Analytical chem question, will upvote correct answer ty :) Aniline (aminobenzene

Question

Analytical chem question, will upvote correct answer ty :)

Aniline (aminobenzene, C6H5NH2) is a weak base. Under acidic conditions in its fully ionized state the anilinium cation (C6H5NH3+) has a +1 charge. Anilinium ion is run in a capillary electrophoresis experiment in a capillary with an inner diameter of 50 µm and a total length of 89 cm. The applied voltage over the capillary's length is 25,000 volts (sample is introduced at positive end of capillary and detected at negative end of capillary). Ultraviolet absorption detection is done at a point 77 cm from the inlet end of the capillary. A neutral (uncharged) marker substance, formamide, is run along with the anilinium ion as a marker of electroosmotic flow. Both the formamide and the anilinium ion migrate from the positive toward the negative electrode. At pH 2.0, the migration time for formamide (the neutral marker compound) is 6.97 minutes, while the migration time of anilinium ion is 4.82 minutes.

Calculate the electroosmotic mobility (µeo) of the system (in units of cm2/volt-sec

Answer Choices:

A.

-2.40 x 10-4

B.

4.54 x 10-2

C.

3.93 x 10-2

D.

3.62 x 10-2

E.

6.04 x 10-4

F.

7.57 x 10-4

G.

2.40 x 10-4

H.

6.55 x 10-4

Explanation / Answer

Electroosmotic Mobility

When an electrical field is applied to a capillary filled with an aqueous buffer we expect the buffer’s ions to migrate in response to their electrophoretic mobility. What we observe under normal conditions. buffer solution moves towards the cathode. This phenomenon is called the electroosmotic flow. Electroosmotic flow occurs because the walls of the capillary tubing are electrically charged.

Solution:

Calculate the electroosmotic mobility (µeo) of the system (in units of cm2/volt-sec

Data are given:

Migration time of Anilinium ion (tm)=4.82 min

Migration time formamide (tm) =6.97 min

Capillary inner diameter=50 um

Length of the capillary tube(L)=89 cm

A distance of anode and detection point (l)=77 cm

Applied Voltage=25000 volts

Formula:

tm=lL/ (eo) V

(eo) total= lL/V tm

(eo) total=77×89/25000×6.97

                  =3.93×10 -2    Cm2/volt.sec

Cations elute first in an order corresponding to their electrophoretic mobilities, with small, highly charged cations eluting before larger cations of lower charge. Neutral species elute as a single band with an elution rate equal to the electroosmotic flow velocity. Finally, anions are the last components to elute, with smaller, highly charged anions having the longest elution time.

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