Answer the following multiple choice questions regarding ion-pair chromatography
ID: 970142 • Letter: A
Question
Answer the following multiple choice questions regarding ion-pair chromatography.
A) What role does the surfactant play in ion-pair chromatography?
Map The charged, hydrophilic end of the surfactant is attracted to the wall of the column. The hydrophobic end of the surfactant attracts the ions as they are introduced into the column Due to the highly controlled, temperature sensitive equilibrium between the hydrophobic end of the surfactant and the ions (cation or anion), the ions can be eluted from the column by increasing or decreasing the temperature O The surfactant is added to the mobile phase at a value equal to its critical micelle concentration. Micelles are formed around the ions of interest in the sample and are passed through the column and separated based on micelle-ion pair size. The larger micelle-ion pair species will elute from the column first. O The surfactant is introduced into the column in the mobile phase and binds to the stationary phase with its nonpolar, hydro phobic end. The charged end of the surfactant then acts as an exchanger, attracting ions in the sample of opposite charge The surfactant is added to form micelles (ion pairs) around the analytes of interest, preventing nonspecific adsorption to the separator column as they are eluted. The surfactant then releases the ions in the suppressor column, which allows them to be detected B) Is the use of gradient elution recommended when performing ion-pair chromatography? Gradient elution is not recommended because of the slow equilibrium between the stationary phase and the surfactant. Gradient elution is not used when performing ion-pair chromatography due to the overly complex nature of the surfactant-ion interaction Gradient elution (pH or ionic strength) is not recommended, or necessary, because the equilibrium of the ion and the stationary phase interaction is not affected by changes in pH or ionic strength O A pH gradient (low pH to high pH) is recommended, and necessary, when performing ion-pair chromatography because the interaction between the ion and the surfactant is strong at low pH and reduced at high pH. As the pH is increased, the interaction weakens and the ions can br aldere from thet suraca.phH is increased, the interaction weakens and the lons can e eluted from the surfactantExplanation / Answer
A) Answer: 3rd option. The surfactant with an ionic end and a hydrophobic tail is added to the mobile phase. The hydrophobic tail of the surfactant gets retained by the stationary phase. Therefore an ion exchange group forms on the surface of the stationary phase.The ions in the sample exchanges with the counter ion of the surfactant retained by the stationary phase.
B) Answer: 1st option. The gradient of elution is nearly impossible due to the slow equilibrium. This is one of the main disadvantages of the column.