WO1998046190A1

WO1998046190A1 - Gastight ampoule

Info

Publication number: WO1998046190A1
Application number: PCT/NL1998/000203
Authority: WO
Inventors: Bartholomeus Henricus Antonius Maas
Original assignee: Euro-Trol B.V.
Priority date: 1997-04-16
Filing date: 1998-04-09
Publication date: 1998-10-22
Also published as: NL1005820C2

Abstract

Described is a gastight ampoule (1), which is closed by locally fusing its wall, which ampoule comprises a volume of medium (2), for example a calibration medium for a blood-gas analysis device, as well as a head space (3) in which a gas phase may be situated. A filler body (4) is accommodated in the head space, in order to limit the volume of the gas phase as far as possible, so as to limit exchange of substances between the medium and the gas phase to a minimum. Media can be stored in a stable manner in these ampoules for a very long time. A description is also given of a method for producing an ampoule (1) of this kind with filler body (4), as well as of a number of filler bodies.

Description

Short title: Gastight ampoule.

The present invention relates to a gastight ampoule, at least comprising a volume of medium, and a head space accommodating a filler body, wherein the ampoule is closed by locally fusing the wall of the ampoule at the location of the head space.

Ampoules of this kind are generally known in the specialist field and are used for packaging various media, such as calibration medium for a blood-gas analysis device. With the said ampoules, gas exchange between the medium and the environment is prevented. Ampoules of this kind are also used for media which have to be packaged and stored under sterile conditions, such as injection liquids. A conventional design of a gastight ampoule of this kind is a glass ampoule, which can be opened by breaking off part of it.

The ampoule is generally locally fused by heating the wall of the ampoule at a distance from the medium, so that the wall melts locally, resulting in a gastight seal by fusion. When sealing an ampoule of this kind by fusion, it is necessary to leave a considerable distance between the liquid and the point of fusion. In the case of a gastight glass ampoule, temperatures of 1200 K are reached during the fusion process. If the liquid comes too close to the point of fusion, the result may be excessive stress in the material of the ampoule, as a result of which this material may break or the sealing may not adequately be ensured. This high temperature may also affect the composition of the liquid, with the possibility of, for example, organic buffers being harmed. A gastight ampoule which is closed by locally fusing its wall therefore has to have a considerable empty space in which a gas phase may be present. In the application, this empty space is referred to as the head space. In order to ensure constant quality and a prolonged shelf life of the medium in a gastight ampoule, it is important that the gas phase in the ampoule is as small as possible. This is of crucial importance in particular in the case of liquid calibration media for blood-gas analysis which function as quality control materials. These materials are generally stored in 3 ml glass ampoules with 2-3 ml buffer solution with an accurately determined quantity of acid/base, oxygen, carbon dioxide, electrolytes, such as Na⁺, K⁺, Li⁺, Ca²⁺ and Cl^", as well as metabolites, such as glucose and lactate . Ampoules of this kind are routinely used in clinical chemical laboratories as control and calibration means for analysis apparatus. Owing to the presence of a gas phase in the ampoule, 0₂ and C0₂ will distribute between the gas phase in the head space and the liquid phase of the medium, in which measurement is eventually carried out. Since the equilibrium which is then produced is temperature-dependent, the glass ampoules have to be incubated at the correct temperature prior to use . The partial oxygen pressure, p0₂, in particular is very sensitive to temperature changes : approximately 1 mmHg per 1°C. During the year, temperature changes of 5-10°C are generally measured in laboratories, and these temperature changes can cause a deviation of approximately 8-17% in the low concentration range, associated with a p0₂ of 60 mmHg, and this is unacceptable for a control material of this nature. In addition, the level of vibrations affects the values to be measured. In practice, this is necessarily of consequence, since a large number of laboratories are not aware of these effects. Moreover, at the measurement location it is very disadvantageous to restore the ampoules to the original state in which they were filled: this state is often unknown to the user, and such action is time-consuming .

The object of the present invention is to solve the abovementioned problems, and is characterized in that the filler body abuts the wall of the ampoule at the location of the fused portion thereof. The presence of a filler body in this way makes it possible to seal the ampoule in a gastight manner at a distance from the medium by locally fusing its wall, without the medium in the ampoule being affected at all by the effects associated with fusing the wall, such as for example heating, and simultaneously minimising the gas phase in the head space.

In a preferred embodiment of the present invention, the filler body substantially completely fills the head space. This reduces any remaining gas phase to such an extent that exchange of substances with the medium is reduced considerably. Depending on the medium used, the intended application and the volume of the remaining gas phase in the ampoule, the exchange of substances can in this way be controlled within specific desired limits, in order for example to limit any measurement error caused by the exchange of substances between the medium and the gas phase to within limits which are permissible for the case in question.

Preferably, the volume of the empty space which is present, in addition to the filler body, in the head space amounts to less than 10% of the medium. The presence of such a small volume of empty space in the ampoule allows the exchange between any gas phase present in this space and the medium to be limited to a desired minimum.

Advantageously, in the ampoule the volume of the empty space which is present, in addition to the filler body, in the head space amounts to less than 1.5% by volume of the medium. In the case of such a volume it is possible to achieve the situation where a control/ calibration medium for a blood-gas analysis device exhibits a maximum deviation of 1% in the 0₂ content, irrespective of temperature. An ampoule of this kind therefore does not have to be brought to a specific temperature in order to obtain very reliable measurement results.

However, it is also possible to seal the gastight ampoule substantially without any gas phase. Although this precludes exchange of gaseous substances, under certain circumstances it may also cause problems, since the medium in the ampoule may expand or contract depending on the temperature, which may cause the ampoule to break. In this case, the filler body may optionally comprise a somewhat compressible material . The ampoule may be closed by locally fusing the wall over the filler body, so that the filler body is located freely in the ampoule. In an advantageous embodiment of the ampoule, the filler body is fused to part of the wall of the ampoule, thereby sealing the ampoule. The fused join between the filler body and the ampoule on the one hand ensures a gastight seal of the ampoule and on the other hand the filler body is immovably joined to the ampoule, a fact which may provide the ampoule with a certain strength and ensures reliable positioning of the filler body.

In a very advantageous embodiment of the ampoule according to the present invention, the filler body consists of the same material as the ampoule. If the filler body and the ampoule consist of the same material, they will both have the same flow properties, thus facilitating sealing by fusion. Even if the filler body is not fused to the wall, it is advantageous that both consist of the same material, since the same demands are placed on the material of both components with regard to gastightness and inertness with regard to the medium. If desired, the filler body may consist of a different material from that from which the ampoule is produced, provided that both materials are inert with respect to the medium. If fusion of the wall is carried out by melting by the supply of heat, the said material is preferably also heat-insulating and heat- resistant .

The filler body advantageously comprises glass. From a chemical point of view glass is virtually inert. Moreover, it is a transparent material which is relatively easy to produce in different colours.

Most preferably, the filler body comprises glass of the first hydrolytic class, such as for example FIOLAX™. Although other glass grades may also suffice, it is important for certain media that the material of both the ampoule and the filler body satisfy the highest requirements with regard to, for example, purity.

Both a solid filler body and a hollow filler body are suitable for fusing the filler body to the ampoule. However, a solid filler body makes the ampoule unnecessarily heavy, or even top-heavy. In a following preferred embodiment of the ampoule according to the present invention, the filler body is of hollow design. A hollow filler body is relatively easy to produce from, for example, a tubular material.

Advantageously, the filler body comprises an identification means. For example, it is possible to provide different ampoules with filler bodies of different colours as identification means. A specific colour may be linked to a specific type of medium, so that the ampoules can be differentiated from one another at a glance. In this case, a hollow filler body can advantageously be used, since the ampoule can be identified by accommodating an identification means, such as a bar code, a small coloured object made of, for example, plastic or coloured sand, in the cavity inside the filler body, in which case the sand may optionally be partly fused to the wall of the filler body. The identification means may also comprise a specific shape of the filler body.

The ampoule advantageously has a constriction at the location of the transition between the head space and the medium, it being possible for the filler body to bear against the constriction. This limits the position of the filler body, and as a result the body virtually cannot move freely in the head space of the ampoule, or can do so only to a very limited extent. The constriction may also serve as a support point for the filler body during fusion of the wall of the ampoule. Particularly advantageously, a weakening line is present in the proximity of the constriction. This weakening line may, for example, be provided on the ampoule from the outside by forming, for example, an encircling groove. The presence of the weakening line allows the ampoule to be broken open in a controlled and simple manner .

In a following embodiment, the wall of the head space comprises a weakening line at the level of the filler body. By thus positioning the weakening line at a distance from the transition between head space and medium, a type of neck will be formed when the ampoule is broken open, thus preventing spillage during opening and possibly lending assistance when the medium is poured out. Moreover, an opened ampoule of this kind can be held in position more easily with a suitable fixing means by attaching to the said neck or a constriction if present. In addition, the risk of any pieces of wall which break off when the ampoule is opened passing into the medium, and consequently destroying the sterility of the medium, for example, is reduced.

The invention furthermore relates to a method for the manufacture of an ampoule according to the invention, and in this respect is characterized in that an open ampoule is at least partially filled with medium via a feed opening, a filler body is introduced into the head space and the ampoule then being closed by fusing part of the wall of the head space at the location of the introduced filler body. The introduction of the filler body allows any gas phase which may be present in the head space to be displaced virtually completely outwards. The sealing of the ampoule by means of fusion can take place, for example, by treating the wall material with solvent; preferably, however, this is carried out by means of a thermal treatment, during which the wall melts and fuses, thus ensuring a good gastight seal. The head space may comprise a small volume, which can be preset, of empty space in which a gas phase may optionally be present . The volume of this space can be adjusted by suitably adapting the volume of medium during filling. By allowing the filler body, for example, to sink partially into the ampoule, for example by making use of a constriction, as already described above, the empty space may be situated at the transition between medium and filler body. In particular, the wall of the head space is closed over the filler body. By fusing the wall, the ampoule will be sealed in a gastight manner, without the filler body necessarily being joined to the wall.

Preferably, the wall of the head space is fused to the filler body, thereby sealing the contents of the ampoule. In this way, the filler body is joined fixedly to the ampoule .

In an advantageous embodiment of the present invention, the wall of the head space of the ampoule is fused to the filler body by clamping a heating wire around that part of the said wall which is to be fused and then heating the heating wire to above the melting point of the material or the materials of the wall and the filler body. This relatively simple operation ensures a good gastight seal and ensures that the filler body is attached to the wall of the ampoule.

In another preferred embodiment of the method according to the present invention, the filler body is locally provided with an electrically conductive material, the filler body being fused to the wall of the head space by inductive heating of the said material, by subjecting the ampoule to an alternating electromagnetic field. By, for example, making the filler body of hollow design and arranging a strip or disc of a suitable metal along the inner circumference and against the inner surface of the filler body, and introducing this filler body into an open ampoule, it is possible to obtain an excellent gastight seal by subjecting the ampoule, with a filler body of this kind, to an alternating electromagnetic field of suitable intensity. It is also possible to arrange the electrically conductive material on the outer surface of the filler body so as to obtain a gastight seal. It is also possible, for example, for semiconductor plastics or suitable small conductive balls to act so as to effect inductive heating of the wall of the head space. The electrically conductive material preferably comprises one electrically conductive component which covers an entire circumference of the internal or external surface of the filler body. However, it is also possible for the material to be composed of a plurality of electrically conductive parts, in which case the material may therefore be arranged in an interrupted manner along the said circumference.

Furthermore, the invention relates to a filler body which is intended for an ampoule according to the present invention. As has already been described above, the filler body may be of hollow design and/or may comprise an identification means and/or glass, the body preferably comprising glass of the first hydrolytic class.

Furthermore, the filler body may be locally provided with an electrically conductive material, in order to be suitable for the method which has already been explained above . The filler body may furthermore comprise an elastic or pasty material, so that it is possible to produce an ampoule without a gas phase in the head space, in which case it is possible to take up any stresses in the ampoule by means of the elastic filler body. If a minimal volume of empty space is desired, it is important that the filler body closely adjoins at least part of the wall of the ampoule, in order to keep the free space between the wall and the filler body as small as possible. By fusing the filler body to the wall of the ampoule close to the medium, provided that the distance is selected in such a manner that the medium will not be subject to any adverse consequences resulting from the fusion, any space between the filler body and the wall of the ampoule can be kept to a minimum. Attention is drawn to GB-A-561 842, describing a glass ampoule comprising, at the location of the breaking point, a cotton or rubber plug or tube to prevent glass pieces falling into the contents of the ampoule during opening thereof. The ampoules are closed by fusing the wall at a distance of the plug or tube, leading to a considerable amount of air or other gas phase in these ampoules .

In the specialist field, ampoules are also known in which it is attempted to limit the empty space present therein to a minimal volume.

DE-B-1 285 947 describes a transport container with a lid, the lid being connected to an inflatable balloon of flexible material. The balloon can be filled with air or another gas through a valve mounted on the container lid. By pumping up the balloon in the closed container, the volume of the air in the container is decreased, but not the amount of gaseous components. Although movement of the medium in the container is therewith restricted, a reaction of the components from the gas phase with the medium may even be enhanced as a result of the increased pressure. Further, DE-A-27 08337 describes a heat-sealed pouch made of flexible aluminium-plastic laminate. EP-A-0 , 016 , 633 describes a hollow cylindrical body, one end of which is sealed by a septum, through which an injection needle can penetrate, and which has a movable rubber piston at the other end. Septum and piston are made from a flexible material. US-A-4 , 960 , 708 describes a flexible ampoule which contains a medium in which a very diffuse gas is held in order to create a specific gas phase in the ampoule.

None of these packaging devices use a filler body inside the ampoule which limits the amount of air/gas in the head space. Moreover, all these packaging devices relate to an ampoule made of aluminium laminate and/or polymers (polyvinyl chloride, rubbers) . These materials are insufficiently inert to be able to serve as an ampoule for very delicate media, such as calibration media for blood- gas analysis devices. The said ampoules cannot be produced from the suitable inert material glass, since, as has already been discussed above, glass has to be melted at very high temperatures, and this is not possible if a liquid which is situated in the ampoule is in contact with the surface to be melted. When used for quality control materials which have to be stable for a long period, for example 1 to 3 years, these forms of packaging, unlike the ampoule of the invention, are not satisfactory. None of the ampoules mentioned in these patent publications has, however, led to the successful introduction of a product onto the market . One reason for this is the excessively low 0₂ barrier and the lack of inertness of the materials used. Aluminium is not satisfactory, since it reacts with oxygen and also because aluminium in direct contact with water can lead to ion exchange. Also, aluminium foil is not completely gastight, since there are always a number of rooster defects and since aluminium foil can only be sealed by adhesive bonding with a polymer. This is because direct melting of aluminium will have to take place at an unacceptably high temperature. The quality control materials have a p0₂ of 0-400 mmHg, and in ambient air a p0₂ of approx. 160 mmHg prevails, so that the 0₂ will be exchanged until an equilibrium has been reached. Obviously, the material is then no longer suitable as a quality control material. Polymers and rubbers (for example brominated/chlorinated butyl rubbers) also fail to prove satisfactory, since they are not inert and they have an excessively low barrier. Some components (such as plasticizers) react with 0₂. The 0₂ permeability of polymers with a very high barrier to 0₂ is still about 30 ml .m^"2. day^"1, measured through a disc of 1 mm thick and a Δp0₂ of 760 mmHg. This is too high, since only 0.004 ml (i.e. approximately 0.2 μmol of 0₂) is dissolved in 1 ml of buffer solution at 25°C and a p0₂ of 100 mmHg. Very small changes in the quantity of 0₂ therefore have disastrous consequences for the composition. In addition, flexible ampoules may cause problems in practice when there are pressure differences, such as when transported by air, with the result that air bubbles are formed in the liquid. In addition, expansion of the liquid may cause leakage.

Furthermore, it is pointed out that the ampoule according to the present invention is very well suitable to accommodate a control or calibration medium for a blood-gas analysis device 13, is however not limited thereto. Any medium, in particular a medium which is sensitive to any gaseous environment, can be stored in an ampoule of this kind, and the ampoule is also not considered to be limited to any particular dimensions.

The ampoules according to the present invention may thus also suitably be designed as transport ampoules for delicate chemicals which can rapidly become degraded as a result of, for example, oxidation from atmospheric oxygen and for substances which generally have to be transported under a nitrogen atmosphere. Packaging of this nature, which may be designed on a large scale, can be opened, for example, by drilling open part of the wall of the ampoule using suitable means. It is also possible to use ampoules of this kind for transporting and storing bacteria and cell cultures under anaerobic conditions.

In such cases, which are not subject to such high demands with regard to gastightness and/or inertness of the material of the ampoule as in the case of e.g. calibration liquid for blood-gas analysis devices, it is possible within the scope of the present invention to produce the ampoule from other materials, for example plastic. It is important for the material selected to be sufficiently inert to the medium present in the ampoule and for it to have a sufficiently low gas permeability, and also for the shelf life of the said medium to remain within desired limits .

The invention will be explained in more detail below with reference to the attached drawing, in which:

Fig. 1 shows a cross-section through a gastight ampoule according to the prior art,

Fig. 2 shows an embodiment of the ampoule according to the present invention, provided with a filler body, before sealing the ampoule by locally fusing the wall,

Fig. 3 shows a gastight ampoule, provided with a filler body according to the present invention, in which the wall of the ampoule has been fused over the filler body,

Fig. 4 shows a gastight ampoule according to the present invention, in which the filler body has been fused in a gastight manner to the wall of the ampoule, and

Figs. 5A-G show examples of various embodiments of the filler body.

Fig. 1 shows an ampoule 1 in accordance with the prior art, which is partially filled with medium 2 and comprises a head space 3. A constriction 5 is situated in the wall of the ampoule, in the region of the transition between head space 3 and medium 2. The ampoule is sealed in a gastight manner by local fusion of the wall at 7.

Fig. 2 shows an ampoule 1 in the open state, having been opened, for example, by burning open the end part 7 of the wall of head space 3, as shown in Fig. 1, forming a feed opening 9 for medium. Medium 2 is accommodated in the ampoule as well . A filler body 4 is situated in contact with the wall of the head space 3 in the ampoule and rests on constriction 5, with the result that a minimal empty head space 6 is formed, in which a gas phase may be situated. Depending on the volume of the medium present, as well as on the shape of the filler body, the volume of the gas phase within the head space can be adjusted as desired. Fig. 3 shows the ampoule in accordance with Fig. 2, after fusing the wall of the ampoule over the filler body 4, at 8, the head space comprising a gas phase (or optionally a vacuum) at 3. Fig. 4 shows the ampoule in accordance with Fig. 2 after a part 10 of the wall of the head space 3 has been fused to the filler body at the location of the filler body 4, thus sealing the contents of the ampoule.

Fig. 5A shows a cross-section through a closed hollow embodiment of a filler body, denoted overall by 4. A hollow chamber 40, which is closed by means of a wall 41, of this filler body may comprise, for example, an identification means, such as a coloured piece of plastic or coloured sand. Figs. 5A to F show cross-sections through possible embodiments of the filler body which can be used when the filler body is fused to the wall of the ampoule; specifically, in that case it is not necessary for the filler body to be completely enclosed by the ampoule and to closely adjoin the whole of the wall of the ampoule.

For example, the filler body in accordance with Fig. 5B can be fused to the ampoule at the location of a thickened part 51 which can closely adjoin the wall of the ampoule locally. A narrower part 52 can be used as a handle when breaking open the ampoule or as a possible attachment point for a reference marking.

The filler body in accordance with Fig. 5C comprises a thickened part 53, which can closely adjoin part of the wall of the ampoule, as well as a conical part 54 which is intended to be immersed in the medium when the ampoule is closed. This form of filler body simplifies breaking open the ampoule. Obviously, this filler body may also be provided with a narrowed part 52, like the filler body in accordance with Fig. 5B, or may, for example, be of hollow design.

Fig. 5D shows a hollow filler body which is closed on only one side. This filler body can be placed in the ampoule (1) with the closed end 55 facing towards the medium, after which the filler body can be fused to the ampoule (1) at the location of a filler body part (56) which closely adjoins the wall of the ampoule (1) . If desired, the open end of this filler body can be closed off, for example by means of a cap of a specific colour. Fig. 5E shows an embodiment of a filler body according to the present invention which is suitable for fusing by inductive heating. A thickened part 57 can closely adjoin part of the wall of the ampoule, which filler body is provided with a strip or ring 58 of an electrically conductive material which is arranged along the circumference. This filler body does not have to be closed on the side facing away from the medium.

Fig. 5F shows a filler body in which a strip or ring 58 of electrically conductive material is arranged along the outer circumference on the external surface of the filler body, the filler body being of open design on the side facing away from the medium.

Finally, Fig. 5G shows a filler body, in which there is arranged a disc 59, at least the edge of which comprises electrically conductive material and which may also be designed as a ring. The disc or ring 59 is situated in contact with an inner circumference on the internal surface of the filler body. In order to facilitate the correct introduction of the disc or ring into the filler body correctly, the filler body may first be partially filled with a non-conductive material in the space denoted by 60, and then the ring or disc 59 can be placed on this non-conductive material. This disc 59 may also be composed of separate small, electrically conductive balls, which can be placed on the said non-conductive material.

It will be clear that numerous forms of the filler body are possible, including any desired combinations of the exemplifying embodiments shown above.

Claims

1. Gastight ampoule (1), at least comprising a volume of medium (2), and a head space (3), accommodating a filler body (4), wherein the ampoule is closed by locally fusing the wall of the ampoule (1) at the location of the head space, characterized in that the filler body abuts the wall of the ampoule at the location of the fused portion thereof .

2. Ampoule (1) according to claim 1, characterized in that the filler body (4) substantially completely fills the head space (3) .

3. Ampoule (1) according to claim 1 or 2 , characterized in that the volume of the empty space which is present, in addition to the filler body (4) , in the head space (3) amounts to less than 10% by volume of the medium.

4. Ampoule (1) according to claim 3, characterized in that the volume of the empty space which is present, in addition to the filler body (4) , in the head space (3) amounts to less than 1.5% by volume of the medium (2) .

5. Ampoule (1) according to one or more of the preceding ^Γûá claims , characterized in that the filler body (4) is fused to part of the wall of the ampoule (1) , thereby sealing the ampoule (1) .

6. Ampoule (1) according to one or more of the preceding claims, characterized in that the filler body (4) consists of the same material as the ampoule (1) .

7. Ampoule (1) according to one or more of the preceding claims, characterized in that the filler body (4) comprises glass .

8. Ampoule (1) according to claim 7, characterized in that the filler body (4) comprises glass of the first hydrolytic class.

9. Ampoule (1) according to one or more of the preceding claims, characterized in that the filler body (4) is of hollow design.

10. Ampoule (1) according to one or more of the preceding claims, characterized in that the filler body (4) comprises an identification means.

11. Ampoule (1) according to claims 9 and 10, characterized in that the identification means is accommodated in the filler body (4) and is selected from a bar code, a coloured object, a plastic object and coloured sand, or a combination of one or more thereof.

12. Ampoule (1) according to one or more of the preceding claims, characterized in that the ampoule (1) has a constriction at the location of the transition between the head space (3) and the medium (2), and in that the filler body (4) can bear against the constriction (5) .

13. Ampoule (1) according to claim 12, characterized in that a weakening line is present in the proximity of the constriction (5) .

14. Ampoule (1) according to one of claims 1-12, characterized in that the wall of the head space (3) comprises a weakening line at the location of the filler body (4) , in order to support opening of the ampoule (1) by breaking off part of head space (3) .

15. Method for the manufacture of an ampoule (1) according to one or more of the preceding claims, characterized in that an open ampoule is at least partially filled with medium (2) via a feed opening (9) and then a filler body (4) is introduced into the head space (3) and the ampoule (1) being closed by fusing part of the wall of the head space (3) at the location of the introduced filler body.

16. Method according to claim 15, characterized in that the wall of the head space (3) is closed over the filler body (4) .

17. Method according to claim 15, characterized in that the wall of the head space (3) at the location of the filler body (4) is fused to the filler body (4) , thereby sealing the contents (2) of the ampoule.

18. Method according to claim 17, characterized in that the wall of the head space (3) of the ampoule is fused to the filler body (4) by clamping a heating wire around the part (10) of the said wall which is to be fused and then heating the heating wire to above the melting point of the wall and the filler body (4) .

19. Method according to claim 17, characterized in that the filler body (4) is locally provided with an electrically conductive material (58, 59), the filler body (4) being fused to the wall (10) of the head space (3) by subjecting the said material (58, 59) to an alternating electromagnetic field.

20. Filler body (4), intended for an ampoule (1) according to one or more of claims 1-11.

21. Filler body (4) according to claim 20, characterized in that it is hollow.

22. Filler body (4) according to claim 20 or 21, characterized in that it comprises an identification means.

23. Filler body (4) according to claim 22, characterized in that the identification means is accom- modated in the filler body and is selected from a bar code, a coloured object, a plastic object or coloured sand, or a combination of one or more thereof.

24. Filler body (4) according to one or more of claims 20-23, characterized in that it comprises glass.

25. Filler body (4) according to one or more of claims 20-24, characterized in that it comprises glass of the first hydrolytic class.

26. Filler body (4) according to one or more of claims 20-25, characterized in that it is locally provided with an electrically conductive material (58, 59).