CA2050951A1 - Method and device for sampling a liquid containing a dissolved gas - Google Patents

Abstract

(57)Abstract A method or sampling a liquid containing a dissolved gas ensures that the liquid by the sampling is collected in a container (6) without contact arising between the liquid and a surrounding atmosphere. A device for use with the sampling comprises a shape-adaptable first container (1) or fluidtight material and a gaslight second container (6) of fixed shape and define size and volume, whose size is adjusted to the first container (1) which is adapted for insertion in the second container (6). After the sam-pling the first container (1) is closed gastight and after insertion of the first container (1) the second container (1) is sealed such that the device also is gastight.

Description

A method and device for sampling a liquid containing a dissolved gas ______________________________________________________ The invention relates to a method of sampling a liquid containing a dissolved gas or other volatile substances or components, especially w,ater with dissolved radon, which liquid during the sampling is to be collected in a container substantially without contact arising between the liquid and a surrounding atmosphere. The invention also relates to a device for use with the method.

In a number of cases where the object of th,e' analysis is a gas dissolved in a liquid or liberates gas which are soluble in a liquid, it is desirable that the sampling or collecting of the ~' liquid can take place without it getting into contact with the surrounding atmosphere. A gas dissolved in the liquid would when the llquld is exposed to the surroundlng atmosphere, escape thereto, especlally when the llquid is naturally absent from the surroundlng atmosphere or only present therein such that its partial pressure is substantially lower than its partial pressure when dissolved in the liquid. If the object of the analysis is a quantitative determination OI the gas dissolved in the liquid, said circumstance may thus lead to that,such an analysis cannot be carried out or gives highly errounous results. Especially is this case in the determination and analysis of radon dissolved in water. Radon is generated from natural occurences of radioactive elements in the earth's crust and is, as it is solutable in water, disposed to accumulate in the ground water in dissolved state. How much radon which is dissolved in the ground water, depends on the amount or radioactive elements in and surrounding the ground-water bearing strata and the ground water flow rate. The radon level of ground water is usually less than 1000 pCi/l, but may in singular cases be much higher; levels above 1 uCi/l has been found. If ground water containing dissolved radon is used as a water source, the water would when drawn at the surface SU8S~ITUT~ T

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( liberate radon to the surrounding atmosphere and this is today commonly regarded as representing a non-negligible health risk in areas with radon-containing ground water.

In order to judge this risk it is hence desirable to make a reliable determination of the radon content of ground water and it is also desirable that such a determination could be made by non-experts, The problem with radon in ground water and determination of radon in ground water which are used for water supply, is discussed in the publication "Removal of Radon From Household Water", United States Environmental Protection Agency, OPA-87-011, September 1987.

Several procedures for sampling have been developed in order to determine the radon content of ground water which are used for instance in househoulds. Usually the water are tapped directly in a container at a tap point of the water supply, whereafter the container is closed and for instance sent to a laboratory for closer analysis. In connection with such a method it has however turned out that a part of the radon content of the water is liberated to the surrounding atmosphere.

Another method ls to place a alpha-particle track detector in a water container, e.g. in a toilet cistern for a certain period and then remove the detector and forward it to a laboratory for analysis. The latter method has, however, turned out to be completely unsuitable for a quantitative determination of the radon content of ground water.

The known methods of sampling of ground water with dissolved radon have hence turned out to be less than suitable and the procedure for direct tapping into a container as given in the mentioned publication of EPA, leads to a much too great radon discharge from the water in order to perform a reliable determination.

By use of direct tapping into a solid container it cannot with known methods be avoided that the water gets into contact with 5~ E3S~

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( the air during tapping and it will then take place an uncontrolled radon discharge to the air. Especially with high radon concentrations the radon discharge to the air will take place so quickly that it attains a decisive significance for the analysis result. The containers commonly used for sampling have often an unsuitable geometry and material for use as analysis packaging and in connection with the analysis it will often be necessary with a transfer to a new container before the analysis takes place.

For instance does SE-B-423 578 disclose a sampling device and a container for collecting a water sample for bacteriological investigations, wherein the container has a flexible wall construction secured to rigid end bodies, the container being expanded by displacing the end bodies, enabling the water sample to be sucked into the container.

US-A-3 006 341 discloses an apparatus with a collapsible bag for handling medical fluids. The bag may be placed in container ~reventing an undesired drying out of the fluid stored in the bag.

~inally, GB-A-2 207 709 a device for collecting fluids from the body, the bag being provided in a container for safety reasons and wherein bag and container each are equipped with a suction tube. '' The above cited publications are all describing devices which might suitable for sampling liquids containing a dissolved gas, but the combination o~ bags and containers disclosed therein are quite unsuitable for the above-mentioned use as a analysis packing in connection with a determination of the radon content of ground water.

The discussed and other problems with sampling of a liquid containing a dissolved gas, particularly water with dissolved radon, are avoided by applying a method of sampling and a device according to the present invention. A first object in "~ 7~ 'C~

( this connection is to avoid contact between the liquid and a surrounding atmosphere. A second object is to avoid a contaminitation of the device used with the method according to the invention and a further object is that the device with the sample contained shall be used directly in the final analysis, without any retapping into special sample contalners being necessary. These and further obiects of the present invention are provided by a method characterized by features disclosed in the characterizing portion of claim 1 and by a device which is characterized by features disclosed in the characterizing portion of claim 2. Further features and advantages appears from the appended dependent claims.

Even though there above essentially are mentioned those problems which are present with radon in water, the invention is not limited to this particular application. It has, however, been chosen to illuminate the problem situation by means of an example of current interest.

The lnvention will be further explained below in connection with the drawing which schematically represents an embodiment of the device according to the present invention.

- Figure 1 is a perspective view of the flexible inner container during filling.
- Figure 2 is a perspective view of the placement of the flexible container in the rigid container, and - Figure 3 is a schematic view through the sealed container.

The device of the Figure comprises a first container 1 which for instance may be a commercially available colostomi bag or a urine bag equipped with a plastic tube 2 for filling the bag.
The bag 1 is watertight and preferably fluidtight and is provided with a one-way valve 3 which prevents outflow as well as possibility for closing the filli.ng device, e.g. the plastic tube 2 by means of a cap and/or a clip 4. The one-way valve 3 may most simply be a flap which prevents outflow, provided in connection with the filling device or the tube 2. Before . :. ; :, . : . ,.
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' f filling takes place, the bag 1 is completely evacuated and the rilling takes place by the filling device or tube 2 being inserted for instance in a water tap 5, as the tap is opened, such that the tube 2 catches the water before the wa~er flow has :Lssued from the tap opening. The bag 1 may during the fill:Lng be placed in the hand or on a tray. Preferably the bag 1 is made of a transparent plastic material such as polyethene and provided with printed strokes which indicates an approximate filling volume. When the desired filling volume has been reached, the filling device 2 is drawn away from the tap and closed with the cap or a clip 4 which are placed on the tube, whereafter the bag is being wiped on the outside and placed in another container 6 of definite shape and whose size is adapted to the bag 1.

After the bag 1 has been placed in the second container 6, this will be closed by means of a suitable gastight closure device.
In connection with for instance gamma-spectrometric analysis of radon in water it is necessary that the second container 6 has a defined shape and geometry and that the detector used for the analysis has been calibrated for this geometry. In preferred embodiment the second container is thus a specially made can 6 of impact resistant polystyrene. After the bag 1 has been placed in the plastic can, a closure or film 7 of aluminium is placed over the bag 1 in the plastic can 6 and secured by welding with for instance an electric iron. Then the plastic can 6 is closed with a further lid 8. The sample is hence immediately after tapping sealed in the final analysis packaging. Concerning the chose of impact resistant polystyrene for the second container 6, it has turned out that this material has a far higher gastightness than many other common plastic materials. With the aluminium lid 7 welded thereto and the final closure it has been established that the completed analysis packaging is practically gastight against diffusion of radon.

With a suitable size of the analysis packaging, i.e~ the bag 1 and the second or outer sample container 6, it can now be :, ' ~

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performed an immediate determination of the radioactivity of the sample, measured in becquerel. It may e.g. for acti~ity measurement be employed a scintillisation detector in the form of a sodium iodide crystal. In this way a measurement of the activity of radon is achieved, as the scintillisation detector detects the gamma radiation emitted by the decay of radon daughters. The measured activity will give a correct determination of the radon content of the ground water. In addition a determination of other isotopes and substances and compounds in the liquid may also be made by using the device, i.e. the analysis pac~aging according to the present invention.
If appropriate, alpha-particle-detectors might of course also be employed when using the analysis packaging according to the present invention.

It is to be understood that the device according to the invention may be made of other materials and that other filling devices and closure devices may be used than those mentioned herein, if only the material and closure devices are fluid- or gastlght.

The bag may have a shape which for instance i3 closely adapted to the rigid container, but may also be foldable and so flexible that it by insertion in the rigid container will adapt its shape to a satisfying degree, such that one may see this as a reproducible filling of the container volume.

The employment of the method and the device according to the invention by sampling of radon containing ground water discussed herein it is of course only intended as an example and the invention is not restricted to this usage alone, as there from the above will evident that the method and the device are suited to sampling liquid substances in general, when it is desirable that the liquid at no instance shall get in contact with the surrounding atmosphere.

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Claims (9)

1. A method of sampling a liquid containing a dissolved gas or other volatile substances or compounds, particularly of water with dissolved radon, the liquid by the sampling being collected in a collapsible first container substantially without a contact arising between the liquid and a surrounding atmosphere, said first container thereafter being placed in a second container, c h a r a c t e r i z e d i n that the liquid is filled in a previously evacuated, shape-adaptable, first container of fluidtight material, preferably an evacuated bag, that the shape-adaptable first container or bag after being filled with liquid is closed fluidtight and thereafter placed gastight in the second container of fixed shape with a size and geometry adapted to the first container, whereby the first container or bag substantially adapts to the shape of the second container and that the second container thereafter is sealed such that the sample is closed in a gastight fashion and in a state of stable shape.

2. A device for use with sampling of a liquid containing a dissolved gas or other volatile substances or compounds, particularly of water with dissolved radon, the liquid by the sampling being collected in a collapsible first container substantially without contact arising between the liquid and a surrounding atmosphere, said first container thereafter being placed in a second container, c h a r a c t e r i z e d i n that the first container is a shape-adaptable evacuated container of fluidtight material, preferably a bag, that the second container has a fixed shape of defined size and geometry, whose size and shape is adapted to the size of the first container, that the first container is adapted for insertion in the second container and comprises a filling device, preferably in the form of a tube or a funnel and further that means for preventing outflow is provided, preferably in connection with the filling device.

3. Means according to claim 2, c h a r a c t e r i z e d i n that at least one of the containers is gastight, with a gastight closure device.

4. Means according to claim 2, c h a r a c t e r i z e d i n that the first container is a fluidtight bag, preferably of polyethene.

5. Means according to claim 2 or 3, c h a r a c t e r i z e d i n that the first container is provided with printed characters and signs which may be instructions for use and/or measuring strokes for approximate indication of filling volume.

6. Means according to claim 2 or 4, c h a r a c t e r i z e d i n that the means preventing outflow is a one-way valve.

7. Means according to claim 2 or 4, c h a r a c t e r i z e d i n that the first container is provided with a closure device, preferably in the form of a clip and/or cap provided in connection with the filling device.

8. Means according to claim 2, c h a r a c t e r i z e d i n that the second container is made of impact resistant material such as impact resistant polystyrene.

9. Means according to claim 2 or 7, c h a r a c t e r i z e d i n that the closure device of the second container comprises a aluminium lid weldable thereon as well as another lid adapted to be mounted over the aluminium lid.