The method of organic contaminant in the online express-analysis liquid of a kind of miniature mass spectrum
Technical field
The invention belongs to mass spectrometer, be particularly related to the new method of organic contaminant in a kind of online express-analysis liquid, this method is used minitype flight time mass spectrum, use the film sampling device to need not to carry out sample pre-treatments, obtain the sample molecule quasi-molecular ions with the coupling of vacuum-ultraviolet light soft ionization, use this method in 2 minutes, to realize on-site sampling, obtain the express-analysis of organic contaminant content in the fluid sample.
Background technology
Water is the natural resources that the mankind depend on for existence, along with the development of society, and the quickening of process of industrialization, water pollution problems is serious day by day.Industrial waste water, sanitary sewage, agriculture recirculation water, trade waste and house refuse etc. all can cause water to pollute, volatile organic matter in the water has pathogenic, carcinogenic, mutagenic effect, and can influence skin and mucous membrane, human body is produced various acute and chronic infringements.Therefore, the detection for the volatile organic matter in the water becomes extremely important.
Current, mainly contain for volatile organic matter on-line detection method in the water: purge and trap gas chromatography mass spectrometry, static headspace gas chromatography and film sample introduction mass spectroscopy.
Static headspace gas chromatography (HSGC) is isolated organic main method at present from water sample.This method utilization be the equilibrium separation of volatile organic matter between gas phase and liquid phase, the collection volatile organic matter of aqueous solution top enters into gas chromatography.Because of its detectability than higher, carry out as saltout, sample pretreatment process such as PH adjusting increases the concentration of volatile organic matter in gas phase.Purge and trap gas chromatography mass spectrometry (P﹠amp; T) be to detect the most frequently used method of volatile organic matter in the water, this method is to adopt inert gases such as nitrogen or helium that water sample is purged, volatile organic matter is equipped with adsorbed, the capture of collecting trap of adsorbent then, at last, collecting trap is heated, resolves, make volatile organic matter enter gas chromatography analysis.
These two kinds of detection methods generally all are to deliver to the laboratory behind the collection in worksite water sample to analyze.Such detection method length consuming time, cost height can't satisfy at present the needs to the continuous monitoring of water environment pollution.In addition analysis time long, the component of sample may change, and influences the accuracy of testing result, and is powerless for the magnanimity sample of facing in the present large-area environment generaI investigation.Therefore it is significant to the water environment pollution monitoring to develop quick, real-time on-the site analysis method.
Film sample introduction mass spectrum is finished sample introduction by film device, can detect the organism of trace in the aqueous solution fast, be widely used in the water and gas in the online detection of trace volatile organic matter.Sample enters into mass spectral ionized region by the pervaporation principle by film device, and this technology is simple, does not need sample pre-treatments; Highly sensitive, detectability can arrive 10
-9(V/V) magnitude; Analyzing and testing when can finish the polycomponent mixed solution in the short period of time.In the analyzing and testing of volatile organic matter, (dimethyl silicone polymer, PDMS) film is the most frequently used to silicon rubber.When aqueous sample stream contacts with the PDMS film through film device, the volatile organic matter in the water sample since shape separately, size and in film the difference of solubleness cause the difference of permeability in film, the big component of permeability obtains enrichment during through film.In general, environmental sample matrix is water, and volatile organic matter can see through film fast, and water then seldom can see through, and therefore, can realize enrichment when volatile organic matter sees through film, and its enrichment multiple can be up to 10-100 doubly.
This method is an analyzer with online minitype flight time mass spectrum instrument, adopts the soft ionization of film sampling device and vacuum UV lamp (10.6eV, Kr lamp), is used for the fast detecting of water environment volatile organic contaminant.
Summary of the invention
The objective of the invention is to use minitype flight time mass spectrum to provide a kind of maneuverability good, need not the method for quick that concentration in the express-analysis liquid of sample pre-treatments is low to moderate 10ppb benzene.
Technical scheme of the present invention is as follows:
At first, by three-way solenoid valve 5, the peristaltic pump 6 of flowing through enters the film Sample Room and contacts with PDMS film 7 sample under the effect of peristaltic pump 6, and volatile organic matter enters into mass spectral ionized region 10 by pervaporation and carries out mass spectrophotometry.After sample is full of in the film Sample Room, flows in the waste liquid bottle 3 through stainless-steel tube again, thereby finish the sample introduction analytic process.Residual in order to prevent sample, need to use 1 pair of film sampling system of pure water to wash.Finish switching between pure water 1 and the sample 2 by the switching of three-way solenoid valve 5.When sample analysis finished, switching solenoid valve 5 made pure water 1 enter the film sampling device, and system washes to film.
The invention discloses the new method of organic contaminant in the online express-analysis liquid of a kind of miniature mass spectrum, adopt fine and close dimethyl silicone polymer laminar film 7 by the pervaporation effect, the organism in the fluid sample becomes the gas phase compound and enters miniature mass spectrum and analyze.This method adopts film sample introduction to need not sample pre-treatments, and sample is by peristaltic pump 6 direct injected, with the vacuum ultraviolet ionized spectrogram that obtains that combines in the miniature mass spectrum molecular ion peak is only arranged, and is convenient to express-analysis.Only need to detect in 1 minute the benzene that content in the water outlet is low to moderate 10ppb, the range of linearity is two orders of magnitude, and analytical precision is controlled at 5%., after sample analysis finished, sample will be drawn out of rapidly through the vacuum control valve 9 of film sampling system, the sample memory-less effect.Can in 2 minutes, realize on-site sampling, obtain the express-analysis of organic contaminant content in the fluid sample for most this method of volatile organic matter sample.
Description of drawings
The total synoptic diagram of instrument that Fig. 1 this method is adopted; Wherein, 2-sample (Sample); 3-waste liquid (Waste); 7-film (Membrane); 8-mechanical pump (Mechanical pump); 11-field-free region (Field-free region); 12-pulse voltage (Pulse voltage); 13-vacuum UV lamp (VUV lamp); 14-turbomolecular pump (Turbomolecular pump); 15-microchannel plate detector (MCP detector);
The structural representation of Fig. 2 film sampling device; Wherein: 1-pure water (Pure water); 2-circulation sample (Cyclical sample); 3-waste liquid (Waste) 4-filtrator (Filter); 5-three-way solenoid valve (Threeway solenoid valve); 6-peristaltic pump (Peristaltic pump); 7-poly dimethyl silane film (PDMS membrane); 8-mechanical pump (Mechanical pump); 9-needle-valve (Valve); 10-ionized region (Ionization region);
The relation of Fig. 3 sample signal and sample flow rate;
The response time of Figure 41 ppm benzene,toluene,xylene and chlorobenzene;
Fig. 5 concentration is at the linear fit figure of 10ppb to benzene,toluene,xylene between the 1ppm and chlorobenzene;
Fig. 6 film sample introduction mass spectrum is used for the online detection of actual sample.
Embodiment
The total figure of this device as shown in Figure 1, instrument is total is divided into two large divisions, film sample introduction design part and mass spectrometry system.TOF-MS adopts quadrature accelerating structure (Fig. 1), sample molecule on the z direction by 13 ionization of VUV lamp, molion enters pulse repulsion district under the effect of ionized region weak electric field, the impulse electric field that the district applies moment is postponed in pulse, ion enters accelerating region in electric field force effect lower edge x direction, is undertaken being detected by detecting device after signal amplifies by microchannel plate detector 15 through the field-free flight district.Ion with identical energy successively arrives detecting device because of mass number is different, thereby obtains mass spectrogram.
Film sampling device such as Fig. 2, film sampling device mainly are made up of sample introduction device, film Sample Room and example enrichment buffer zone three parts.The introducing device of sample comprises sample bottle 2, three-way solenoid valve 5 and peristaltic pump 6, and peristaltic pump 6 is used for draw samples makes its film surface of flowing through, and the switching between T-valve 5 control samples 2 and the pure water 1 keeps the clean of system.The film Sample Room can be regarded a little sample cell as, after sample enters through flowing out behind the film surface.Sample is through entering the enrichment buffer zone behind the film, air pressure between atmospheric pressure and mass spectral high vacuum, the buffer zone side have a vacuum difference mouth, can control the air pressure in the buffer zone by needle-valve 9 switches.
Technical scheme of the present invention is as follows:
At first, by three-way solenoid valve 5, the peristaltic pump 6 of flowing through enters the film Sample Room and contacts with PDMS film 7 sample under the effect of peristaltic pump 6, and volatile organic matter enters into mass spectral ionized region 10 by pervaporation and carries out mass spectrophotometry.After sample is full of in the film Sample Room, flows in the waste liquid bottle 3 through stainless-steel tube again, thereby finish the sample introduction analytic process.Residual in order to prevent sample, need to use 1 pair of film sampling system of pure water to wash.Finish switching between pure water 1 and the sample by the switching of three-way solenoid valve 5.When sample analysis finished, switching solenoid valve 5 made pure water 1 enter the film sampling device, and system washes to film.
Adopt peristaltic pump 6 to carry out the sample introduction of solution in the experiment.Regulate the flow velocity of peristaltic pump 6 and observe the influence of flow velocity for the film bioaccumulation efficiency.As can be seen from Figure 3, along with the raising of flow velocity, the signal intensity of sample also is significantly improved.Therefore, the detection of trace volatile organic matter is convenient in the sensitivity that the flow of raising water sample helps improving sample.
Being applied to the detection of volatile organic matter in the on-the-spot water fast, is the important indicator of instrument fast.In the flight time mass spectrum, the ion that is ionized is delicate level the analysis time in mass analyzer, so the processing time of sample, promptly the response time of sample in film is a maximum step of elapsed time in this analytic process, so it is unusual important parameters for express-analysis.Response time in film sample introduction mass spectrum usually to calculate 10~90% o'clock needed time with sample signal intensity.The benzene,toluene,xylene of preparation 1ppm, the response time that the chlorobenzene mixed solution comes test membrane.Refer to testing sample signal starting point during the response time to time of signal stabilization, define the response time of film sample introduction here according to sample signal intensity in the time period of 10%~90% maximum signal.Response time comprises rise time and fall time, the speed of rise time reaction film sample introduction, and reacted the memory effect of test sample fall time at film.
The thickness of the PDMS film that instrument adopts is 50 μ m.Fig. 4 is the continuous monitoring to benzene,toluene,xylene, the whole sample introduction process of chlorobenzene mixed solution.Table 1 is the concrete data of extracting from figure about the response time.
Table 1
|
Benzene |
Toluene |
Dimethylbenzene |
Chlorobenzene |
Rise time/s |
30 |
43 |
95 |
70 |
Fall time/s |
24 |
24 |
63 |
11 |
The rise time of benzene,toluene,xylene and chlorobenzene and fall time help the quick online detection of volatile organic matter all less than 100s.And after the sample introduction valve closing, signal intensity returned to the background signal state in about 1 minute, and the sample memory-less effect exists.
Respectively linear fit (Fig. 5) is carried out in the concentration and the response of benzene,toluene,xylene and chlorobenzene, benzene,toluene,xylene and chlorobenzene is linear good as can be seen, linearly dependent coefficient R
2Be respectively: 0.9988,0.9988,0.9968 and 0.9982, can detect the sample of 10ppb, the range of linearity reaches 3 orders of magnitude, show this method can use with fluid sample in the qualitative and quantitative analysis of volatile organic matter.
Film sample introduction mass spectrum is used for the online detection of actual sample, and the sewage of gathering the chemical plant, Daliang City experimentizes.Sewage sample is behind film enrichment 1min, mass spectrum obtains Fig. 6 with the data acquiring frequency continuous sampling 200s of 12.5KHz, the compound that can detect from mass spectrogram comprises toluene (m/z92), dimethylbenzene (m/z106), trimethylbenzene (m/z120), butyl benzene organism such as (m/z134) can be told more than 20 kind of organism from figure.According to the quantitative curve of Fig. 5, can draw wherein that toluene concentration is about 83ppb, xylene concentration is about 101ppb.