Study Of Miniaturized Sample Preparation Device For VOCs In Soil

As a part of environmental pollution that cannot be underestimated,soil pollution has the characteristics of strong mobility,complex matrix,irreversible,accumulation over time,and multiple sources of pollution.Volatile Organic Compounds(VOCs)in the soil have irreversible harm to human health and ecological balance,but the concentration of it is low,so how to extract and concentrate organic compounds quickly and efficiently and detect them has always been the focus of attention.The purge-trap method uses carrier gas to sweep out VOCs in soil samples,the adsorbent enriches the components to be detected,and then thermal analyzes and injects them into the gas chromatograph so as to achieve the purpose of concentrating the target components and removing impurities.This method is simple to operate,has a wide range of applications,high concentration factor and high sensitivity.It plays a major role in the analysis and detection of organic pollutants in soil.This paper designs and develops a miniaturized sample pretreatment instrument,which is used in conjunction with a gas chromatograph for the detection of VOCs in soil samples.The sample preparation instrument is composed of purge device and concentration device,and the concentration device includes concentrator,condensation device and thermal analysis device.The purge device is composed of a sample bottle and a PEEK tube.Epoxy resin is applied to the inside and outside of the bottle and cured to ensure the air tightness between the PEEK tube and the port channel wall.A thin-diameter quartz tube is used as a concentrator filled with a multi-stage solid adsorbent.The injection side is designed to be a conical structure to minimize the dead volume,to reduce the injection band width,and prevent peak tailing.A small cold trap device is designed based on the TEC semiconductor refrigeration chip,which has a small size and high refrigeration efficiency,which greatly improves the concentration multiple of low-boiling substances.Ni-Cr resistance wire with an oxide insulating layer is selected to be evenly wound on the outer wall of the quartz tube to achieve heating process.The stepped voltage application method greatly increases the heating speed.It takes only 10 s to reach 350°C.The width of the thermal analysis band is significantly narrowed,which improves sample utilization rate.Tenax-TA + Carbopack-C + Carboxen 572 was selected as the adsorbent.Fill the adsorbent into the adsorption tube in the order from weak to strong according to the sample collection direction.Through experimental optimization of chromatographic conditions,purge conditions,and concentration-thermal analysis conditions,a complete set of analytical methods was obtained.The concentrator performs sample enrichment at an enrichment temperature of-10℃,and performs thermal desorption after the concentration.The chromatographic can separation of 32 kinds of VOCs within 20 minutes.The resolution is greater than 1.1.The time to complete a process of sample collection,injection and chromatographic analysis does not exceed 30 minutes.The detection limit of the method is between 0.001 and 0.141 ng/g(S/N=3).The sensitivity of the method conforms to the analysis standard of VOCs in soil.Experiments show that the instrument has high concentrate factor,simple and portable operation,and can realize rapid analysis.It has a wide range of application scenarios in the detection and analysis of compounds with a wide boiling point range in soil.