Sample preparation

Question 1

what can occur in a sample preparation to alter the concentration of the drug in time

Answer 1

1. suppress analyte concentration
2. deteriorate the analyte
3. interference
4. incompatible with instrument

Question 2

how are blood samples prepared

Answer 2

1. whole blood collected in tubes with or without agents to prevent clotting
2. collected in empty tubes and left for the blood to clot
3. collected in tubed containing EDTA and centrifuged

Question 3

describe how a sample can be collected

Answer 3

1. patch applied to the skin- absorbent utilised to capture sweat
2. sample of hair
3. urine sample- amount of metabolites present from a particular drug
4. blood samples

Question 4

what is sample preparation

Answer 4

taking a blood sample and being able to get a drug out of it in a precise and accurate way
- need to preserve the concentration of the blood so that it replicates what it was at the time that the sample was obtained

Question 5

what is albumin useful for

Answer 5

allows binding of acidic drugs to its surface for distribution around the body

Question 6

what is the importance of plasma protein drug binding in therapeutic monitoring

Answer 6

it can have an important influence on the free concentration of the drug
- only the free sample of the drug can have the desired therapeutic effect

Question 7

what processes can be used to improve a sample or measurement

Answer 7

1. protein precipitation
2. liquid-liquid extraction
3. Solid phase extraction

Question 8

what is protein precipitation

Answer 8

a process where a reagent is added to the serum (which contains albumin, glycoproteins and possibly interferants)
- the reagent or chemical completely denatures these proteins
- can use an acid or base to break the protein structure
- can use a solvent
- or can use heat as enzymes will denature at high concentrations
Once the enzymes are denatured, the tube can then be centrifuged, producing a clear solution

Question 9

what is liquid-liquid extraction

Answer 9

A way of segregating out specific chemicals in one layer over another layer to improve the selectivity
- add immiscible solvent and shake layers

Question 10

what is solid phase extraction

Answer 10

Similar to chromatography
1. condition cartridge
2. apply sample and based on affinity to interact with the properties of the material on the sorbent bed, they will either stick to that material or move away in solution
3. elute contaminants
4. elute analytes
- can see different fractions appearing at different times

Question 11

which sample preparation technique provides the means to reduce interferants the most

Answer 11

protein precipitation

Question 12

what are the challenges in monitoring urine

Answer 12

metabolism in the liver
- majority of the drug collected will be conjugated from Phase II metabolism
- so if we want to have a true estimation of the amount of drug that has been eliminated from the patient, we need to be able to measure the free drug and the conjugate