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1. Why use solid phase extraction?

Solid phase extraction is a physical extraction process that includes liquid and solid phases. In solid-phase extraction, the adsorption force of the solid relative to the separated product is greater than that of the solvent that dissolves the separated product. When the sample solution passes through the adsorbent bed, the separated substance is concentrated on its surface, and other sample components pass through the adsorbent bed; through the adsorbent that only adsorbs the separated substance and does not adsorb other sample components, a high-purity and concentrated separator can be obtained. There are many reasons why laboratories perform SPE, but there are three main points about why laboratories do this.

Purification: The main reason for using SPE in the laboratory is to purify the samples you are interested in. This will affect downstream analysis, thereby improving your chromatographic analysis. It will also reduce the amount of garbage placed on the instrument, which may reduce the amount of system maintenance required. Concentration: The second reason why laboratories use solid phase extraction is to concentrate samples of interest. If you are trying to reach a low detection level or a low quantification level, you can use this method. The advantage of this is that it can maximize the service life of the old instruments in the laboratory. 3. Solvent conversion: If you are processing aqueous alkali samples, and you want to inject samples on the GC instrument, from the original alkali to volatile organic compounds, you can consider using solid phase extraction.

2. What are the factors affecting solid phase extraction?

  • Adsorbent

At present, the commonly used adsorbents include positive and reversed adsorbents, ion exchange adsorbents and antibody-bonded adsorbents. Try to choose adsorbents with similar polarity to the target compound. Volatility) and its concentration in the water sample are directly related.

  • Elution solvent

In solid phase extraction, the choice of elution solvent is related to the properties of the target substance and the adsorbent used. Lou Manteng et al. gave the polarity and elution strength of common organic solvents, which can be determined during the test. Selection of physical and chemical properties. The volume of the eluent should be based on the premise of complete elution. Smaller volume Z is better. You can find the best eluent volume for Z according to the change curve of recovery rate through multiple elution method (small volume). Obviously, wash The smaller the de-volume, the higher the enrichment factor.

  • Retention volume

In the process of sample addition, the retention volume is one of the key factors of solid phase extraction technology. It represents the volume of water sample that can be effectively processed for trace enrichment. According to the detection amount of the small Z of the chromatograph and the concentration of organic matter in the water sample, the volume of the small Z water sample to be enriched can be estimated. In addition, the pH value of the sample solution also affects the adsorption efficiency of the sample.

  • Flow rate

The control of flow rate is very important for solid phase extraction. Excessive flow rate will cause leakage of the solid phase extraction column. If the flow rate is too small, the processing speed will be too slow. During the column pretreatment process, the flow rate is moderate to ensure that the solution fully wets the adsorbent. The loading and elution process requires the flow rate to be as slow as possible, so that the analyte remains in the column as much as possible or achieves complete elution, otherwise it will cause the analyte Loss affects the size of the recovery rate. Especially the ion exchange process is relatively slow, and a lower flow rate (0.5-2.0 mL/min) should be used. 

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