UV-VIS application and infrared spectroscopy

UV-VIS application and infrared spectroscopy

Absorption and emission of radiation:

  • UV-vis absorption is where electrons are excited

  • Fluorescence emission is when electrons return back

  • Infra-red is where vibrations are excited

BP drug content assay:

  • Beer lambert law: C= A/A1% 1cm

  • Tablets and capsules have specific dissolution profiles to make sure they dissolve in a certain amount of time to prevent passing though body without providing a therapeutic effect

  • Coated tablet >> coating dissolves>> tablet>> disintegration>> granules >> disaggregation>> powder>> dissolution >> solution

  • Capsule>> opening of capsule>> granules >> disaggregation>> powder>> dissolution >> solution

Acceptance criteria- Q value:

  • For immediate release produces that have a specification on the quantity of drug that should be released in a specified time

  • Q value is % of drug content released in given unit of time

  • Typical q specification for active ingredient ranges from 70-80%

Infrared spectroscopy (IR)

  • Near IR is 780-2500nm this used for physical properties

  • Middle IR is 2500-15000nm and is used for characterisation

  • IR spectroscopy uses wavenumbers

Energy states:

  • IR causes vibrational and rotational excitations which have smaller energy gaps

  • Molecules are excited to high vibrational state

  • Absorption is quantized to match energy gap between vibrational states

  • Only frequencies corresponding to natural vibrational frequencies of bonds are absorbed

  • IR is absorbed and converted to molecular vibrations with higher amplitude

  • Vibrational levels have rotational levels which result in broader peaks

Vibration rules:

  • No fixed bond length

  • Frequent at which a given bond can vibrate is constant

  • Certain bonds can only absorb certain frequencies

  • In Mid IR region can only go from V0 to V1, V1 to V2 not directly from V0 to V2

  • Different bonds vibrate at different natural frequencies

  • Vibration is dependent on environment

  • No two molecules will have the exact same fingerprint (region)

Types of vibration

  • Stretch

    • Symmetrical stretch

    • Asymmetrical stretch

  • Bending

    • In plane bending:

      • Scissoring

      • Rocking

    • Out of plane bending

      • Wagging

      • Twisting

  • Stretching requires more energy than bending

Are all vibrations IR active?

  • Not all vibration are IR active

  • Only the vibration which result in a net change in polarity of a bond give rise to IR bands

  • Bigger the dipole moment change the stronger the absorption

  • Dipole moment must change during vibration otherwise no IR absorption - symmetrical stretches have no peaks

Dipole moment:

  • A dipole moment is where two atoms with different electronegativities connected by bond exhibit unequal sharing of electron density

Uses of IR spectroscopy:

  • Identify drugs by matching spectrum

  • Functional group analysis

  • Detect polymorph of drugs

Instrumentation

  • Dispersive instrument

    • Infrared radiation passes through the sample and a reference cell. The reference ensures peaks due to water/ carbon dioxide in air can be cancelled out

    • Frequencies are determined by passing through a rotating prism to focus frequency at a time on detector

  • Fourier transform instrument:

    • Instead of monochromator a interferometer is used

    • Interferometer produces pattern of frequencies that are possible to resolve by mathematical transformation (Fourier transform)

    • High data acquisition speed

Sample preparation:

  • Can be any nature

  • Liquid:

    • Prepare liquid film between Nacl,Kcl or KBr

    • Solid can be grinded to form a paste between liquid paraffin

    • Drop of sample placed between two circular plates

    • Plates placed in a holder

  • Solids/disk prepartion

    • Use powdered sample with dry KBr and grind finely

    • Using spanner + nuts and bolts compress under high pressure

    • Forms a disk which can be placed in IR machine

Application of near IR:

  • Quality control

  • Particle size

  • Blend uniformity

  • Identification of polymorphic drugs

  • Determination of moisture