Calculate the amount of glycine in the mixture:

Isotope dilution analysis was employed for the determination of glycine in 5.83 g protein hydrolysate mixture by using ¹⁴C labelled compound. 5.3 mg labeled compound with an activity of 39856 cpm was added to the mixture. The counter had background counts of 11790 counts in 90 min. After thorough mixing, the solution was passed through an ion-exchange column when 3.7 mg pure glycine was separated which showed an activity of 10900 counts in 50 min using the same counter. Calculate the % amount of glycine in the mixture.

Answer:

The counter had a background of 11790 counts in 90 min

or Background count rate =  131 cpm

Amount of radiolabeled tracer added, m*           =          5.3 mg

Specific Activity of the radiotracer added, SA₁   = (39856 -131)/25.7

= 39725/25.7

=   1545.7 cpm/mg

Amount of pure fraction of glycine = 23.7 mg

Net Activity of glycine = 10900 counts in 50 min = 218 cpm - 131 cpm(background)

= 87 cpm

Specific Activity of separated fraction of glycine = 87 / 3.7 = 23.5 cpm/mg

Amount of glycine in mixture = 5.3 (1545.7/23.5 - 1) = 343.1 mg

Percent amount of glycine in the mixture = (0.343/5.83) ×100

= 5.89%