Instant Notes: Analytical Chemistry

SPE can be semi- or fully-automated to increase sample throughput and to

improve both precision and accuracy. The degree of automation ranges from the

parallel off-line processing of batches of up to about 10 samples using a vacuum

manifold to provide suction, to on-line autosamplers, xyz liquid handlers and

robotic workstations.

Several alternative formats for SPE are available. These include

● Disks, which have relatively large cross-sectional areas compared to packed-

bed cartridges and thin sorbent layers (0.5–1 mm thick) containing about

15 mg of material. This reduced bed-mass results in low void volumes (as

little as 15ml) thus minimizing solvent consumption in the rinsing and

elution steps, improving selectivity and facilitating high solvent flow rates

when large volumes of sample are to be processed.

● Plastic pipette-tipsincorporating small sorbent beds designed for processing

D1 – Solvent and solid-phase extraction 117

Conditioning
Conditioning the sorbent prior to sample
application ensures reproducible retention
of the compound of interest (the isolate)

Retention

Adsorbed isolate

Undesired matrix constituents

Other undesired matrix components

Elution

Undesired components remain

Purified and concentrated isolate ready

for analysis

Rinse
Rinse the columns to remove undesired
matrix components

Fig. 2. Diagrammatic representation of a cartridge-based solid phase extraction procedure.