BACKGROUND 
     The present invention relates to an apparatus and a method for the detection of the level of the different phases present in at least one tube or vessel the content of which is intended for filling the different wells of a microplate-format container for an automated analysis system. According to the invention, this detection is carried out by reflecting light on a point zone on the outside of the tube, during a displacement of the tube along an optical reader or the optical reader along the tube in a rectilinear movement and in a known manner. 
     It relates moreover to such an apparatus or method operating by illumination with monochromatic light and detection of the amount of reflected light, with the phase differences being recognized by the sudden variation in the amount of reflected light. 
     Increasingly, many methods in laboratory chemistry are automated, for example chemical analyses or DNA sequencing. The different products to be mixed together are handled by robotic equipment, and the entire procedure is controlled and monitored by computer. The rapid growth of large-scale DNA analyses, for example by PCR-type methods, has increased the requirements in this field and makes even the smallest improvement in the productivity and reliability of these procedures and the corresponding equipment worthwhile. 
     Within the technical capabilities of each facility, an effort is made, as far as possible, to carry out the procedure while minimizing the manual operations that give rise to loss of time and the risk of error. 
     Typically, an integrated automated facility is used that includes computerized monitoring of the products and samples processed. Such a facility comprises one or more robot operating heads, for example a pipetting instrument which takes an accurate shot of a liquid from a vessel in order to transfer it to another vessel, where a reaction will then take place. This vessel can then be moved to another slot for another operation, and/or stored in a waiting slot during the reaction, possibly in a reactor ensuring specific conditions of temperature, pressure, humidity, etc. 
     For reasons of reliability of analysis and productivity, receptacles of a standardized so-called “microplate” type are most usually used. Such a receptacle usually comprises a monolithic surface area pierced by a large number of wells of a few millimeters in diameter which are independent of each other. Other types of microplates also exist which are here included under the same name, for example a tray or rack comprising positions in which the same number of moveable individual tubes are inserted, and performing a function similar to the wells of a monolithic plate. Depending on the versions, a single plate can contain for example 96 or 384 wells. Several wells of a single microplate are often processed in parallel by multi-head pipetting instruments, which can be controlled together or separately. 
     These plates all have a single external geometry, in particular in their base footprint. This geometry is governed by a standard called “SBS” (ANSI/SBS 1-2004), which allows compatibility of all the plates with the majority of the robots and specialized machines in this field. This geometry comprises for example a rectangular base having two cut off chamfered angles, and is equipped with a rim having a slight horizontal extension around the base. This standardized shape allows all the compatible robots to use a robot arm equipped with a compatible slot for receiving, gripping and holding all the plates in a firm, precise and repeatable manner. 
     In some circumstances, and in particular for most analyses of blood or biological fluids, the automated analysis or processing comprises a separation phase, for example by centrifugation or decantation, which makes it possible to separate the different constituents present within the fluid initially taken. 
     For example in the case of blood, the initial sample is poured into a test tube, also called a sample tube, which is then centrifuged. The result of this centrifugation gives a distribution of the different constituents on several different levels, forming the following phases:
         at the bottom of the tube is found a thick, dark red phase containing the red blood cells;   above this is found a thin, whitish phase forming a sort of emulsion called “buffy coat”, which mainly contains white blood cells;   at the top is found a lighter red fluid phase formed by the plasma, which represents approximately 55% of the blood volume.       

     In order to use a single one of the constituents separated in this way, a pipetting instrument is used that is made to descend in the tube until reaching the depth where the constituent in question is found, for example into the buffy coat for sampling white blood cells. The component thus sampled is then poured into one or more receptacles, for example for a series of wells within a microplate, an operation which is often called “filling” the microplate. 
     In the centrifugated tube, the vertical position of the different phases varies according to many parameters, such as the initial amount of fluid or the diameter of the tube. In order to make it possible to automate sampling in a particular phase, it is therefore necessary for the robot to be provided with an apparatus for the detection of the levels of the different phases in each of the tubes to be sampled. 
     Different types of apparatus are known for carrying out this detection. Certain equipment measures for example the variation in the light transmitted by the content of the tube. These methods have drawbacks owing for example to the variability of the transmission factors. Furthermore, the transmission does not make it possible to distinguish between opaque phases even if they contain different constituents. Other methods measure fluorescence emitted by the content of the tube under chemiluminescence, but require relatively complex, costly high-power instruments for this purpose. 
     U.S. Pat. No. 4,683,579 proposes to measure the scattering of incident light of 400 to 1000 manometers at a narrow angle of the order of 20°. The precision of this technique however can be insufficient, and represents a significant space requirement around the tube which is inconvenient for incorporation in a robot system. 
     U.S. Pat. No. 7,450,224 proposes to carry out computerized graphical analysis of a complete colour image of the tube. For this purpose, the tube is gripped by a robot gripper and brought into an imaging chamber containing a CCD multipixel colour camera and uniform multidirectional lighting. The tube is extracted from a rack positioned on a table with XY displacement. 
     This technique however has drawbacks, for example requiring relatively costly components and complex computer processing requiring a certain computing power. Furthermore, such an apparatus permanently occupies a certain space and requires a table with robotized displacement in order to make an automated choice of the tube to be sampled. 
     SUMMARY 
     A purpose of the invention is to overcome all or part of the drawbacks of the prior art, in particular with respect to the following aspects:
         simplicity, compactness, reliability;   versatility in use and for programming;   adaptation to the variability of the tubes, their positioning, the presence of opaque parts, such as a label;   adaptation to the presence or absence of requirements of the procedure carried out;   possibility of use in an integrated robot.       

     Furthermore, it is useful to be able to minimize the occupation of the operating heads available on a robot facility, for example in order to allow a better integration of the entire analysis procedure while reducing the limitation due to the number of available slots or operating heads. 
     The invention proposes an apparatus for the detection of the level of the different phases present in at least one tube or vessel, transparent or at least partially transparent and for at least certain wavelengths, the content of which is intended for automated filling of at least one analysis container for an automated analysis system, typically for filling the different wells of a microplate-format container. According to the invention, the apparatus comprises:
         means for displacing the tube along an optical reader, or the optical reader along the tube in a known manner i.e. controlled or measured;   means for recording data representing the vertical position of at least one phase change within the content of this tube.       

     Preferably, the device is designed with kinematics carrying out a displacement of the tube in a rectilinear or substantially rectilinear movement, for example vertically. 
     In a variant, the movement can be designed to carry out a linear movement that is not rectilinear, and the recording means are arranged or programmed to adapt their calculation to the trajectory of the tube, for example by comparison with a chart or by a calculation formula taking account of the trajectory of the tube. 
     According to the invention, this apparatus operates by measuring the variation in wavelength of light reflected off the content of this tube. It is moreover equipped with a fixing portion arranged to allow it to be itself held and/or handled instead of a microplate-format container, for example by a robot arm provided for handling microplates. 
     Preferably, the apparatus is provided with displacement means operating along a single axis of displacement, or even a one-piece monaxial displacement actuator (outside of the gripping means). 
     The apparatus can thus be used for measuring the content of a conventional vessel arranged among others in a standard rack, within an automated procedure processing and managing all of these vessels. 
     It is thus possible to program the sampling of all the different phases, in each of the vessels of a rack, in order to fill one or more microplates and to carry out the analysis or the automated processing thereof, in a single automated global process. 
     The reading method allows a design that is relatively simple and compact as well as economic in comparison to other more elaborate techniques. It makes it possible moreover to detect differences between several opaque phases provided that they have different colours, unlike the technique using a transmission. This compactness facilitates the design of an apparatus the geometry of which is similar to the microplate format and suitable for the corresponding handlers. 
     This mechanical compatibility with the microplate format allows the use of the apparatus to be easily integrated into an overall cycle of automated processing. In fact, it is possible to fix it onto an existing operating head which can then be programmed to move and position it as required, according to the requirements of the procedure. 
     The apparatus itself can thus dispense with multi-axis and/or long-reach operating heads, as it can itself be displaced until close to the vessel to be measured. It is simpler, more compact and robust. 
     By placing the apparatus in a slot managed by the robot system, the problems of handling and picking up plates or containers in the automated cycle are limited or avoided, as well as the floor space occupied. Integration becomes more flexible and easier, in particular when a complete integrated facility is available that has a limited and compact workspace. 
     Furthermore, once in place on a microplate slot or “gripper” of the robot facility, the apparatus has its own means of gripping and moving the vessel to be measured. Thus the use of a second slot or robot operating head is avoided, or the shortage of one if there is no other available. 
     Furthermore, whenever the apparatus is not required, it is then possible to remove the apparatus in order to free up a microplate slot and save the space in a robot facility. 
     According to a feature, the apparatus comprises a base the lower periphery or footprint of which has a geometry compatible with the microplate format. These displacement means are moreover arranged to have access to the tube to be read via at least one displacement of the tube or of the optical reader situated in a region within and below said footprint. 
     Preferably, the displacement means have at least one so-called retracted position in which they do not extend below or outside the microplate-format footprint. These displacement means can for example be folded back into a base that does not extend beyond the outer and lower contours of the microplate-format footprint, and preferably within an upper protective casing. 
     The apparatus thus occupies only a small space during the movements of the arm which bears it and facilitates the organisation of the overall analysis or processing procedure. 
     It is apparent that in this way a compact, robust apparatus is obtained that is versatile in use and for programming, easy to handle and store without damage both by the robot and when it is not in operation. 
     In a preferred embodiment, the apparatus comprises means of gripping the tube, for example a pair of grippers, which have a geometry that is determined in order to allow them to be inserted from above around a tube arranged within a plurality of tubes that are substantially parallel inside a holding rack, for example vertical tubes in a horizontal rack. 
     In another embodiment (not shown), the displacement means move the optical reader along a tube situated below this apparatus. These displacement means and this optical reader together have a geometry that is determined in order to allow them to be displaced upwards, along a tube arranged within a plurality of tubes that are substantially parallel (for example in the same transverse plane, i.e. not longitudinal) within a holding container (for example vertical tubes in a horizontal rack). 
     This embodiment can also be combined with the previous one, for example in a configuration where the tube and the reader move in relation to each other and both move in relation to the base, and/or the frame. 
     According to the invention, the optical reader comprises at least one sensor detecting the wavelength of the light reflected by the content of the tube or at least by the outer surface of this content, in a determined restricted zone, mobile along said tube during the reading displacement. 
     According to a feature of the invention, the optical reader ( 14 ,  6 ) comprises a plurality of optical reading modules ( 6   a  to  6   d ) distributed in several different angular positions around the tube ( 9 ) and in the same horizontal plane, arranged in order to carry out a measurement in these different angular positions. 
     These modules can each comprise one or more sensors, and/or a light source. 
     The optical reader can also comprise one or more mirrors arranged around the tube so as to reflect the light originating from the source to a plurality of angular measurement positions distributed around the tube, and/or so as to send the light reflected by the content of the tube to a single sensor from a plurality of angular positions around the tube. 
     By combining several measurement points around the tube in this way, the invention makes it possible in particular to find at least one usable reading position even if the tube is not transparent over the whole of its periphery, for example as a result of a label stuck to its wall. 
     According to a preferred feature of the apparatus:
         on the one hand, it comprises one or more light sources emitting only in a determined portion of the light spectrum; and   on the other hand, the optical reader comprises one or more reading modules each comprising one single-pixel sensor sensitive to the colour of said light source, for example a simple single photodiode.       

     The recording means are then arranged in order to use the amount of reflected light received by the sensor(s) to recognise the change in the wavelength of this reflected light. 
     At each moment the coloured light is reflected more or less according to the colour of the illuminated phase. The wavelength(s) of the coloured light are chosen as a function of the colour differences between the different phases the separation of which it is sought to detect. 
     Thus, if one phase is red and the other white, a blue light will be reflected much more by the white phase than by the red phase, which will thus appear much darker. 
     By detecting the marked variations in the amount of reflected light, with all wavelengths merged, it is then possible to note the colour change of the zone from which the measured reflected light originates. 
     It is understood that this type of detection allows a simple, compact and economic design, in particular from the point of view of the electronics, which contributes to the compactness of the assembly. 
     According to another aspect, the invention also proposes a method for detecting the level of the different phases present in at least one tube or vessel intended for filling the different wells of at least one container for an automated analysis system, said method comprising:
         a displacement, in a rectilinear movement in a known manner, of the tube along an optical reader, or of the optical reader along the tube;   recording of data representing the vertical position of at least one phase change within the content of the tube.       

     According to the invention, this recording comprises a recording of the amount of light originating from a coloured source and reflected by the content of said tube at least one determined point that is mobile along said tube, i.e. mobile relative to the tube. 
     By reading point is meant a restricted zone, for example with respect to the dimensions of the tubes or the height of the phases measured in the tube. The measurement can also be done at several determined points, i.e. in that case in several restricted zones that are isolated from each other. 
     Various embodiments of the invention are envisaged, incorporating according to their possible combinations as a whole the different optional features disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other characteristics and advantages of the invention will become apparent from the detailed description of an embodiment which is in no way limitative, and the attached drawings in which: 
         FIG. 1 ,  FIG. 2 ,  FIG. 3  and  FIG. 4  are perspective views illustrating an example embodiment of the invention, in the following positions: 
         FIG. 1  in the low position during the gripping of a tube, 
         FIG. 2  during reading while being raised, 
         FIG. 3  in the high position at the end of reading, and 
         FIG. 4  in the retracted position when a reading operation is not taking place; 
         FIG. 5  is a graph showing the results of the measurement of reflected light intensity, which are interpreted by the recording means in order to identify the position of the phase changes within the tube; 
         FIG. 6  is a diagrammatic top view showing an example of an optical reader having a single source and four reading modules each equipped with a single-pixel sensor, measuring at four different points; 
         FIG. 7  is a flowchart showing filling operations in an analysis or processing method, comprising detection of phase levels in an embodiment of the invention; 
         FIG. 8 ,  FIG. 9  and  FIG. 10  are partial perspective views of an automated facility in different phases of filling operations according to  FIG. 7 , with: 
       in  FIG. 8 : detection of the phase levels in one of the tubes of a rack of tubes, 
       in  FIG. 9 : sampling of a phase in this tube according to the results of the detection, and 
         FIG. 10 : filling a microplate with the sampled phase. 
     
    
    
     DETAILED DESCRIPTION 
     In the embodiment described here, the apparatus forms a “detection module” which can easily be mounted on a microplate slot for measuring with precision the heights of the different phases of a tube with a centrifuged blood sample. In order to carry out this measurement the “optical assembly” will travel the entire height of the tube. During this translational movement, the light reflection is measured and the position of the optical assembly relative to the tube at the moment of the changes in the level of reflection will determine the heights of the different phases. 
     The detection module has a device for gripping the blood sample tubes, making it possible to grip the tubes up to a distance for example of 100 mm below the module, in order to make them in their entirety transversally pass the detection module in order to carry out the phase detection. This gripping device is composed for example of a “lever” and a “gripper”. 
     Once closed, the module has the complete format of a microplate (SBS format) 
     The phase detector can be used with a robotic arm within a robot platform. It can also be used alone, in which case the operator feeds the detector by hand, which will be mounted on a single base allowing the tube to rise and fall along the axis perpendicular to the light beam. 
     Detection by the phase detection module is based on a principle of absorption/reflection of a wavelength determined by the different phases of a tube containing a centrifuged blood sample. The different phases being, starting from the bottom of the tube: dark red (red blood cells), whitish (cell compounds including approximately 45% white blood cells), and reddish (plasma); the wavelength chosen here is in the blue region of the visible spectrum (400 to 500 nm). This wavelength is thus absorbed by the red blood cell and plasma phases and reflected by the cell compounds phase. 
     The tube is driven in a movement perpendicular to the axis of the light beam using a motorized arm, for example controlled by a microprocessor. This allows the exact position of each phase with respect to the top and/or the bottom of the tube to be known. 
     The measurement is made by detecting the amount of reflected light during the displacement. 
       FIG. 1 ,  FIG. 2 ,  FIG. 3  and  FIG. 4  show a currently-preferred example embodiment of the invention. 
     In this embodiment, the apparatus comprises a base  11  the lower periphery or footprint of which has a geometry compatible with the microplate format. This geometry includes a rectangular form with standardized dimensions for this base, and comprises:
         on the one hand, a rectangular rim  111  extending around the base, and   on the other hand, two adjacent angles of the base  11  each having a cut vertical face  112  of standardized dimensions, framing a short side of this base.       

     In this example embodiment, the displacement means  12 ,  13  comprise gripping means  13  of the tube  9 , here a gripper formed by a plate  13  bearing an operating head equipped with a collar  131  that will grip the tube against the plate. 
     These gripping means are displaced by a mechanism  12  having mobile rods  121 ,  122 ,  123 ,  124  which are mobile within a rectilinear through-slot  115  arranged in the base  11 . 
     These rods are linked together by pivot joints  1213 ,  1223 ,  1212 ,  1221  with axes perpendicular to the plane of displacement, producing a pantograph for displacement of the gripping means  13  or of the optical reader in a rectilinear direction D 12   a  and D 12   b  included in this plane of displacement P 12  and parallel to the axis of the tube  9  to be read. 
     This mechanism  12  comprises in particular two main rods  121 ,  122  hinged in a parallelogram between the base and the gripping plate  13 . This mechanism  12  comprises moreover two shorter secondary rods  123 ,  124 , themselves hinged in a parallelogram between the base  11  and an intermediate or central portion  1221 ,  1212  of the main rods  121 ,  122 . 
     On the extremity of the base, the ends of the two parallelograms are displaced in relation to each other by actuation means in order to vary the distance between them, thus upwardly displacing the gripping means  13 . This variation is carried out for example by motor-driven endless screw, causing the end of the main parallelogram  121 ,  122  to slide along the slot  115  of the base, while the end of the secondary parallelogram pivots at a fixed point inside this slot. 
     In this figure, it is apparent that the displacement means  12 ,  13  allow access to the tube  9  to be read, by:
         a downward displacement D 12   a  to reach and grip the tube, then   an upward displacement D 12   b  with the tube  9  which allows it to be extracted from its position longitudinally to its axis, then   a further downward displacement (not shown) in order to return the tube to its place.       

     These different displacements are all situated in a region  110 , shown in dotted lines, situated inside the footprint formed by the microplate-format geometry  111 ,  112  of the base  11 . Gripping and extracting the tube take place more particularly below the base, which allows access to one or more tubes from above, even when they are closely arranged in a holding rack, as shown in  FIG. 8 . 
     Inside the microplate-format footprint ( 111 ), the slot  115  of the displacement mechanism  12  extends via a through-hole ( 114 ) sufficiently wide to allow the gripping means and the tube  9  to pass through during a complete vertical displacement. 
     Reading means  14  are arranged in the walls of this through-hole  114 , so as to carry out the measurement during the passage D 12   b  of the tube through this opening, in one direction or the other. 
     The reading means  14  are thus well protected, not very susceptible to damage and not very bulky. 
     As is apparent in  FIG. 4 , the displacement means  12 ,  13  can be folded back into a so-called retracted position in which they do not extend below or outside the microplate-format footprint  111 , or above a protective casing on the top of the base, the assembly having for example the standardized microplate dimensions  100 . 
     When not in use, the apparatus forms approximately a simple and compact rectangular parallelepiped, without parts extending outside the rim  111 , which is easy to handle and store without damage. 
       FIG. 6  shows an example of an optical reader having a single source and four reading modules each equipped with a single-pixel sensor, measuring at four different points. 
     In this example, the apparatus comprises on the one hand, a light source  601  emitting in only a determined portion of the light spectrum, and on the other hand, the optical reader  14 ,  6 . This optical reader comprises here four reading modules  6   a  to  6   d  each comprising one single-pixel sensor  607 ,  611 ,  615 ,  619  sensitive to the colour of this light source, for example a photodiode. 
     The different sensors of the optical reader  14 ,  6  detect the wavelength of the light  604   a  to  604   d  reflected by the content  99  (essentially by its outer surface) of the tube  9  in a determined restricted zone  99   a  to  99   d  each forming a “reading point”, each being mobile along the tube during the reading displacement D 12   b.    
     In this example, the light source  601  illuminates the furthest reading point  99   d  via a set of reflecting mirrors  608 ,  612 ,  616  and  618  forming an optical path for routing the illumination light  603  after collimation by a lens  602 . 
     On this illumination light path  603 , three semi-reflecting mirrors  605 ,  609  and  613  each become a part of the illumination light  603  in order to each illuminate one of the three other measurement points  99   a ,  99   b  and  99   c.    
     Each of these reading points receives the illumination light through the restriction means which make it possible to limit the illuminated surface to the surface of the content  99  of the tube, for example collimation means or an aperture  606 ,  610 ,  614  and  618  respectively. It would also be possible to use a sufficiently narrow source such as a laser diode. The restricted zone has for example dimensions less than a circle of 0.5 or even 0.2 mm diameter. 
     In this way the different layers are illuminated using a light beam which will reflect the light in a different manner according to their constitution. 
     Each reading module  6   a  to  6   d  comprises one single-pixel sensor  607 ,  611 ,  615  and  619  respectively, which measures the light  604   a  to  604   d  reflected by its respective reading point  99   a  to  99   d.    
     The recording means (not shown) are arranged and programmed to use the amount of reflected light  604   a  to  604   d  received by these sensors to recognise the change in the wavelength of the reflected light. 
     In the case of several sensors, a selection can be made between the different readers, or a mathematical or logic operation in order to provide a single result. 
     In this way “multiplexed photosensors” are produced, making it possible to measure the reflected light covering a periphery of a minimum 60% of this tube. 
     The different cell layers absorb a different amount of light according to their constitution and thus reflect an amount of light that is inversely proportional to the amount of light absorbed. 
       FIG. 5  shows the results of the measurement of reflected light intensity, which are interpreted by the recording means in order to identify the position of the phase changes within the tube; 
     As is apparent in the figure, the value of the amount of reflected light varies over the course of the displacement of the tube with respect to the reader. 
     Starting from the left of the figure, a first rising edge  501  corresponding to the detection of the top of the tube can be seen, followed by a plateau  511  corresponding to the empty part at the top of the tube.
         A first falling edge  502  followed by a plateau  512  corresponds to the detection of the light red phase  93  of the plasma.   Two successive inverse edges  503  and  504  then form a region  513  that is sufficiently narrow to adopt the form of a peak, corresponding to the height of the whitish phase of emulsion or buffy coat  92 .   The falling edge  504  and the plateau  514  then denote the dark red phase  91  of the red blood cells.   The following rising edge  505  denotes the passage of the lower end of the tube  9  in front of the optical reader  14 .       

     This analysis of the edges and plateaus is programmed to provide a measurement of the heights and levels of the different phases present in the content of the tube  9 , as well as the total height L 9  of the tube. 
     By displacing the tube over its whole length, it is thus possible to know the total height of the tube and to disregard its variability from one tube to another. The device is then compatible with any tube height provided that the height is sufficient to be picked up by the “gripper” of the detector. 
     A computer generates digital data corresponding to the results of the measurement, for example a file indicating:
         the height of the tube (difference between the highest point of the tube and the bottom of the tube);   the amount of reflected light in relation to a pre-defined height in mm.       

     This file is generated for example in a .txt, .csv, or .xml format, or any compatible format capable of being used in an automated pipetter. 
     It is thus possible to selectively pipette one phase or another, or even all three, in a manner that is precise and reproducible from tube to tube, and independently for each of the tubes according to the processing requirements. 
       FIG. 7  shows the filling operations in an analysis or processing procedure in an automated facility, comprising detection of phase levels in an embodiment of the invention;  FIG. 8 ,  FIG. 9  and  FIG. 10  show certain operations carried out during this procedure. 
     A filling step  711  comprises the filling of a rack  90  comprising a set of tubes  9   n , in the working area of an automated facility  8 . This rack  90  is placed in the entry of a detection apparatus  1  according to the invention, which is fixed to the gripper of a robot arm  81  of this facility  8 . 
     The robot arm  81  positions  712  the detector  1  above a tube  9   i  chosen by the program. 
     The detector  1  extracts D 12   b  the chosen tube  9   i  from the rack and carries out  713  the measurement of the levels of the different phases contained in this tube  9   i , as well as the height of the tube. 
     These items of information are stored  715  associated with the references of the tube  9   i.    
     These detection and storage steps can be repeated automatically for all of the tubes  9   n  contained in the rack  90 . 
     Once all the tubes have been measured, an automated pipetting apparatus is positioned above the rack  90 , or vice-versa. 
     For each chosen tube  9   i , a pipetting point  82  is positioned  716  above the tube, and descends into in the tube to the depth necessary for accessing the chosen phase “j”, on the basis of the information on the phase levels and height previously stored  715  for this same determined tube  9   i . A chosen shot of the chosen phase is then sampled  717  by the pipetting tip. 
     This pipetting tip  82  will then fill an analysis container with the sampled shot of the chosen phase “j” from the chosen tube  9   i , for example from one or more wells of a microplate  80 . 
     These sampling and filling steps can be repeated automatically for all of the tubes  9   n  contained in the rack  90 . 
     The filling procedure thus comprises a robotic sampling step  717  in the same tube  9   i , detected, commanded or controlled based on the information  715  stored during the detection step  713 . 
     It is understood that the invention allows an automated selection and sampling of one or more phases in one or more sample tubes, with a good adaptation of the automated methods to the variability of the tubes, their positioning, and to the presence of opaque portions, such as a label. 
     Of course, the invention is not limited to the examples which have just been described, and numerous adjustments can be made to these examples without exceeding the scope of the invention.
An apparatus and a method are provided for the detection of the level of the different phases present in at least one tube or vessel intended for filling the different wells of a microplate-format container for an automated analysis system. The apparatus is equipped with a fixing portion arranged to allow it to be itself held and/or handled instead of a microplate-format container, and carries out this detection by measuring the variation in wavelength of light reflected on a point zone of the content of the tube, during a displacement of the tube along an optical reader or of the optical reader along the tube in a rectilinear movement in a known manner. Such a device or method is also operated by illumination with monochromatic light and detection of the amount of reflected light, with the phase differences being recognized by the sudden variation in the amount of reflected light.