Question

The amount of camphor in an analgesic ointment can be determined by GC using the method of internal standards. A standard sample was prepared by placing 45.21 mg of camphor and 2.000 mL of a 6.000 mg/L internal standard solution of terpene hydrate in a 25-mL volumetric flask and diluting it to volume with CCl4. When an approximately 2 microliter sample of the standard was injected, the FID signals for the two components were measured as 67.14 for camphor and 19.13 for terpene hydrate. A 53.61 mg sample of an analgesic ointment was prepared for analysis by placing it in a 50 mL Erlenmeyer flask along with 10 mL of CCl4. After heating to 50 °C in a water bath, the sample was cooled to below room temperature and filtered. The residue was washed with two 5-mL portions of CCl4, and the combined filtrates were collected in a 25-mL volumetric flask. After adding 2.000 mL of the internal standard solution, the contents of the flask were diluted to volume with CCl4. Analysis of an approximately 2 microliter sample gave FID signals of 13.43 for the terpene hydrate and 24.31 for the camphor. Report the %w/w camphor in the analgesic ointment

Answer 1

45.21 mg camphor in 25 ml solution

concentration of camphor = 45.21 mg/152.23 g/mol x 25 ml = 0.012 M

2 mol of 6 mg/L has = 6 x 2/1000 = 0.012 mg of terpene hydrate

concentration of terprene hydrate = 0.012/190.28 x 25 = 2.52 x 10^-6 M

It gave a GC value of 67.14 for camphor and 19.13 for terpene hydrate

Unknown 53.61 mg in 25 ml was analyzed

2 ml of internal standard gave value of 13.43

concentration of standard in solution = 13.43 x 2.52 x 10^-6/19.13 = 1.77 x 10^-6 M

weight of terpene hydrate = 1.77 x 10^-6 x 25 x 190.28 = 0.0084 mg

Camphor in unknown gave GC value of 24.31

concentration of camphor in unknown = 24.31 x 0.012/67.14 = 0.0043 M

weight of camphor in unknown = 0.0043 x 25 x 152.23 = 16.53 mg

w/w% of camphor in unknown = (16.53/53.61) x 100 = 30.83%