A peak elutes from an HPLC column 17.7 cm in length in 11.1 min. What would be the width at half‑height of the peak (in seconds) if the plate height were 8.68 μm?

10.98 s

Explanation:

To solve this problem we first use the formula:

H = L/N

Where:

H = Plate height (8.68 μm, or 8.68x10⁻⁶m)L = Column length (17.7 cm, or 0.177 m)N = Number of theoretical plates (unknown)

And solve for N:

N = 0.177 m / 8.68x10⁻⁶mN = 20392 plates

Then we use the formula:

N = 5.54*

Where:

N is the number of theoretical plates previously calculated. tr is the retention time (11.1 min, or 666s)W₀.₅ Is the width at half-height (unknown)

And solve for W₀.₅:

W₀.₅ = 10.98 s