In the realm of analytical chemistry, the quest for precision and sensitivity is a perpetual journey. The integration of solid phase extraction (SPE) with analytical chromatographic techniques has emerged as a pivotal strategy to elevate the quality and reliability of analytical results.
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Table 1 Comparison of some aspects of SPE techniques (Badawy MEI, et al. 2022)
| Parameter |
Cartridge |
PT-SPE |
Disk |
Multi-well SPE |
SPME |
IT-SPME |
| Classification |
Exhaustive flow-through equilibrium and pre-equilibrium |
Non-exhaustive batch equilibrium and pre-equilibrium |
Non-exhaustive flow-through equilibrium and pre-equilibrium |
| Weight of sorbent |
4-30 mg |
4-400 µg |
4- 200 mg |
3-200 mg |
– |
– |
| Applicable volume |
500-50 mL |
0.5-1 mL |
0.5-1 L |
0.65-2 mL |
– |
– |
| Application |
Wide variety of sample matrices |
Biological samples |
Substantial samples |
Biological samples |
Environmental and biomedical samples |
Environmental and biomedical samples |
| Benefits |
Easy to assemble in the laboratory
Wide range of uses
Low cost
Possibility of storage of analytes enriched on solid sorbent |
Simplicity and shorter extraction time
High sensitivity and recovery factors
A small quantity of elution volume
Conditioning steps are not required
Amenable to automation by available tools (micropipette) |
Operated with a smaller elution volume
Greater cross-sectional area
Fast flow rates
Smaller void volume
Ignored the filtration of the extract
Slighter extraction period for substantial samples |
Rapid preparation of a large number of samples
Less labor and time-consuming
Less solvent waste
Fast flow rates
Amenable to automation |
Green extraction
Rapid extraction
Miniaturized technique
Low analysis cost
Easiness of automation
Friendly-eco |
Miniaturized technique
Large volume samples
Compatible with analytical instruments |
| Limitations |
Partially small cross-section
Sluggish flow rate
Tremendous unavailable rented volume
Plugging
Channeling
Costly with a large number of samples |
Restricted flow rates and plugging
A large amount of plastic waste |
Decrease in breakthrough volume
Small samples would be lost
Costly |
Due to open-bed configuration, the technique is unsuitable for volatile analytes |
Low adsorption capacity
Limited effectiveness |
A large amount of solvent needed |
Integration with Gas Chromatography (GC)
Gas Chromatography, a widely employed chromatographic technique, separates volatile compounds based on their affinity for a stationary phase. The marriage of SPE with GC harnesses the strengths of both techniques, resulting in a potent analytical tandem.
Enhanced Sensitivity and Selectivity
SPE provides a pre-concentration step that significantly amplifies the concentration of analytes before they enter the GC system. This heightened concentration not only boosts sensitivity but also improves the signal-to-noise ratio, enabling the detection of trace compounds that might otherwise escape notice.
Moreover, SPE selectively removes unwanted matrix components during sample preparation, preventing them from interfering with GC analyses. This selective purification enhances the specificity of the analysis, ensuring that the chromatogram reflects the true composition of the sample.
Minimization of Matrix Effects
GC is susceptible to matrix effects, where co-elution of matrix components can hinder the accurate determination of analytes. By integrating SPE before GC, matrix effects are mitigated. The purified sample eluent from SPE contains a more focused target analyte band, reducing the likelihood of co-elution and improving the accuracy of compound identification.
Extended Column Lifespan
Matrix components and contaminants in unprocessed samples can accumulate on GC columns, leading to a gradual decline in column performance. The implementation of SPE as a sample clean-up step prevents the introduction of impurities into the GC system, thereby extending the lifespan of the chromatographic column and ensuring consistent and reproducible results over time.
Integration with Liquid Chromatography (LC)
Liquid Chromatography, a versatile technique for separating non-volatile compounds, also stands to benefit significantly from the incorporation of SPE into the analytical workflow.
Fig 1 Scheme of the automated on-line SPE-HPLC system (Badawy MEI, et al. 2022)
Improved Sensitivity and Quantitation
The pre-concentration capabilities of SPE are particularly advantageous for LC, where non-volatile compounds often necessitate more intricate sample preparation. SPE enables the concentration of analytes of interest, enhancing sensitivity and facilitating lower limits of detection and quantitation in LC analyses.
Compatibility with Diverse Sample Matrices
LC is often employed in the analysis of complex sample matrices, such as biological fluids or environmental samples. SPE offers the flexibility to adapt to various sample types, ensuring efficient extraction and purification across a wide range of matrices. This adaptability enhances the applicability of LC in diverse analytical scenarios.
Reference
- Badawy MEI, El-Nouby MAM, Kimani PK, Lim LW, Rabea EI. A review of the modern principles and applications of solid-phase extraction techniques in chromatographic analysis. Anal Sci. 2022, 38(12):1457-1487.
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