-4 HCl concentration decrease 9 times ( = ) 0.2/10 x 9 = = ml ( 99.9%) HCl remain = = 0.02ml. The x and y values for 4. Intermediate point = ph = 4, V = 19,98 ml Prof. J. J.Al-Zehouri

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19 Titration jump End point Equivalent point Titration curves for strong acid (20 ml HCl 0.1N with strong base ( NaOH 0.1 N) Prof. J. Al-Zehouri

20 Compare between strong acid and weak acid Prof. J. Al-Zehouri

21 Acid-base titration in aqueous media Reference electrode (Ag/AgCl) Indicator electrode Glass, Prof. J.Al-Zehouri

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23 Azelastine Hydrochloride Assay: Dissolve 0.3 g in 5 ml of anhydrous formic acid, add 30 ml of acetic anhydride and carry out Method I for nonaqueous titration, Appendix VIII A, determining the end- point Potentiometrically. Each ml of 0.1M Perchloric acid VS is equivalent to mg of C22H24ClN3O,HCl. Prof. J.Al-Zehouri

24 Trazodone Hydrochloride Assay: Dissolve 0.3 g in 60 ml of glacial acetic acid, add 5 ml of mercury (II) acetate solution and carry out Method I for nonaqueous titration, Appendix VIII A, determining the end point Potentiometrically. Each ml of 0.1M Perchloric acid VS is equivalent to mg of C19H22ClN5O,HCl. Prof. J.Al-Zehouri

25 Amprolium Hydrochloride Assay : Carry out Method I for non-aqueous titration, Appendix VIII A, using 0.3 g and 1- naphtholbenzein solution as indicator. Each ml of 0.1M Perchloric acid VS is equivalent to mg of C14H19ClN4,HCl. Prof. J.Al-Zehouri

26 Sulfaguanidine ASSAY : Dissolve g in 50 ml of dilute hydrochloric acid R. Cool the solution in iced water. Carry out the determination of primary aromatic amino-nitrogen (2.5.8), determining the end-point electrometrically. 1 ml of 0.1M sodium nitrite is equivalent to mg of C7H10N4O2 S. Prof. J.Al-Zehouri

27 Non aqueous Neutralization Titration Prof.J. Al-Zehouri

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30 Titration of weak base in nonaqueous solvents Prof. J. Al-Zehouri

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33 Titration of halides weak base in nonaqueous solvents Prof. J. Al-Zehouri

34 Titration of haloids weak base in nonaqueous solvents 2 R 3 NH + Hal - + Hg(OAC) 2 2R 3 NH +.2OAC - + HgHal 2 Prof. J.Al-Zehouri

35 Titration of weak acid in nonaqueous solvents Prof. J.Al-Zehouri

36 Titration of weak acid in nonaqueous -SH, -SO2,-OH ( Sulphathiazole, Phenobarbital.. The most common standard solution: Sodium methoxide, Tetrabutylamoniumhydroxide (TBAH) in MeOH, The most comment nonaqueous solvent: DMF, Butyl amine, Pyridine,Toluene Indicators ( Thymole blue, Brome thymolblue, Prof. J.Al-Zehouri

37 Adrenaline / Epinephrine C9H13NO3 Assay Carry out Method I for non-aqueous titration, Appendix VIII A, using 0.3 g and crystal violet solution as indicator. Each ml of 0.1M perchloric acid VS is equivalent to mg of C9H13NO3. Prof. J. Al-Zehouri

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39 Sulfathiazole C9H9N3O2 S2 ASSAY Dissolve 0.2 gram of sulphathiazole in 20 ml of DMF, add 2 drops of thymol blue solution which prepared in DMF. Titrate with 0.1 M Sodium methoxide solution VS, until the color change from yellow to blue. Each 1 ml of 0.1 M of NaOCH 3 is equivalent to gram of C 9 H 9 N 3 O 2 S 2. Prof. J. Al-Zehouri

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43 Potentiometry The equipment required for Potentiometric methods is simple and inexpensive and includes : 1- a reference electrode( SHE,SCE,Ag/Ag Cl) 2- an indicator electrode ( glass) 3- and a potential measuring device Prof. J.Al-Zehouri

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45 Acid-base titration in aqueous media When we measure the Potential =Potentiometric When we measure the ph = ph-meter. Reference electrode ( SCE = Saturated Calomel electrode ) ph = Constant ( Dose not effect with proton concentration. Indicator electrode (= working electrode) glass electrode ( ion selective electrode) ph=variable. Prof. J.Al-Zehouri

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