Model of Solid Phase Extraction

Solid phase extraction (SPE), developed in the 1970s, can replace the traditional liquid-liquid extraction in many fields and has been applied more and more widely in the laboratory.

The common solvent of SPE
Hexane, isooctane, tetrahalide carbon, trihalomethane, dihalomethane, tetrahydrofuran, ether, ethyl ester, acetone, cyanogen, isopropanol, methanol, water, acetic acid.

Model of SPE
1. Positive phase: polarity of adsorbent is greater than that of eluent; polar compounds can be adsorbed from nonpolar solvent samples.
Reverse phase: polarity of adsorbent is less than that of eluent; the interaction between the target compound and the adsorbent is hydrophobic.
2. Ion exchange: the target compounds extracted are those with an electric charge.
3. The adsorption. The more similar the polarity between the target compound and the adsorbent, the better the retention.
The adsorbent used in SPE is the same as the fixed phase commonly used in liquid chromatography, but the particle sizes are the difference.

When selecting separation modes and adsorbents for SPE, should be considered:
1. The solubility of polar or non-polar solvents;
2. Possibility of ionization;
3. Whether it is possible to form a covalent bond with the adsorbent.