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Principles of Instrumental Analysis, 6th ed. Chapter 32
 
 6
32-13. We will use Equation 32-23 with Rm being the activity of the sample containing the tracer 
and Rt being the activity of the tracer itself. We will modify this equation by letting mm, 
mx, and mt be the volumes of the sample, the unknown, and the tracer respectively. 
 Rm = 15.8 cps 
 1 Ci = 3.70 × 1010 Bq = 3.70 × 1010 cps 
 iC
0.120 tR
μ
=
mL
 2.00 mL× 10
i
cps 3.70 10 
C
× × i6 C
 10 −×
iCμ
 = 8880 cps 
 blood volume = t
x m
m
Rm m
R
= − tm (Equation 3-23) 
 = 8880 cps 1.00 mL 2.00 mL = 560 mL
15.8 cps
× − 
32-14. A0 = 5.42 × 103 cpm mg–1 × 0.981 mg = 5317 cpm 
 Substituting into Equation 32-23 
 mx = mg penicillin = 5317 cpm 0.406 mg 0.981 mg = 5.31 mg
343 cpm
× − 
32-15. We first convert the activity to specific activities in terms of Cl–. 
 For NaCl, 
 Rt = 
4
44.0 10 cps/mg NaCl = 6.59 10 cps/mg Cl
35.45 mg Cl /58.44 mg NaCl
−
−
×
× 
 Rm = 35 cps = 0.354 cps/mg Cl
400 mg AgCl 35.45 mg Cl /143.32 mg AgCl
−
−×
 
 In order to correct Rm for the time delay, we use Equation 32-5 to obtain λ. 
 λ = ln(2)/37.3 min = 1.858 × 10–2 min–1
 Equation 32-8 is rearranged to give the counting rate before any decay. Thus,