Practical: Drug stocks, solutions and dilutons

Question 1

Beer-Lambert law + define symbols

Answer 1

A = log10 (Io/I) = ϵcl

A = absorbance of light
Io = intensity of beam before passing through sample
I = intensity of beam of light emerging from sample
ϵ = absoption coefficient
c = concentration
l = pathlength

Question 2

what does a greater absorption coefficient mean?

Answer 2

more light absorbed

Question 3

what’s the relationship between the concentration of a substance and the absorbance?

Answer 3

linear

Question 4

what does a longer pathlength l mean?

Answer 4

more light absorbed

Question 5

what’s used to measure absorbance?

Answer 5

spectrophotometer

Question 6

what can we use absorbance to calculate?

Answer 6

the concentration of the sample solution

Question 7

how long should we switch on a colorimeter for before using?

Answer 7

15 mins

Question 8

what do we zero a colorimeter with?

Answer 8

distilled water

Question 9

is it more accurate to pipette small or large volumes?

Answer 9

large volumes

Question 10

what’s the standard method for diluting in pharmacology and why?

Answer 10

serial dilutions - accurate

Question 11

what’s the method of choice for preparing drug solutions and why?

Answer 11

serial solutions
it uses volumes that don’t differ by more than 10x (less likely to have experimental errors)

Question 12

disadvantage of serial dilutions

Answer 12

irreversible (start again if you get a step wrong)

Question 13

which pipettes use a blue tip?

Answer 13

P1000

Question 14

which pipettes use a yellow tip?

Answer 14

P20 and P200

Question 15

what’s more accurate - using serial dilutions or making each dilution separately from a starting stock solution?

Answer 15

serial dilutions

Question 16

how do we know that serial dilutions are more accurate than making each dilution separately from a starting stock soluton?

Answer 16

will give a better fit when a linear regression analysis is used

Question 17

what’s the best indication of accuracy and consistency?

Answer 17

the variability in the standard deviation

Question 18

when are errors more likely in terms of how much volume is dispensed from a pipette?

Answer 18

more likely when the volume dispensed with a pipette is less than 10% of the maximum volume