Solid Phase Extraction for Sample Preparation
Solid phase extraction (SPE) is a physical extraction process that involves both liquid and solid phases. In the solid phase extraction process, the adsorption of the solid relative analyte is greater than the liquid phase. As the sample passes through the SPE column, the analyte is adsorbed on the solid surface and the other sample components pass through the column. The analyte is then eluted with a suitable solvent to achieve separation and enrichment with the sample matrix and interfering compounds.
(1) Instead of the traditional liquid-liquid extraction, a large amount of mutually incompatible solvents are not required;
(2) No emulsification occurs during the treatment;
(3) Adopting high-efficiency and highly selective adsorbent, the extraction selectivity is high and the repeatability is good;
(4) Simplify the sample processing process and reduce costs.
2. Separation mode of solid phase extraction
Solid phase extraction separation mode is the same as liquid chromatography.
(1) Normal phase (adsorbent polarity is greater than eluent polarity)
(2) Reversed phase (adsorbent polarity is less than eluent polarity)
(3) Ion exchange
3. Selection of elution solvent
Follow the “similar compatibility” principle and meet the following requirements.
(1) The solubility of the tested component is large;
(2) The solubility to interfering impurities is small;
(3) Effective release of the component to be tested;
(4) The ability to dissociate proteins or fats well;
(5) moderate boiling point (40 ~ 80 °C), low viscosity, low toxicity, easy to purify, low cost, and easy to further purification treatment.
4. Common SPE column types
Polar column: CN, NH2, PSA, Si-, etc.;
Non-polar columns: C18, C8, C2, CN,
Cation exchange column: SCX, PRS
Anion exchange column: SAX, PSA, NH2
According to the nature of the target compound and the type of sample, choose the appropriate SPE column and eluent.
5. Application of SPE
Separation and enrichment of trace or trace target compounds in complex samples;
For example, analysis of biological fluids (such as blood, urine, etc.), analysis of traditional Chinese medicines and their metabolites, analysis of active ingredients or harmful components in foods, and sample preparation of analysis of organic pollution in environmentally friendly water samples.
Application example: Determination of ginsenosides in health foods
(1) Sample processing: Weigh the appropriate amount of sample + water solution. Ultrasonic extraction for 30 min, make up to volume, shake well, and place.
(2) Chromatography column: 3 mL XAD-2 macroporous resin column (polyaromatic microspheres) + neutral alumina (100-200 mesh).
(3) Column pretreatment: 25 mL of 70% ethanol, 25 mL of water.
(4) Injection: Take 1 mL of sample solution into column chromatography.
(5) Column washing: 25 mL of water.
(6) Elution: 25 mL of 70% ethanol, collected, and evaporated.