In the Internal Standard Method, the unknown concentration of B, cB, can be obta
ID: 475726 • Letter: I
Question
In the Internal Standard Method, the unknown concentration of B, cB, can be obtained from the known concentration of the internal standard A, CA, according to c_B = k S_B/S_A c_A Where S_B and S_A are the signals for B and A, respectively, and k is a proportionality constant that must be obtained by calibration. A calibration solution containing 10.5 middot 10^-3 mol A and 6.5 middot 10^-4 mol B generated signals of 70.0 mV for A and 92.0 mV for B. First, determine k. A mixture of A (8.25 middot 10^-4 mol/L) and unknown B gave signals of 36.1 mV for A and 25.3 mV for B. What is the concentration of B in this mixture?Explanation / Answer
From the equation K=CB*SA/(SB*CA) = 6.5*10-4* 92/(10.5*10-3*70) =0.8136
for the given concentration of A, CB= 0.8136* 25.3*8.25*10-4/36.1=0.00047