Chapter 24, Problem 24.2P

Interpretation Introduction

Interpretation:

The reason why open tubular columns offers higher resolution than packed columns in gas chromatography has to be explained.

Concept Introduction:

Packed columns:

These are fitted with solid support c made of fine particles. The solid support is coated with a stationary phase (non-volatile liquid) or solid. These are usually made of stainless steel or glass that are around $\text{1-5}\text{m}$ in length and $\text{3-6}\text{mm}$ in diameter. Silanzied silica is generally used as solid support for the reduction of hydrogen bonding to polar solutes. Teflon can also be used as support but limitation of Teflon is within $\text{<200°C}$ .

Advantages and disadvantages of packed columns:

Packed columns provides greater capacity of the sample instead they show broader peaks, longer retention times and lower resolution.

Open tubular columns:

The open tubular columns are made of silica (in fused form) and is coated with Polyimide for the support and to protect from atmospheric moisture. The most common type of open tubular column is wall coated column and the less common type is porous layer column. The columns are coiled in such way that they fit within a particular temperature controlled column oven.

Advantages and disadvantages of open tubular columns:

Open tubular columns provides higher resolution but short time analysis and show greater sensitivity when compared to packed columns. These columns have less capacity of the sample.

Deemter equation:

The Deemter equation is given as,

$\text{H}\approx \text{A+}\frac{\text{B}}{{\text{U}}_{\text{x}}}{\text{+Cu}}_{\text{x}}$

Where A is multiple paths

$\frac{\text{B}}{{\text{U}}_{\text{x}}}$ is Longitudinal diffusion

${\text{Cu}}_{\text{x}}$ is equilibration time

$\text{H}$ is height of plate

To explain the reason why open tubular columns offers higher resolution than packed columns in gas chromatography