Advance Pharmaceutical Analysis PDF

Advance pharmaceutical analysis Dr. Ahmed Thamer Al-Saffer Pharmaceutical analysis Classic Odor Color Melting point Boiling point derivatives Spectroscopic UV-Vis FTIR NMR(H1 C13) Mass SCHN X-ray  Spectroscopic methods depend on the interaction between matter and electromagnetic radiation each one...

Advance pharmaceutical analysis Dr. Ahmed Thamer Al-Saffer Pharmaceutical analysis Classic Odor Color Melting point Boiling point derivatives Spectroscopic UV-Vis FTIR NMR(H1 C13) Mass SCHN X-ray  Spectroscopic methods depend on the interaction between matter and electromagnetic radiation each one has specific uses  UV-Vis used to know the unsaturation and resonance in the compounds  FTIR used to identifying the functional group  NMR identifies the environments of protons and carbons in compounds  Mass indentifies the molecular weight of the compounds  SCHN element analysis gives the percentage of the presence of sulfur ,carbon, nitrogen and hydrogen in the compound respectively  Introduction  Every spectrometer must consisted of 5 parts  1- electromagnetic radiation source which depends on the type of radiation to be used  2- sample holder  3- monochromator which select the wavelength  4- detector for signals  5- recorder the output signal data Electromagnetic waves are characterized by a wavelength, a frequency, and an amplitude. (a) Wavelength (l) is the distance between two successive wave maxima. Amplitude is the height of the wave measured from the center. (b)–(c) What we perceive as different kinds of electromagnetic radiation are simply waves with different wavelengths and frequencies. UV-Vis spectroscopy The wavelengths of UV light absorbed by a molecule are determined by the electronic energy differences between orbitals in the molecule. The range of vacuum ultraviolet (vacuum UV) is below 200nm The range of UV radiation is between (200-380)nm The range of visible radiation is (380-800) nm UV-Vis can be used in qualitative and quantitative In quantitative we can know the concentration of compounds by using calibration curve In qualitative each compound has its own wavelength like tetracycline has ƛmax 220nm while amoxicillin trihydrate ƛmax 230 nm Selection rules  Each material absorbs specific amount of energy  The electron excitation happened when the electron absorbs the radiation and transferred from ground state to excited state  The irradiation of organic compounds does not always give rise to excitation of electrons from any filled orbital to any unfilled orbital, because there are selection rules based on symmetry governing which transitions are allowed. The intensity of the absorption is therefore a function of the ‘allowedness’ or otherwise, of the electronic transition and of the target area able to capture the light Absorption low  Beer - Lambert laws is widely used in UV-visible spectroscopy, for quantitative analysis such as concentration determination; and qualitative analysis such as identification of molecule properties. The Beer Lambert law is given as  A= ε l c  where, A is the absorbance (=log(І0\ Іt) ),  I0 is the intensity of incident light, Іt intensity of transmitted light  ε is molar absorption coefficient,  l is the sample length  c is the concentration. Measurement of the Spectrum  The ultraviolet or visible spectrum is usually taken using a dilute solution. An appropriate quantity of the compound (often about 1 mg when the compound has a molecular weight of 100–400) is weighed accurately,  The excitation of electrons is accompanied by changes in the vibrational and rotational quantum numbers so that what would otherwise be an absorption line becomes a broad peak containing all the vibrational and rotational fine structure. Because of interactions of solute with solvent molecules this is usually not resolved, and a smooth curve is observed  E total = E electronic + E vibrational + E rotational The spectrum of UV-Vis The spectrum is drawn between A (absorbance) and wavelength ƛ the wavelength at which the absorbance will be the highest (peak) Called ƛmax Some important definitions  Chromophore a chemical group (such as an azo group) in the molecule responsible for the colour in any compound. A chromophore may correspond to a functional group (e.g. the double bond in a carbonyl group or alkene).  Auxochromes (auxiliary chromophores) are groups which have significant effects on the absorption (both ƛ max and ε) of a chromophore to which they are attached. Or is the part of the molecule responsible for the intensity of colour in any compound Generally, auxochromes are atoms with one or more lone pairs of electrons e.g. -OH, -OR, -NR2, halogen  Red shift or bathochromic effect. A shift of an absorption maximum towards longer wavelength. It may be produced by a change of medium or by the presence of an auxochrome.  Blue shift or hypsochromic effect. A shift towards shorter wavelength. This may be caused by a change of medium and also by such phenomena as the removal of conjugation.  Hypochromic effect. An effect leading to decreased absorption intensity.  Hyperchromic effect. An effect leading to increased absorption intensity   Types of electronic transition δ-δ* very high energy needed vacuum UV happens in saturated hydrocarbons π- π* happens in unsaturated compounds (contain π bond) alkene , alkyne  n- π* happens in compounds containing N,O,S and P atoms with π bonds like ketone and nitrile  n- δ* happens in compounds containing N,O,S and P atoms with no π bonds like amines and alcohols (saturated compounds)  δ is bonding orbital δ* is anti-bonding orbital  π is bonding orbital π* is anti-bonding orbital  n is non-bonding orbital   Sigma bonds are very stable, and the electrons in sigma bonds are usually unaffected by UV wavelengths of light above 200 nm. Pi bonds have electrons that are more easily excited into higher energy orbitals. Conjugated systems are particularly likely to have low-lying vacant orbitals, and electronic transitions into these orbitals produce characteristic ultraviolet absorptions Light of wavelength between about 4000 A and 7500 A (400-750nm ) is visible. Just beyond the red end of the visible spectrum  nm =nanometer Solvent effect π-π*  the excited state π* is more polar then the ground state πthe dipoledipole interactions of molecules with solvent molecules will lower the energy of π* more than π. Thus the difference in energy in polar solvent is less then in nonpolar solvent leading to red shift (lower energy and higher wavelength ) Solvent effect on n-π*  The polarity of n electrons are more then π* The solvent effect is now can make hydrogen bond in the ground state n more than in the state (π*) leading to lowering energy of (n) more then π*here the difference in energy in the polar solvent is more then nonpolar solvent leading to blue shift (lower wavelength and higher energy) The effect of conjugation As we can see in the following figure the conjugation in the molecules lead to lowering energy red shift