Waters Sep-Pak Cartridges and Plates - Manual (Page 3)

[ Care and Use ManUal ]
Sep-Pak Cartridges and Plates 3
IV. stePs oF An sPe ProCedure
The following section describes the steps involved in a complete solid-phase
extraction procedure:
1. Pretreatment of Sample
Solid samples (soil, tissue, etc.)
• Shake, sonicate or use soxhlet extraction.
- extract sample with polar organic solvent (methanol,
acetonitrile) for polar analytes.
- extract sample with organic solvent and drying agent
(dichloromethane, acetone) for non-polar analytes and
multiresidue extraction.
Non Aqueous Liquid
• If the sample is soluble in water, dilute it with water for
reverse-phase SPE.
• If the sample is soluble in hexane, dilute it with or exchange to
hexane for SPE.
Wastewater
• Filter or centrifuge as necessary.
2. Condition Step
For reversed-phase sorbents, preconditioning of the sorbent with an
organic solvent, such as methanol, acetonitrile, isopropanol, or tetrahy-
drofuran, is usually necessary to obtain reproducible results. Without
this step, a highly aqueous solvent cannot penetrate the hydrophobic
surface and wet the sorbent. Thus, only a small fraction of the sorbent
surface area would be available for interaction with the analyte. For the
same reason, it is important not to let silica-based SPE cartridges dry out
between the solvation step and the addition of the sample. A complete
preconditioning of a reversed-phase cartridge includes the solvation step
and an equilibration with a low-strength solvent such as water or buffer.
a. Retention-Cleanup-Elution Strategy
As the sample is loaded onto the cartridge, the analytes of interest are
retained by the sorbent. If needed, an optimized series of washes are
used to remove matrix interference from the cartridge. A strong solvent
is used to elute the analytes from the cartridge. Sample enrichment
results when the final elution volume is smaller than the load volume.
Figure 1: Retention-Cleanup-Elution
b. Pass-Through Cleanup Strategy
Pass-through cleanup methods optimize matrix retention while the
analytes of interest pass-through the cartridge unretained. No sample
enrichment occurs during the solid-phase extraction (SPE) step.
1. Sample is passed through sorbent and collected
• No sample enrichment
2. Matrix interferences are retained on sorbent
Figure 2: Pass-Through
Load Sample
(Black)
Step
Elute 1
Step
Elute 2
One cartridge can separate all three dyes
Step
Elute 3
NOTE: Different
strength solvents
can be used to
separate the dyes.
Stationary
Phase
Particles