Question

Smaller particles affect HPLC column efficiency in what ways?

A)increase the mass transfer term.

B)diminish the pressure constraints of the mobile phase.

C)reduce stationary phase retention

D)enable lower slopes inthe C term

E)cause higher temperature as a result of increased frictional heating.

Gradient elution used in HPLC. How is the gradient created for a reverse-phase HPLC experiment over the course of the run?

A)Increase the pH of the mobile phase.

B)Decrease the pH of the mobile phase.

C)Increase the vapor pressure of the analytes by increasing the temperature.

D)Increase mobile phase polarity by increasing the fraction of polar solvent in a binary mobile phase.

E)Decrease mobile phase polarity by mixing with a less polar solvent to better compete with the nonpolar stationaryphase.

Answer 1

Option (C) is Correct i.e, Smaller particles increases HPLC column efficiency by reduce stationary phase retention . In HPLC practice, the less the particle size distribution the more uniform packing in the chromatographic column can be achieved, and the more efficient the column will be. The presence of the larger sized particles only effect the column efficiency, but the presence of the very small particles (fine), less than 1 mm, may lead to the column frit clogging and rising of the column backpressure.

Option (E) is correct i.e, gradient is created for a reverse-phase HPLC experiment over the course of the run by decreasing mobile phase polarity by mixing with a less polar solvent to better compete with the non polar stationary phase. The gradient is formed by increasing the percentage of organic solvent. Consequently – at the beginning of the analysis, when the mobile phase strength is low, the analyte will be partitioned wholly into the stationary phase (or ‘focussed’) at the head of the column.