AMPEROMETRY ppt

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AMPEROMETRY P.GOUTAMI, M.PHARM (Pharmaceutical analysis and quality assurance) JNTU, Hyd.

Flow of presentation :: 

Flow of presentation : Definition Principle Criteria for performing amperometric titrations Apparatus Rotating platinum electrode Types of amperometric titrations Commercially available amperometers Advantages Applications

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Definition: Amperometric titration refers to a class of titrations in which the equivalence point is determined through measurement of the electric current produced by the titration reaction. It is a form of quantitative analysis . Otherwise called as Polarographic or polarometric titrations. Indicator microelectrode: DME or RPE Reference electrode: SCE

Principle:: 

Principle : According to Ilkovic equation id is proportional to concentration keeping all other factors of the equation constant. So, if some of the electroactive material in the solution is removed by interaction with some other reagent the diffusion current will decrease proportionally. i d = 607 n C D 1/2 m 2/3 t 1/6

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The diffusion current at an appropriate applied voltage is measured as a function of the volume of the titrating solution . The end point is the intersection of two lines giving the change of current before and after the equivalence point.

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The migration current is minimised by adding sufficient qty of supporting electrolyte. Mechanism of the supporting electrolyte???

Difference between amperometry and polarography????? : 

Difference between amperometry and polarography ?????

Criteria for performing amperometric titrations: : 

Criteria for performing amperometric titrations: Either the titrate or titrant ot both should be electroreducible . The potential applied should correspond to the limiting current.

Apparatus : 

Apparatus Rotating Pt micro electrode burette SCE

Apparatus : 

Apparatus Pyrex glass, that is a three necked , flat−bottomed flask a micro burette, dropping mercury electrode( ind ’- polarisable ) gas outlet tube for N2 with an additional inlet N2 provision connected to a reference electrode( SCE - non- polarisable )

Rotating platinum electrode : 

Rotating platinum electrode Y Platinum???

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Mercury cannot be used as electrode at positive potentials because of its oxidation rotating platinum electrode is used

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y rotating ???

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With platinum as electrode, the attainment of steady state diffusion current is slow One has to wait for a considerable time after each addition of the reagent Therefore platinum electrode is rotated at 600 rpm .

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RPE

RPE: 

RPE Glass rod with a bent Pt wire at its tip – 600rpm. Wire contacts are made through a mercury reservoir so that potential can be applied and the current is measured . Nitrogen gas is bubbled through the titrate to remove oxygen.

Types of amperometric titrations : 

Types of amperometric titrations Titration of electro reducible ion Vs non reducible ion Titration of non reducible ion Vs electro reducible ion. Titration of electro reducible ion Vs electro reducible ion. Biamperometry

Titration of electro reducible ion Vs non reducible ion : 

Titration of electro reducible ion Vs non reducible ion Ex: lead( )Vs sulphate ions ( ) Addition of sulphate ions

Titration of non reducible ion Vs electro reducible ion. : 

Titration of non reducible ion Vs electro reducible ion . Ex: chloride( ) Vs silver ions( ) Addn of silver ions

Titration of electro reducible ion Vs electro reducible ion. : 

Titration of electro reducible ion Vs electro reducible ion. Ex: lead ( ) Vs dichromate ions( ) Addn of dichromate ions

At the applied potential substance gives anodic current and titrant cathodic current.: 

At the applied potential substance gives anodic current and titrant cathodic current. Ex: ( eg . I− ion with Hg(NO3)2 )

Biamperometry : 

Biamperometry Difference from amperometry ??? a pair of identical metallic or solid microelectrodes/polarized electrodes are used. SCE is replaced with platinum electrode in the electrolysis cell. a magnetic stirrer is used.

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A fixed potential difference of 10-20 mV is applied between the two electrodes through the adjustment of resistance variable potentiometer, R (1000 ohms). One electrode as anode and the other cathode .

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Applicable when redox system is present before and after the end point. Ex: KARL FISCHER TITRATION (end pt) A small potential is applied between the 2 similar Pt electrodes. Initially when water is present both electrodes are depolarised .

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Addition of KF reagent (sol of iodine and in pyridine and methanol) till the end pt - decreases at the end point . is almost zero at the end point. After the end point gradually increases due to the addition of the titrant . Dead- Stop End Point Method

KF Titrator manufactured by Metrohm India ltd: 

KF Titrator manufactured by Metrohm India ltd

Other examples of dead stop end point technique: : 

Other examples of dead stop end point technique: Titration of sodium thiosulphate with iodine . Determination of nitrate ion by titrating with ammonium iron (II) sulphate solution in a strong sulphuric acid medium.

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Commercially available amperometers

vintage amperometer (about 1950) : 

vintage amperometer (about 1950)

(mechanical guage)amperometer: 

(mechanical guage ) amperometer

Product details: : 

Product details: Mnf company : Ruian Kangertai Automobile Parts Co., Ltd. Brand Name: Kangertai Place of Origin: China Model No: CS033

4-20 mA Amperometer(HI 931002) by Hanna instruments services,italy : 

4-20 mA Amperometer (HI 931002) by Hanna instruments services,italy

Product details: : 

Product details: Mnf company : Xiamen Dexing Imp. & Exp. Co., Ltd. Place of Origin : Fujian, China (Mainland) Brand Name : Dexing Model Number : D26-A,D61-A,D76-A,D9-A,T51-A,T77-A,T63-A Display Type : Analog and Digital Measuring Range : 0-75-150-300-600V Accuracy Class : 0.5

Hach company AutoCAT 9000 chlorine amperometric titrator: 

Hach company AutoCAT 9000 chlorine amperometric titrator

Advantages of amperometry:: 

Advantages of amperometry : Rapid , simple apparatus. Titrations can be carried out in cases in which the solubility relations are such that potentiometric or visual indicator methods are unsatisfactory . Ex:? can be carried out at dilutions (10−4 M) at which many visual or potentiometric titrations no longer yield accurate results.

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supporting electrolyte( without interference ) - to eliminate the migration current which is not possible in case of conductometric titration. The temperature need not be known provided it is kept constant during the titration. The reactions can be reversible or irreversible. Non reducible ions which cannot be determined by polarography can be determined easily.

Applications of amperometric titrations : 

Applications of amperometric titrations

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wider range of applications than polarography because even electro-inactive substances can be determined using electro-active titrant . Quantitative (end point) Determination of water using KF reagent ( biamperometry ) Quantification of ions or mixture of ions.

Determination of various species:: 

Determination of various species: Titrant Electrode Species determined 1.Complexometric rxns EDTA DME Many metallic ions 2.Pptn titrations Dimethyl glyoxime Lead nitrate Mercury(II) nitrate Silver nitrate Sodium tetraphenyl borate DME DME DME RPE Graphite Ni2+ Sulphate , F- I- Cl -, Br-, I-, CN- K+ 3.Oxidation rxns KBrO3 RPE As(III), Na2S2O3 4.Addition rxns RPE Alkenes Substitution rxns RPE Some phenols, aromatic amines

Amperometric detection in HPLC : 

Amperometric detection in HPLC Amperometric Detection in HPLC for Determining Organic Acids in Fermented Foods. http://www.electrochem.org/dl/ma/203/pdfs/2933.pdf HPLC with amperometric Detection of Medroxyprogesterone Acetate in Human Plasma. http://www.scienceasia.org/2007.33.n4/v33_405_410.pdf

Amperometric detector: 

Amperometric detector Optimum for High-sensitivity Analysis of Carbohydrates and Polyols in the pharmaceuticals !!! Derivatization and other complex pretreatments are not necessary. The sensitivity is about 10 to 100 times greater than that of a differential refractometer . http://www.dionex.com/en-us/webdocs/5046-An117.pdf

AutoCAT 9000 Chlorine Amperometric Titrator Pre-Programmed for Easier Use: 

AutoCAT 9000 Chlorine Amperometric Titrator P re-Programmed for Easier Use

AutoCAT 9000 Chlorine Amperometric Titrator : 

AutoCAT 9000 Chlorine Amperometric Titrator Automatic calculation of analyte concentration. Automatic hands-free operation. Easy to use. Real-time graphics and graphic print output. Automatic archiving of results. Titrant calibration. Electrode cleaning. Greater accuracy and precision than manual titrations.

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Amperometry uses a carbon electrode to record changes in the chemical composition of the oxidized components of a biological solution. used for studying exocytosis in the neural and endocrine systems bcoz many monoamine tansmitters are oxidisable . http://en.wikipedia.org/wiki/Electrophysiology

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Amperometric determination of acetylsalicylic acid in drug formulations using copper electrode in alkaline solutions. http://144.206.159.178/FT/1000/73279/1255808.pdf

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Amperometer measures glucose levels from tears - A report appears in ACS journal Analytical Chemistry . ( ongoing effort ) http://www.knowabouthealth.com/amperometer-measures-glucose-levels-from-tears/9097/

Amperometry Videos on :: 

Amperometry Videos on : http://www.youtube.com/watch?NR=1&v=OUN8oY6kcXw&feature=endscreen

References : 

References Wikipedia http://vedyadhara.ignou.ac.in/ Vogel's TB of Quantitative Chemical Analysis 5ed.

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Thank u