Abstract:
An analysis cell arranged in a flow path of a fluid to be analyzed includes a cavity adapted for receiving the fluid, a detection unit coupled to the cavity for detecting a property of the fluid, and a curved pipeline for supplying the fluid to the cavity connected to an orifice of the cavity.

Description:
BACKGROUND  
       [0001]     The present invention relates to fluid analysis.  
         [0002]     Fluid analysis is becoming increasingly important in chemical analysis especially for mixed chemical compounds. One example for fluid analysis is liquid chromatography measurement, wherein a liquid with the chemical components in a chromatography cell is illuminated with light of different wavelength and the light absorption of the liquid is measured. The wavelength dependent absorption provides information about chemical components in the liquid.  
         [0003]     In fluid analysis measurement results often depend on design parameters of the cell or the measurement system, resulting in analysis error.  
         [0004]     U.S. Pat. No. 5,917,606 discloses s photometric flow apparatus for sample analysis.  
       SUMMARY OF THE INVENTION  
       [0005]     It is an object of the present invention to provide an improved fluid analyzing. Those objects are solved by the independent claims. Preferred embodiments of the invention are provided by the dependent claims.  
         [0006]     During analysis the liquid flow can cause random noise &amp; wander resulting in measurement errors or even preventing clear and repeatable results. One origin of such noise is the velocity of the fluid, which causes turbulence. If two or more liquids with different refractive indices are mixed, noise &amp; wander can be seen due to imperfect mixing. The invention provides an analysis cell wherein random noise &amp; wander during measurement is reduced. Additionally the mixing behavior is improved resulting in a further improvement. The invention also provides a method for analyzing a fluid, wherein results are improved due to less noise &amp; wandering.  
         [0007]     According to the invention the analysis cell comprises a cavity adapted for receiving a fluid. A detection unit for detecting a property of the fluid is coupled to the cavity. A pipeline for supplying a fluid is connected to an orifice of said cavity. According to one aspect of the invention the pipeline comprises a curvature. In another aspect the pipeline is connected to the cavity in such manner, that a fluid is streaming into the cavity along a sidewall of the cavity. Therefore at least some parts of a wall of the pipeline are connected almost parallel to the curved sidewall. In other words the angle between said parts of the wall of the pipeline and the sidewall of the cavity is very small, providing a stream along the sidewall of the cavity.  
         [0008]     Thus according to the invention the fluid is mechanically forced to flow along a curvature in the area of the orifice. The fluid will make a smooth transition when streaming into the cavity without flowing around sharp edges. Turbulence caused by such edges will be prevented.  
         [0009]     In a preferred embodiment of the invention at least a first part of the detection unit is coupled to a first opening of the cavity having a first radius and a second part of the detection unit is coupled to a second opening having a second radius.  
         [0010]     In another preferred embodiment of the invention the curved pipeline comprises a uniformly continuous curvature following the orifice between the curved pipeline and a sidewall of the cavity. In accordance to a preferred embodiment of the invention the curved pipeline comprises a spiral curvature following the orifice. Such pipelines result in a uniformly continuous flow of the liquid. Any turbulence caused by sharp edges or different velocities of one area in the liquid compared to another are prevented.  
         [0011]     In a preferred embodiment of the invention the curved pipeline with a spiral curvature comprises an angle dependent inner and an outer radius. In the area of the orifice between the pipeline and the cavity the outer radius of the pipeline is similar to the radius of the cavity. Hence the outer sidewall of the curved feeding pipe is blended into the sidewall of the cavity with a smooth transition. Any sharp edges or rough transition causing turbulence are prevented.  
         [0012]     A further embodiment relates to an aspect, where the diameter of the curved pipeline is less than half of the radius of the cavity of the cell body in the area of the orifice between the curved pipeline and the curved sidewall of the cavity. Preferably, the curved pipeline comprises a diameter in the range of 0.1 to 0.3 of the radius of the cavity.  
         [0013]     In accordance with a preferred embodiment the cavity is formed in a conical or in a cylindrical shape. A conical shape provides a better optical path in a chromatographic system due to the spreading of the emitting light rays.  
         [0014]     According to an embodiment of the invention the cavity is arranged in a cell body having a volume and further having a first side and a second side of a surface, the second side preferable opposite to the first side. Thus the analyzing cell comprises a cavity within said cell body, the cavity having a curved sidewall and further comprising a first opening to the first side of the surface of the cell body and a second opening to the second side of the surface of the cell body.  
         [0015]     Preferable a first cell window is arranged on said first side and a second cell window is arranged on said second side of the surface according to yet another embodiment.  
         [0016]     In an embodiment of the invention, the cell body comprises a first recess on the first side of the cell body The recesses are provided as a dent, a small hollow or an imbedding and formed around the cavity. According to an embodiment of the invention the cell body comprises a curved sidewall shaped around the cavity and the at least first recess, on which the pipeline is connected.  
         [0017]     Alternately the analyzing cell comprises a tube arranged within the cavity. In this embodiment the length of the cavity within the cell body is then defined by the distance between the first and second side of the surface less the depth of the at least first recess. The tube comprises a tube length larger then the length of the cavity. Thus some parts of the tube are rising above the lower surface of the at least first recess. The cell further comprises at least one curved feeding pipe connected an orifice on said some parts of the tube rising above the lower surface. Preferable the cavity is completely filled by the tube and of the same material as the cell body. In a further embodiment the cell body comprises a second recess formed around an opening of the cavity on the second side.  
         [0018]     According to yet another embodiment of the invention the analysis cell comprises at least one curved pipeline for supplying a liquid to said cavity within said cell body. The curved pipeline is connected to an orifice on a curved sidewall of the cavity.  
         [0019]     In an embodiment of that invention the curved pipeline or the curved feeding pipe is provided as a curved feeding channel within the cell body. In another embodiment of the invention the curved pipeline or the curved feeding pipe is shaped as a curved recess in the first side of the surface of the cell body with an orifice the curved sidewall of the cavity. In an embodiment a recess in the surface of the first side comprises the shape of a half-tube.  
         [0020]     The liquid flow in the curved pipeline or feeding pipe respectively as well as in the cavity is mechanically forced to run along the shape of the curved pipeline. The optical path lies within the cavity or tube respectively and preferable between parts of the detection unit. Due to the mechanical force, there will be no flow edges within the optical path of the cavity to disturb the homogeneity of the flow while the liquid has to change flow direction in the area of the orifice between the curved pipeline and the cavity. The flow through the curved pipeline and the cavity will therefore remain laminar or orderly forced respectively even for high flow velocities and not become undirected turbulent. Such laminar flow will reduce any random noise &amp; wander significantly. Furthermore mixing between two liquids with different refractive indices is improved.  
         [0021]     In accordance with a preferred embodiment of the invention the analysis cell further comprises a second pipeline for supplying a liquid to the cavity wherein the second pipeline is connected to a second orifice on the curved sidewall of the cavity. In another preferred embodiment of the invention a second recess is formed on the second side of the cell body&#39;s surface around the second opening. A small wall around the second opening will remain intact. A second curved pipeline or feeding pipe is connected to an orifice in the remaining wall around the second opening. Alternately the pipeline is shaped as a recess in the second side of the surface.  
         [0022]     Therefore the analysis cell comprises a flow-in and a flow-out path for the liquid wherein the optical path lies between the first and the second cell window. Due to the circular-shaped pipelines turbulence are reduced in the area wherein the liquid has to change the flow direction.  
         [0023]     In an embodiment of the method for using an analysis cell the liquid is supplied from a curved pipeline to the cavity of the cell body. The method further comprises the step of detecting a property of the fluid.  
         [0024]     Preferable the step of supplying comprises mechanically forcing the liquid to run in a spiral-like manner such, that there are no flow edges within the optical path to disturb the homogeneity of the flow while the liquid has to change the flow direction into the cell. Thus the step of feeding the liquid into and out of the cavity comprises the steps of forcing the liquid along a curved direction, wherein the direction of the curvature does not change in the area into or out of the cavity.  
         [0025]     In an embodiment of the invention, the step of detecting a property comprises the step of emitting light into the cavity and determining the absorption of the light within the liquid. In this embodiment of the invention the liquid fed to the cavity gains a preferred direction and keeps that direction when flowing into the cell. The preferred direction reduces turbulence generated during the flow through the orifice. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Other objects and many of the attendant advantages of the present invention will be readily appreciated and better understood by reference to the following detailed description when considering the invention in connection with the accompanied drawings. However the embodiments of the present invention are not restricted to the examples and drawings discussed herein and can also be combined together or used in connection with different analysis systems or flow through cells in other analysis systems like for example in spectral photometric systems. Features that are substantially or functionally equal or similar will be referred to with the same reference signs.  
         [0027]      FIG. 1  shows a schematic illustration of liquid chromatographic system according to a first embodiment of the present invention.  
         [0028]      FIG. 2  shows a schematic illustration of cell body according to a second embodiment of the present invention.  
         [0029]      FIG. 3  shows a schematic illustration of a cell body&#39;s area according to the first embodiment of the present invention.  
         [0030]      FIG. 4  shows a schematic illustration of a cavity&#39;s opening with a feeding pipe according to the second embodiment of the present invention.  
         [0031]      FIG. 5  shows a schematic illustration of a cavity&#39;s opening with a feeding pipe according to a third embodiment of the invention  
         [0032]      FIG. 6  shows a diagram of a chromatogram comparing an embodiment of the present invention with a known liquid chromatography cell.  
         [0033]      FIG. 7  shows a schematic illustration of a cell body&#39;s area according to the fourth embodiment of the present invention.  
         [0034]      FIG. 8  shows a schematic illustration of a cavity&#39;s opening with a feeding pipe according to a fifth embodiment of the invention 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0035]     Referring now in greater detail to the drawings,  FIG. 1  shows a schematic illustration of a first embodiment of the present invention providing an analysis cell for liquid chromatography in accordance to the present invention within a part of the liquid chromatographic system.  
         [0036]     The liquid chromatographic cell comprises a cell body  1  having a volume, a surface and a first side  11  and second side  12  opposite to the first side on the surface. The cell body is preferably made of steel or other materials like ceramics or metals with very good temperature coefficients. A recess  13  is formed in the first side  11  and second side  12 , having a recessed surface  131 . The recesses are formed in a ring like shape, having an outer radius r″ or R″ respectively and an inner radius r′ or R′ respectively.  
         [0037]     Furthermore a cavity  2  is formed within the cell body  1 . The cavity comprises a first opening with the radius r in the area of first side  11  not recessed. The radius r is slightly smaller than the radius r′, resulting in a small ring shaped wall remaining. A second opening is formed on the second side of the cell body  1  in the same way. The radius R of the second opening is bigger than the radius r, but slightly smaller than the inner radius R′ of the second recess. Thus a small wall between the opening and the surrounding recess  13  is formed. One can see this structure also as a cavity  2  filled with a tube, whose sidewall is rising above the recess  13  on the first and second side. The tube comprises the same material as the cell body and completely fills the cavity.  
         [0038]     Due to the different radiuses on both sides of the cell body, the cavity  2  is formed in a conical shape having a smaller radius r at the first opening on the first side  11  and a bigger radius R on the second side  12 .  
         [0039]     On the first side  11  a cell window  3  is arranged on the first recess  13  and partly on areas  111  of the surface of the first side  11 . It is also directly connected to the remaining parts of the wall between the opening and the recess  13 . An illumination system  4  is placed on the cell window  3 . The illumination system emits light of different wavelength through the cell window into the cavity  2 . The material of the cell window is transparent to the light radiated by the illumination system. For ultra violet light starting at 190 nm for example the cell window  3  is made of quartz glass. For other wavelength or frequencies cheaper and similar transparent materials can be used, for example normal glass or PMMA. The typical range in liquid chromatography is 190 nm up to 900 nm.  
         [0040]     The illumination system  4  used in the liquid chromatographic system provides white light including the whole visible spectra, but can also provide, for example, laser light with a predefined wavelength.  
         [0041]     A second cell window  5  is arranged on the second recess of the second side  12  of cell body  1 . Parts of the surface  121  of the second side  12  as well as the opening of cavity  2  are covered by the cell window  5 . A detector system  51  is arranged opposite to the illumination system  4  on the side of the cell window  5  for measuring the amplitude and wavelength of the time dependent signal. The detector might also include additional optics for focussing the incoming light. It can be arranged on the cell window using ceramics or other materials with low temperature drift, thus reducing any temperature effects in the detector system. The detector system might comprise a sensor array, preferable a semiconductor diode sensor array.  
         [0042]     For feeding liquid into the cavity  2  a spiral-formed pipeline  6  is arranged in the recess  13  of side  11  around the remaining wall or ring respectively between the recess  13  and the cavity  2 . The pipeline has a uniformly continuous curvature in the area of the recess with a decreasing spiral radius. One end of the pipeline  6  is connected to an orifice in the wall between the recess and the cavity  2  providing a flow-in for the liquid into the cavity  2 .  
         [0043]     The second end of the pipeline  6  is connected to a supply unit  7  outside the cell body  1  for supplying liquid and the chemical components to be analyzed. Due to the spiral curvature of the pipeline  6  the liquid is mechanically forced to run in a spiral like shape and then with a silent transition into the cell core and the cavity  2 . Thereby the liquid turns its overall direction by 90°. However there are no sharp edges, on which the flow velocities are strongly different between small parts of the liquid. The solution for the Navier-Stokes equation will result in a laminar flow through the pipeline the orifice and the cavity. The Reynolds number characterizing the flow remains small. Due to the lack of sharp edges any possibility of turbulence is prevented.  
         [0044]     On the other side of the cavity an outlet area comprising an orifice as well as a spiral pipeline  81  and  8  connected to the orifice is formed. The second pipeline  8  is connected to an area  9 .  
         [0045]     In this embodiment of the invention the liquid are fed into the pipeline  6  via the supply unit  7  and  71 . The illumination system will emit light, which might be absorbed partly by the liquid flowing through the cavity  2 . The conical shape of the cavity compensate the spreading of light due to diffraction and other effects. The wavelength dependent amplitude of the light is measured by the spectrometer  51  and taken as a reference. Due to the reference any static effects will be compensated. Then the chemical component is added and mixed with the liquid. The spiral shape of the pipeline allows a good mixing and prevents any turbulence causing refraction changes in the liquid visible in the spectrometer. The absorption is measured by the spectrometer  51  again and processed together with the reference data.  
         [0046]     An example of such measurement can be seen in  FIG. 6 . The chromatogram shows a comparison between a standard cell and a liquid chromatographic cell according to an embodiment of the invention. The X-axis shows the time after the chemical components are added to the liquid, while the Y-axis shows the relative absorption for a specific wavelength. As one can see from the  FIG. 6  the measurement data of the standard cell STD shows a strong signal change for a wavelength of 210 nm beginning at roughly 90 seconds after adding the component. Those changes have their origin in turbulence caused by the high flow velocity of 5 ml/min as well as in imperfect mixing between the liquid and the chemical component. Absorption by the chemical component can not be clearly identified.  
         [0047]     On the contrary, the curve “New” shows data measured with a liquid chromatographic system with a cell body according to the invention. As one can see the turbulence induced noise is strongly reduced while at around two minutes some real peaks can be identified, giving information about the chemical components and their concentration. With this invention the peak form of the signals become better in symmetry and the peaks are now better comparable to a Gaussian profile. Peaks that could not be identified before as such are now clearly seen due to the new flow geometry. It is therefore possible to distinguish between turbulence-induced noise and real peaks even for high flow velocities. Additionally cells according to the embodiments of the invention provide better flushing behaviour.  
         [0048]     A detailed view of the cell body according to a preferred embodiment of the invention can be seen in  FIG. 2 . In this The cell cavity  2  has a conical shape with a radius r at an opening of an inlet area  21  and a second radius R at an opening of an outlet area  22 .  
         [0049]     The cavity  2  comprises an orifice  62  at the inlet area  21 , on which the curved pipeline  61  is connected. The pipeline  61  is formed as a counter clockwise spiral-formed recess in the surface of side  11 , starting from the orifice  62  to the point  63 . The recess may be formed by an etching or a milling process. At point  63  the recess makes a transition into a tube channel  6  connected to the supply area  71  within the cell body  1 . The spiral-formed recess is defined by different radiuses x(φ) depending of the angle g. Starting from the orifice  62 , wherein the spiral-formed pipeline  61  comprises the smallest radius the radius increases to the point  63 .  
         [0050]     The cell window,—not shown here—which is arranged on the surface of side  11  does not include a recess. Thus the recess  61  in the surface of side  11  along with the cell window comprises the shape of a spiral formed half-tube.  
         [0051]     Of course it is possible to form a recess in the cell window as well. However the window must be arranged properly, so that both recesses are opposite to each other. The pipeline itself can also be built in the cell body directly as well.  
         [0052]     In the outlet area  22  a second curved pipeline  81  is provided as a recess on side  12  of the cell body. The pipeline  81  is connected to the outlet  91 , which is also build within the cell body  1 . The curvature of the second recess  81  on side  12  respectively is also formed counter clockwise. Thus, the overall liquid flow between the pipeline  61 , the cavity  2  and the pipeline  81  comprises the same continuous curvature. The liquid flowing into the pipeline  81  will make a smooth transition without causing turbulence at the outlet area  22 .  
         [0053]      FIG. 3  shows a detailed view of the inlet area according to another embodiment of the invention. For a better understanding of the embodiment of the invention the cell body is cut perpendicular to side  11 . The inlet area  21  is equal to the inlet area of the embodiment according to  FIG. 1  except for the cavity&#39;s shape. The cavity according to the embodiment of  FIG. 3  is cylindrical, contrary to the conical shape of the cavity  2  according to  FIG. 1 . However a recess  13  with a bottom  131  is formed on the first side  11  of the surface. Between the cavity  2  and the recess  13  a small circle shape wall  23  remains intact. Thus the structure can be seen as a cavity filled with a tube, wherein the outer wall of the tube becomes the sidewall  23   a  and is connected to the sidewall of the cavity except for part  23 .  
         [0054]     Furthermore a spiral formed pipeline is arranged on the recess. In this view the pipeline is cut parallel to side  11 , thus comprising a first wall  611  with an inner radius x and a second sidewall  612  with an outer radius y. As one can see the inner sidewall  611  is connected to the sidewall  23  at the area  211 , wherein the radius r is almost equal to the angle depending radius x. the outer sidewall is connected at area  212  to the sidewall  23 . Between areas  211  and  212  the orifice  62  is formed. Any liquid in the pipeline  61  is mechanically forced by its sidewalls to move with a silent transition into the inlet area  21  and the cavity  2  through the orifice  62  and then turns its overall direction by 90° and moves along the cavity  2 . The mechanical forced geometry provided by the pipeline is limited to the inlet and outlet area.  
         [0055]     Preferable in the embodiments of the invention the same structure comprising a pipeline with the same curvature direction is arranged in a recess near the outlet area of the cavity  2 . This allows to build the cell body independent from the curved pipelines. No special structure has to be manufactured into the cell body itself which makes the cell part cheaper.  
         [0056]      FIG. 4  shows a detailed top view of the opening of the cavity  2  as well as the cavity&#39;s orifice  62  connected to the spiral formed pipeline  61  according to the embodiment of  FIG. 2 . The diameter D of the pipeline  61  in  FIG. 4  is about half of the cavity&#39;s radius R. Using a smaller diameter D of the curved pipeline  61  compared to the cavity&#39;s radius, the possibility of turbulence, especially at high liquid velocities are reduced and the mixing behaviour becomes better. According to this embodiment of the invention the center of the cavity&#39;s opening C and the center of the radius of the inner sidewall  611  and the outer sidewall  612  are the same. The outer sidewall  612  of the pipeline  61  is smoothly blended into the sidewall of the cavity  2 . At the area  212  the cavity&#39;s radius r is similar to the radius of the outer sidewall  612  resulting in a smooth transition without sharp edges.  
         [0057]     A similar detailed top view of another embodiment of the present invention is shown in  FIG. 5 . On side  12  of the rectangular shaped cell body  1  a recess  13  is formed in the shape of an ellipsoid. Within the recess a cavity  2  with an opening and a surrounding sidewall  23  rising above the bottom of the recess  13  are formed. The opening comprises the radius R. A tube or feeding pipe  61  respectively is arranged on the recess, having a diameter D and an inner sidewall  611  and an outer sidewall  612 . The diameter D is about half the radius R of the opening. The tube or feeding pipe  61  is formed in a spiral like manner, but is not be a spiral in the strict mathematical sense.  
         [0058]     However the curvature is uniformly continuous and clockwise, the curvature direction does not change to counter clockwise along the pipeline  61 . The sidewall of the cavity and the outer sidewall of the feeding pipe are connected in the area  212 , wherein they share the same radius and curvature. This is clarified further by the tangent line T. The inner sidewall  611  is also connected to the cavity&#39;s sidewall, forming a slightly round edge. However this edged does not produce any turbulence in a liquid due to a preferred flow direction given by the curvature direction of the feeding pipe. At the end the pipeline  61  is connected to a further pipeline illustrated by the dotted circle.  
         [0059]     Another embodiment according to the invention can partly be seen in  FIG. 7 . The cell body  1  comprises a first side  11  without any recess and a cavity  2  within the cell body  1 . A gasket ring  13 A is arranged on the first side on top of the area  131 . The gasket ring  13 A comprises a cavity  61  or a channel  61  within its material respectively. On end of that cavity is connected to an orifice on the inner sidewall  13 B of the gasket ring  13 A thereby providing a connection to the cavity  2 . The spiral-formed channel  61  is connected to the inner side of the gasket ring&#39;s cavity as seen in  FIG. 8 . On top of the gasket ring  13 A the cell window  3  is arranged and an illumination system is arranged on cell window  3 .  
         [0060]     A further embodiment according to an important aspect of the invention shows  FIG. 8 . A detailed top view of a cavity&#39;s opening and a pipeline  61  or recess respectively connected to an orifice  62  can be seen. The pipeline  61  comprises a diameter D, smaller than the radius r of the opening. However the pipeline  61  does not comprise a curvature. Nevertheless the outer wall  612  according to this view is connected almost parallel to the sidewall of the opening in the area  62 . In other words the angle between the sidewall  612  of pipeline  61  or recess  61  respectively and the sidewall of the cavity is very small in the range of less than 10 degree. As one can see, sharp edges on the outer wall in the area of the orifice can be significantly reduced, if the virtual extension of the pipeline, shown by the dotted lines is not crossing the center C of the cavity&#39;s opening. This will allow a liquid to flow through the orifice along the sidewalls of the cavity. The smooth transition reduces turbulences.  
         [0061]     A person skilled in the art may appreciate the various possibilities for arranging and forming the feeding pipe. The present invention is not restricted to spiral formed pipelines. For example it can be formed in a parabolic shape. However the direction of the sidewall in the area of the orifice and the pipeline&#39;s wall connected to it should comprise a continuous curvature following the orifice and not comprise of sharp edges to allow any liquid to make a smooth transition when flowing into the cavity  2 . Due to a curvature, the liquid is mechanically forced along the curvature and has already gained a preferred direction when flowing through the orifice  62 . The preferred direction the connection between the inner wall  611  and the sidewall  23  does not produce turbulence, decreasing measurement quality.  
         [0062]     It will also be appreciated that different forms of pipelines are possible. It is possible to include them in or outside the cell body as channel pipelines, tubes or recesses as shown in the examples. The feeding pipes may comprise turn of more or less than 360° degree depending on the application. The may even not comprise a curvature as long as according to the invention at least some parts of the sidewall make a smooth transition without edges into the curved sidewall of the cavity.