Question

A prescription calls for 50 mg of chlorpheniramine maleate. Using a prescription balance with a sensitivity requirement of 6 mg, explain how you would obtain the required amount of chlorpheniramine maleate with an error not greater than 5%.

Weigh 150 mg drug; Use 200 mg as aliquot

Answer 1

To weigh out 50 mg of chlorpheniramine maleate accurately with a balance sensitive to 6 mg and limit the error to less than 5%, one should weigh a larger quantity and use aliquoting, ensuring precise measurement by starting with 150 mg and considering 200 mg as the standard aliquot for calculations.

Step-by-step explanation:

To obtain the required 50 mg of chlorpheniramine maleate using a prescription balance with a sensitivity requirement of 6 mg and an error not greater than 5%, a specific weighing and aliquoting method must be used. First, you have to weigh a quantity greater than the required amount. In this case, you would weigh out 150 mg of the drug. Then, you would divide this weighed amount into aliquots that, when combined, total the desired 50 mg dose. If 200 mg is used as the standard aliquot for the calculations, it's important to ensure that the amount of the drug divided into aliquots is such that the 50 mg can be accurately dispensed. The aliquot method reduces the percentage error in weighing by using a larger quantity that is easier to weigh precisely and then diluting it to obtain the desired concentration. Keep in mind to adjust the calculations accordingly if 200 mg is the standard aliquot but you begin with 150 mg.