Chapter 24, Problem 24.12P

a)

Interpretation Introduction

Interpretation:

The working of solid-phase microextraction technique along with the necessity of cold trapping during injection with solid-phase microextraction and also the extraction of an analyte into the fibre in solid-phase micro extraction has to be explained.

Concept Introduction:

Solid-phase microextraction:

The extraction of compounds from liquids, air or sludge without any solvent is called as solid-phase microextraction. The major component is the fused-silica fibre coated with $\text{10-100μm}$ thickness in film of stationary phase exactly to those used in gas chromatography.

The mass of analyte absorbed in the coated fibre is calculated using the formula,

$\text{m=}\frac{{\text{KV}}_{\text{f}}{\text{c}}_{\text{0}}{\text{V}}_{\text{s}}}{{\text{KV}}_{\text{f}}{\text{+V}}_{\text{s}}}$

Where ${\text{V}}_{\text{f}}$ = volume of film on the fibre

${\text{V}}_{\text{s}}$ = volume of solution that is extracted

${\text{c}}_{\text{0}}$ = initial concentration of analyte in the solution that is extracted

$\text{K}$ = partition coefficient for solute between film and solution.

Cold trapping:

Cold trapping is one of the alternative method for the condensation of solute in narrow band at the starting of the column.

To explain the working of solid-phase microextraction technique along with the necessity of cold trapping during injection with solid-phase microextraction and also the extraction of an analyte into the fibre in solid-phase microextraction

b)

Interpretation Introduction

Interpretation:

The differences between stir-bar sorptive extraction and solid phase microextraction has the explained. The one is which is sensitive and reason has to be given.

Solid-phase microextraction:

The extraction of compounds from liquids, air or sludge without any solvent is called as solid-phase microextraction. The major component is the fused-silica fibre coated with $\text{10-100μm}$ thickness in film of stationary phase exactly to those used in gas chromatography.

The mass of analyte absorbed in the coated fibre is calculated using the formula,

$\text{m=}\frac{{\text{KV}}_{\text{f}}{\text{c}}_{\text{0}}{\text{V}}_{\text{s}}}{{\text{KV}}_{\text{f}}{\text{+V}}_{\text{s}}}$

Where ${\text{V}}_{\text{f}}$ = volume of film on the fibre

${\text{V}}_{\text{s}}$ = volume of solution that is extracted

${\text{c}}_{\text{0}}$ = initial concentration of analyte in the solution that is extracted

$\text{K}$ = partition coefficient for solute between film and solution.

Stir-bar sorptive extraction:

Stir-bar asorptive extraction is closely related with solid-phase microextraction but is found to be $\sim \text{100}$ ~times more sensitive for trace analysis.

The mass of analyte that is extracted is given as,

$\text{m=}\frac{{\text{KV}}_{\text{f}}{\text{c}}_{\text{0}}{\text{V}}_{\text{s}}}{{\text{KV}}_{\text{f}}{\text{+V}}_{\text{s}}}$

Where ${\text{V}}_{\text{f}}$ = volume of film on the fibre

${\text{V}}_{\text{s}}$ = volume of solution that is extracted

${\text{c}}_{\text{0}}$ = initial concentration of analyte in the solution that is extracted

$\text{K}$ = partition coefficient for solute between film and solution.

But there is raise in the volume of sorbent ( ${\text{V}}_{\text{f}}$) from $\sim \text{0}\text{.5μL}$ in solid-phase microextraction to $\text{25-125μL}$ in stir-bar asorptive extraction. Hence, the analyte is $\text{50-250}$ times more extracted with stir bar.

To explain differences between stir-bar sorptive extraction and solid phase microextraction and to give the most sensitive technique with reason