DSC and DTA

Differential thermal analysis & differential scanning

calorigraphy

By wilwin edara (I/II M.Pharm) CHIPS

Thermal Analysis Techniques

A group of techniques in which a physical property is measured as a function of temperature. The sample is subjected to a predefined heating or cooling program.

Types of thermal analysis

TG (Thermo gravimetric) analysis: weight

DTA (Differential Thermal Analysis): temperature

DSC (Differential Scanning Calorimetry): temperature

Differential thermal analysis

Le-Chateliar studied clays & minerals by an examination of temperature –time curves.Later Robert Austen improved technique by introducing thermocouples. Definition: DTA is a technique in which the temperature between sample & thermally inert reference substance is continuously recorded as a function of temperature /time.

In DTA both test sample & an inert reference material (alumina) – controlled heating or cooling programming.

If zero temperature difference b/w sample & reference material – sample does not undergo any chemical or physical change.

If any reaction takes place temperature difference (∆T) will occur b/w sample & reference material .

DTA Principle

Differential thermal analysis is a technique in which the temperature of the substance under investigation is compared with the temperature of a thermally inert material.

Differential Thermal Analysissample holder sample and reference cells (Al)

sensorsPt/Rh or chromel/alumel thermocouples one for the sample and one for the reference joined to differential temperature controller

furnacealumina block containing sample and reference cells

temperature controllercontrols for temperature program and furnace atmosphere

Recording system

DTA Instrument

Differential Thermal Analysis

advantages:

instruments can be used at very high temperatures

instruments are highly sensitive

flexibility in crucible volume/form

characteristic transition or reaction temperatures can be accurately determined

disadvantages:

uncertainty of heats of fusion, transition, or reaction estimations is 20-50%

Applications of Differential thermal analysis

Qualitative and Quantitative Identification of Minerals: detection of any minerals in a samplePolymeric Materials: DTA useful for the characterization of polymeric materials in the light of identification of thermo physical , thermo chemical, thermo mechanical and thermo elastic changes or transitions.Measurement of Crystalline: measurement of the mass fraction of crystalline material in semi crystalline polymers.Analysis of Biological Materials: DTA curves are used to date bone remains or to study archaeological materials.

Differential Scanning Calorimetry

this technique is developed by E.S.Watson and M.J.O’Neill in 1962. introduced commercially at the Pittsburgh Conference on analytical Chemistry and Applied Spectroscopy.First Adiabatic differential scanning calorimeter that could be used in Biochemistry was developed by P.L.Privalov in 1964.

Principle

In DSC the heat flow is measured and plotted against temperature of furnace or time to get a thermogram. This is the basis of Differential Scanning Calorimetry (DSC).

The deviation observed above the base (zero) line is called exothermic transition and below is called endothermic transition.

The area under the peak is directly proportional to the heat evolved or absorbed by the reaction, and the height of the curve is directly proportional to the rate of reaction.

DSC Curve

Heat Flux DSC•sample holder •sample and reference are connected by a low-resistance heat flow path Al or Pt pans placed on constantan disc•sensorschromel®-constantan area thermocouples (differential heat flow) chromel®-alumel thermocouples (sample temperature)•furnaceone block for both sample and reference cells•temperature controllerthe temperature difference between the sample and reference is converted to differential thermal power, dDq/dt, which is supplied to the heaters to maintain the temperature of the sample and reference at the program value

Heat flux DSC

Power Compensation DSC

sample holder Al or Pt pans

sensorsPt resistance thermocouples separate sensors and heaters for the sample and reference

furnaceseparate blocks for sample and reference cells

temperature controllerdifferential thermal power is supplied to the heaters to maintain the

temperature of the sample and reference at the program value

samplepan

DT = 0

inert gasvacuum

inert gasvacuum

individualheaters controller DP

referencepan

thermocouple

Applications of DSC Protien Stability and FoldingLiquid Biopharmaceutical Formulations Process DevelopmentProtien EngineeringRank order BindingAntibody Domain StudiesCharacterisation of Membranes,lipids,nucleiec acids & micellar systemsAssesment of the effects of structural change on a molecules stabiityMeasurement of Ultra-light molecular interactionsAssesment of biocomparability during manufracturing.

Applications of DSC

Polymers:composition of polymers is determined.Melting point and lass transition temp can be determinedThis can show the polymer degradation by lowering the melting point(Tm).Molecular weight(low grade –low melting point) can be determained.Percentage Crytallinity Thermal degradation and impurities

Liquid crystals

Oxidative Stability: stability & optimum storage conditions

Drug analysis: widely used in Pharmaceutical industry(defining processing parameters) and polymer industry(curing process.).

General Chemical analysis: Freezing point depression can be used as a purity analysis tool.Functional Applications:Binding Studies

Of DSC

Binding Sites;

References:

Instrumental methods of Chemical analysis-GURDEEP R.CHATWAL ,pg-no;701 to 739.

Instrumental methods of chemical analysis-B.K.SHARMA,pg-no;M-390 to 421.

Instrumental methods of Chemical analysis,H.KAUR.pg.no-919 to 932.

www.wikipidia.com www.microcal.com/technology/dsc.asp