Question

The amount of camphor in an analgesic ointment can be determined by GC using the method...

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

Homework Answers

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%

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