10 / 144
10
Introduction
Thermo Scientific HyperSep Columns
The Importance of SPE
Sample preparation is a critical step prior to LC or GC
analysis. Over the last few years, the requirement for
higher sensitivity, selectivity, accuracy, precision and
sample throughput has increased significantly. This is due
to reduced sample volumes, greater drug efficacy, and
greater awareness of toxicity levels of pollutants.
Improved sample preparation techniques ensure accurate
LC/GC and MS analysis in the following ways:
•
Maximize detection selectivity
– Reduce ion suppression
– Reduce protein binding
– Reduce matrix interferences
•
Improve analytical system performance
– Longer column lifetimes
– Less maintenance on detector
– Syringes less likely to block
– Less contamination
•
Improve sensitivity
– Lower limits of detection
– More accurate quantitation
– Improved data processing
Sample Preparation Techniques
Solid phase extraction (SPE) is a sample preparation technique
that is widely used by chromatographers in pharmaceutical,
environmental, forensics and food safety applications. Solid
phase extraction is very selective with a wide number of
phases available. The technique can be automated and uses
significantly smaller volumes of solvent compared to
liquid/liquid extraction (LLE) and supported liquid extraction
(SLE) methods.
In general, SPE can be used for three important purposes
in sample preparation:
•
Concentration of the analyte
•
Removal of interfering compounds
•
Transfer of analyte into a suitable solvent for analysis
SPE has a number of benefits over other sample preparation
techniques, such as protein precipitation (PPT) and LLE.
Protein precipitation is a relatively fast technique to
perform, but it has a number of limitations. The process is
non-selective and only removes proteinaceous material. Because
there can be significant matrix interference, subsequent
cleanup stages may be required, adding costs and time to the
cleanup process.
LLE presents additional drawbacks. This process uses
large volumes of potentially hazardous solvent and often
involves laborious method development. It is a less selective
technique for polar compounds.
Selection of the Correct SPE Phase
To maximize the benefits of SPE, there are a number of factors to consider:
•
Select the correct SPE column size
– Consider the volume of the sample
•
Select the correct SPE bed weight
– Consider the concentration/amount of analyte
•
Determine the correct phase for an application by considering the physicochemical properties of the analyte
– pH, pK
a
etc.
– Solubility log P