CN101509893B - Measuring method and device for volatile organic in water - Google Patents

Abstract

The invention discloses a detection method of volatile organic compounds in water and a device thereof which can be used for detecting compositions of the volatile organic compounds in water and the concentration thereof. The device consists essentially of three parts: an extraction device for the volatile organic compounds in water, the chemical ionization mass spectrometry and a computer control system. The detection method comprises the following steps of: introducing clean air or inert gas into water sample to be detected by a sand-core filter plate and generating a plurality of small bubbles; extracting the organic compounds into the gas above the liquid surface when the organic compounds in the water sample to be detected diffuse and enter into the bubbles in the ascending process of the bubbles; introducing the gas above the liquid surface into the chemical ionization mass spectrometry by a pipeline; adopting high-purity oxygen or water vapor which is introduced into the chemical ionization mass spectrometry as ion source gas; utilizing the chemical ionization mass spectrometry for analysis; and finally using a computer for analysis and processing, and giving information of the compositions of the volatile organic compounds in water and the concentration thereof.

Description

The measuring method of volatile organic matter and measurement mechanism in the water

Technical field:

The present invention relates to environmental technology field, specifically is volatile organic matter measuring method and device in a kind of water.

Background technology:

Composition and the measurement of concetration thereof of volatile organic matter mainly is to pass through chromatographic technique in the water at present, needed in the past water sample to be measured is carried out concentrating and separating at analysis to measure, main concentrating and separating technology has: the separation of liquid direct injected, liquid-liquid extraction, Solid-Phase Extraction, semipermeable partition sample introduction and headspace technique etc.These technical deficiency parts are: 1) the concentration extraction process can cause the loss of volatile organic matter, causes measurement result less than normal; 2) (such as liquid-liquid extraction) can introduce poisonous organic solvent in the concentration process, causes secondary pollution; 3) concentration of the volatile organic matter in present potable water and the environmental water sample is at ng/L～μ g/L, the volume that capillary chromatographic column in the chromatogram injects is the microlitre magnitude, cause direct analytical test sensitivity not reach requirement, need the concentrated of larger volume specimen could guarantee detection sensitivity usually.

The volatile organic matter weak point mainly is that detection sensitivity is limited in the chromatographic technique measurement water, therefore need concentrate sample, the chemical ionization mass spectrometry technology detection sensitivity height that the present invention adopts, can directly measure concentration is the volatile organic matter concentration of pptv magnitude, can direct injected, do not need concentrating and separating, analysis speed is fast, and simple to operate.

Summary of the invention:

The purpose of this invention is to provide volatile organic matter measuring method and device in a kind of novel water, have that measuring speed is fast, detection sensitivity is high, absolute magnitude measure do not need calibration, instrumentation easy, can in-site measurement etc. advantage, be suitable for volatile organic matter analysis of components and measurement of concetration in the water.

Technical scheme of the present invention is as follows:

The measuring method of volatile organic matter in a kind of water is characterized in that may further comprise the steps:

(1), clean air or inert gas source feed in the water sample to be measured through the core filter plate, the minute bubbles of generation can extract the organism in the water;

(2), the bubble of collecting is fed chemical ionization mass spectrometry through pipeline, adopt high-purity oxygen or water vapour to insert in the described chemical ionization mass spectrometry as ion gun gas;

(3), according to the Henry's constant of volatile organic matter in the water, chemical ionization mass spectrometry measures the partial pressure of volatile organic matter in the water, in conjunction with the measurement parameters such as Henry's constant of volatile organic matter in the water, given composition and the concentration of volatile organic matter in the water outlet by Computer Processing; The partial pressure of described volatile organic matter adopts following method to measure:

In the chemical ionization mass spectrometry, enter into the reactive ion H of drift reaction tube ₃O ⁺Or O ₂ ⁺In the process of motion downstream with volatile organic matter M following ion-molecule reaction takes place:

Wherein k is reaction rate constant; Number density [the MH of product ion in the drift reaction tube ⁺] or [M ⁺] time dependent pass is:

$\frac{d\left[{\mathrm{MH}}^{+}\right]}{\mathrm{dt}}=k\left[H_3{O}^{+}\right]\left[M\right]$

$\frac{d\left[M^{+}\right]}{\mathrm{dt}}=k\left[{O_2}^{+}\right]\left[M\right]---\left(2\right)$

In the following formula, [H ₃O ⁺], [O ₂ ⁺] and [M] be respectively the drift reaction tube in H ₃O ⁺, O ₂ ⁺Number density with volatile organic matter M; When volatile organic matter M in the water that carries out trace measures, the number density [H of the reactive ion in the drift reaction tube ₃O ⁺] or [O ₂ ⁺] can be far longer than the number density [M] of M, at this moment, before and after reaction, the number density [H of reactive ion ₃O ⁺] or [O ₂ ⁺] can think constant; At drift reaction tube end, the number density [MH of product ion ⁺] will for:

[MH ⁺]＝[H ₃O ⁺][M]kt ₁

[M ⁺]＝[O ₂ ⁺][M]kt ₁

(3)

T wherein ₁Be the time of ion-molecule reaction, equal the time that ion moves in the drift reaction tube; Because the ion signal i (H that mass spectrum detects ₃O ⁺), i (O ₂ ⁺) and i (MH ⁺) be proportional to the number density [H of drift reaction tube intermediate ion ₃O ⁺], [O ₂ ⁺] and [MH ⁺], the concentration of trace volatile organic matter M is in the reaction tube that therefore drifts about:

$\left[M\right]=\frac{i\left({\mathrm{MH}}^{+}\right)}{i\left(H_3{O}^{+}\right)}\frac{1}{{\mathrm{kt}}_1}$

$\left[M\right]=\frac{i\left(M^{+}\right)}{i\left({{\mathrm{<figure-callout\; id="2"\; label="O"\; filenames="DEST\_PATH\_RE-H200710191277701E00011.png"\; state="\{\{state\}\}">O</figure-callout>}}_2}^{+}\right)}\frac{1}{{\mathrm{kt}}_1}---\left(4\right)$

Measure ionic strength i (MH ⁺), i (H ₃O ⁺) or i (O ₂ ⁺), utilize known ionic reaction rate constants k and ionic reaction time t ₁, can be by (4) formula obtain the drifting about number density of volatile organic matter M in the reaction tube; Because drift reaction tube gas inside is all extracted the gas that contains volatile organic matter after the aqueous solution, therefore, the dividing potential drop concentration of M remains unchanged before and after entering the drift reaction tube, like this, the dividing potential drop concentration of the M that records of chemical ionization mass spectrometry is exactly the concentration of volatile organic matter in the gas that extracts after the aqueous solution.

Described high-purity oxygen concentration is 99.999%.

The measurement mechanism of volatile organic matter in the water, it is characterized in that: formed by volatile organic matter sampler and chemical ionization mass spectrometry, described volatile organic matter sampler comprises inert gas source or clean air source, connected mass flow controller, the gas outlet of mass flow controller is connected with the tracheae that feeds in the water, the filter plate of tracheae end, tracheae has the uncovered outer cover in bottom outward, the outer cover top is connected with the injection port that pipeline is linked into chemical ionization mass spectrometry, be connected to stop valve and needle-valve in the described pipeline, have high-purity oxygen or water vapour to be linked into described chemical ionization mass spectrometry as ion gun gas.

Clean air or pure inert gas flow through aqueous solution and also volatile organic matter are wherein extracted, utilize chemical ionization mass spectrum to be extracted composition and the concentration thereof of volatile organic matter in the gas, analyze, handle by computer software at last, and give organic composition and concentration information thereof in the water outlet.

Chemical ionization mass spectrometry of the present invention mainly is made up of ion gun, ionic reaction drift reaction tube and mass spectrum probe unit three parts as shown in Figure 1.Ion gun is for generation of initial reaction ion R ⁺(H ₃O ⁺Or O ₂ ⁺), the drift reaction tube is the ion-molecule reaction zone, is used for the ionization of organic molecule.Terminal difference vacuum chamber and the mass spectrum detection system of connecting of drift reaction tube, mass spectrum is used for the identification of ion and the detection of ionic strength.Ion massspectrum signal input computing machine is handled and is analyzed.

Ion gun is made up of three stainless steel electrodes of internal diameter 2cm.Water vapor or O ₂Enter discharge cavity in the ion gun by flow controller, between two electrodes of discharge cavity, add 500V voltage, can form glow discharge and with the ion gun gas ionization, can generate stable reactive ion R ⁺(H ₃O ⁺Or O ₂ ⁺).The terminal mechanical pump that connects of ion gun is taken remaining water vapor or O in the discharge cavity away ₂, prevent that it from flowing into the drift reaction tube.

The reactive ion R that ion gun produces ⁺Be injected into the drift reaction tube through small holes, so as with the organism generation ion-molecule reaction that from water, extracts.The drift reaction tube is by forming each ring thickness 1cm, internal diameter 5cm through 10 stainless steel rings of seal with elastometic washer and insulation each other.Connect the identical resistance of resistance between the adjacent ring, add certain voltage at drift reaction tube two ends, thereby in the drift reaction tube, form a uniform electric field.Effect of electric field is to increase the ion molecule collision energy, stops the formation of cluster ion.When the upstream feeding of drift reaction tube contains the extraction gas of volatile organic matter, organic molecule and reactive ion R ⁺Ion molecule reaction takes place, and forms product ion.Ion enters the difference vacuum chamber through drift reaction tube end, enters into the mass spectrum detector through the 1mm aperture under the lens focussing force.The mass spectrum vacuum chamber is kept vacuum by the molecular pump of 600L/s, and exemplary operation pressure is 10 ^-6The torr magnitude.

The mass spectrum detection system is made up of quadrupole rod, electron-multiplier and ionometer number system.Ion carries out mass resolution through quadrupole rod, and is amplified by electron-multiplier, and signal is sent into the step-by-step counting unit and carried out the ion counting.Scanning of the mass spectrum and ionometer number average are by computer control.

The reactive ion H that chemical ionization mass spectrometry adopts ₃O ⁺Or O ₂ ⁺, not with clean air in Main Ingredients and Appearance such as N ₂, O ₂, CO ₂Deng reacting, but can ion-molecule reaction take place with most volatile organic matter molecule M and obtain single product ion MH ⁺Or M ⁺Therefore the gas direct injected that contains volatile organic matter M that will extract from water is behind the drift reaction tube, pass through ion-molecule reaction, M just is converted into product ion, by the mass spectrophotometry to product ion, can obtain the molecular weight information of volatile organic matter, and according to the concentration formula in the chemical ionization mass spectrometry measurement of concetration principle, finally obtain the concentration of volatile organic matter.

Glass tube outer cover by source of the gas, mass flow controller, the long 3cm internal diameter of 20cm is formed volatile organic matter sampler in the water.Pure air or pure oxygen through water sample to be measured pond, form the micro-bubble that upwards floats after mass flow controller is set flow.In the process that bubble rises, volatile organic matter diffuses into the minute bubbles from aqueous solution, the volatile organic matter partial pressure increases gradually in the bubble, finally and between the volatile organic matter concentration in the aqueous solution reach balance, and observe Henry's law: in the water in the concentration C of volatile organic matter and this bubble the partial pressure p of volatile organic matter be directly proportional, be C=H * p, wherein H is Henry's constant.Measure the partial pressure of the volatile organic matter that clean gas extracts, just can measure volatile organic matter concentration in the testing sample according to known Henry's constant.

In the process of analyzing water sample to be measured, may there be difference in the Henry's constant of water sample with the difference of temperature, salinity or potential of hydrogen.But to same water sample, Henry's constant H does not change with concentration change.For the accuracy that guarantees to measure, can at first carry out the real-time measurement of Henry's constant by the present invention:

By the gas that contains volatile organic matter that purity oxygen extracts, a part enters chemical ionization mass spectrometry through noticeable degree and finishes the partial pressure measurement, and remainder is discharged in the atmosphere.In the aqueous solution volatile organic matter by pure taking away after, its concentration C in water relation in time is:

$-V\frac{\mathrm{dC}}{\mathrm{dt}}=\frac{\mathrm{pF}}{\mathrm{RT}}=\frac{\mathrm{FC}}{\mathrm{HRT}}---\left(4\right)$

Wherein V is the volume of liquid, and F is that R is mol gas constant by the clean gas flow in the water, and T is absolute temperature.By formula (4) and Henry's law as can be known:

$\ln \left(\frac{C_t}{C_0}\right)=\ln \left(\frac{{\mathrm{Hp}}_t}{{\mathrm{Hp}}_0}\right)=\ln \left(\frac{p_t}{p_0}\right)=\frac{-F}{\mathrm{HVRT}}t---\left(5\right)$

C wherein ₀, p ₀It is respectively the partial pressure of measuring volatile organic matter in the concentration of volatile organic matter in (t=0) water zero hour and the clean gas.In formula (2), F, V, R, T are the known parameters in the experiment, measure ln (p _t/ p ₀) variation relation of t in time, just can calculate Henry's constant H.

If the organic concentration in the water sample than higher, can be measured Henry's constant and P by method described above ₀, namely can obtain the concentration of volatile organic matter in the water.If the organic concentration in the water sample to be measured close to detectability, can be got a part of water sample, add an amount of volatile organic matter sample, be configured to the solution of high concentration, measure Henry's constant, and then remove to survey the P in the water sample to be measured ₀, namely can obtain the concentration of analytic sample in the water.If the organic Henry's constant in the known water sample only needs to measure P ₀Get final product the concentration of volatile organic matter in the water outlet, the time of measuring once is less than 3 minutes.

The present invention can measure volatile organic matter in the water by sampling mode, and also measurement environment water sample in real time is such as the volatile organic matter in lake or the rivers water.The present invention is installed on the ship, according to method described above, can realizes volatile organic matter measurement of concetration in the water body.

Description of drawings:

Fig. 1 is the chemical ionization mass spectrometry structural representation.

Fig. 2 is the structural representation of the present invention's volatile organic matter in sample mode measurement water.

Fig. 3 is the structural representation of the volatile organic matter of the present invention in real-time measurement environment water.

Fig. 4 utilizes the present invention to measure relation between the benzene concentration of benzene concentration and configuration in the water.

Fig. 5 is the Henry's constant measurement result of utilizing benzene in the water of the present invention.

Embodiment:

The measurement mechanism of volatile organic matter in the water, formed by escaping gas sampler and chemical ionization mass spectrometry, described escaping gas sampler comprises inert gas source or source of water vapor, connected mass flow controller, the gas outlet of mass flow controller is connected with the tracheae that feeds in the water, there is the core filter plate tracheae end, tracheae has the uncovered ring glass pipe outer cover in bottom outward, glass tube outer cover top is connected with the injection port that pipeline is linked into chemical ionization mass spectrometry, be connected to vent valve and needle-valve in the described pipeline, have high-purity oxygen or water vapour to be linked into described chemical ionization mass spectrometry as ion gun gas.

Concentration with benzene in the measurement water is the concrete operations mode that example is introduced measurement mechanism.After clean gas (as inert gas) is controlled flow through mass flowmeter, enter in the water sample by the sintering glass plate that is immersed in the water sample to be measured, the gas that bubble is taken out of is introduced in the chemical ionization mass spectrometry through the teflon pipeline and measurement volatile organic matter concentration wherein.Computing machine just can calculate the concentration of volatile organic matter in the water outlet according to the volatile organic matter concentration of measuring and the Henry's constant in the water sample to be measured.

Henry's constant is different and difference to some extent with environmental water sample characteristic and temperature, and for same temperature and water sample, Henry's constant does not change with concentration change.Therefore if organic concentration ratio is higher in the water sample to be measured, the method for utilizing above technical scheme to describe can directly be measured Henry's constant and concentration thereof; If organic concentration ratio is lower in the water sample to be measured, can get the higher organic aqueous solution of water sample compound concentration to be measured earlier, measure Henry's constant, utilize Henry's constant, and then water sample is carried out organic concentration measure.

Claims (3)

1. the measuring method of volatile organic matter in the water is characterized in that may further comprise the steps:

(1), clean air or inert gas source feed in the water sample to be measured through the core filter plate, the minute bubbles of generation can extract the organism in the water;

(2), the bubble of collecting is fed chemical ionization mass spectrometry through pipeline, adopt high-purity oxygen or water vapour to insert in the described chemical ionization mass spectrometry as ion gun gas;

(3), according to the Henry's constant of volatile organic matter in the water, chemical ionization mass spectrometry is measured the partial pressure of volatile organic matter in the water that comes, composition and the concentration of being given volatile organic matter in the water outlet by Computer Processing;

In the chemical ionization mass spectrometry, enter into the reactive ion H of drift reaction tube ₃O ⁺Or O ₂ ⁺In the process of motion downstream with volatile organic matter M following ion-molecule reaction takes place:

Wherein k is reaction rate constant; Number density [the MH of product ion in the drift reaction tube ⁺] or [M ⁺] time dependent pass is:

$\frac{d\left[M{H}^{+}\right]}{\mathrm{dt}}=k\left[H_3{O}^{+}\right]\left[M\right]$

$\frac{d\left[M^{+}\right]}{\mathrm{dt}}=k\left[{O_2}^{+}\right]\left[M\right]$

In the following formula, [H ₃O ⁺], [O ₂ ⁺] and [M] be respectively the drift reaction tube in H ₃O ⁺, O ₂ ⁺Number density with volatile organic matter M; When volatile organic matter M in the water that carries out trace measures, the number density [H of the reactive ion in the drift reaction tube ₃O ⁺] or [O ₂ ⁺] can be far longer than the number density [M] of M, at this moment, before and after reaction, the number density [H of reactive ion ₃O ⁺] or [O ₂ ⁺] can think constant; At drift reaction tube end, the number density [MH of product ion ⁺] will be [MH ⁺]=[H ₃O ⁺] [M] kt ₁(3) [M ⁺]=[O ₂ ⁺] [M] kt ₁

T wherein ₁Be the time of ion-molecule reaction, equal the time that ion moves in the drift reaction tube; Because the ion signal i (H that mass spectrum detects ₃O ⁺), i (O ₂ ⁺) and i (MH ⁺) be proportional to the number density [H of drift reaction tube intermediate ion ₃O ⁺], [O ₂ ⁺] and [MH ⁺], the concentration of trace volatile organic matter M is in the reaction tube that therefore drifts about:

$\left[M\right]=\frac{i\left(M{H}^{+}\right)}{i\left(H_3{O}^{+}\right)}\frac{1}{k{t}_1}$

$\left[M\right]=\frac{i\left(M^{+}\right)}{i\left({O_2}^{+}\right)}\frac{1}{k{t}_1}$

Measure ionic strength i (MH ⁺), i (H ₃O ⁺) or i (O ₂ ⁺), utilize known ionic reaction rate constants k and ionic reaction time t ₁, can be by (4) formula obtain the drifting about number density of volatile organic matter M in the reaction tube; Because drift reaction tube gas inside is all extracted the gas that contains volatile organic matter after the aqueous solution, therefore, the dividing potential drop concentration of M remains unchanged before and after entering the drift reaction tube, like this, the dividing potential drop concentration of the M that records of chemical ionization mass spectrometry is exactly the concentration of volatile organic matter in the gas that extracts after the aqueous solution.

2. the measuring method of volatile organic matter in the water according to claim 1 is characterized in that described high-purity oxygen concentration is 99.999%.

3. the measurement mechanism of volatile organic matter in the water, it is characterized in that: formed by volatile organic matter sampler and chemical ionization mass spectrometry, described volatile organic matter sampler comprises inert gas source or clean air source, connected mass flow controller, the gas outlet of mass flow controller is connected with the tracheae that feeds in the water, the filter plate of tracheae end, tracheae has the outer cover of bottom-open outward, the outer cover top is connected with the injection port that pipeline is linked into chemical ionization mass spectrometry, be connected to stop valve and needle-valve in the described pipeline, have high-purity oxygen or water vapour to be linked into described chemical ionization mass spectrometry as ion gun gas.

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