The Main Influencing Factors of Solid Phase Extraction Cartridges

Solid phase extraction and its cartridges

SPE (solid phase extraction) technology is based on the theory of liquid-solid phase chromatography. It is a physical extraction process that includes liquid and solid phases, which is approximately taken as a simple chromatographic process. What we frequently used method is to make the liquid sample solution pass through the adsorbent, retain the measured substance, select the appropriate strength of the solvent to flush out the impurities, and then quickly elute the measured substance with a small amount of good solvent, to separate, purify and concentrate. What’s more, it is able to absorb the interfering impurities selectively and allow the measured substances to flow out, or adsorb the impurities and the measured substance simultaneously and then elute the measured substance selectively with a suitable solvent.

SPE cartridge can be operated in a medium pressure column chromatography system and a high pressure liquid phase system. It separates the target compound from the interfering compound in the liquid sample (solid sample can also be made into a liquid sample) through the selective adsorption and elution of the solid adsorbent, so as to achieve the purpose of enrichment, separation, and purification of the sample.

Various kinds of SPE cartridges are available in the market. In the specific experiments, it is necessary to reasonably select suitable packing and reasonable specifications of solid phase extraction columns according to the analytical objects, detection methods, and laboratory conditions.

Main influencing factors of SPE cartridges

Solid phase extraction is a process of adsorption, desorption/elution of the target substance on the stationary phase, so the factors that affect the adsorption, desorption/elution will directly affect the extraction efficiency, such as the type of filler, the strength of the elution solvent, and the pH, flow rate, etc.

1. Packing
Packing is the core of solid phase extraction technology. Choosing SPE column packing with moderate adsorption to the target is a prerequisite to ensure accurate detection. Of course, we can choose different column materials for the same target, but we must pay attention to the adjustment of the method.

2. The strength of the elution solvent
Solid phase extraction is the competitive adsorption of the stationary phase-filler and mobile phase-loading solvent/elution solvent on the target. Therefore, when loading the sample, choose a loading solution with the appropriate organic solvent content or pH to avoid the target objects were missed during sample loading. When the HAWACH solid phase extraction cartridge is eluted, it is necessary to select a suitable elution solvent, that is, the content or pH of the organic solvent, to ensure that the target substance adsorbed on the packing can be eluted.

3. pH
For ion exchange stationary phases, the pKa (isoelectric point) of the analyzed component and the interfering substance is different. By adjusting the pH of the solvent, the stationary phase can be charged, the analyte is oppositely charged, and the interfering substance is uncharged; or the stationary phase is charged, the interfering substance is oppositely charged, and the analyte is uncharged.

4. Flow rate
The loading flow rate and elution flow rate will affect the effect of adsorption or desorption/elution. The flow rate of loading and elution is generally controlled within 1 mL/min. For the enrichment of large amounts of trace samples, such as the enrichment of organic matter in environmental water samples, the sample flow rate should not exceed 5 mL/min.

In addition to the above factors that affect the use of HAWACH solid phase extraction cartridges, the completion of some operation steps, such as the degree of activation, the draining of the rinsing step, etc., will also affect the recovery or reproducibility of the results.