CHEM - Weekly Questions 9-12

True or False: For quantitative analysis, a resolution > 1.5 (baseline resolution) is desired.

• True
• False

Two compounds were separated using gas chromatography. The retention times were 628 and 642 s, and the widths at half-height were 8.3 and 9.4 s, respectively. Find the resolution for these two compounds. Are the peaks well resolved?

• 1.6, yes
• 0.93, no
• 0.93, yes
• 7.5, yes
• 3.8, yes

How does plate height relate to the width of the peaks?

• The smaller the plate height, the wider the peak width.
• Peak width remains constant as the plate height changes.
• The larger the plate height, the narrower the peak width.
• The smaller the plate height, the narrower the peak width.
• There is no relationship between plate height and peak width.

What is the plate height (H) for a column that is 10.0 m long and has 1.6 × 10^4 plates?

• 0.63 mm
• 1.6 × 10^3 m
• 1.6 × 10^5 m
• 0.063 m
• 0.006 3 mm

True or False: Resolution is proportional to the number of plates on the column.

• True
• False

The van Deemter equation is H ≈ A + B/ux + Cux. Which statement is TRUE?

• Broadening due to longitudinal diffusion can be reduced by using a slower linear velocity.
• Broadening due to the multiple paths term increases as the linear velocity increases.
• Broadening due to mass transfer can be reduced by using a slower linear velocity.
• The multiple paths term is important for open tubular columns.
• The multiple paths term is 0 for packed columns.

True or False: Broadening due to the multiple paths term in the van Deemter equation is independent of the linear velocity.

• True
• False

True or False: Narrower columns provide higher resolution but require higher operating pressure and have a smaller sample capacity.

• True
• False

True or False: Raising the column temperature increases the retention time.

• True
• False

Which gas CANNOT be used as a carrier gas in gas chromatography?

• N2
• CO2
• H2
• N2O
• Ar