Cuvette
BACKGROUND OF THE INVENTION 
     The invention relates to a cuvette for liquid or gaseous samples, particularly for absorption spectrum analysis, the cuvette comprising a multi-part housing structure which encloses a thin sample chamber that is delimited by two radiation transmitting discs and is provided with two bores leading to the sample chamber. 
     The bores serve as fill and ventilation channel for the sample chamber and, in prior art cuvettes of this type, are provided with a screwed-in connecting nipple which itself is provided with a precisely ground, hollow, conical connecting piece or a screw connection as is well known for the tight connection of injection needles with multi-use injection syringes. To fill the cuvette, the syringe containing the sample fluid is connected with the fill end and, if fluid escapes at the other end after filling of the sample chamber, the latter is closed by means of a stopper. Then the syringe is removed and the fill end is likewise closed. 
     The drawbacks here are that, compared to the small capacity of the sample chamber, a relatively large volume of sample fluid is required to fill the connecting nipples and that sample fluid is usually pressed out when the ends or nipples are sealed, which is annoying and makes work more difficult. On the other hand, air inclusions often remain in the channels. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to provide a cuvette which is simpler, can be filled and sealed cleanly without the inclusion of air and which requires less sample fluid. 
     This is accomplished by the invention, starting with a cuvette of the above-mentioned type, in that plastic stoppers are inserted into the bores, each stopper being provided with a thin longitudinal channel which can be closed by means of the tip of a hollow needle or a closing needle. As a practical matter, the longitudinal channel is conically tapered toward the interior. Preferably, the stopper is composed of polytetrafluoroethylene, a common sealing material which is resistant to most sample fluids. The stopper may have a simple cylindrical shape and may be provided with sealing collars at its outer end, if required. Moreover, for easier insertion, the stopper may be given a flange-like extension. Preferably it is flush with the surface of the housing. 
     The hollow needle for filling or extracting the sample chamber may be an injection needle which means that advantageously the needle need not be removed from the syringe for this process phase. In particular, however, the conventional throw-away tip of a pipette may also be used as the hollow needle and may be connected tightly with the sample chamber simply by inserting it. Needles having a solid cross section which, for easier manipulation, may be provided with a handle member, serve to seal the opening. Any air possibly still contained in the fill channel is thus expelled toward the exterior. 
     Since the bore in the housing need not have an internal thread, such cuvette closures can be manufactured extremely simply and inexpensively. Due to the fact that the cross section of the fill and ventilation channel as a whole is thin, not much sample fluid beyond the capacity of the sample chamber is required. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the invention will be described below with reference to the drawing, in which: 
     FIG. 1 is a exploded view of a cuvette. 
     FIG. 2 is a sectional view of a closing stopper, drawn to a larger scale and taken along line II--II. 
     FIG. 3 is another embodiment of the closing stopper in a corresponding view. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to FIG. 1, the housing structure of the cuvette is composed of a base plate 1 as well as a linear and an angular mounting block 2 and 3. The base plate is provided with a rectangular window 4. Between mounting blocks 2 and 3, there is inserted an elastic insert 5 which is likewise provided with a window. This is followed by an infrared transmitting window pane 6 of a salt crystal, a spacer member 7 less than 0.1 mm thick and provided with a cut-out which forms the sample chamber, a further window pane 9 provided with two bores, a sealing disc 10 provided with a window and two bores, and finally a metal pressure member 11, likewise provided with a window. All of the components 6 to 11 have the same outlines. Pressure member 11 is provided with two bores 12 and 13 which are flush with the bores of seal 10 and window pane 9 and thus are in communication with sample chamber 8. All parts are held together by means of hollow screws 14. 
     FIG. 2 shows pressure member 11 and bore 12 in a sectional view. A stopper 15 of polytetrafluoroethylene is inserted into the bore and is provided with a central longitudinal channel 16 which is conically tapered toward sample chamber 8. 
     In the embodiment according to FIG. 3, the stopper has a collar 17 and a non-tapered central longitudinal channel 18. 
     Either the injection needle of a syringe or the tip of a pipette or a closing needle can be tightly inserted into the longitudinal channels. Examples of closing needles are shown in FIG. 1. They are composed of a handle member 19, which may be made of plastic, and a needle tip 20.