Page 72 - Analytical Electrochemistry 2d Ed - Jospeh Wang

EXAMPLES 57

0.4 mM solution of dopamine in phosphate buffer at a glassy carbon disk electrode of
1
2
2.6 mm area with a scan rate of 25 mV s . What will i be for v ˆ 100 mV s 1 and
p
1.2 mM DA?
Solution From equation (2-1):

i ˆ kCv 1=2 2:2 ˆ k 0:4 25† 1=2 k ˆ 1:1
p
Under the new experimental conditions, i is given by
p
1=2
i ˆ 1:1 1:2 100† ˆ 13:2 mA
p
Example 2-2 The following cyclic voltammogram was recorded for a reversible
couple: Calculate the number of electrons transferred and the formal potential for the
couple.

Solution From equation (2-3),

n ˆ 0:059=DE ˆ 0:059= 0:555 0:495†ˆ 0:983  1:0
p

The formal potential can be calculated from equation (2-2):

0
E ˆ 0:555 ‡ 0:495†=2 ˆ 0:525 V

Example 2-3 The electropolymeric growth of 2 ng polyphenol onto a gold QCM
2
crystal A ˆ 1cm ; f ˆ 5 MHz) resulted in a frequency change of 12 Hz. Calculate
0
the frequency change associated with the deposition of 4 ng polyphenol onto a
2
0.5 cm crystal ( f ˆ 8 MHz).
0