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Question 1

Explain the difference between WCOT, SCOT and PLOT

Answer 1

• WCOT and SCOT have liquid SP and PLOT has solid SP
• SCOT and PLOT use solid support beads

Question 2

Define

• SP
• WCOT
• SCOT
• PLOT

Answer 2

• Stationary Phase
• Wall Coated Open Tubular
• Support Coated Open Tubular
• Porous Layer Open Tubular

Question 3

What is the advantage of a bonded SP in GC?

Answer 3

• Bonded SP reduces column bleeding and degradation over time
• Improves SP stability at high temperatures

Question 4

Why is make-up gas added before the detector?

Answer 4

To operate properly, the detector requires a higher flow rate of gas then what
is emerging from the column, therefore a makeup gas is added

Question 5

Explain why plate height increase at very low and very high flow rates for
5 um and 3 um particles?

Answer 5

• At low flow rates, longitudinal diffusion in primary source of peak broadening
• At high flow rates, the analytes/solutes does not spend enough time in the SP to
  differentially separate
• Also at high flow rates, resistance to mass transport is the primary source of peak broadening.

Question 6

Plate height does not increase for high flow rates for the 1.8 µm particles, what does this observation imply about the rate of equilibrium of solute between the MP and SP?

Answer 6

• Resistance to mass transport is not causing significant peak broadening with smaller particles
• Smaller particles allow analytes to diffuse shorter distances before equilibrating between the SP and MP
• The rate of equilibrium of analytes/solutes is fast since peak spreading is not observed at high flow rates.

Question 7

Why does a TCD respond to all analytes?

Answer 7

• It measures an analyte’s ability to transfer heat or thermal conductivity

Thermal Conductivity Detector

Question 8

Why is a FID detector not universal?

Answer 8

A FID detector is not universal because it requires the ionization of hydrocarbons

Flame Ionization Detector