Pharmaceutical Instrumental Analysis Prof.Dr.Joumaa Al- Zehouri Damascus university Faculty of Pharmacy
An Introduction to Electroanalytical Chemistry ( Potentiometry) Reference Indicator
Electroanalytical chemistry Potentiometry Coulometry Voltammetry ( Polarography) Prof. J.Al-Zehouri
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
Potentiometric Titration (Ph. Eur. method 2.2.20) 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.
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
Prof. J. Al-Zehouri
Principle of volumetric titration A + B C + D B A A C D C D C D B Equivalent Point Prof. J. Al-Zehouri
Anhydrous Citric Acid C 6 H 8 O 7 192.1 ASSAY Dissolve 0.550 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 64.03 mg of C6H8O7. Prof. J. Al-Zehouri
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 5.844 mg of NaCl. Prof. J.Al-Zehouri
Prof J. Al-Zehouri
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
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
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
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( 0.1-0.01 = 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
At ph = 3 ph = 3 3 = - log [HCl] = - log 0.001 = - log 10-3 The HCl concentration decrease 9 times ( 0.01 0.001= 0.009) ( 2 /10 x 9 = 1.8 ml ) 18+1.8= 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
At ph = 4 0.2 ml ph= 4 = - log[hcl] =- log0.000 = - log 10-4 HCl concentration decrease 9 times ( 0.001-.0001 = 0.009 ) 0.2/10 x 9 = 0.18 + 19.8 = 19.98 ml ( 99.9%) HCl remain = 0.2-0.18 = 0.02ml. The x and y values for 4. Intermediate point = ph = 4, V = 19,98 ml Prof. J. J.Al-Zehouri
Prof. J. Al-Zehouri
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
Compare between strong acid and weak acid Prof. J. Al-Zehouri
Acid-base titration in aqueous media Reference electrode (Ag/AgCl) Indicator electrode Glass, Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
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 41.84 mg of C22H24ClN3O,HCl. Prof. J.Al-Zehouri
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 40.83 mg of C19H22ClN5O,HCl. Prof. J.Al-Zehouri
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 15.77 mg of C14H19ClN4,HCl. Prof. J.Al-Zehouri
Sulfaguanidine ASSAY : Dissolve 0.175 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 21.42 mg of C7H10N4O2 S. Prof. J.Al-Zehouri
Non aqueous Neutralization Titration Prof.J. Al-Zehouri
Prof. J. Al-Zehouri
Prof. J. Al-Zehouri
Titration of weak base in nonaqueous solvents Prof. J. Al-Zehouri
Prof. J. Al-Zehouri
Prof. J. Al-Zehouri
Titration of halides weak base in nonaqueous solvents Prof. J. Al-Zehouri
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
Titration of weak acid in nonaqueous solvents Prof. J.Al-Zehouri
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
Adrenaline / Epinephrine 183.2 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 18.32 mg of C9H13NO3. Prof. J. Al-Zehouri
Prof. J. Al-Zehouri
Sulfathiazole 255.3 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 0.025532 gram of C 9 H 9 N 3 O 2 S 2. Prof. J. Al-Zehouri
CH 3 ONa CH 3 O - + Na + Prof. J. Al-Zehouri
Prof. J. Al-Zehouri
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
Prof. J.Al-Zehouri
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
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
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Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri
Prof. J.Al-Zehouri