1. The Importance of Sample Pre-treatment

1. The time used for sample pretreatment is much longer than the chromatographic separation time.
2. Sample pretreatment consumes a lot of solvents and chemicals. It accounts for the largest total cost of analytical consumption.
3. Sample pretreatment is part of the experiment in terms of reproducibility and accuracy. But it is the most important factor affecting the good or bad experimental results.

2. The Purposes of Sample Pre-treatment

• Removal of particles and reduction of interfering impurities.
• Concentration of trace components.
• Improve the selectivity and sensitivity of detection.
• Improve the separation effect.
• To facilitate the protection of the column and instrument.
• Make the sample form and the solvent used to meet the requirements of HPLC.

3. Requirements For Sample Pre-treatment

• The sample is fully converted into a low concentration solution.
• The elution strength of the sample solution is lower than that of the mobile phase, and it is soluble with the mobile phase.

4. Principles of Sample Pre-treatment

• Prevent and avoid chemical reactions with the tested components during sample pretreatment.
• During the sample pretreatment process, if there is a chemical reaction with the tested component, this reaction must be known and can be done quantitatively.
• Prevent and avoid the contamination of the tested components during sample pretreatment. Minimize the introduction of extraneous compounds into the preparation process.
• The sample handling process should be as simple and easy as possible. The size of the sample processing device used should be appropriate for the volume of samples to be processed.

5. Sample Pre-treatment Methods

• Filtration & Centrifugation
  • Commonly used filter membrane materials are cellulose, polytetrafluoroethylene and polyamide.
• Accelerated Solvent Extraction
  • Accelerated solvent extraction is to extract solid or semi-solid samples with solvent under increased temperature (50-200 ℃) and pressure (10.3 ~ 20.6 MPa).
• Supercritical Fluid Extraction
  • Supercritical fluid extraction is the use of supercritical fluids on the principle of the special solubility properties of substances and the establishment of extraction methods.
• Solid-phase Extraction
  • Solid-phase extraction is the enrichment, separation and purification of samples by using selective adsorption and selective elution, which can be approximated as a simple liquid-solid chromatographic process.
• Solid-phase Microextraction
  • Solid-phase microextraction is a solvent-free sample microextraction method based on the principle of sorption-desorption equilibrium between the polymer coating or sorbent applied to the fiber and the sample, which integrates sampling, extraction, concentration, and injection. There are direct solid-phase microextraction, headspace solid-phase microextraction, membrane solid-phase microextraction, and capillary solid-phase microextraction.
• Liquid-phase Microextraction
  • Liquid-phase microextraction is an environmentally friendly sample microextraction method based on the principle of distributional equilibrium between the sample and micro- or even nano-upgraded organic solvent, integrating sampling, extraction, and concentration.
    There are direct liquid-phase microextraction, hollow fiber liquid-phase microextraction and headspace liquid-phase microextraction, etc.
• Derivatization
  • There are UV derivatization, fluorescence derivatization, and electrochemical derivatization, etc.