The technical analysis methods of portable SPME (Solid Phase Microextraction) extraction device mainly include selection of extraction head, sample processing, optimization of extraction conditions, desorption and detection, data processing and quantitative analysis. The following are the specific methods:
1、 Extraction head selection
The extraction head is the core component of SPME technology, and its selection directly affects the extraction efficiency and accuracy. Portable SPME extraction devices are typically equipped with multiple types of extraction heads to meet the needs of different samples and analytes.
Fixed phase type: Select the appropriate fixed phase based on the polarity and molecular weight of the analyte. Non polar analytes (such as benzene and toluene) can be analyzed using non-polar stationary phases (such as PDMS and polydimethylsiloxane); Polar analytes (such as phenols and organic acids) should use polar stationary phases (such as PA and polyacrylamide); For complex matrices (such as multi-component foods and wastewater), mixed phases (such as PDMS/DVB, polydimethylsiloxane/divinylbenzene) can be used to simultaneously extract polar and non-polar compounds.
Extraction head thickness: Thick film (such as 100 μ m) extraction heads are commonly used for small molecules or volatile substances to increase extraction yield; For larger molecules or semi volatile substances, a thin film (such as 7 μ m) extraction head is used to avoid excessive extraction and long equilibrium time.
2、 Sample processing
Sample processing is an important step in SPME technology, which directly affects the extraction efficiency and accuracy of analysis results.
Sample uniformity: Ensure that the sample is uniformly mixed to avoid differences in extraction efficiency caused by uneven sample distribution.
Pre processing steps: Based on the properties of the sample and analysis requirements, appropriate pre-processing steps such as dilution, acid-base adjustment, filtration, etc. are carried out to remove interferences or improve sample properties.
Headspace processing: For volatile compounds, headspace SPME technology can be used, which means that the extraction head only contacts the gas phase space above the sample, avoiding direct contact with the sample matrix and reducing matrix interference.
3、 Optimization of Extraction Conditions
Extraction conditions are key factors affecting the extraction efficiency of SPME technology, including extraction time, extraction temperature, stirring/oscillation, etc.
Extraction time: The extraction time should be determined from the time of fiber exposure to adsorption equilibrium, usually through experimental optimization. Short time may lead to insufficient adsorption, while long time may waste time and increase errors.
Extraction temperature: An increase in temperature can accelerate mass transfer rate, but may reduce the adsorption capacity of the fixed relative target substance. Therefore, it is necessary to select an appropriate extraction temperature based on the properties of the analyte and optimize the equilibrium.
Stirring/oscillation: accelerates the flow of sample matrix, reduces mass transfer resistance, and shortens equilibrium time. Commonly used magnetic stirring, the speed can be adjusted according to the properties of the sample.
4、 Desorption and detection
Desorption is the process of transferring the analyte adsorbed on the extraction head to the analytical instrument, while detection is the qualitative and quantitative analysis of the analyte.
Desorption method: Select the appropriate desorption method based on the type of analytical instrument. For gas chromatography (GC), the commonly used thermal desorption method is to insert the adsorbed extraction head into the GC injection port and maintain it at high temperature for a certain period of time, allowing the target substance to desorb from the stationary phase and enter the chromatographic column with the carrier gas for separation; For high-performance liquid chromatography (HPLC), solvent desorption method is commonly used, which involves inserting the extraction head into a small volume injection bottle containing desorption solvent, and using ultrasound or oscillation to elute the target substance. The eluent is then injected into HPLC for analysis.
Testing instruments: Portable SPME extraction devices are typically used in conjunction with portable analytical instruments such as GC or HPLC to achieve rapid on-site analysis.
5、 Data Processing and Quantitative Analysis
Properly process and analyze the obtained data to obtain accurate results.
Calibration curve: Quantitative analysis is achieved through calibration curves. The calibration curve should be prepared based on a standard sample of known concentration, taking into account factors such as extraction efficiency and desorption efficiency.
Data correction: Perform data correction and calibration as needed to eliminate the influence of matrix interference, instrument errors, and other factors on the analysis results.