Question

A protein sample is analyzed by a kjeldahl process during which ammonia is formed. Ammonia
formed is titrated coulometrically with electrogenerated hypobromite (OBr). If the titration is
performed using 19.3 milliamperes current and end point occur at 2 minutes. Calculate the
milligrams of protein present in the sample if one gram of protein nitrogen is contained in each
6.25gof protein (H=1 and N=14).

Answer 1

Equivalent mass of NH₃ 17 g (NH₃ is monobasic)

$m = ZIT$

for NH₃ , $z= \frac{17g}{faradey}$

$= \frac{17g}{96500c}$

Mass deposited $=$ $\frac{17g}{96500c}\times 19.3\times10$ ^-3$A\times2\times60$ sec

$= 0.408\times10$ ^-3g

In NH₃ 17 g contains 3g of H and 15 g of N

17g NH₃ -------------- 15g N

1g NH₃ ----------------$\frac{15}{7}N$

NH₃ ---------------- 0.36$\times 10$ ^-3N

0.36$\times 10$ ^-3N contain in 6.25$\times$ 0.36$\times 10$ ^-3g protein

$= 6.25\times0.36$ mg protein

$= 2.25 mg$ protein