m5 Miscellaneous Methods of Analysis

potentiometry

A branch of electrochemistry which deals with the study and measurement of electrode potential

POTENTIOMETRIC TITRATION

The voltage across the analyte is measured

neutral electrode

responsible for the response for the changes in solution

standard reference electrode

gives standard potential

Hydrogen electrode (SHE)

Ultimate reference electrode

Calomel electrode (SCE)

Commonly used reference electrode

Ag/AgCl electrode

Reference electrode

Membrane electrode

Ex: pH electrode)

Liquid membrane electrode

Ex: Ca2+ electrode

Membrane electrode

An electrode that relies on a glass membrane, measures a potential difference across a membrane

Liquid membrane electrode

Similar to a membrane electrode except that the membrane is an organic polymer saturated with a liquid ion exchanger, measures potential difference upon interaction of the exchanger with target ions

Solid state electrode

A very popular type of ion specific electrode

Enzyme electrode

Measures a change in pH, it is a normal pH electrode coated with a urease impregnated gel; urea will permeate the gel where the enzyme will attack resulting to the formation of ammonium

Gas sensing electrode

Measures an equilibrium change upon permeation of the target analyte through a permeable membrane

POLAROGRAPHY

A method of analysis based on the measurement of current resulting from the electrolysis of an electroactive species at a given electrode potential under controlled conditions

POLAROGRAM

The resulting graph in polarography

direct current (DC) polarography

Also known as “conventional polarography

DC Polarography

Simplest method consisting of Reference Electrode and Indicator Electrode

Reference Electrode

Acts to maintain a constant potential throughout the measuremen

Indicator Electrode

Assumes the potential impressed upon it from external source

o Animal assay

o Microbial assay

types of special methods (biological methods)

ASSAY OF VOLATILE OILS

Acetalization method

ASSAY OF VOLATILE OILS

Alcohol

bisulfite method (Cassia flask) or hydroxylamine method (titration)

ASSAY OF VOLATILE OILS

Aldehyde and Ketone

KOH method (Cassia flask)

ASSAY OF VOLATILE OILS

Phenol

Babcock bottle

ASSAY OF VOLATILE OILS

Volatile Oil in Spiri

KJELDAHL METHOD

For quantitative determination of nitrogen in organic substance

ASH CONTENT

Residue left after incineration of an organic material which represents the amount of inorganic impurity

total Ash

Residue after incinerating at 325 ± 25°C

Acid-Insoluble Ash

Residue after boiling the total ash with 3N HCl and ignitingthe remaining insoluble matter

Water-Soluble Ash

Difference in weight between total ash and residue after treatment of total ash with water

METHOD 1: KARL FISCHER METHOD

A widely used method for the quantitative analysis of water content in a variety of products.

5mg H2O = 1mL KFR

Titer Value

 High accuracy & precision

 Selectivity for water

 Small sample quantities required

 Easy sample preparation

 Short time of analysis

 Nearly unlimited measuring range

 Suitability for analysis of all forms of samples

 Independence of presence of other volatiles

 Suitability for automation

ADVANTAGES OF KARL FISCHER METHOD

METHOD II:AZEOTROPIC TOLUENE DISTILLATION

The water collected in the moisture tube during water content determination is immiscible & heavier than toluene

METHOD III: GRAVIMETRIC METHOD

Methods of choice for 1-2 g chemical sample, vegetable drugs (10g) dried for 5hrs, biologics

METHOD III: GRAVIMETRIC METHOD

The moisture content of a drug may be water of hydration or water in absorbed form

LOSS ON DRYING (LOD)

A classic laboratory method of measurement of high level moisture in solid or semisolid materials

LOSS ON DRYING (LOD)

A sample of the material is weighed, heated in an oven, cooled in a dry atmosphere of a dessicator, then re-weighed.

POLARISCOPE OR POLARIMETER

Used to measure the optical activity of liquid substances

POLARIZING MICROSCOPE

Used to measure the optical activity of solid substances

ROTATORY POWER

Also known as “optical activity”

Dextrorotatory

when the direction of the rotation is toward the right [+] (clockwise)

Levorotatory

when the direction of the rotation is toward the left [-] (counterclockwise)

volatile oils; quartz;

OPTICAL ROTATION

o Sucrose, peptides, __

o Solids w/ rotated crystal planes (__)

o __

GLUCOSE / DEXTROSE

It causes linearly polarized light to rotate to the right or to the dexter side

INVERT SUGAR SYRUP

Gets its name from the fact that the conversion causes the direction of rotation to “invert” from right to left

 Length of the column through which the light passes

 Concentration of sample

 Wavelength of light employed

 Temperature

 Nature of substance

FACTORS AFFECTING THE ANGLE OF ROTATION

 In the sugar industry – to measure syrup concentration

 In optics – to manipulate polarization

 In chemistry – to characterize substances in solution

 In optical mineralogy – identify certain minerals, in thin sections

 In medicine – to measure blood-sugar levels in diabetic patients

APPLICATIONS OF OPTICAL ROTATION

REFRACTOMETRY

It deals with the study and measurement of index of refraction of substances in order to assess their composition of purity

REFRACTOMETRY

A technique that measures how light is bent/refracted, when it passes through a liquid substance

REFRACTOMETER

An instrument that measures the extent to which the light is bent/ refracted, when it moves from the air / vacuum into the sample

ABBE REFRACTOMETER

a bench top instrument, offers the highest precision

REFRACTIVE INDEX

It is the ratio of the velocity light in air to the velocity of light in a liquid sample being measured

REFRACTIVE INDEX

It is a physical property/characteristic of a PURE COMPOUND

REFRACTIVE INDEX

The amount by which light is refracted determines its “__“

UNITLESS

REFRACTIVE INDEX

Refractive index number or values are __

589 nm

REFRACTIVE INDEX

Both temperature of the sample and the wavelength of light (the sodium D line of __) should be held constant

1.3000 to 1.7000

REFRACTIVE INDEX

It usually ranges between __ for most compounds

Normally determined up to a 5-digit precision

REFRACTIVE INDEX

Confirmation of the IDENTITY of an unknown liquid compounD

REFRACTIVE INDEX

Assessment of the PURITY of a liquid compound, in comparison with a known /standard