Lecture 15 - Analytical Methods Flashcards
What does pharmaceutical analysis do?
determines the quality of drug products via analytical chemistry
What are the variety of analytical techniques?
spectroscopic, chromatographic and diffraction
What does each technique play a role in?
determining the quality of the pharmaceutical product and excipients
How to analyse pharmaceutical products?
UV/Vis spectroscopy
high pressure liquid chromatography
How to analyse the solid product?
Infrared spectroscopy
xray diffraction
UV/Vis spectrum?
radiate a UV light source through the sample, molecules absorb different wavelengths of radiation and the light which isn’t absorbed reaches a detector which allows us to plot absorbance vs wavelength
What is the lowest energy transitions?
rotational
What radiation induces transitions within rotational energy levels?
microwave raidation
What induces transitions within the vibrational energy levels?
Infrared radiation
What induces transitions within the electronic energy levels?
UV/Vis wavelengths
What are transitions?
electrons jumping from low energy states to high energy states
What else is related to electronic?
fluorescence and phosphorescence - related to changes in electronic structure
At room temp, what states are most molecules in?
ground vibrational and electronic states
How do molecules absorb radiation?
if polychromatic light of the correct wavelength interacts with the molecules
What happens to certain types of electrons?
they will be excited to higher energy states (electron transition)
What is the excitation accompanied by?
invariably accompanied by an increase in the energy levels of rotational and vibrational states
Where can transitions occur between?
between low electron energy levels to higher electron energy levels
can also get transitions from within the rotational energy levels, e.g. from first rotational level in the lower state to first in the higher state
What type of electronic transitions do not follow the specific pattern?
one that goes from the highest rotational energy level on the lower level, to the first rotational energy level on the higher level
How does a conventional spectrophotometer work?
polychromatic light source hits a diffraction grate, which splits the light up into its individual wavelengths (spectrum)
the exit slit then selects particular wavelengths of light that have come off the diffraction grate and allow it to pass through our sample
the sample absorbs some of the light and what isnt absorbed passes through to the PMT, which amplifies the signal
What is the PMT?
photomultiplier tube
How does a PDA spectrophotometer work?
polychromatic light passes through the whoe sample and the light is absorbed by the molecules contained
the light which is not absorbed passes through the diffraction grating, which seperates out the polychromatic light into a spectra
we then have a photodiode array which is a series of photosensitive diodes and each wavelength of light hits a specific diode
Benefits of PDA spectrophotometer?
increases the speed of analysis and allows us to asses the effect of interfering peaks more accurately
they are more expensive and have few moving components
Disadvantages of conventional spectrophotometer?
require more maintenance because they have many moving components
What is beer’s law?
the intensity of a beam of parallel monochromatic light decreases exponentially with the number of absorbing molecules
absorbance is proportional to the concentration
