Gareth Price Flashcards
What are the advantages of monitoring the use of drugs using hair samples?
Easy sample collection Sample is readily contaminated Tracks over a long time Less invasive Easy storage
What are the disadvantages of using hair samples to monitor drug use?
Recovery of samples from the matrix is difficult Concentrations in samples is very low Won’t show immediately Hard to obtain a representative sample Establishing a baseline is difficult
What are some of the advantages of using blood/urine samples to monitor drug use?
More difficult to get samples
Sample is cleaner
Looks at recent activity - effects are shorter term
Samples are readily extracted and separated from the matrix
Describe the separation that will occur on a non-polar stationary phase
Separation on a non polar stationary phase is dependant on the mass/size of the molecule
They will elite in order of size which is reflected by the number of carbons
Describe the separation that will occur on a polar stationary phase
Separation is to do with the strength of interaction
The most polar molecules will interact most strongly with with stationary phase so will spend longer in the column and hence be elated last
Comment on the resolution factor of the peaks
Peaks are sufficiently resolved to allow good quantification
1.2 is just sufficient
Signal returns to baseline
What could be done to improve the resolution of the peaks
Could be modified by raising temperature
Changing flow rate
Modifying the mobile phase (HPLC)
Using a different column or stationary phase
Longer column
What are the advantages of using an internal standard
Small changes in conditions have the same proportional effect on the standard and the sample and so are cancelled out
It also accounts for slightly different sample sizes
Hence the method covers some experimental problems
Also loses the need for extensive calibrations so can be cheaper in time and materials
Suggest some factors that an analyst must take into consideration to ensure that their results are reliable when performing this analysis
How many samples taken Accuracy/precision of the method How the sample is stored The method itself If there are low concentrations- nature of the matrix - some extraction/ pre concentration step needed What precautions need to be taken Consideration of statistics
Outline some factors to be considered in developing a chromatographic method to quantify levels of i in food
Recovery from foodstuff ( extracting from matrix)
Consider polarity of molecule and suggest a way of extracting
Type of chromatography - which type and what mobile phase would you use
Uv detector and mass spec
Need standard (known) sample to confirm identity (if UV) and allow calibration
Would have to confirm detection limits and sensitivity if present at low levels
List the factors which can affect the rate of separation of a gas column chromatography
Temperature Flow rate Length of column Thickness of s phase film Analyte sample size
Suggest with reasons an appropriate chromatographic technique which could be used for concentration of H2S in natural gas
All gaseous components so gas chromatography
H2S is flammable so FID with n2 carrier gas
Nature of gases - porous solid stationary phase to separate by boiling point
Suggest with reasons an appropriate chromatographic technique which could be used for trace levels of chlorinated pesticides in river water
Extract with solvent
Use gc
Chlorinated suggests using ECD detector
Suggest with reasons an appropriate chromatographic technique which could be used for concentrations in a mixture of several chiral sugars
Sugars are water soluble so use reverse phase HPLC
Aqueous mobile phase
Chiral stationary phase
Describe Thermal Conductivity Detectors (TCD) and some adv and disadvantages
Other detectors will not respond to gases like oxygen nitrogen and carbon dioxide
Not very sensitive so need large sample sizes
Cheap, easy to use, responds to most species
Used for gases and non combustible samples
Can be used without calibration
Describe flame ionisation detectors (FID) and some adv and disadv
Works on organic and flammable compounds
Sensitive so can use small samples
Doesn’t show nitrogen as carrier gas
Can only detect molecules with a C-H bond
The FID flame oxidises all oxidisable samples that pass through it so it cannot be used for preparatory work
Describe a mass spectroscopy detector and adv and disadv
Very useful for identification using libraries of unknown determination
Good for large ranges of unknown compounds
More expensive
Allows identification of species
Describe electron capture detector
Particularly sensitive to halogens, organometallic, nitriles, and nitro compounds
Very sensitive
What considerations do you need to take into account when carrying out an analysis
Cost Convenience Ease of analysis Time availability Equipment Personnel
What is accuracy
How close result is to the true value
What is precision
How close together are repeat measurements
What steps are involved in a typical analytical process
1 formulate the problem 2 select the analytical method 3 obtain samples 4 sample preparation 5 make the measurements 6 consider the significance of the results 7 draw conclusions and report
What is the IUPAC definition of chromatography
A physical method of separation in which the components to be separated are distributed between two phases one of which is stationary while the other (mobile) moves in a definite direction
What physical interactions are used in chromatography
Solubility Ionic Van deer Waals Hydrogen bonding Size Shape
