About 30 years ago MACHEREY‑NAGEL designed and introduced CHROMABOND SPE cartridges containing silica-based adsorbents.
SPE is a form of digital (step-wise) chromatography designed to extract, partition, and / or adsorb one or more components from a liquid phase (sample) onto a stationary phase (adsorbent or resin). An adsorbed substance can be removed from the adsorbent by stepwise increase of elution strength of the eluent (step gradient technique).
SPE extends a chromatographic system’s lifetime, improves qualitative and quantitative analysis, and the demand placed on an analytical instrument is considerably lessened.
Mixture of polystyrene-divinylbenzene copolymer (PS/DVB) in H⁺ form (PS-H⁺), strong cation exchanger (SCX) and OH⁻ form (PS-OH⁻), strong anion exchanger (SAX)
Column type
SPE cartridge
Hardware
Polypropylene (PP) cartridges with polyethylene (PE) filter elements
Column shape
Tubular syringe-shaped cartridge with Luer tip inlet and outlet
Conditioning of the adsorbent is necessary in order to ensure reproducible interaction with the analyte. Conditioning, also called solvation, results in a wetting of the adsorbent and thus produces an environment, which is suitable for adsorption of the analyte. Nonpolar adsorbents are usually conditioned with 2–3 column volumes of a solvent, which is miscible with water (methanol, THF, 2-propanol etc.), followed by the solvent in which the analyte is dissolved (pure matrix, e.g., water, buffer). Polar adsorbents are conditioned with nonpolar solvents. After the conditioning step the adsorbent bed must not run dry, because otherwise solvation is destroyed (deconditioning).
2) Sample application (adsorption)
Sample application can be performed with positive or negative pressure with a flow rate of ~3 mL/min. Sample volumes vary from a few mL up to liters.
3) Washing
Washing of the adsorbent is usually achieved with a special wash solution; however, in some cases it may not be necessary. If the polarity difference between wash solution and eluent is very large, or if both are not miscible, drying of the adsorbent bed after washing is recommended to improve elution and recovery.
4) Elution
Elution with a suitable eluent should not be too fast. The elution speed depends on the column or cartridge dimension and the quantity of adsorbent (about 1 mL/min).
Since analytes can either be adsorbed on the SPE packing material or directly flown through while the interfering substances are retained, two general separation procedures are possible – both cases are shown in the figure below.
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