Analytical Techniques Flashcards
to analyse small drug molecules what analytical technique would you use?
uv
to analyse carbohydrate and sugar what analytical technique would you use?
light scattering detector or refractive index
give examples of possible things that can be used as a mobile phase?
- gas
- liquid
- superficial fluid
give examples of possible things that can be used as a stationary phase in chromatography?
- solids
- liquids
- gels
how do you calculate the distribution constant (Kc)?
concentration in the stationary phase / concentration in mobile phase
how do we calculate the retention volume of a retained sample (VR)?
retention time of retained sample (tR) x mobile phase flow rate (F)
how do we calculate the retention volume of an unretained sample?
retention time of unretained sample (tM) X mobile phase flow rate (F)
what happens to the retention volume in a given chromatographic system?
it stays constant
what is retention time directly proportional to?
Retention time is directly proportional to
the flow rate of the mobile phase
what is the distribution constant (Kc) for non-retained compounds?
zero
what happens to Kc as a compound becomes more retained?
it increases
what effect does changing column length have on retention volume and time?
Changing for example the column
length will change the retention volume, and thus the
retention time
when k=1, what does that mean?
the sample spends half its time in the mobile phase and half in the stationary phase
if k=3 what does that mean?
the sample spends 1/4 of its time in the mobile phase and 3/4 in the stationary phase
how do we calculate the separation factor between two adjacent peaks?
K2/K1 (peak 2/peak 1)
what is the resolution of an elution?
a quantitative measure of how well 2 elution peaks can be differentiated in a chromatographic separaton
what are the types of chromatography principles?
- Normal phase chromatography
- Reverse phase chromatography
- Hydrophilic interaction chromatography
- Chiral chromatography
- Size exclusion chromatography
- Ion exchange chromatography
how does a normal phase chromatography work?
- has a polar stationary phase and non-polar mobile phase
- the substances are separated according to the strength of interactions b/w the molecules and the stationary phase silica
what types of molecules are retained the most in normal phase chromatography?
small molecules and molecules with a high number of polar functional groups
how does a reverse phase chromatography work?
- stationary phase is non-polar and mobile phase is polar
- so the hydrophobic components interact with the column the best
what is the stationary phase in thin layer chromatography?
silica or alumina (polar)
what is the mobile phase in thin layer chromatography?
polar or non-polar organic solvent
how does gas chromatography work?
-a small sample of a mixture of compounds is vapourised
what is used as the mobile phase in gas chromatography?
- Inert gases (He, N2, H2)
what does it mean if the gasses have a faster flow rate?
- the quicker the separation
- the poorer the efficacy
what plot describes the optimum flow rate for different gases
the Van Deemter plot
what is required for good separation of samples in gas chromatography?
Samples have to be both
thermally stable and volatile
what can happen with a low isothermal temperature?
may
lead to peak broadening due to
poor volatility
what can happen with a high isothermal temperature?
may
lead to compound decomposition
what factors control separation?
- type and amount of stationary phase
- column dimension (longer column = better resolution)
- type and speed of the carrier gas
how are samples detected in gas chromatography?
- using flame ionisation detector
1. analytes enter the flame
2. ions are formed
3. electrical current is measured
4. rise in current is proportional to the amount of the ions
why are polar compounds not suitable for gas chromatography?
as they are non-volatile
what does derivatisation do?
reduces the polarity of the molecules
In HPLC what are systems with a single pump called and multiple pumps called?
single: isocratic
multiple: binary (2 pumps), ternary (3 pumps), quaternary (4 pumps)
what is the advantage of using a multiple pump system?
allows for gradient separation where the composition of the mobile phase is changed during the run
what are HPLC detectors?
- UV-visible spectroscopy
- Photo diode array
- Refractive index
- Fluorescence detector
how does UV-vis work?
the electrons transition from a bonding molecular orbital to an anti-bonding molecular orbital when the UV light is absorbed. This gives an energy value equivalent to the energy change from bonding to antibonding orbital
what is the beer-lambert law?
A = ecl A = absorbance e = molar absorptivity of the analyte (L/molcm) c = concentration of analyte (mol/L) l = path length (cm)
how do we calculate the transmittance of light through the analyte?
T = Io/I T = transmittance Io = initial light intensity I = final light intensity (after passing through analyte)
what parameters influence the absorbance of light in uv-vis?
- wavelength of light
- solvent
- pH of the solution if analyte is basic or acidic
- temperature
what is the maximum concentration your sample has to be for the beer-lambert law to work?
0.1M
what is the difference between a single beam and a split beam spectrophotometer?
- single beam uses one source of light but the split beam uses 2 sources
- single beam only has one cuvette in at a time but the split beam has the calibrating cuvette and the sample cuvette in at the same time
what are the pharmaceutical applications of UV-vis?
- Determination of concentration of APIs and excipients
- Detector in HPLC
- Detector in dissolution testing
- Detector in capillary electrophoresis
what is the schematic of a mass spectrometer?
- Inlet (for the sample to enter through)
- Ion source (makes gaseous sample into ions)
- mass analyser (separates ions by their mass/charge ratio)
- detector (counts number of ions for each mass/charge)
- computer (instrument control and data acquisition?
What are the possible ionisation methods?
- Electron ionisation
- Chemical ionisation
- Electrospray ionisation
- Matrix assisted laser desorption/ionisation mass spectrometry
how does electron spray ionisation work?
- the sample molecules are bombarded with fast moving electrons which travel along the electromagnetic field
- this knocks an electron off the outer shell of the sample molecules forming positively charged ions
explain how chemical ionisation works?
- the reagent gases added can either be CH4, NH4, or isobutane(C4H10)
- ions are produced through collision of analyte with ions of a reagent gas present in the ion source
- electrons ionise the reagent gas
- these ionised reagent gases collide creating an ionisation plasma.
- positive and negative ions form by reaction with this plasma
which is a better analyser electron or chemical ionisation?
electron ionisation
what are the available detection methods?
- Magnetic and electrostatic analysers
- Quadrupole detectors
- Time-of-flight analysers
- Ion trap analyser
- Ion cyclotron analyser
what are the 2 principle types of 2D NMR experiments?
- through-bond correlations (COSY)
- through-space correlation (NOESY)
what are examples of linked techniques?
1• Gas chromatography-mass spectrometry (GC-MS)
2• High-performance liquid chromatography–mass spectrometry (HPLC-MS)
3• Liquid chromatography-infrared spectroscopy (LC-IR)
4• Chromatography-diode-array detection (LC-DAD)
5• Capillary electrophoresis-mass spectrometry (CE-MS)
6• Capillary electrophoresis-ultraviolet-visible spectroscopy (CE-UV)
7• Ion-mobility spectrometry–mass spectrometry
