Research And Design Of An Airflow Microenrichment System

Headspace liquid phase microextraction (HS-LPME), which integrates extraction, cleanup and concentration, is a sample pretreatment technique that widely used in the enrichment of volatile and semivolatile target compounds from many different kinds of samples. In this technique, improving the temperature of sample matrixes and reducing the temperature of extraction solvent are key points to improve enrichment efficiency. In order to obtain a high temperature of sample matrix and a low temperature of extraction solvent, many scholars have proposed various kinds of heating and refrigerating methods. These methods have some shortcomings such as bigness of the device, inconvenience of the operation, difficult control of the temperature and difficult achievement of online enrichment. In addition, enrichment experiments are performed in closed system in HS-LPME technique. Under a given temperature and pressure, the amount of target compounds entering the headspace in HS-LPME is constant with the result that the enrichment factor for the low vapor pressure target compound is not good.To achieve rapid, automatic and efficient extraction of volatile and semivolatile trace target compounds which include low vapor pressure target compound from different kinds of samples, an airflow microenrichment system based on gas purge microsyringe extraction was researched and developed in this dissertation. In this system, semiconductor condenser and microheater were designed respectively to cool the extraction solvent and to heat the sample. The control of refrigerating and heating temperatures were achieved by AT89C52 microcontroller, which compared the temperature value that collected by temperature collecting circuit with the set one and then used improved PID control algorithm to export PWM control signal for driving the execution components-refrigeration piece and heater band, making the inert gas introduced into the system reach the set value. The system adopted LCM141 LCD module to display the current refrigerating and heating temperatures, gas flow rate and timing time.The airflow microenrichment system researched and designed in this dissertation has been proved to be of better enrichment characteristics after usages of it and original HS-LPME technique respectively for the enrichement of 18 PAHs in spiked sample. Then, enrichment experiments for the spiked Changbai Mountain plant and soil samples were performed using this system. GC-MS analysis results indicated that high enrichment efficiency was obtained from airflow microenrichment system and the system revealed good reproducibility. For the real plant and soil samples from Changbai Mountain, the results of this system were similar to the results obtained from Soxhlet extraction technique. The experimental results demonstrate that airflow microenrichment system is potential in analysis of volatile and semivolatile chemicals from various kinds of samples.