Passive sampling device

FIELD: investigating or analyzing materials.

SUBSTANCE: sampling device has sampler, changeable batching member which is made separately from the sampler, housing, and wind-protection device. The wind-protection device is made of porous diaphragm mounted in the base of the housing and overlaps it. The sampler is mounted to provide the distance between the inlet port of the sampler and diaphragm to be 0.1D<L<0.3D, where D is the diameter of diaphragm and L is the distance between the inlet port of the sampler and diaphragm.

EFFECT: improved design.

3 cl, 1 dwg

 

The invention relates to devices for air samples for subsequent determination of average concentrations of selected substances in the air during the exposure. The device can be used in field conditions in systems of control over the content of radioactive substances in the atmospheric surface layer. Can also be used to determine the average humidity during the exposure.

Known gas sampler for sampling almostcaused gases from soils and subsurface rocks in the field (RF Patent No. 2055340 priority from 15.06.92, publ. 27.02.96, IPC 601 N 1/22). The sample represents a column Packed with the adsorbent. The column is equipped on one end cap with fitting, with a fixed intake funnel, and at the other end - fitting with mounted on it a protective umbrella with holes. Intake funnel and protective umbrella installed with the possibility of removal. In the above sampler role of protection from wind and precipitation performs an umbrella.

A disadvantage of known construction is the following. This design does not allow the field to conduct air sampling in the surface layer, because the design of the intake funnel with an open channel designed to mount directly to the well, and the umbrella is unable to provide reasonable protection against wet is and when sampling from the air. The latter circumstance will cause a significant increase in the rate of supply of selected substances (more than 20 times) and thus increasing the error in determining the average concentration of selected substances in the air during the exposure.

The closest in purpose and technical nature of a passive sampler for sampling of tritium oxide (R.L.OTLET, A.J.WALKER, C.J.CALDWELL-NICHOLS PRACTICAL INVIRONMENTAL, WORKING AREA AND STACK DISCHARGE SAMPLERS, PASSIVE AND DYNAMIC, FOR MEASUREMTNT OF TRITIUM AS utrs AND HT, FUSION TECHNOLOGY, vol 21, MAR, 1992. p.550-555). This sampler is selected as a prototype. The sampler is a plastic bottle with silica gel, placed in a waterproof container. In the neck of the bottle is the diffusion tube, closed on the outside by a stainless steel mesh. The last two elements perform the role of a windbreak, and the receiver also performs the function of the metering element regulating the rate of admission of selected substances by replacing the tube with a larger or smaller diameter. In known passive sampling device used tube diameter 15 mm and length 60 mm, closed mesh stainless steel number of cells per one inch equal to 100. This design windbreak provides the coefficient windbreaks (with whom oresti entering the sampler at a wind speed of 2-3 m/s to the arrival rate in a stationary environment) 1.2. While the sampler is gaining 0.3 g of moisture during exposure 6 days. When using a tube with a diameter of 25 mm coefficient of windbreaks is 1.3, while the sampler is gaining 1 g moisture for 6 days.

This design has the disadvantage that due to the following circumstances. Windproof device consists of two elements - tube and the grid. The grid reduces the turbulence of the air flow at the entrance to the tube. Further, in the tube, due to the predominance of length over diameter, is the damping of the turbulence and the formation of the diffusion flow. In view of the fact that the grid does not provide a complete damping of the turbulence of the air, the depth of penetration of the air flow in the tube and, accordingly, the effective distance from the surface sorption to the border of the beginning of the diffusion flow will vary depending on wind speed. The latter circumstance causes an increase in the error of determining the concentration of selected substances from the air during operation in a wide range of changes in wind speed due to the deviation from the proportionality between the rate at the sampler and the concentration of selected substances in the air. In addition, in view of the availability of a relatively long tube, this design windbreak creates significant diffusion with the opposition coming into the sampler substance. This reduces the arrival rate and number of samples collected during the exposure. On the other hand it is not possible to recruit a minimum number of required samples in a shorter exposure time. The combination of wind and dosing constructively in a single element (tube) leads to an increase in the degree of influence of the wind by increasing the diameter of the tube, which will cause an increase in error when selecting a similar number of samples in a shorter exposure time.

The present invention is the creation of a universal sampling device for sampling air, in particular, elemental tritium and its oxide, and water vapor in the short time exposure (1 day), ensuring proportionality between the rate at the sampler and the concentration of selected substances in the air when operating in field conditions in a wide range of changes in wind speed. Ensuring the above requirements, you can minimize the error in determining the average concentrations of selected substances in the air during the exposure.

The technical result of the proposed passive sampling device is getting under variable wind speed and short time Expo is icii samples selected substances from the air, the number that is proportional to the medium-integral value of selected substances in the air for the exposure time according to the relation M=K··τwhere M is the mass selected samples, With average concentrations of selected substances in the air during the exposure, τ - the exposure time, K - coefficient of proportionality.

The technical result is achieved by the fact that in known passive sampling device containing the actual sampler, interchangeable metering element, the housing and windproof device, interchangeable metering element is made independent, and windproof device made in the form of a porous membrane, is placed in the base and overlying it, while the sampler is located so that the distance between the inlet of the sampler and the membrane meets the condition:

0,1D<L<0,3D,

where D is the diameter of the membrane;

L is the distance between the inlet of the sampler and the membrane.

As the porous membrane is selected film with a pore size of less than 0.2 μm. The membrane may be made of multiple layers of film.

The use of a windbreak in the form of a porous membrane (e.g., with a pore size of less than 0.2 μm) reduces the susceptibility to changes in wind speed through the formation diffusing the flow of selected substances in a relatively thin layer, separating the external environment from the environment, which creates a diffusion stream to the sorbent. In this case ensures the constancy of the effective distance of the boundary of the beginning of the diffusive flux to the surface sorption, which is necessary to maintain the proportionality between the rate at the sampler and the concentration of selected substances in the air with a change in wind speed. As a consequence decreases the error in determining air concentrations of selected substances in a changing wind speed.

In view of the high hydrodynamic resistance to air specific throughput of such membranes is relatively low. Therefore, to ensure the necessary number of samples during the exposure area of the membrane is brought to the area of the base body.

The use of the metering element, structurally designed as a separate item allows you to adjust the speed of delivery of the selected substance in the sampler in a wide range preserving windproof characteristics of the device at a constant level.

The limitation of the distance from the membrane to the inlet of the sampler in the range from 0.1 to 0.3 of the diameter of the membrane can form an approximate uniform distribution of concentrations of selected substances is tion on the perimeter of the hole in the sampler, what is required to distribute the stream to the surface sorption inside the passive sampler. The increasing distance from the membrane by more than 0.3 of the diameter of the membrane will cause a decrease in the rate of supply in the sampler that will increase the exposure time or the decrease in the number of samples.

Placing the membrane in the base allows you to use the housing made in the form of an inverted Cup, as a means of protection from atmospheric precipitations.

The execution of the multilayer membrane allows to use the device in a wider range of wind speeds change.

The drawing shows a diagram of the inventive device.

The device consists of a passive sampler 1 containing interchangeable metering element 8 of the housing 2 windproof device that comprises the membrane 3 and the frame 4 for fixing the membrane, which includes 5 mesh designed to protect the membrane from mechanical damage, mount sampler 6 and spacers 7, intended for sealing windproof frame of the device.

Passive sampling device operates as follows.

In the attachment 6 is installed pre-loaded sorbent, passive sampler 1. Then through the gasket 7 sets the I windproof device, frame 4 which is fixed by screws. Depending on the type of selected substances from the air sampler is loaded the appropriate sorbent. So for sampling of tritium and its oxide is used catalyst, providing the low-temperature oxidation of hydrogen. For selection of water vapor used synthetic zeolite or silica gel. Set the required number of samples for different time of exposure under conditions of changes in seasonal humidity is provided by changing the dosing element 8 located in the passive sampler 1. To increase the exposure time is set to the metering element with a lower reduced section. In the exposure process is the transfer of selected substances from areas of high concentration formed at the inner surface of the membrane, in an area of low concentration, i.e. in the sampler. When exposed to the sampling device of the wind, the changing speed in the membrane layer, due to the small size of the pores is the damping of the air flow and the formation of the diffusion flow directly over the membrane. Due to this, the arrival rate at the sampler 1 selected substances is maintained in proportion to the magnitude of the concentration thereof in the ambient air. After exposure, windproof element 3 is ustanavlivaetsya sealing transport cover (not shown) and the sampling device is transported to the laboratory for desorption of the sample from the sampler 1 and determining the average concentration of selected substances in the air during the exposure.

An example of a specific implementation can serve as a passive sampling device for sampling of tritium oxide made according to the claimed device, in which the applied passive sampler (1) with two entrances, each of which has a removable metering element made in the form of a plate with a hole and located on the membrane (4) at a distance of 30 mm as a membrane used porous film with a pore size of 0.15 μm. The diameter of the membrane is chosen equal to 200 mm

Tests conducted in the field showed that in the conditions of changing wind speed with a maximum value of up to 5 m/s the stated sampling device provides a coefficient of windbreaks at the level of 1.2, as compared with the approved prototype similar number of samples were obtained during the exposure of 0.8 days. After performing thermal desorption using the calibration factor used by the dosing element, was used for calculation of average concentration of STS in the air during the exposure. Error of the sample was 9%. Thus, the claimed passive sampling device confirmed the claimed technical result.

1. Passive sampling device containing a sampler replacement dairou the second element, case and windproof device, characterized in that the interchangeable metering element is made independent, and windproof device made in the form of a porous membrane, is placed in the base and overlying it, while the sampler is located so that the distance between the inlet of the sampler and the membrane meets the condition 0,1D<L<0,3D, where D is the diameter of the membrane, L is the distance between the inlet of the sampler and the membrane.

2. Passive sampling device according to claim 1, characterized in that the porous membrane is selected film with a pore size of less than 0.2 microns.

3. Passive sampling device according to claim 2, characterized in that the membrane is made of several layers of film.



 

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