Question

A torsion prescription balance has a sensitivity requirement of 6 mg. If you would like to weigh 7 mg of hydromorphone hydrochloride with the balance with an error no greater than 5%. You need to use aliquot method to provide the amount of drug and use lactose as a diluent? Assume to use as little as possible of  hydromorphone hydrochloride and lactose to satisfy the requirement. What would be the minimum amount of lactose (mg) needed to make the lactose hydromorphone mixture?

Answer 1

According to aliquot method ,

The smallest amount to be weighed on this balance is SR÷ ERROR × 100

Here Sensitivity requirement = 6 mg

Error = 5 %

= 6÷5 × 100 = 120 mg

The amount of drug required is = 7 mg which is too small to be weighted so 120 mg is the total amount of mixture = drug + diluent

Diluent = 120 mg ( total mixture ) - 7 mg ( drug )

=113 mg is the minimum amount of lactose required .