Development Of Portable Headspace Sampler And Its Application In On-site Emergency Detection Of VOCs In Water

Headspace injection is an efficient sample pretreatment technology,which has been widely used in the detection of volatile organic compounds(VOCs)in water and solid waste.The traditional desktop headspace sampler has the advantages of large volume,high power consumption and poor environmental adaptability,and doesn’t have the ability of on-site emergency detection.Therefore,the development of portable headspace sampler with on-site detection ability has become one of the research hotspots in the field of environmental detection.As a kind of sample pretreatment equipment,portable headspace sampler usually can’t work alone.It needs to be combined with portable analytical instrument for on-site detection.The existing portable headspace sampler products in the domestic and foreign markets generally have the following limitations:poor detection sensitivity for VOCs with low boiling point;The residue of high concentration samples is large,and there is crosstalk between adjacent analyses;Complex operation and low intelligence.In order to solve the problems of the existing portable headspace sampler,a new type of portable headspace sampler is independently developed in this paper.On the basis of theoretical research,the instrument structure,circuit control system,embedded software,workflow and control method are developed,and the engineering prototype of portable headspace sampler is built,which is combined with the portable gas chromatography-mass spectrometer made in the laboratory.The combined system realizes the rapid and accurate determination of 55 kinds of VOCs in water specified in the national standard《Water quality-Emergency determination of volatile organic compounds-Portable headspace/gas chromatography-mass》(HJ 1227-2021).The main innovations and research contents of this paper are as follows:1)The technical route of portable secondary adsorption thermal desorption is proposed,and the design of corresponding key modules is completed,which improves the sample enrichment efficiency and so as to improve the overall sensitivity of the instrument.Firstly,the first stage adsorption thermal desorption module is placed in the portable headspace sampler,and the new structure of high-temperature inorganic glue thin-layer insulation is adopted,which greatly reduces the thermal mass and realizes the rapid temperature rise and fall on the basis of low power consumption;Secondly,the second stage adsorption thermal desorption module is placed in the sampling flow path of the chromatographic system.Two stage adsorption thermal desorption modules cooperate efficiently.The first stage realizes sample enrichment and the second stage realizes sample focusing,which finally improves the detection sensitivity of the samples.2)A new headspace injection gas path is designed to realize the full-automatic injection of gas phase samples,and the overall structure design of portable headspace Sampler is completed.In the process of gas path design,the route of using a large number of stainless steel pipelines and adapters in small headspace injection instruments at home and abroad is abandoned.In this paper,the gas path is integrated in the stainless steel matrix to reduce the problems of air tightness and sample adsorption caused by pipelines and adapters.At the same time,the method of purging headspace gas injection greatly reduces the analysis crosstalk caused by sample residue and improves the accuracy of detection results.3)The work flow of portable headspace sampler is designed,and the function of each step and the working state of each component of the instrument are formulated.What’s more,This paper writes embedded software code to realize the functions of process control,logic control and touch human-computer interaction,which greatly improves the intelligence of the instrument.4)The construction and debugging of the combined system of portable headspace sampler and portable gas chromatography-mass spectrometer are completed.Using this system,a portable headspace secondary adsorption gas chromatography/mass spectrometry method is developed to rapidly determine 55 VOCs in water which are specified in the national standard.The results show that the system and method can complete the qualitative and quantitative analysis of VOCs in all 55 kinds of water in 16.8 minutes,all samples show good linearity in the rang of 0～200 μg/L,the correlation coefficient is r>0.991,the method detection limit is 0.32～1.18 μg/L,the recovery was 88.9%～101.9%,and the relative standard deviation(RSD)was 2.4%～9.0%.The experimental results show that the combined system equipped with the self-developed portable headspace sampler has greatly improved the detection sensitivity of low boiling substances,accuracy and intelligence.The key performance is better than that of similar commercial products.