DE3919601A1 - Device for acid-decomposition of a substance for elementary analysis under controlled pressure in a microwave field - Google Patents

Abstract

The invention relates to a device for acid decomposition for elementary analysis which consists of an outer container and an inner container, with a lid guided vertically movably in a decomposition vessel acting on a rod having a pin guided upwards through a central orifice in the cap. In order in particular to allow secure and reliable checking that the internal pressure in the decomposition device has not exceeded an allowed limit value, it is proposed to detect the position of the pin 19 using a measurement-value pick-up which is inert to microwaves and use it in a regulating circuit as the control element for the microwave heating of the microwave oven. The measurement-value pick-up should preferably work mechanically, that is to say using a lever, hydraulically, pneumatically or optically. <IMAGE>

Description

The invention relates to a device for Acid digestion of a substance for the Elemental analysis under controlled pressure in one go a microwave oven generated microwave field, be standing out of a pressure-resistant outer container with a pot-like jacket and a cap that go together ver releasably via an external / internal engagement connection are bound and an inner container with an opening and a lid for this, which at its opening applied a cylinder fitting into the opening Has set, which is mounted in an annular groove Gasket has the lid off against the inner container seals, with a stamp on the top of the lid an upward, through a central through the bore of the cap guided pin rests between the inside face of the cap and the top of the stamp an annular elastomer spring is arranged and all Parts are made of microwave-transparent material.

Under the elementary analysis is a procedure for investigation development of the gross formula of organic compounds stood. A method for elemental analysis is the so-called. Acid digestion, in which the substrate to be analyzed contains With the help of one or more acids completely broken down or on is closed, so that be in the structure of the substance divided elements at the end of the dismantling as the smallest, element-specific molecules or ions are present. These can then be determined qualitatively or quantitatively.  

When using strong acids as digestion reagents one is essentially limited to bomb vessels Platinum, quartz and teflon. However, these vessels are very expensive, cannot withstand major internal pressures or are not dimensionally stable at higher temperatures. Therefore has gone over to it, in addition a print and to use temperature-resistant jacket vessel. At the Er However, the bomb vessels are heated from the outside Heat transfer problems and the different expansion prepare coefficients of jacket and insert vessel Difficulties.

To eliminate these disadvantages, you can use the on conclusion required thermal energy inside the digestion generate the vessel using a microwave oven. For this it is necessary to use digestion vessels made of microwaves to use indifferent or transparent material; in any case, metals are unsuitable as a vessel material.

However, the microwave energy input creates a Digester new problems. So with microwaves heating the temperature and pressure in the digestion vessels room can not be easily monitored.

The permissible upper temperature for the digestion vessels values are dependent on the vessel materials used but at about 300 ° C so high that it is exceeded this limit value can be largely excluded. On the other hand, the pressure is different watch.

In a known device of the type described above you tried to shift the internal pressure with a little check the lid.  

As a seal between the in the opening of the inner container protruding cylinder neck of the lid and the container wall an O-ring is used according to the prior art. These However, seal can function at relatively high pressures or insufficient vascular deformation. The resulting leak can lead to an increase lead to loss of sample substance.

In the known device, the elastomer spring is quite Lich flat, the travel and thus the work of the The lid of the digestion vessel is therefore short and the control The printable area is also small. Measures for con controlled pressure relief in the border area are not there intended.

If the lower edge of the cylinder shoulder of the cover the reached the top of the inner container, it can therefore an explosive escape in the digester gases are coming. In extreme cases, this not only leads to completely destroy the seal, but also to Vascular deformation.

The visual observation of the through the central passage bore of the cap guided pin or its movement is in any case far too imprecise to be timely could be taken to open the interior by pushing the lid up before the end of the opening to prevent the final reaction.  

In the known device, it has also proven to be Proven in part that the cap of the outer container is radial Has holes. When opening (unscrewing) one under Pressurized digestion vessel escape aggressively Vapors from the side and endanger the user of the device.

The present invention is therefore based on the object a device of the type described above stalten that the pressure in the digestion reaction in the micro wave field without being influenced by the microwave field can be measured and controlled so that the device is safer despite allowing higher reaction pressures. In addition, the tightness of the decomposition vessel should be increased and the handling of the device can be improved so a danger to the operator from escaping gases is largely avoided. Finally, the invention appropriate device largely protected against deformation be.

This object is achieved in a device of the type described above solved in that a microwave transparent transducer on the one hand with a protruding from the cap of the jacket vessel The end of the pin is in operative connection or releasably connected to it is and on the other hand with an outside of the microwave oven arranged pressure indicator or control unit for the microwave heating connected is. The position of the pen is thus determined by a measured value sensor recorded and in a control loop as an actuator for the micro wave heating of the microwave oven used. By this measure microwave energy is advantageously only to the extent that Lichen digestion vessel supplied as it for the digestion reaction is required and it is prevented in time that an uncontrolled Reactions triggering excess pressure is built up.  

The sensors available on the market are usually not usable as they contain metal parts, metal cables etc. and therefore not are microwave indifferent. According to the invention, however, microwaves indifferent, preferably hydraulically or pneumatically via a lever, d. H. each touching or optically (contactless) working Sensor used.

In the simplest case, the pin of the stamp grips the lid of the Inner vessel outside the outer container at one end of a two-armed Lever at the other end indirectly a switch or controller for the Microwave heating actuated.

Especially when you have the control device for the Microwave heating outside of the microwave irradiated Arranging space, it is recommended, preferably via a spring-loaded Bowden cable and a rocker arm to operate the switch so that the first lever on the device is in the microwave oven and the Bowden pull through a corresponding hole from the microwaves oven is brought out. The end of the Bowden cable is in turn connected to a rocker arm which, when actuated presses a switch.

As an alternative, there is also a hydraulic pressure monitoring possible. For this, the pen preferably acts on a piston-like slide plate, which in a over the Pin end arranged cylinder with simultaneous Ver reduction or enlargement of the cylinder and the Plate formed, having a hydraulic medium inside space is displaceable. In the same way as above described for the Bowden cable, can also be used here hydraulic line the hydraulic medium so outside of the microwave oven that change of the internal volume finally for actuating a pressure display or a switch. In particular, the hydraulic fluid  preferably enclosed in a bellows over the ver mentioned hydraulic line with another bellows is bound, over the free end of a switch, to the play via a rocker arm, can be actuated. With pneumatic working sensor is the one in the through hole the cap guided part of the pin preferably as a slide a slide valve, the axial displacement is caused solely by the pressure in the inner container. He is at a certain axial level radially with a be agreed pressure of a pressure switch device and points at an axial level below the level of radial pressurization an outward leading drain bore on which is the pneumatic connection to the pressure monitor opens when the slide is in the pressure due to the Inner container with its drain hole the level of pressure has reached exposure. The forehead advantageously points the cap drilled at least one radial hole from the Perimeter of the cap leads to the slide, each one Line with one arranged outside the microwave oven Pressure generating device is connected and that of the radial Pressurization of the slide serves.

In a very advantageous other embodiment of the pneumatic path monitoring is in the end face of the cap an annular groove is milled into the jacket. This surrounds the Through hole for the pin of the stamp. She is with a valve plate completely covered. The scope of the valve plate engages so far over the outer circumference of the ring groove the face of the cap, as for a good seal of the Ring groove required. The valve plate and / or the under region of the end face of the cap located on the valve plate have sealants, which seal the Ensure ring groove. The ring groove is above a vacuum tight line with a pressure switch and one behind it lying vacuum pump in connection so that it from the Pump can be placed under vacuum. When creating the  Vacuum is the valve plate from the pressure of the surrounding Atmosphere firmly on the face of the cap and on the "Open" side of the ring groove pressed.

The connection between the ring groove and the evacuation line can advantageously be made through a hole that next to the valve plate or on the side wall of the cap the latter exits.

The pin of the stamp is slidable and advantageous led centrally through the valve plate and protrudes from the last out. It advantageously points at the outstanding end a head that prevents the valve plate from falling off, if the latter is only loosely on the ring groove, d. H. if the The ring groove is not under vacuum. The pen points under the Valve plate, d. H. a stop inside the cap, with which he lifts the valve plate when the elastomer spring is compressed by the amount equal to the desired pressure in the inner container. In this case, that is Lifting the valve plate, air enters the under vacuum standing ring groove and causes a pressure drop. The latter is detected by the pressure switch and as a signal to switch off the heater used.

The distance between the pin stop and the bottom of the Valve plate thus corresponds to the length of the part of the Cylinder shoulder on the lid of the inner vessel at rest condition via the relief holes in the side wall of the Inner vessel protrudes into the inner vessel.

The pen can also be easily spaced from the bottom end of the valve plate that corresponds to the Ab stood between the pin stop and the underside of the valve plate corresponds. In this case the valve plate is raised when the end of the pin presses against the valve plate.  

In addition to the above-mentioned touch sensors is a touch after a development of the invention optical measuring transducer working, the in the simplest case from an optical transmitter (LED) and a receiver (photodiode), which is from the transmitter incoming light beam receives until the rays gear is interrupted by the pen moving upwards. The missing received signal then triggers a shutdown of the Microwave heating off.

To avoid radiation losses, the optical Radiation preferably guided in an optical fiber. Around use only one conductor for the entire radiation path the pen is equipped with a reflector and preferably the light guide with a beam splitter  provided, which is transparent to the light coming from the transmitter is and the light reflected by the pen to the receiver directs.

The used after a development of the invention Lip seal ensures that even at high pressures impeccable sealing, since they are exposed to pressure expands and attaches more firmly to the vessel wall than the O-ring known in the art. Besides, is their lubricity in the interior of the outcrop vascular enlarging movements of the lid better.

In a further embodiment of the invention are immediately below half of the opening edge of the inner container and above the level like the lip seal of the cylinder attachment when depressurized the inner wall rests, at least two evenly on the circumference shared radial holes arranged in the side wall of the inner container, which are connected to the space between the cap and the lid. These become effective when the pressure in the reaction vessel is so high rose is that the cover or the cylinder neck in the direction of Opening is shifted by the length of the working path of the elastomer spring and releases the radial holes with its sealing lips. To this An early pressure relief occurs and an overload or even an explosion can be avoided.

Preferably in the front of the cap near the circumference, where the elastomer spring is insufficient on the inside, axial passage bores with the radial bores mentioned above through the Space between the cap of the jacket vessel and the lid of the interior allow an end gas exit from the device. This axial discharge option protects the operator and him facilitates the handling of the device when it is opened under There is pressure.  

This preferably consists of the inner container and the lid formed decomposition vessel made of quartz, teflon or an art High heat resistance fabric with Teflon inner lining. The walls are dimensioned so that they each ge Hold the desired reaction pressure (up to 150 bar). As art High heat resistance material can be z. B. a polyether imide or polysulfone with a higher heat resistance use as polytetrafluoroethylene (Teflon). It is advantageous the elastomer spring in the uncompressed state, for example 1.5-3 times, especially twice as high as the cylinder the lid of the inner container. You can e.g. B. from a silicone rubber z. B. with a shore Hardness of 60-80 exist.

The height or length of the cylinder extension on the inside cover vessel should be approximately the length of the commute Correspond to the elastomer spring. At maximum pressure in the inner vessel the lid, which acts like a slidable piston Cylinder shoulder and sliding seal against the force of the elastomer spring driven so far out of the inner container that the radial relief bores in the edge zone of the inner container become free and perform their relief function.

The stamp on the lid with his through the cap of the Jacket pin protruding shows the pressure inside shift proportional. If this pen as Valve slide is designed, as described above, corresponds the distance between the drain hole in the slide and the Mouth of the pressure line of the pressure switch in the valve body (Location of the radial pressurization of the slide) one desired fraction of the working distance of the elastomer spring. The drain hole in the slide is advantageously in a ring groove of the slide, a positioning of the slide with respect the mouth of the pressure line is therefore unnecessary.  

Include all parts of the device according to the invention Lich transducers, transmission lines and z. B. Hydraulic fluids used in the microwave field consist of microwave indifferent or -transparent material, e.g. B. from plastics such as perfluorinated plastics, e.g. B. Teflon, made of poly amides, silicones, polyetherimides, polysulfones etc. As a hydraulic fluid you can e.g. B. use silicone oil the. Particularly heat is generated for parts under pressure dimensionally stable plastics are used.

Embodiments of the invention are in the drawings shown and will be explained in more detail below. It shows

Fig. 1 is a schematic representation of a microwave oven with the inventive apparatus

Fig. 2 shows a cross section through the inventive Before direction,

Fig. 3 is a partial cross-section through the inventive device with a fixed pin on the lever arm,

Fig. 4 is a partial cross-sectional view with a hydrauli's transmission of the pin layer,

Fig. 5 is a partial view with an optical transmission of the pin position and

Fig. 6 + 7 is a partial view with a pneumatic transmission of the pin position.

As can be seen in particular from Fig. 2, he device according to the invention has an outer container which consists of a pot-like jacket vessel 10 and a cap 11 which, for. B. are connected via an external / internal engagement 12 . In the present case, the cap has an internal thread which engages in a corresponding external thread of the jacket vessel. Embedded in this outer container is the actual digestion container, which consists of a cylindrical vessel 13 , one end of which is open, and a lid 14 . The lid 14 has a fitting in the vessel opening Zy linderansatz 15th At its lower edge, an annular groove 16 is embedded on the circumference, in which a lip seal 17 rests, which lies sealingly against the inner casing 13 a . On the upper lid side 14 a rests a roughly the same diameter stamp 18 with an upward pin 19 which partially protrudes from the cap through a correspondingly formed central through bore of the cap 11 . Between the top of the stamp 18 a and the inner end face 11 a of the cap 11 , a ring-shaped elastomer spring 20 is inserted which counteracts the outward movements of the cover 14 and the stamp 18 .

When pressure in the decomposition vessel 13, 14 , the lid 14 is pushed up against the spring force of the elastomer spring 20 , taking the stamp 18 and thus the pin 19 with it. The vertical upward movement of the pin 19 is thus a measure of the pressure increase in the decomposition vessel 13, 14th This upward movement is determined by a transducer 21 , which is optionally connected to a control unit 22 via a connecting line. This control unit is used directly to control the heating of the microwave oven 23 , into which the device according to the invention is placed ( FIG. 1).

The vessel 13, the lid 14, the walled vessel 10 and the cap 11 are made of a microwave transparent material, in particular made the decomposition vessel 13 and the lid 14 made of quartz, Teflon or a plastic, such as polyetherimide, z. B. Ultem 1000 or polysulfone with a Teflon lining to protect against aggressive reagents. Preferably, the decomposition vessel 13 is supported on a base plate 24 , which lies over a bottom opening of the jacket vessel 10 and serves as a predetermined breaking point.

As can be seen from Fig. 2, the vessel 13 has radial through holes 25 in the upper edge region, which are load bores as Ent holes with the free interior 26 of the outer container 10, 11 in connection. For this purpose, 13 ring grooves are embedded in the outer jacket of the vessel. The cap has axial through holes 27 so that a free exit of the gases flowing out of the relief bores 25 is made possible to the outside as soon as the lip seal is pushed so far up that the load bores 25 are released.

The different types of Wegüber surveillance according to the invention are shown in detail in FIGS . 3 to 6.

Thus, in the embodiment according to FIG. 3, the pin 19 is connected to a free end 28 a of a two-armed lever 28 which can be pivoted about a pivot point 29 . This pivot point 29 is located at the free end of an angle arm 30 , the second end of which serves as a stop for a flexible sleeve 32 of a Bowden cable 31 . One end of the Bowden cable 31 is connected to the second free end 28 b of the lever 28 in such a way that movements of the lever 28 are transmitted via the Bowden cable 31 to a rocker arm 33 which, depending on the position, presses on and releases a switch contact 34 . The reset of the Bowden train 31 is ensured by a spring 31 a .

In the embodiment according to FIG. 3, an upward movement of the pin 19 leads to a lowering of the free lever arm 28 b , whereby the lever 33 is pivoted to the right by means of the Bowden cable 31 and the spring 31 a and releases the switching contact 34 . As a result, the microwave heating is switched off at the same time, ie a further temperature and pressure increase in the closing vessel is prevented.

In the embodiment according to FIG. 4, the movement of the pin 19 is transmitted to a slide plate 36 guided in a cylinder 35 , which is connected to a bellows 37 . The bellows 37 is filled with a microwaved liquid 38 , which can pass via a line 39 led from the microwave oven into a second bellows 41 arranged in a further cylinder 40 . This bellows 41 is limited by a second slide plate 41 a , which is connected via a spring-loaded coupling piece 42 to a one-armed lever 43 . If the pin 19 is now pushed upward when the pressure in the digestion vessel increases, the internal volume of the bellows 37 is reduced while the hydraulic fluid 38 is being carried over into the second bellows 41 . As a result, the second slide plate 41 a moves to the right and pivots the lever 43 accordingly to the side. The switch contact 34 is released and the microwave heating is switched off.

An optical path monitoring of the pin 19 according to FIG. 5 works with a reflector 44 at the upper end of the pin 19 . On the top of the cap, a light guide 45 is fastened, which is guided outside the furnace and has a beam splitter 46 there . Via this light guide, an LED 48 emits monochromatic light into the light guide, which is reflected by the reflector 44 when a certain pressure is exceeded and is transmitted from the beam splitter 46 to a receiver, e.g. B. a photodiode 47 is thrown. As soon as the receiver receives 47 light signals, the microwave heating is switched off. In a corresponding modification of the measuring method shown in FIG. 5, it is equally possible to work without a light guide and the receiver lies in the radiation path of the radiation emitted by the transmitter 48 . This beam path crosses the plane in which the pin 19 can be moved up and down, so that the radiation is interrupted when a pressure limit is exceeded. In this case, a missing reception signal triggers the microwave heating to be switched off.

Finally, a very advantageous pneumatic path monitoring is shown in Fig. 6. Here, the upper part of the pin 19 is formed as a slide 49 of a valve, the housing wall of the central through hole in the end wall of the cap 11 , and that with three on various axial levels attached radial through holes 50-52 in the end wall of the cap 11 cooperates. The slider 49 has an outwardly leading bore 56 in an annular groove 57 . This ring groove lies at the bottom of the slide's working path. Depending on the position of slide % 9 , one of the bores 50-52 is released, which leads to a pressure drop in the pneumatic pressure line connected to the bore of a pressure switch located outside the microwave oven. This process is displayed there or a pressure switch 53 is actuated directly, which switches off the micro wave furnace or throttles its output. The pressure in the line is provided by a diaphragm pump 55 via a throttle 54 .

Another very advantageous pneumatic path monitoring is shown in FIG. 7. Here, an annular groove ( 58 ) is milled into the end face of the cap ( 11 ). This includes the through hole for the pin ( 19 ). It is completely covered by a valve plate ( 59 ). Sealant on the valve plate ( 59 ) and / or on the end face of the cap ( 11 ) ensure that the valve plate ( 59 ) seals the annular groove ( 58 ) completely against the surrounding atmosphere and, if appropriate, against the interior of the jacket vessel ( 10 ) when vacuum is applied to the ring groove.

A bore leads from the annular groove ( 58 ) to the side wall of the cap ( 11 ). A vacuum line ( 39 ) is connected to the outlet of the bore and leads to a vacuum pump ( 60 ) via a pressure switch ( 53 ). The pin ( 19 ) protrudes from a central bore in the valve plate ( 59 ). It has a stop under the valve plate. When compressing the elastomer spring ( 20 ) this stop abuts against the valve plate, lifts it and triggers a fall in pressure in the line ( 39 ), which is detected by the pressure switch ( 53 ). This switches off the heating.

Reference symbol list

10 pot-like jacket vessel
11 cap
11 a inner face
12 threaded connection
13 inner container
13 a wall of the inner container
14 lid
14 a top of cover
15 cylinder extension
16 ring groove
17 seal
18 stamps
18 a stamp top
19 pen
20 ring-shaped elastomer spring
21 sensors
22 control unit
23 microwave oven
24 base plate
25 relief bores (radial bore)
26 free interior of the outer container
27 axial bore in the cap
28 levers
28 a , 28 b lever arms
29 fulcrum
30 angle arm
31 Bowden cable
31 a spring
32 flexible cover
33 rocker arm
34 switch contact
35 cylinders
36 plate (slide plate)
37 bellows
38 microwave-lined liquid
39 Management
40 cylinders
41 second bellows
41 a second slide plate
42 coupling piece
43 lever (one arm)
44 reflector
45 light guides
46 beam splitters
47 receiver (photodiode)
48 transmitters (LED)
49 slide valve
50-52 radial holes
53 pressure switches
54 throttle
55 diaphragm pump
56 drain hole
57 ring groove
58 second ring groove
59 valve plate
60 vacuum pump

Claims (20)

1. Device for acid digestion of a substance for elemental analysis under controlled pressure in a microwave field generated by a microwave oven, be standing from a pressure-resistant outer container with a pot-like jacket and a cap, which are releasably connected to one another via an external / internal engagement connection and one Inner container with an opening and a cover therefor, which on its side facing the opening has a fitting cylinder fitting in the opening, which has a seal mounted in an annular groove, which seals the lid against the inner container, with a stamp on the top of the lid with an upward, through a central through hole of the cap pin rests, an annular elastomer spring is arranged between the inner end face of the cap and the top of the stamp and all parts are made of microwave-transparent material, characterized in that a microwave-transparent measurement sensor ( 21 ) is in operative connection with one end of the pin ( 19 ) protruding from the cap ( 11 ) of the jacket vessel ( 10 ) or is detachably connected to it and on the other hand with a pressure display device or control device arranged outside the microwave oven ( 23 ) ( 22 ) is connected for microwave heating. 2. Device according to claim 1, characterized by a mechanically, hydraulically, pneumatically or optically working measuring sensor ( 21 ). 3. Apparatus according to claim 2, characterized in that the mechanically working transducer comprises a two-armed lever ( 28 ) which at one end ( 28 a) with the end of the pin ( 19 ) and at the other end ( 28 b) a spring-loaded Bowden cable ( 31 ) is connected to the pressure indicator or a rocker arm ( 33 ) actuating a switch ( 34 ). 4. Apparatus according to claim 2, characterized in that in the hydraulically operating measured value, the end of the pin ( 19 ) acts on a piston-like slide plate ( 36 ) which is displaceable in a cylinder ( 35 ) filled with hydraulic medium arranged above the pin end, wherein the hydraulic medium ( 38 ) actuates a display and / or a switch ( 34 ) via a hydraulic line ( 39 ) leading out of the microwave oven. 5. The device according to claim 4, characterized in that the hydraulic fluid ( 38 ) inside the cylinder ( 35 ) in a bellows is closed. 6. The device according to claim 5, characterized in that the bellows ( 37 ) via a hy draulic line ( 39 ) with the interior of a further bellows ( 41 ) is connected, via the free end ( 41 a), a switch ( 34 ) , preferably via a rocker arm ( 43 ). 7. The device according to claim 2, characterized in that in the pneumatically working transducer in the through bore of the cap ( 11 ) ge led part of the pin ( 19 ) is designed as a slide ( 49 ) of a slide valve, the axial displacement of which is solely by the Pressure in the inner container ( 13 ) is effected, which is struck at a certain axial level radially with a certain pressure of a pressure monitoring device and which has an outwardly leading drain hole ( 56 ) at an axial level below the level of the radial pressure application, which has the pneumatic Connection to the pressure switch opens when the slide ( 49 ) due to the pressure in the inner container ( 13 ) with its drain hole ( 56 ) has reached the level of pressurization. 8. The device according to claim 7, characterized in that the end wall of the cap ( 11 ) min least has a radial bore ( 50-52 ) which leads from the periphery of the cap ( 11 ) to the slide ( 49 ), each of which Line is connected to a pressure generating device ( 55, 54 ) which is arranged outside the microwave oven and which serves to pressurize the slide ( 69 ) radially. 9. The device according to claim 2, characterized in that the cap ( 11 ) of the jacket vessel ( 10 ) in the pneumatically working transducer has a through hole for the pin ( 19 ) comprising an annular groove ( 58 ) in its end face, which with a valve plate ( 59 ) is covered and connected via a line ( 39 ) to a pressure monitor device and a vacuum pump ( 60 ) behind it, and that the pin ( 19 ) of the plunger ( 18 ) has a stop with which the pin ( 19 ) plates the valve ( 59 ) lifts when the elastomer spring ( 20 ) is compressed by a certain amount. 10. Device according to one of claims 7, 8 or 9, characterized in that the pressure switch has a pressure switch ( 53 ). 11. The device according to claim 2, characterized in that in the optical transducer that protrudes from the cap ( 11 ) part of the pin ( 19 ) when a limit value is exceeded, the beam path of a radiation coming from an optical transmitter (LED 48 ), which interrupts a receiver ( 47 ) can be registered. 12. The apparatus according to claim 11, characterized in that the optical radiation is guided in an optical fiber ( 45 ). 13. The apparatus according to claim 11 or 12, characterized in that the pin ( 19 ) has a reflector ( 44 ). 14. The apparatus according to claim 13, characterized in that a beam splitter ( 46 ) is arranged in the light guide, which is transparent to the light coming from the transmitter ( 48 ) and the light coming from the reflector ( 44 ) deflects the receiver ( 47 ). 15. Device according to one of claims 1-14, characterized in that the cover ( 14 ) by means of a set at the lower edge of the cylinder ( 15 ) attached lip seal ( 17 ) against the vertical inner wall ( 13 a) of the inner vessel ( 13 ) is sealed. 16. Device according to one of claims 1-15, characterized in that close below the opening edge of the inner container ( 13 ) and above the level where the lip seal ( 17 ) of the cylinder extension ( 15 ) in the unpressurized state on the inner wall ( 13 a ) is present, at least two radial bores ( 25 ) are arranged in the side wall of the inner container ( 13 ) and are connected to the space ( 26 ) between the cap ( 11 ) and the lid ( 14 ). 17. Device according to one of claims 1-16, characterized in that the end face ( 11 a) of the cap ( 11 ) in the vicinity of the circumference, where the elastomer spring ( 20 ) is not sufficient, has axial bores ( 27 ) . 18. The device according to any one of claims 1-17, characterized in that from the inner container ( 13 ) and the lid ( 14 ) existing decomposition vessel made of quartz, Teflon or a plastic high Wärmformbe resistance with Teflon inner lining. 19. The apparatus according to claim 18, characterized records that the plastic of high heat molding resistance a polyetherimide or polysulfone with a higher heat resistance than polytetrafluoroethylene (Teflon) is. 20. Device according to one of the preceding claims, characterized in that the elastomer spring ( 20 ) in the uncompressed state is about 1.5-3 times, in particular twice as high as the cylinder extension ( 15 ) of the cover ( 14 ).