Abstract:
A flow cell for a particle analyzer using an electrical sensing zone method, includes: a detecting member having a through hole; a first cell for supplying a particle containing liquid to the through hole; a second cell for receiving and discharging the particle containing liquid that has passed through the through hole; electrodes provided in the first cell and the second cell respectively, for supplying an electrical current to the liquid passing through the through hole; and a sliding member for sliding at least one of the first and second cells to change a distance therebetween; wherein the first and second cells cooperate with the sliding member to detachably sandwich the detecting member therebetween so that the detecting member is connected to the first and second cells in a watertight state.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to Japanese application No. 11-203282 filed on Jul. 16, 1999, whose priority is claimed under 35 USC §119, the disclosure of which is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flow cell for a particle analyzer using an electrical sensing zone method. More particularly, it relates to a flow cell for a particle analyzer that employs, for the measurement in size and number of powdery particles such as fine ceramic particles, pigments and cosmetic powders, an electrical sensing zone method in which a particle containing liquid is passed through an aperture so that particles in the liquid are measured based on changes in electrical impedance, and a so-called sheath flow method in which a flow of the particle containing liquid is enclosed by a sheath liquid to pass through the aperture. 
     2. Description of Related Art 
     The electrical sensing zone method has been utilized to measure in size and number of blood cells in blood or industrial particles such as cement powders, latexes and toners. In this method, a barrier having an aperture is provided in an electrolyte solution, electrodes are arranged to sandwich the aperture, and subject particles dispersed in the solution are passed through the aperture. When the particle passes through the aperture, an electrical resistance between the electrodes is instantaneously changed and a voltage pulse is generated. The height of the voltage pulse reflects the particle volume, so that a spherical equivalent diameter can be measured regardless of its shape. From the measurement, the volume-based particle size of the sample particles can be obtained. Further, the number of the particles can be counted from the number of the pulses. 
     In the electrical sensing zone method, the height of the voltage pulse varies depending on a position in the aperture where the particle passes through. Further, a plurality of particles passing together through the aperture may be measured as one particle, or the particles that have passed through the aperture may stay near the aperture and cause noise. To solve these demerits, the sheath flow method has customarily been employed. In a particle size distribution measurement utilizing the sheath flow method, a flow of the particle containing liquid in the flow cell is enclosed with another liquid (sheath liquid) flow to narrow down the particle containing liquid flow so as to introduce the particles in a row into the approximate center of the aperture. Accordingly, the particle size can be obtained with less margin of error. 
     There is a limitation to the measurable size of the particle in the electrical sensing zone method depending on the diameter of the aperture. For example, where the size of the particle is less than {fraction (1/50)} of the aperture diameter, the signal from the particle is hard to be distinguished from the noise. On the contrary, where the size of the particle is too great, the pulse height and the particle volume lose their linearity, and the aperture tends to be clogged. To replace the flow cell to change the aperture diameter requires removal and attachment of wirings led to the electrodes and pipes connected to the flow cell. Further, where the subject particles have a wide particle size distribution, the measurement will be complicated. 
     As means to deal with the above demerits, there has been known a measuring apparatus comprising a flow cell which can be divided into two segments and a detecting member sandwiched therebetween, the detecting member having an aperture through which a sheath liquid enclosing a particle containing liquid can pass (for example, see Japanese Unexamined Patent Publication No. HEI 8-15125). The detecting member includes a detachable member sealingly connected to the segments. As the detachable member, both sides of the detecting member are formed each with a thread of the opposite hand so that the detecting member can be removed from the segments by rotating the detecting member only, without rotating the segments. 
     However, in such a conventional particle measuring apparatus, in the step of attaching the detecting member to the separated segments again, it is difficult to thread both sides of the detector into the segments to the same extent. If one side is tightly threaded before the other side is not threaded enough, the other side loses the watertightness. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in view of the above circumstances, and provides a particle measuring apparatus capable of easy and ensured replacement of the detecting member in the flow cell. 
     The present invention provides a flow cell for a particle analyzer using an electrical sensing zone method, comprising: a detecting member having a through hole; a first cell for supplying a particle containing liquid to the through hole; a second cell for receiving and discharging the particle containing liquid that has passed through the through hole; electrodes provided in the first cell and the second cell respectively, for supplying an electrical current to the liquid passing through the through hole; and a sliding member for sliding at least one of the first and second cells to change a distance therebetween; wherein the first and second cells cooperate with the sliding member to detachably sandwich the detecting member therebetween so that the detecting member is connected to the first and second cells in a watertight state. 
     These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view illustrating a flow cell according to the present invention; 
     FIG. 2 is a cross sectional view taken along the arrow A—A of FIG. 1; 
     FIG. 3 is a cross sectional view taken along the arrow B—B of FIG. 1; 
     FIG. 4 is a bottom plan view of the flow cell shown in FIG. 1; 
     FIG. 5 is a view corresponding with FIG. 3, indicating when to replace a detecting member in the flow cell according to the present invention; 
     FIG. 6 is a top plan view illustrating the detecting member according to the present invention; 
     FIG. 7 is a front view of the detecting member according to the present invention; 
     FIG. 8 is an enlargement of a major part of FIG. 5; and 
     FIG. 9 is a fluid circuit for the particle measurement using the flow cell according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the flow cell of the present invention, the sliding member is provided to slide at least one of the first cell and the second cell to bring them closer to each other or separate them from each other. When the first and second cells are brought closer, the detecting member is sandwiched therebetween to be connected to them, and when the first and second cells are separated from each other, the detecting member is isolated from them. Thus, the replacement of the detecting member can be easily performed. 
     That is, when the detecting member is spaced from the first and second cells by the sliding member, the detecting member having the through hole is replaceable with another detecting member having a through hole of a different diameter. 
     The present invention may further comprise a fixing member for fixing the cell on the sliding member, by which the detecting member can more surely be sandwiched between the first and second cells. 
     The detecting member may comprise an engaging member for detachably engaging with the sliding member, by which the detecting member can easily be aligned relative to the first and second cells upon the replacement thereof. 
     The detecting member is preferably adapted to be arranged between the first and second cells in a specific position, by which the detecting member is prevented from being arranged upside down. 
     The sliding member may comprises a plurality of parallel shafts (e.g., two shafts) projecting from one of the first and second cells and the other cell has a plurality of openings (two holes in this case) for receiving the parallel shafts, and thereby the sliding member can easily and firmly be constructed. 
     In this case, the detecting member may have U-shaped grooves for detachably fitting with the parallel shafts to slide along them. 
     The U-shaped grooves may be different in groove width. The parallel shafts preferably have sectional sizes that can fit into the corresponding U-shaped grooves, by which the detecting member is prevented from being arranged upside down. 
     EXAMPLE 
     Hereinafter, the present invention will be detailed by way of example with reference to the drawings, but the invention is not limited thereto. 
     FIG. 1 shows a top plan view of a sheath flow cell as the particle measuring apparatus of the present invention, FIG. 2 is a sectional view taken along the arrow A—A of FIG. 1, FIG. 3 is a sectional view taken along the arrow B—B of FIG.  1  and FIG. 4 is a bottom plan view of the sheath flow cell. 
     As shown in FIG. 2, a flow cell  1  comprises a detecting member  3  having an aperture (through hole)  2  for detecting particles, a first cell  4  for supplying a particle containing liquid enclosed with a sheath liquid to the aperture  2 , a second cell  5  for discharging the particle containing liquid and the sheath liquid that have passed through the aperture  2  and electrodes  6  and  7  provided in the first cell  4  and the second cell  5 , respectively. Electrodes  6  and  7  are connected to a constant current d.c. power source (not shown) and supply an electrical current to the liquid passing through the aperture  2 . 
     The first cell  4  forms on the top thereof a connection hole  8  to be connected with a tube for injecting a particle containing liquid (hereinafter referred to as a sample) and on the sides thereof nipples  11 ,  12   a  and  13  to be connected with an outer fluid circuit (described later). Cavity portions  9  and  12  are provided inside the cell  4 , and the connection hole  8  and the nipple  11  are connected to a proximal end of a jet nozzle  10  coaxially projecting downward in the cavity portion  9 . A distal end of the jet nozzle  10  reaches the proximity of the aperture  2 . The cavity portions  9  and  12  are communicated with each other. The electrode  6  is provided in the cavity portion  12  which is connected to the nipple  12   a.    
     The detecting member  3  comprises an upper block  3   a  and a lower block  3   b  that are integrally fixed to each other with screws (not shown). The aperture  2  is opened in the center of a disc  15  pressed by a packing  14  between the upper block  3   a  and the lower block  3   b  as seen in FIG.  8 . 
     The second cell  15  is provided with cavity portions  16  and  19  in the inside thereof and nipples  18 ,  20  and  21  on the outside thereof. A collection pipe  17  projecting upwardly is provided in the cavity portion  16 , a proximal end thereof is conneted to the nipple  18  and a distal end thereof reaches the proximity of the aperture  2 . The cavity portions  16  and  19  are connected to each other. The electrode  7  is provided in the cavity portion  19  which is connected to the nipples  20  and  21 . 
     As shown in FIG. 3, the second cell  5  is slidably supported by two parallel shafts  22  and  23  of the same diameter projecting downward from the first cell  4  as a sliding member. The detecting member  3  is sandwiched between the first cell  4  and the second cell  5 . 
     As shown in FIG. 4, the second cell  5  includes elongate slits  5   a  and  5   b  and bolts  24  and  25  each having a handle that are screwed orthogonally to the slits  5   a  and  5   b . Tightening the bolts  24  and  25  reduces the widths of the slits  5   a  and  5   b , so that the second cell  5  can be fixed to the shafts  22  and  23 . 
     On the other hand, loosening the bolts  24  and  25  makes the second cell  5  slidable along the shafts  22  and  23 , so that the second cell  5  can be moved to abut stopper screws  22   a  and  23   a  provided at the distal ends of the shafts  22  and  23 . 
     By sliding the second cell  5  and the detecting member  3  to the positions as shown in FIG.5, the detecting member  3  can be removed from the shafts  22  and  23  in a vertical direction to the drawing sheet for the replacement thereof. That is, as shown in FIGS. 6 and 7, the detecting member  3  has U-shaped grooves  26  and  27  for fitting with the shafts  22  and  23 , respectively. The width of the groove  27  is W 1  in both the upper block  3   a  and the lower block  3   b  to fit with the shaft  23 . The width of the groove  26  in the upper block  3   a  is W 1  to fit with the shaft  22 , but in the lower block  3   b  the width is W 2  which is smaller than W 1 . 
     Corresponding to the above, as shown in FIG. 5, the shaft  22  in a region L is thinned to have opposite plane sides so as to fit into the U-shaped groove having the width of W 2 . 
     The structural relationship between the U-shaped grooves  26  and  27  and the shafts  22  and  23  is established to prevent the detecting member  3  from being arranged upside down at the replacement thereof. 
     After the replacement of the detecting member  3  in the state shown in FIG. 5, the detecting member  3  is slid along the shafts  22  and  23  toward the first cell  4  to fit a convex portion  29  of the first cell  4  into a concave portion  28  of the detecting member  3 . Thus, the first cell  4  and the detecting member  3  are connected and an O-ring  30  gives the watertightness to the connection. Next, the second cell  5  is slid along the shafts  22  and  23  toward the detecting member  3  to fit a convex portion  32  of the second cell  5  into a concave portion  31  of the detecting member  3 . Thus, the second cell  5  and the detecting member  3  are connected and an O-ring  33  gives the watertightness to the connection. Then, if the bolts  24  and  25  are tightened to fix the second cell  5  on the shafts  22  and  23 , the apparatus turns back into a state shown in FIG.  3 . 
     In this example, the detecting member  3 , the first cell  4  and the second cell  5  (FIG. 2) are made of a material which is easy to cut and highly chemical-resistant such as PET (polyethylene terephthalate). The jet nozzle  10  and the collection pipe  17  (FIG. 2) are constituted of ceramic pipes. The disc  15  having he aperture  2  (FIG. 8) is an artificial ruby disc having a thickness of 0.4 mm and a diameter of 6 mm. A plurality of kinds of detecting members  3  are provided, in which the apertures  2  are sequentially doubled in area within a diameter range of 30 to 300 μm. The electrodes  6  and  7  are made of stainless steel and platinum, respectively. 
     Referring to FIGS. 2 and 9, a fluid circuit to perform a particle measurement using the flow cell  1  is explained hereinafter. 
     Referring to FIG. 9, first, valves V 6 , V 7  and V 19  are turned ON to supply a sheath liquid to a syringe route starting from a sheath liquid chamber  100  through the valve V 6 , a syringe  101 , the valve V 7  and the valve  19  to a waste chamber  102  in order to remove bubbles from the route. A positive pressure is applied to the sheath liquid chamber  100  and a negative pressure is applied to the waste chamber  102 . 
     Next, valves V 10  and V 13  are turned ON to supply the sheath liquid to a front sheath liquid route in order to remove bubbles from the route. After a certain period, these valves are all closed. 
     Then, valves V 12 , V 16 , V 17  and V 22  are turned ON to supply the sheath liquid to a back sheath liquid route in order to remove bubbles from the route. After a certain period, these valves are all closed. An insulating chamber  105  is provided between the valves  11 ,  12  and the flow cell  1 , and an insulating chamber  106  is provided between the valve V 16  and the valve V 17 . 
     Then, valves V 18  and V 19  are turned ON to introduce the sample from a sample chamber  103  into a route between the valves V 18  and V 19  using a pipette  104 . After the introduction, the valves V 18  and V 19  are turned OFF. 
     Then, the valves V 10 , V 11  and V 16  are turned ON to supply a front sheath liquid into the cavity portion  9  and a back sheath liquid to the cavity portion  16  (FIG.  2 ). Simultaneously, the valve V 7  is turned ON and the syringe  101  is operated so that the sample contained in the route between the valves V 18  and V 19  is discharged from the jet nozzle  10  (FIG. 2) by the pressure generated by the operation of the syringe  101 . The discharged sample is enclosed with the front sheath liquid and passes through the aperture  2 . The passed sample and the front sheath liquid are further enclosed with the back sheath liquid and discharged though the collection pipe  17  and the valve V 16  into the insulating chamber  106 . The waste liquid held in the insulating chamber  106  is discharged into the waste chamber  102  by turning the valve V 17  ON. 
     When the sample enclosed with the front sheath liquid is passed through the aperture  2 , a change in impedance between the electrodes  6  and  7  (FIG. 2) is measured by a measurement device (not shown). After the measurement is completed, the syringe  101  is stopped working. Simultaneously, the valve V 19  is turned ON to pass the sheath liquid backward in the jet nozzle  10  for a certain period to wash the jet nozzle  10 . 
     The front and back sheath liquids are kept passing for a certain period to wash the flow cell  1 . After a certain period, the valves V 10 , V 11 , V 16  and V 17  are closed to finish the washing of the flow cell  1 . After the washing of the jet nozzle  10  is finished, the valve V 19  is turned OFF and the valves V 6 , V 7  and V 18  are turned ON to wash the sample introduction route and the pipette  104 . The washing is finished after a certain period by turning the valves V 6 , V 7  and V 18  OFF. 
     According to the present invention, the detecting member having the aperture for the particle measurement is sandwiched between the first cell and the second cell that are slidably supported, so that the detecting member can easily be replaced by slidingly separating the first and second cells from the detecting member.