Question

The following solutions are prepared for HPLC.

Stock A: 250 mL of a stock solution containing 12.5 mg of each of disopyramide phosphate, lidocaine hydrochloride, procainamide hydrochloride and quinidine dissolved in the mobile phase

Standard 1: 25 mL of ~1mg/L of each drug diluted with mobile phase

Standard 2: 25 mL of ~2mg/L of each drug diluted with mobile phase

Standard 3: 25 mL of ~5mg/L of each drug diluted with mobile phase

Standard 4: 25 mL of ~10 mg/L of each drug diluted with mobile phase

Standard 5: 25 mL of ~20 mg/L of each drug diluted with mobile phase

Question: Calculate the required volume of Stock A (~50 mg/L of each drug) that need to be added to each of the five 25mL volumetric flaks so that when diluted to 25 mL, each will yield the desired drug standard concentrations listed above.

Answer 1

Stock A: 12.5 mg in 250 ml

concentration of each drug = 12.5 mg/0.250 L = 50 mg/L

Standard 1: for a 25 ml of 1 mg/L solution

Volume of stock to be taken = 1mg/L x 25 ml/50 mg/L = 0.5 ml

So mix 0.5 ml of stock with 24.5 ml of mobile phase

Standard 2: for a 25 ml of 2 mg/L solution

Volume of stock to be taken = 2mg/L x 25 ml/50 mg/L = 1.0 ml

So mix 1.0 ml of stock with 24.0 ml of mobile phase

Standard 3: for a 25 ml of 5 mg/L solution

Volume of stock to be taken = 5mg/L x 25 ml/50 mg/L = 2.5 ml

So mix 2.5 ml of stock with 22.5 ml of mobile phase

Standard 4: for a 25 ml of 10 mg/L solution

Volume of stock to be taken = 10mg/L x 25 ml/50 mg/L = 5 ml

So mix 5.0 ml of stock with 20.0 ml of mobile phase.

Standard 5: for a 25 ml of 20 mg/L solution

Volume of stock to be taken = 20mg/L x 25 ml/50 mg/L = 10.0 ml

So mix 10.0 ml of stock with 15.0 ml of mobile phase