Lecture 3: Challenges of CV disease - Formulation and practice Flashcards
What are the strengths of UV/Vis spectroscopy in pharmacy? (3)
- Easy to use, cheap and robust
- Quantitative measurements of drugs in formulations
- Routine methods to asses physiochemical properties of drug
What are the limitations of UV/Vis spectroscopy in pharmacy? (4)
- Only moderately selective
- Drugs need to have a chromophore
- Not readily applicable to analysis of mixtures
- Lack specificity
What is spectroscopy?
The study of molecular structure and dynamics through the absorption, emission and scattering of light
What is light?
An electromagnetic field characterised by a frequency f, velocity v and wavelength
What is the relationship of light
f = v/ wavelength
What colour does the human eye see when light is transmitted?
The colour complementary to that which is absorbed
How is transmittance calculated?
T = lt/l0
How is absorbance calculated?
A = log10 l0/lt
What is the beer lambert law?
A=abc
What is a?
Absorptivity
What are the two forms of absorptivity?
Molar and specific
What is b?
Pathlength
What is c?
Concentration of analyte / chromophore in solution
What is quantitative analysis?
Single absorbing substance - two ways of determining the concentration of an unknown solution
What are the two methods of quantitive analysis?
- Use of a literature A (1%, 1cm) or E values
- Use of a calibration line/ curve
When is a literature value used?
- When a pure standard is not available
- Used in many blood pressure assays
How do you calculate absorbance and wavelength scales of the spectrophotometer?
y = mx + c
What is y?
Absorbance
What is m?
Slope of the line
What is x?
Concentration (how far along)
What is c?
Intercept
- Should be zero or negligible
How is the validity of Beers Law checked?
- Use calibration line to determine concentration of the sample either manually or by linear regression (equation)
- For linear regression, rearange the equation to solve for x (ie unknown concentration)
- Need to use pure standard, prepare standard solutions
What absorbing components can pharmaceutical samples contain?
- Active ingredients
- Excipients: preservatives/ anti- oxidants, binders, disintegrants, colouring/ flavouring agents
- Impurities from synthesis: starting materials, byproducts, intermediate products
What are the units of ε ?
liters/mole cm
what is ε?
Molar absorptivity
What can ε be known as?
- Molar absorption coefficient
- Extinction coefficient
What is A (1%, 1cm)
The absorbance of a 1g/100ml solution in a 1cm cell
How can drug release be monitored?
UV visable spectroscopy
What is esmolol?
Beta blocker
How does UV spectroscopuy lack specificity?
On an abosrbance graph the shape of the graph for different drugs may be the same so cant differentiate between different drugs.
What range does UV vis specrometry cover?
Ultraviolet / visable range
What is used to calculate how much energy a specific type of EM radiation carries?
E=hc/ wavelength
How does a spectrophotometer work?
Select a wavelength that we know will excite electrons to go to a higher level.
Spectrophotometer has a light source that is split into the different components of the light.
A selector selects the correct wavelength to be shown on the sample
The spectrophotometer detects ho much light is being shone on the detector
Where does the UV spectra start?
200nm
Where does the visable spectra start?
700nm
What is a chromophore?
A chemical structure that loves to absorb specific wavelengths of light
Name a good chromophore
Benzene rings are good chromophores because of the type of orbitals it has. The electrons can be excited to higher orbitals.
What is transmittance?
The transmitted light
what is Io?
Incidence light - the light shone onto the sample, it has a certain length. Some of this light is absorbed by the compoundd present in the cuvette, the compound in the solution has a chromophore and can absorb some of the light. The amount of transmited light is less than what is being shined into the sample.
What is It
The amount of light that comes out at the end of the cuvette
What is Io?
How much light is put into the cuvette
What does an increase in chromophore mean?
The concentration of the compound is increased so less light is transmitted from the cuvette
What effect does making the cuvette wider have?
More chromophore in the cuvette, so less light comes out the other end as more is absorbed by the chromophore in solution
What is the pathlength?
Length the light travels in the cuvette.
How does a high concnetration of chromophore affect the transmittance value?
Transmittance value becomes small
What is the Beer lamberts law?
A simple version of calculating the absorbance
What does the beer lambarts law state?
Absorbance is porportional to pathlength and concnetration
What is beer lamberts law used to calculate?
How much drug is in solution
What is another name for molar absorptivity?
Molar exctinction coefficiant
Why is y=mc+c a straight line?
Absorptivity is porportional to concentration
