Weight & Measurements Arya Mehr

Question 4: Part A  You have a prescription balance with a sensitivity requirement (SR) of 1mg. What is the percentage error when weighing 30mg?

Question 4: Part b  What is the minimum weighable quantity (MWQ) if the sensitivity requirement is 1mg and the desired accuracy is 99%? If no desired accuracy is provided… Assume 95% accuracy (5% error)

Question 5: Part A  You are using a prescription balance with a SR of 6mg. Assume a desired accuracy of 95%. What is the MWQ?  Fill the following prescription with little wastage:  DHEA 20mg  Lactose qs 400mg  50 capsules

Question 5: Part B  How much DHEA will you use?  Fill the following prescription with little wastage:  DHEA 20mg  Lactose qs 400mg  50 capsules Since 1100mg is above MWQ we can measure it accurately

Question 5: Part C  How much lactose will you use?  Fill the following prescription with little wastage:  DHEA 20mg  Lactose qs 400mg  50 capsules What in the world is qs? “qs” is shorthand for the Latin term “Quantum satis” Quantum satis: amount which is needed

Question 6: Part A  You are using a prescription balance with a SR of 5mg. Assume a desired accuracy of 95%.  Fill the following prescription with little wastage:  Atropine sulfate 2.5mg  Lactose qs 400mg  10 capsules You can only measure up to 100mg unless you want to be more than 5% off!

Question 6: Part B  How much Atropine will you use?  Fill the following prescription with little wastage:  Atropine sulfate 2.5mg  Lactose qs 400mg  10 capsules

Question 6: Part B  But wait!  Remember that our MWQ (minimum weighable quantity) was 100mg  You can not weight compounds less than 100mg unless you are willing to accept an error of more than 5% (it will NOT be accurate)  Since 27.5mg is not above 100mg MWQ we need to multiply! NO YES

Question 6: Part B  So now you have 110mg of Atropine which is four times the amount that you need.  REMEMBER you can NOT weight anything less than 100mg since it is the MWQ  We must dilute the atropine with lactose so that 1/4 th of the total mixture will be above 100mg MWQ 1 part atropine (27.5mg) 3 parts lactose (3 x 27.5mg) 4 parts mixture (110mg, which is above MWQ)

Question 6: Part B  But wait!  That you have 4 parts of atropine sulfate (110mg)  You have to then multiply everything by 4 1 part atropine (27.5mg) x 4 3 parts lactose (3 x 27.5mg) x 4 4 parts mixture (440mg, which is above MWQ) (330mg lactose used)

Question 6: Part C  How much lactose did you use including initial dilution?  Fill the following prescription with little wastage:  Atropine sulfate 2.5mg  Lactose qs 400mg  10 capsules Since you have 110mg of Atropine and Lactose you must subtract from the number (remember it is qs) However… we used 330mg during the initial dilution (previous slide) so we must add that to the total