CHEM 428 | Homework for Class #3 What is the functional group on the surface of
ID: 1034372 • Letter: C
Question
CHEM 428 | Homework for Class #3 What is the functional group on the surface of a fused silica capillary column? Would the nature of the interior surface of the capillary be different if the background electrolyte was at pH 2 versus pH 10? What would happen to the electroosmotic flow rate at pH 2.5 versus pH 10? Fluorescent derivatives of amino acids were prepared and separated by capillary electrophoresis at pH = 9.3. Predict the elution order of the four amino acids. Explain your reason?ng Glycine NHCHCO2 Amino acid HN CO2 C-NH2 Phenylalanine Fluorescent label OH Arginine Serine pKa 12.5 (protonated form or arginine ?? side chain is shown) This activity is adapted from materials developed by Tom Wenzel (Bates College)Explanation / Answer
Ans 1. Silanol (Si-OH) are the functional groups on the surface of the fused silica capillary column are ionized to negative charge silanoate (Si-O?) groups at pH values greater than three.
Yes, the nature of the interior surface of the capillary will be different due to running a basic solution such as NaOH and KOH. Attracted to the negatively charged silanoate groups, the positively charged cations of the buffer solution will form two inner layers of cations (called the diffuse double layer or the electrical double layer) on the capillary wall. The first layer is referred to as the fixed layer because it is held tightly to the silanoate groups. The outer layer, called the mobile layer. The mobile cation layer is pulled in the direction of the negatively charged cathode when an electric field is applied.
The electroosmotic flow rate (EOF) will increases at pH 2.5 and 10. The wall's charge density is proportional to the pH of the buffer solution.The rate of EOF is dependent on the field strength and the charge density of the capillary wall.