Patent Publication Number: US-11389792-B2

Title: Syringe for powered positive displacement pipette

Description:
TECHNICAL FIELD 
     Exemplary embodiments of the general inventive concept are directed to a handheld powered positive displacement pipette and pipette assembly, including novel syringes for said pipette, and associated mechanisms for the releasable retention, ejection, and possible automatic identification of said syringes. 
     BACKGROUND 
     As would be understood by one of skill in the art, pipettes are generally of either air displacement or positive displacement design. In contrast to an air displacement pipette in which a cushion of air separates aspirated liquid from the pipette piston, a positive displacement pipette is designed for direct contact between the pipette piston and the aspirated liquid. 
     The positive displacement pipette design eliminates potential air displacement pipette inaccuracies that may result from the effects of different liquid properties and/or environmental conditions on the air cushion of the air displacement pipette. For example, altitude changes, evaporation and other conditions to which an air displacement pipette may be subjected can affect air displacement pipette accuracy. 
     While a positive displacement pipette can provide the aforementioned advantages over an air displacement pipette, known positive displacement pipettes have their own shortcomings. One such shortcoming has traditionally been the inability of known positive displacement pipettes to provide accurate, non-contact dispensing of very small liquid volumes, including volumes below 1 μl. More specifically, when dispensing very small liquid volumes using known positive displacement pipettes there is a tendency for some amount of liquid to adhere to the inside of the pipette tip after the dispensing stroke, which then requires subsequent physical contact (“touch-off”) of the pipette tip with the liquid receiving vessel to discharge said adhering liquid from the pipette tip. 
     Additionally, direct contact between the piston of a positive displacement pipette and the liquid of interest during normal use means that the piston cannot be reused. Consequently, positive displacement pipettes typically use a “consumable” in the form of a disposable syringe that includes not only a hollow barrel (capillary) with a tip portion, but also a piston that resides and seals within the capillary and is reciprocatable within the capillary by the pipette to aspirate and dispense a desired amount of a liquid of interest while the capillary and piston are releasably attached to the pipette. After the pipetting operation is complete, the entire syringe is normally removed from the positive displacement pipette and discarded. 
     The complexity associated with the insertion, retention and ejection of a positive displacement pipette syringe is greater than that associated with a typical air displacement pipette tip, which is far more simplistic in construction and commonly held in place on the dispensing end of an air displacement pipette body by mere friction. In a positive displacement pipette, the syringe must be securely retained on the pipette body until deliberately ejected, while the piston is simultaneously properly positioned within the pipette for releasable engagement and reciprocation by an aspiration/dispensing mechanism of the pipette. 
     There is an existing need for a positive displacement pipette that can provide accurate and repeatable non-contact dispensing of various volumes of liquid, including very small liquid volumes. There is also an existing need for a positive displacement pipette having an improved mechanism by which syringes may be easily and reliably installed to, releasably retained by, and ejected from the pipette. Exemplary positive displacement pipettes according to the general inventive concept, and various features of said exemplary positive displacement pipettes, satisfy these needs. 
     SUMMARY 
     An exemplary embodiment of a handheld, powered positive displacement pipette according to the general inventive concept will generally include a substantially hollow body that is preferably shaped for ergonomic gripping by a user and acts as a housing for the various internal components of the pipette. A proximal end of the body may include a user interface portion, while a distal end of the body is configured for and serves as the connection end for a syringe. 
     An exemplary pipette will generally further include a motorized drive assembly, a dispensing solenoid assembly, a syringe retention mechanism, a syringe piston grasping mechanism, and a syringe ejection mechanism, all of which are housed within the pipette body. At least some of the aforesaid components may further reside within an internal housing that is also located within the pipette body. 
     A syringe is releasably installed to the distal end of the pipette for aspirating and dispensing fluids of interest. Syringes may be provided in a number of different volumes. Regardless of the volume, however, each syringe includes a generally hollow external capillary of circular cross section, or of some other cross-sectional shape such as but not limited to an elliptical or obround shape. The capillary includes a tip with an orifice at its distal end, and functions to contain a fluid specimen to be dispensed. At a top of each capillary resides a syringe retention element, which may be an integral part of the capillary. The shape and dimension of the syringe retention elements cooperates with the syringe retention mechanism of the pipette. 
     Each syringe also includes a piston having a first, fluid-contacting portion that is arranged within the capillary, and a piston head that is connected thereto and resides proximally of the syringe retention element when the piston is located in the capillary. The piston head is configured for releasable engagement with a piston carrier of the syringe piston grasping mechanism of the pipette. 
     The motorized drive assembly is responsible for setting various positions of the syringe attached to the pipette, for drawing the syringe piston toward the proximal direction of the pipette to aspirate fluid into the syringe, for moving the syringe piston in a distal direction to dispense fluid from the syringe, and for producing a syringe-ejecting movement. 
     The dispensing solenoid assembly includes an armature that floats within a bore in a solenoid body and is linearly displaceable relative thereto. The armature includes a shaft that extends through an opening in the solenoid body and connects the armature to the piston carrier, which forms a portion of the syringe piston retention mechanism of the pipette and is engaged with the piston head of the syringe piston. 
     The dispensing solenoid assembly and the syringe piston grasping mechanism reside substantially within a piston carriage, which is coupled to the output of a drive motor of the motorized drive assembly by a lead screw. In one exemplary embodiment, operation of the drive motor may rotate a drive nut that is engaged with the lead screw but restrained from linear displacement, thereby transferring the rotational output of the motor into a linear displacement of the lead screw and piston carriage, and of components such as the dispensing solenoid that are coupled to the piston carriage. In another exemplary embodiment, operation of the drive motor may rotate the lead screw within a drive nut that is linearly displaceable but rotationally restrained, thereby transferring the rotational output of the motor into a linear displacement of the lead screw, the piston carriage and various components coupled to the piston carriage. In other exemplary embodiments, the lead screw and or drive nut may be replaced with other components that result in a desired, controlled displacement of the piston carriage and various components coupled to the piston carriage. 
     The dispensing solenoid assembly of an exemplary pipette is configured to, depending on the selected dispensing volume and dispensing mode, produce a pulsed dispensing of a selected volume of fluid on its own or to assist the motorized drive assembly with the dispensing function by ensuring that all of each selected dispensing volume is actually dispensed from the syringe without the need to touch-off the syringe tip against a sample-receiving vessel. More specifically, energizing the solenoid body (coil) produces a rapid and forceful displacement of the solenoid armature toward the distal end of the pipette, thereby causing a like rapid movement of the piston carrier and syringe piston, and expelling a jet of fluid from the syringe tip. The general concept of pulsed fluid dispensing relative to a bench top pipette instrument may be reviewed in European Patent Application EP1344565A1. The displacement of the piston carriage followed by an actuation of the dispensing solenoid assembly can be repeated as desired to dispense multiple aliquots each representing a fraction of the entire liquid volume held by the syringe. 
     Operation of the motorized drive assembly and the dispensing solenoid assembly is governed by a controller that receives instruction signals from user inputs and/or from internal programming. The controller also receives position information signals from an encoder. 
     A selected syringe is securely but releasably retained on the pipette by the syringe retention mechanism and the syringe piston is coupled to the solenoid armature via the piston carrier of the syringe piston grasping mechanism as well as to the motorized drive system. 
     Once an aspiration and dispensing operation is complete, the syringe ejection mechanism is operative to decouple the syringe retention element of the syringe from the syringe retention mechanism and to decouple the syringe piston head from the piston carrier. The motorized drive system then drives the piston carriage toward the distal end of the pipette which, via release elements associated with the piston carriage, causes the syringe retention mechanism to release the syringe capillary and the syringe piston grasping mechanism to disengage from the syringe piston head, whereafter the syringe will be automatically ejected from the pipette. 
     Various dispensing operations using an exemplary pipette may be accomplished in an automatic mode or via a manual mode. A user is able to access and selectively initiate a desired automatic pipetting program through the user interface portion of the pipette. 
     Auto mode dispensing may encompass a number of different and selectable dispensing procedures. These dispensing procedures may result, for example: in aspiration of a full syringe volume of fluid, followed by dispensing of the entirety of the aspirated fluid volume in one dispensing operation; in aspiration of some volume of fluid into the syringe, followed by dispensing of the aspirated fluid in multiple doses of equal volume; in aspiration of some volume of fluid into the syringe, followed by dispensing of the aspirated fluid in multiple doses of variable volume; or in aspiration of some volume of fluid into the syringe, followed by dispensing of the aspirated fluid in multiple doses of equal or variable volume until some portion (e.g., 50%) of the aspirated volume has been dispensed, and then performing another aspiration operation. A dispensing operation may also be performed by a user in a manual mode rather than by the controller of the pipette operating in auto mode. 
     Performance of a titration procedure may also be possible. A titration program of an exemplary pipette may include a titrated volume counter that indicates the volume of titrant that has been dispensed, and the counter may be resettable to allow for multiple titration operations from a single aspirated volume of titrant. 
     An exemplary pipette may also include fluid viscosity detection capability, such as by, for example and without limitation, providing the pipette with appropriate circuitry or other means for monitoring an increase in current draw of the motorized drive assembly motor required to move the syringe piston relative to the syringe capillary during an aspiration or dispensing operation; through use of a provided load cell that measures the force required to move the syringe piston relative to the syringe capillary during an aspiration or dispensing operation; by way of a mechanical spring; or via another technique that would be understood by one of skill in the art. The value of the current draw may be used to categorize the viscosity of the fluid, and the pipette controller may adjust the dispensing operation parameters of the pipette based on the identified fluid viscosity category. 
     An exemplary pipette may be further provided with an automatic syringe identification system. Such a system would allow the controller of the pipette to automatically select the appropriate operating parameters for the given syringe volume, thereby simplifying the setup process and possibly eliminating operator error associated with mistakenly identifying the volume of a syringe being used. Such a system may be effectuated, for example, by associating each syringe volume with a different color, placing an area of corresponding color on the syringe, locating in the pipette a color sensor that is configured and located to image the colored areas on the syringes, and transmitting imaging data from the color sensor to the pipette controller. The signal to the pipette controller is indicative of the color of the colored area on the syringe, and the controller is programmed to analyze the signal and to resultingly identify the volume of the installed syringe. 
     An exemplary pipette according to the general inventive concept is able to accurately and repeatably dispense fluid doses of sub-microliter volume through volumes of milliliters or more. The ability to automatically dispense selected volumes of fluids of interest without the need to touch off the syringe tip means that the dispensing operation is also user independent, and therefore insulated from possible user-introduced error. These are significant improvements over the capabilities of known positive displacement pipettes. 
     Other aspects and features of the general inventive concept will become apparent to those of skill in the art upon review of the following detailed description of exemplary embodiments along with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following descriptions of the drawings and exemplary embodiments, like reference numerals across the several views refer to identical or equivalent features, and: 
         FIG. 1  is a perspective view of an exemplary embodiment of a motor-driven positive displacement pipette according to the general inventive concept, and includes a syringe shown prior to insertion into the pipette; 
         FIG. 2  shows an assembly of the exemplary pipette of  FIG. 1  with the syringe installed into and retained by the pipette; 
         FIG. 3  is enlarged view of a user end of the exemplary pipette of  FIGS. 1-2 ; 
         FIG. 4  represents an exemplary user interface provided on the user end of an exemplary pipette according to the general inventive concept; 
         FIG. 5A  is cross-sectional side view of the exemplary pipette assembly of  FIG. 2 , with various internal components of the pipette and a piston of the syringe shown in an aspirating position; 
         FIG. 5B  is an enlarged transparent view of a portion of the pipette of  FIG. 5A ; 
         FIGS. 6A-6B  are a perspective view and a cross-sectional side view, respectively, of an exemplary 0.1 ml syringe for use with an exemplary inventive pipette; 
         FIGS. 7A-7B  are a perspective view and a cross-sectional side view, respectively, of an exemplary 1.0 ml syringe for use with an exemplary inventive pipette; 
         FIGS. 8A-8B  are a perspective view and a cross-sectional side view, respectively, of an exemplary 10 ml syringe for use with an exemplary inventive pipette; 
         FIGS. 9A-9B  are a perspective view and a cross-sectional side view, respectively, of an exemplary 25 ml syringe for use with an exemplary inventive pipette; 
         FIGS. 10A-10B  are a perspective view and a cross-sectional side view, respectively, of an exemplary 50 ml syringe for use with an exemplary inventive pipette; 
         FIG. 11  is a cross-sectional side view of the exemplary pipette of  FIG. 1A , with a housing portion of the pipette removed to better reveal various internal components of the pipette; 
         FIG. 12  is an enlarged, cross-sectional perspective view of various internal drive components of the exemplary pipette of  FIG. 11 ; 
         FIG. 13  is an enlarged, cross-sectional view of a distal portion of an exemplary motor-driven positive displacement pipette, showing various internal components that form an exemplary syringe retention mechanism; 
         FIG. 14A  is a perspective view and  FIGS. 14B-14C  are elevation views of a piston carrier element of an exemplary syringe piston grasping mechanism; 
         FIG. 15A  is a deconstructed view showing the piston head of an exemplary syringe inserted into the piston carrier element of  FIGS. 14A-14C , with certain piston release elements of an exemplary syringe ejection mechanism also present; 
         FIG. 15B  is a slightly less deconstructed view of  FIG. 15A , with additional elements of an exemplary syringe ejection mechanism also present; 
         FIG. 16  indicates how an exemplary syringe is inserted into an exemplary motor-driven positive displacement pipette; 
         FIG. 17A  is an enlarged view showing the syringe and pipette of  FIG. 16  with the syringe partially inserted into the pipette such that the piston head of the syringe is only partly engaged by the piston head grasping mechanism of the pipette; 
         FIG. 17B  is an enlarged view showing the syringe and pipette of  FIG. 17A  with the syringe inserted farther into the pipette but not yet fully engaged by the syringe retention mechanism thereof; 
         FIG. 18  shows the syringe and pipette of  FIG. 17  with the syringe fully inserted into the pipette, such that the syringe is engaged by the syringe retention mechanism of the pipette and a piston head of the syringe is engaged by the syringe piston grasping mechanism of the pipette; 
         FIG. 19  is an enlarged, cross-sectional view of a portion of  FIG. 18  showing the interaction of various components of the syringe retention mechanism and the syringe piston grasping mechanism with elements of the syringe; 
         FIGS. 20A-20D  illustrate various components of an exemplary syringe ejection mechanism of an exemplary motor-driven positive displacement pipette; 
         FIG. 21A  illustrates the position of the various syringe ejection mechanism components of  FIGS. 20A-20D  along with other associated components of the pipette shortly after initiation of a syringe ejection operation; 
         FIGS. 21B-21E  further illustrate the position of the various syringe ejection mechanism components of  FIGS. 20A-20D  as a syringe ejection operation progresses; 
         FIG. 21F  represents the retractive movement of a piston carrier portion of the pipette during a last phase of an exemplary syringe ejection operation; 
         FIG. 22  is an enlarged cross-sectional side view of a portion of an exemplary motor-driven positive displacement pipette showing the various internal components thereof when the pipette is in a home position; 
         FIGS. 23A-23B  are cross-sectional side views of an exemplary motor-driven positive displacement pipette with attached syringe according to the general inventive concept, and illustrate the change in position of various internal components of the pipette and the syringe piston when the pipette is moved from the home position to a ready to fully aspirated position, such as might result from a fluid aspiration operation; 
         FIG. 24  depicts the change in position of various internal components of the exemplary pipette and syringe assembly from the fully aspirated position shown in  FIG. 23B  during one exemplary type of fluid dispensing operation; and 
         FIG. 25  is a bottom perspective view of an exemplary motor-driven positive displacement pipette where a color sensor is visible along with various other components. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
       FIG. 1  depicts one exemplary embodiment of a handheld, motor-driven positive displacement pipette  5  (hereinafter “pipette” for brevity) according to the general inventive concept. Also shown in  FIG. 1  is a consumable in the form of an exemplary disposable syringe  600  (see  FIGS. 8A-8B ) that is installed to the pipette in order to perform a pipetting operation. Various exemplary syringes for use with exemplary inventive pipettes are shown in  FIGS. 6A-10B  and described in more detail below.  FIG. 2  shows an assembly of the pipette  5  and syringe  600  of  FIG. 1 . 
     The exemplary pipette  5  of  FIGS. 1-2  includes a body  10  for gripping by a user. The body  10  is generally a substantially hollow structure that also serves as an external housing for various internal components of the pipette  5 . The body  10  may be of different shape and/or size in other embodiments, although the shape and size will typically be dictated to at least some extent by the ergonomics of use. 
     The body  10  further includes a proximal (user) end  10   a  and distal end  10   b  that serves as the connection end for the syringe  600 . In this example, the proximal end  10   a  of the body  10  includes a user interface portion  15 . Referring also to  FIGS. 3-4 , it may be observed that the user interface portion  15  of this exemplary pipette  5  further includes a display  20  and various actuators such as input/selection buttons  25   a ,  25   b , and a joystick  27  that allow a user to observe and select pipette functions, observe and change pipette settings and engage in various other interactions with a programmable controller of the pipette, as would be understood by one of skill in the art. In this exemplary embodiment of the pipette  5 , a trigger switch  30  is also provided for initiating pipette operation, and an eject button  32  is provided for initiating a syringe ejection operation. 
       FIG. 5A  is a cross-sectional side view of the exemplary pipette  5  and syringe  600  assembly of  FIG. 2 , which reveals the various internal components of the pipette that are concealed by the body  10 . As may be observed, the exemplary pipette  5  includes, among other components, a motorized drive assembly  40 , a dispensing solenoid assembly  250 , a syringe retention mechanism  150  and syringe piston grasping mechanism  200 , all of which are described in more detail below. The assembly of  FIG. 5A  also includes the syringe  600 , which is releasably retained by the syringe retention mechanism  150  of the pipette  5  and is shown in a post-aspiration and pre-dispensing position. An enlarged and transparent view of a portion of the proximal end  10   a  of the pipette body  10  is shown in  FIG. 5B , and reveals additional pipette components such as a printed circuit board and various electronic components, including motor control circuitry comprising a controller  90 . 
     A variety of exemplary syringes that are usable with an exemplary pipette according to the general inventive concept are represented in the perspective and cross-sectional elevation views of  FIGS. 6A-10B . The exemplary syringes  500 - 600  are arranged in order of increasing of volume, with  FIGS. 6A-6B  representing an exemplary syringe  500  having a volume of 0.1 ml,  FIGS. 7A-7B  representing an exemplary syringe  550  having a volume of 1.0 ml,  FIGS. 8A-8B  representing an exemplary syringe  600  having a volume of 10 ml,  FIGS. 9A-9B  representing an exemplary syringe  650  having a volume of 25 ml, and  FIGS. 10A-10B  representing an exemplary syringe  700  having a volume of 50 ml. Thus, while the exemplary syringe  600  of  FIGS. 8A-8B  has been arbitrarily selected as the syringe component of an exemplary pipette and syringe assembly for purposes of illustration, it should be understood that an exemplary inventive pipette is usable with a number of different syringes to accurately and repeatably dispense samples across a wide volume range. 
     Each of the exemplary syringes  500 ,  550 ,  600  shown in  FIGS. 6A-8B  includes an external barrel, referred to herein as a capillary  505 ,  555 ,  605 , which is of generally hollow and tubular construction and functions to contain the fluid specimen to be dispensed. A distal end of each capillary  505 ,  550 ,  605  includes a tip  510 ,  560 ,  610  having an orifice  515 ,  565 ,  615  through which fluid previously aspirated into the capillary may be dispensed. A top of each capillary  505 ,  555 ,  605  forms a syringe retention element  520 ,  570 ,  620  of like shape and dimension. The shape and dimension of the syringe retention elements  520 ,  570 ,  620  allows for engagement thereof by the syringe retention mechanism  150  located in the pipette  5 . For example, in particular syringe embodiments shown, each syringe retention element  520 ,  570 ,  620  extends laterally outward beyond the perimeter of its associated capillary  505 ,  555 ,  605  to form a rim that includes a circumferential edge  535 ,  585 ,  635  and a lower face  540 ,  590 ,  640  that may be engaged by elements of the syringe retention mechanism  150 . 
     Each syringe  500 ,  550 ,  600  also includes a piston  525 ,  575 ,  625  (sometimes also referred to as a plunger) having a first, fluid-contacting portion that is concentrically arranged within the capillary  505 ,  555 ,  605  for aspirating and dispensing fluid, a head  530 ,  580 ,  630  portion that resides proximally of the syringe retention element  520 ,  570 ,  620 , and a connecting portion that passes through an aperture in the syringe retention element to connect the piston head with the fluid-contacting portion. The piston heads  530 ,  580 ,  630  of the exemplary syringes  500 ,  550 ,  600  shown herein are substantially bell-shaped, and include opposing arms  530   a - 530   b ,  580   a - 580   b ,  630   a - 630   b  that permit at least some degree of elastic deformation thereof. Other piston head shapes and other numbers of arms may be possible in other embodiments. 
     When a syringe  500 ,  550 ,  600  is properly installed to the pipette  5 , the syringe is retained in a stationary position by engagement of the syringe retention element  520 ,  570 ,  620  of the syringe and the syringe retention mechanism  150  of the pipette, and a head  530 ,  580 ,  630  portion of the piston  525 ,  575 ,  625  is engaged by the piston grasping mechanism  200  of the pipette, such that the fluid-contacting portion of the piston is reciprocatable within the capillary  505 ,  555 ,  605  by the pipette. The syringes  500 ,  550 ,  600  are ejectable from the pipette  5  after use, as described in more detail below. 
     The exemplary syringes  650 ,  700  shown respectively in  FIGS. 9A-9B and 10A-10B  are designed for use in the pipetting of larger fluid volumes. In these exemplary syringe embodiments, a capillary  655 ,  705  having a tip  660 ,  710  with an orifice  665 ,  715  is again included, and a piston  670 ,  720  is again arranged to reciprocate within the capillary. However, unlike the exemplary syringe embodiments  500 ,  550 ,  600  depicted in  FIGS. 6A-8B , the capillaries  655 ,  705  of the syringes  650 ,  700  have open tops (proximal ends) and do not include a syringe retention element. Instead, each syringe  650 ,  700  includes a reusable adaptor  675 ,  725  for connecting the syringe to the pipette  5 . 
     Each adaptor  675 ,  725  has an open distal end that is dimensioned to receive the proximal end of the syringe  650 ,  700 . Retention elements at the proximal end of the capillary  655 ,  705  and in the distal end of the adaptor  675 ,  725  cooperate to secure the capillary to the adaptor. The proximal end of the adaptor  675 ,  725  forms a syringe retention element  680 ,  730  that is shaped and dimensioned to engage with the syringe retention mechanism in the pipette  5 . For example, in particular syringe embodiments shown, each syringe retention element  680 ,  730  extends laterally outward beyond the perimeter of its associated capillary  655 ,  705  to form a rim that includes a circumferential edge  690 ,  740  and a lower face  695 ,  745  that may be engaged by elements of the syringe retention mechanism  150 . 
     Each syringe  650 ,  700  includes a piston  620 ,  720  having a first, fluid-contacting portion that is concentrically arranged within the capillary  655 ,  705  for aspirating and dispensing fluid, a head  685 ,  735  portion that resides proximally of the syringe retention element  680 ,  730  of the adaptor  675 ,  725 , and a connecting portion that passes through an aperture in the syringe retention element to connect the piston head with the fluid-contacting portion. The piston heads  685 ,  735  of the exemplary syringes  650 ,  700  shown herein are again substantially bell-shaped, and include opposing arms  685   a - 685   b ,  735   a - 735   b  that permit at least some degree of elastic deformation thereof. Other piston head shapes and other numbers of arms may be possible in other embodiments. 
     When a large volume syringe  650 ,  700  is properly installed to the pipette  5 , the syringe is retained in a stationary position by engagement of the syringe retention element  680 ,  730  of the adaptor  675 ,  725  and the syringe retention mechanism  150  of the pipette, and the piston head  685 ,  735  is engaged by the piston grasping mechanism  200  of the pipette, such that the fluid-contacting portion of the piston is reciprocatable within the capillary  655 ,  705  by the pipette. The syringes  650 ,  700  are ejectable from the pipette  5  after use, as described in more detail below. 
     It is to be understood that the syringes of  FIG. 6A  through  FIG. 10B  have been provided for purposes of illustration only, and variations are certainly possible. For example, and without limitation, the piston head and the piston of a given syringe may be separate, engageable elements, rather than integral parts of a single element as shown ad described herein. 
     Likewise, although only the exemplary larger volume syringes  650 ,  700  of  FIGS. 9A-10B  are shown and described as employing an adapter with an open-top capillary, it is equally possible that the smaller volume syringes  500 ,  550 ,  600  of  FIGS. 6A-8B  may be of a like design and also include an adapter. When a given syringe includes an adapter, the adapter may be a reusable component rather than a consumable component as will be the remainder of the syringe in most syringe embodiments. 
     A cross-sectional side view of the exemplary pipette  5  of  FIG. 1  is illustrated in  FIG. 11 , with the body  10  thereof removed to better reveal the various internal components of the pipette. As briefly described above, the pipette  5  can be seen to include a motorized drive assembly  40  at a proximal end, a syringe retention mechanism  150  at a distal end, and a dispensing solenoid assembly  250  and a syringe piston grasping mechanism  200  interposed therebetween. The pipette  5  also includes an internal housing  35  that contains each of the dispensing solenoid assembly  250 , the syringe piston grasping mechanism  200  and the syringe retention mechanism  150 . The motorized drive assembly  40  is attached to a proximal end of the internal housing  35 . 
     The motorized drive assembly  40  is responsible for setting various positions of the syringe  600  attached to the pipette  5 , for moving the syringe piston in a distal-to-proximal direction to aspirate fluid into the syringe, for moving the syringe piston in a proximal-to-distal direction to dispense fluid from the syringe, and for producing the movement necessary to eject the syringe. Referring also to  FIG. 12 , it may be observed that in this exemplary pipette  5 , the motorized drive assembly  40  includes a drive motor  45  having its output shaft coupled to a rotatable drive nut  50  by a drive belt  55 , whereby rotation of the drive nut by the drive motor causes a linear displacement of a lead screw  95  that passes through the drive nut and is in threaded engagement herewith. Other drive schemes may be utilized in other embodiments, such as for example, a direct drive scheme where the output of the drive motor is connected to the lead screw  95  directly by a coupling, or possibly through a speed reduction gear assembly. 
     In this exemplary motorized drive assembly  40 , the drive belt  55  may connect an output pinion  60  affixed to the output shaft of the motor  45  to an input pinion  65  that is coupled to or integral to the drive nut  50 . The drive nut  50  may be provided with bearings  70  to facilitate rotation of the drive nut, and the drive nut may also be preloaded with a spring  75  (e.g., wave spring) that will bias the drive nut toward the proximal end of the pipette  5  to help account for any manufacturing (e.g., stack-up) tolerance variations within the motorized drive assembly  40  and to minimize backlash that may otherwise contribute to inaccuracies during a dispensing operation. A mounting block  80  or a similar structure/component may be provided to facilitate mounting of the various components of the motorized drive assembly  40 . 
     The dispensing solenoid assembly  250  is configured to, depending on the selected dispensing volume, dispense the selected volume of fluid on its own or to assist the motorized drive assembly  40  with the dispensing function by ensuring that all of a selected dispensing volume is actually dispensed from the syringe  600  without the need to touch the syringe tip  610  to the sample-receiving vessel (as explained below). The dispensing solenoid assembly  250  includes a solenoid body (coil)  255  that resides within and is coupled to the piston carriage  100 , such that the solenoid body moves axially with the piston carriage. The solenoid body  255  includes an axial bore  270  that extends some distance into the solenoid body from the axial end thereof. An armature  260  is concentrically located within the bore  270  and is linearly reciprocatable within the bore and relative to the pipette  5  by a magnetic field that is generated within the bore, as would be understood by one of skill in the art. As the armature  260  floats within the bore  270  as opposed to being coupled to the piston carriage  100  like the solenoid body  255 , the armature is not constrained (for some distance) to move linearly with the piston carriage. A bottom wall of the bore  270  acts as an armature hard stop  275  during proximal-to-distal movement of the armature  260 . In the exemplary dispensing solenoid assembly  250  shown, the armature  260  includes a shaft  265  that extends through an opening in a bottom wall of the bore  270  toward the distal end of the pipette  5 . 
     Operation of the motorized drive assembly  40  and the dispensing solenoid assembly  250  is governed by the controller  90  (see  FIG. 5B ). The controller  90  receives instruction signals from user inputs such as the actuators,  25 ,  30  and/or from internal programming. The controller  90  also receives position information signals from an encoder  85  that is coupled to the drive nut  50 . 
     Rotational motion of the drive nut  50  is converted to linear (axial) motion by the lead screw  95  that passes through the drive nut and is in threaded engagement therewith. Whereas the drive nut  50  is freely rotatable, the lead screw  95  is rotationally constrained but linearly displaceable. Thus, rotation of the drive nut  50  by the drive motor  45  will cause the lead screw  95  to move in a proximal or distal direction along the longitudinal axis of the pipette  5 . 
     The distal end  95   b  of the lead screw  95  is attached to a proximal end of a piston carriage  100  in a manner that prevents rotation of the lead screw  95 . The piston carriage  100  is located in a carriage holder  105  that is mounted within the internal housing  35  so as to be restrained from movement relative thereto. The piston carriage  100  is axially displaceable and reciprocatable within the carriage holder  105 , and relative to the longitudinal axis of the pipette  5 , but is rotationally restrained. 
     The dispensing solenoid assembly  250  and the syringe piston grasping mechanism  200  (both described in detail below) reside substantially within the piston carriage  100 . Therefore, both the dispensing solenoid assembly  250  and the syringe piston grasping mechanism  200  move with the piston carriage  100  during linear displacement of the piston carriage within the pipette  5 . 
     For proper pipetting, the syringe  600  must be securely retained on the pipette  5  and the motorized drive system  40  of the pipette  5  must be coupled to the syringe piston  625  to reciprocate the syringe piston within the syringe capillary  605 . These syringe retention and piston coupling functions are respectively performed by the exemplary syringe retention mechanism  150  and syringe piston grasping mechanism  200  of the pipette  5 . 
     A better understanding of the exemplary syringe retention mechanism  150  of the pipette  5  may be obtained by additional reference to  FIG. 13 , which provides an enlarged cross-sectional view of the distal end of the exemplary pipette  5 . The exemplary syringe retention mechanism  150  is shown to include a plurality of spaced apart syringe latching elements  155  that are affixed within the distal end of the pipette  5 , such as by a pinned connection  185  to the body  10  (see, e.g.,  FIG. 20C ), so as to be pivotable within some rotational range of motion but restrained against axial movement. In this exemplary pipette  5 , there are three syringe latching elements  155  (only two visible in  FIG. 11 ), but a different number of latching elements may be utilized in other embodiments. 
     The syringe latching elements  155  of the syringe retention mechanism  150  are shown in a closed position in  FIG. 11 , and are maintained in a normally closed position by an elastic O-ring  160  or similar elastic element that encircles the three syringe latching elements  155  and resides within a slot  165  provided in each latching element. The syringe latching elements  155  are coupled to the piston carrier  205  using a mounting pin  185  (see  FIG. 20D ), which allows the syringe latching mechanisms to pivot during a syringe insertion procedure as will be more fully explained below. 
     Each syringe latching element  155  of the syringe retention mechanism  150  also includes a latching hook  170  at its distal end. The latching hooks  170  of the syringe latching elements  155  are designed to engage the syringe retention element on the syringe capillary when the syringe is inserted into the distal end of the pipette  5 . For example, with respect to the arrangement of the pipette  5  and the syringe  600  shown in  FIG. 5 , the latching hooks  170  of the syringe latching elements  155  are designed to engage the syringe retention element  620  (e.g., along the lower face  640 ) on the syringe capillary  605 . 
     While the syringe retention mechanism  150  secures the capillary of the syringe  600  to the pipette  5  and maintains the capillary in a stationary position relative thereto, the syringe piston grasping mechanism  200  engages and releasably retains the head  630  of the syringe piston  625 . To this end, the syringe piston grasping mechanism  200  includes a piston carrier  205  that is located substantially within the piston carriage  100 . As may be observed in more detail in  FIGS. 14A-14C , at least the internal shape of the piston carrier  205  may substantially conform to the external shape of the syringe piston head  630 . The exemplary piston carrier  205  further includes a distally located actuation collar  285  having a piston head retention lip  210 , and a plurality of radially spaced apart apertures  215  that permit access through the wall of the piston carrier to the arms  630   a ,  630   b  of the piston head  630  by piston head release elements  305  of an exemplary syringe ejection mechanism, as further described below. 
     A plurality of spaced apart piston head release element guides  220  extend transversely outward from the actuation collar  285  of the piston carrier  205 . As may be observed (see also  FIGS. 17A-17B and 21A-21E ), the inwardly-directed face  220   a  of each piston head release element guide  220  has a ramped (cammed) shape that directs movement of a distal portion of a corresponding one of the piston head release elements  305  during a syringe ejection operation. The outwardly-directed surface  220   b  of each piston head release element guide  220  may facilitate axial movement of the piston carrier  205  within the internal housing  35  and/or may function to rotationally restrain the piston carrier. 
     A proximal end  205   a  of the piston carrier  205  is configured to facilitate coupling of the piston carrier to a distal end of the armature shaft  265  of the dispensing solenoid assembly  250 . Thus, in an assembled pipette  5 , the piston carrier  205  is reciprocatable along with the piston carriage  100  by the motorized drive assembly  40 , and is further independently reciprocatable within the piston carriage by the dispensing solenoid assembly  250 . 
     A better understanding of the operation of the piston carrier  205  may be obtained by reference to the deconstructed views of  FIGS. 15A-15B .  FIG. 15A  shows the exemplary syringe  600  with the piston head  630  thereof inserted into the piston carrier  205  of  FIGS. 13 and 14A-14C , with the piston head release elements  305  of the exemplary syringe ejection mechanism pivotably located in the apertures  215  in the piston carrier. The piston head  630  preferably fits snugly within the interior of the piston carrier and, as may be observed, distal ends of the piston head arms  630   a ,  630   b  are engaged with the piston head retention lip  210  in the piston carrier  205 , thereby preventing withdrawal of the piston head  630  from the piston carrier. Consequently, the piston head  630  is securely grasped by the piston carrier  205  and it is ensured that the piston  625  of the syringe  600  will move axially along with any axial movement of the piston carrier. 
     Referring now to  FIGS. 16-17B , the process of inserting the exemplary syringe  600  to the exemplary pipette  5  may be observed.  FIG. 16  shows the syringe  600  located below the distal end of the pipette  5  and in substantial axial alignment therewith. The arrow indicates the direction of engaging movement of the syringe  600  toward the pipette  5 . 
     In  FIG. 17A , the syringe  600  has been partially inserted into the pipette  5 . During insertion of the syringe  600 , the piston head  630  of the syringe piston  625  begins engagement with the piston carrier  205  of the syringe piston grasping mechanism  200 . It may be observed in  FIG. 17A  that, during the syringe insertion process, the piston head arms  630   a ,  630   b  of the piston head  630  are inwardly compressed (i.e., undergo an inwardly-directed elastic deformation) via contact with a wall formed by the distal opening  290  in the actuation collar  285  of the piston carrier  205 . The inward compression of the piston head arms  630   a ,  630   b  allows the syringe piston head  630  to pass through the distal opening in the actuation collar  285 . 
       FIG. 17B  depicts partial engagement of the syringe  600  and the pipette  5  resulting from continued insertion of the proximal end of the syringe  600  into the distal end of the pipette  5  beyond the point shown in  FIG. 17A . Such continued insertion of the syringe  600  results in an outward pivotal movement of the distal ends of the syringe latching elements  155  under the insertion force applied to the syringe  600 . More specifically, as the syringe  600  is inserted into the pipette  5 , a resulting outwardly-directed force is exerted on the distal ends of the syringe latching elements  155  by the syringe retention element  620 , which force is sufficient to overcome the inwardly-directed force exerted on the syringe latching elements by the O-ring  160 . 
     As insertion of the syringe  600  into the pipette  5  continues, a proximal (upper) face of the syringe retention element  620  of the syringe capillary  605  comes into abutting contact with one or more springs  300  that are retained within the pipette  5 . As may be observed in  FIG. 17B , at the point of contact between the proximal (upper) face of the syringe retention element  620  and the spring(s)  300 , the syringe retention element  620  has preferably moved past the latching hooks  170  of the syringe latching elements  155  (although a slight compression of the spring(s) may alternatively be required to reach said point), which permits the syringe latching elements  155  to be returned to their normally-closed positions by the contractive force of the O-ring  160 . Upon return of the syringe latching elements  155  to their normally closed positions (see also  FIGS. 18-19 ), a flat  175  on each syringe latching element hook  170  overlies and engages the lower face  640  of the syringe retention element  620  while an inward-facing surface  180  of each syringe latching element  155  is preferably pressed against the circumferential edge  635  of the syringe retention element by the contractive spring force of the O-ring  160 . The syringe capillary  605  is thereby trapped against and releasably locked to the pipette  5 , meaning that the syringe capillary is also securely retained in a stationary position relative to the pipette. 
     Subsequent to the releasable locking of the syringe  600  to the pipette  5 , as shown in  FIG. 17B  and described above, the continued application of an insertion force on the syringe results in a slight but additional proximally-directed movement of the syringe into the pipette. This additional movement of the syringe  600  results from compression of the spring(s)  300  in the pipette by the insertion force being exerted on the syringe. 
     As illustrated in  FIG. 18 , the additional proximal movement of the syringe  600  into the pipette  5  allows the piston head  630  of the syringe to become fully inserted into the piston carrier, whereafter the piston head arms  630   a ,  630   b  will elastically return toward their normal static positions and become engaged with the piston head retention lip  210  located in the actuation collar  285  of the piston carrier, as shown in  FIG. 18 . The engagement of the piston head arms  630 ,  630   b  with the actuation collar  285  retains the piston head  630  in the piston carrier  205 . It may also be observed in  FIG. 18  that the piston head  630  fits snugly within the interior of the piston carrier  205  in this exemplary embodiment of the pipette  205 . 
     In  FIGS. 18-19 , the syringe  600  is fully installed to the pipette  5 . In the fully installed position, the syringe  600  is releasably locked to the pipette  5  as described above, and the piston head of the syringe is fully engaged by the syringe piston grasping mechanism  200  of the pipette. The syringe  600  is usable to aspirate and dispense fluids once placed in the fully installed position shown. 
     In addition to providing for additional insertion of the syringe  600  into the pipette  5  after the syringe retention element  620  of the syringe capillary  605  has reached an engaged position with the syringe retention mechanism  150  of the pipette, the spring(s)  300  also provides for increased retention security and stationary engagement of the syringe  600  to the pipette  5 . More specifically, with the syringe  600  installed to the pipette  5 , the spring(s)  300  exerts a distally-directed force against the upper face of the syringe retention element  620 , which presses the lower face  640  of the syringe retention element tightly against the flats  175  of the hooks  170  of the syringe latching elements  155 . The distally-directed force exerted by the spring(s)  300  also urges the piston head  630  toward the distal end of the pipette  5 , which presses the distal ends of the piston head arms  630   a ,  630   b  tightly against the piston head retention lip  210  in the actuation collar  285  portion of the piston carrier  205 . Therefore, any possible unintended movement of the syringe retention element  620  relative to the syringe latching elements  155  of the syringe retention mechanism  150  and/or movement of the piston head  630  relative to the piston carrier  205  is discouraged by the axially-directed force exerted by the spring(s)  300 , thereby further securing the syringe  600  to the pipette  5 . The spring(s)  300  may be, for example and without limitation, a sheet metal spring(s). The use of other types of springs may also be possible. 
     Because a positive displacement pipette syringe is disposable—i.e., intended to be discarded subsequent to completion of an associated pipetting operation—the exemplary syringe  600  must be ejectable from the pipette  5 . As may be best understood from a review of the deconstructed perspective views of  FIGS. 20A-20D  and the cross-sectional views of  FIGS. 21A-21F  (see also  FIGS. 13, 15A-15B, and 17A-19 ) the pipette  5  is provided with an exemplary syringe ejection mechanism for this purpose. Generally speaking, the syringe ejection mechanism is operative to decouple the syringe retention element  620  of the syringe  600  from the syringe retention mechanism  150  and to decouple the syringe piston head  630  from the piston carrier  205 , whereafter the syringe will be automatically ejected from the pipette  5 . As is explained in more detail below, the syringe ejection mechanism of the exemplary pipette  5  is comprised generally of the motorized drive assembly  40  and the lead screw  95 , the piston carriage  100  and the wedge-shaped syringe latching element release portions  335  thereof, the syringe latching elements  155 , the piston head release element guides  220  on the actuation collar portion  285  of the piston carrier  205 , and a plurality of piston head release elements  305 . 
       FIG. 20A  essentially provides the same view of the piston head  630  of the exemplary syringe  600  inserted into the piston carrier  205  that is shown in  FIG. 15A , except that in  FIG. 20A  the piston carrier  205  has been removed for further clarity. It may be observed in  FIG. 20A  that the piston head release elements  305  (which are shown to be aligned with the apertures  215  in the piston carrier  205  in  FIG. 15A ) of the syringe ejection mechanism are arranged to at least partially overlie the opposing arms  630   a ,  630   b  of the syringe piston head  630  when the piston head is inserted into the piston carrier  205 . Each of the exemplary piston head release elements  305  may include a roller  310  at its distal end. The rollers  310  function to reduce friction between the piston head release elements  305  and the inwardly-directed ramped face  220   a  of each piston head release element guide  220  of the piston carrier  205 , as well as between the piston head release elements and the arms  630   a ,  630   b  of the syringe piston head  630 . However, it may be possible to eliminate the rollers  310  in other syringe ejection mechanism embodiments such as through the use of low friction materials, etc. 
     The piston head release elements  305  are pivotably secured within the piston carriage  100  by pins  315 , such that an inwardly-directed movement of a proximal end of the piston head release elements will result in an outwardly-directed movement of a distal end of the piston head release elements. While not shown in  FIGS. 20A-20D  for purposes of clarity, the piston head release elements  305  are maintained in a normally open position (see, e.g.,  FIGS. 13, 16-19, 21A-21B, 22, and 24 ) by an O-ring  320  or another similar elastic element that encircles the piston head release elements  305  and resides within a slot  325  provided in each piston head release element. The O-ring  320  applies an inwardly-directed force against a proximal end of each piston head release element  305  so that the normally open position of the piston head release elements is a position where the distal ends of the piston head release elements are urged away from the piston carrier  205 . 
     An exemplary syringe ejection operation is illustrated in  FIGS. 21A-21F . During a syringe ejection operation, the piston carrier  205  is placed against a hard stop  225  and the motorized drive assembly  40  is commanded to cause a distally-directed movement of the piston carriage  100  of some predefined distance. In this exemplary embodiment of the pipette  5 , the piston carriage is moved approximately 3.25 mm in the distal direction during a syringe ejection operation, but this distance may be different in other embodiments. 
     Because the piston carrier  205  is constrained against further distally-directed axial movement when against the hard stop  225 , the aforementioned distally-directed axial displacement of the piston carriage  100  will cause a distally-directed axial displacement of the syringe latching element release portions  335  thereof relative to the piston carrier, as well as the piston head release elements  305  that are pivotably coupled to the piston carriage  100 . 
     Referring to  FIG. 21A , it may be observed that as the piston carriage  100  moves distally, the syringe latching element release portions  335  of the piston carriage, which are arranged to be aligned with the syringe latching elements  155  and are positioned to move in a space between the syringe latching elements and the piston carrier  205 , begin to contact the proximal ends of the syringe latching elements. Likewise, distal movement of the piston carriage  100  produces contact between the rollers  310  of the piston head release elements  305  and the inwardly-directed ramped face  220   a  of each piston head release element guide  220  associated with the actuation collar  285  of the piston carrier  205 . 
       FIG. 21B  illustrates that a continued distal movement of the piston carriage  100  eventually results in sufficient contact between the wedge-shaped syringe latching element release portions  335  thereof and the proximal ends of the syringe latching elements  155 , to cause the distal ends of the syringe latching elements to pivot outward about the mounting pins  185  and against the countering contractive force of the O-ring  160  and the axially-directed force of the spring(s)  300 . As indicated, this pivoting movement of the syringe latching elements  155  causes the latching hooks  170  thereof to disengage from the syringe retention element  620  of the syringe  600  (as also shown in  FIG. 20D ), thereby releasing the syringe retention element and the syringe capillary  605  from retentive engagement with the pipette  5 . 
     Referring now to  FIGS. 21C-21E , it may be further observed that additional distal movement of the piston carriage  100  causes the rollers  310  of the piston head release elements  305  to follow the ramped face  220   a  of the correspondingly aligned piston head release element guides  220  of the piston carrier actuation collar  285 . As a result, the distal ends of the piston head release elements  305  are pivoted inward toward the piston carrier  205 . As shown in  FIGS. 21D-21E , this inward movement of the distal ends of the piston head release elements  305  causes the rollers  310  attached thereto to enter the piston carrier  205  through the apertures  215  therein and to contact and begin to inwardly compress (deform) the opposing arms  630   a ,  630   b  of the syringe piston head  630 . 
     As depicted in  FIG. 21E , the amount of inward deformation of the syringe piston head arms  630   a ,  630   b  produced by the piston head release elements  305  is eventually sufficient to disengage the arms from the piston head retention lip  210  in the actuation collar  285  of the piston carrier  205 . This disengagement of the syringe piston head arms  630   a ,  630   b  releases the piston head  630  from the piston carrier  205  and allows the syringe piston head  630  to be thereafter withdrawn in a proximal-to-distal direction through the distal opening  290  in the piston carrier. 
     As the piston head arms  630   a ,  630   b  are being inwardly compressed by the distal ends of the piston head release elements  305  during downward movement of the piston carrier  100 , a proximally-located ejection tab  340  of each piston head release element simultaneously exerts a distally-directed (ejecting force) on the top of the piston head  630 . This distally-directed force results in a like displacement of the piston head  630  and the capillary  605 , and also causes the free ends of the piston head arms  630   a ,  630   b  to enter the distal opening  290  in the piston carrier  205 . 
     With the syringe elements positioned as described above, the entire syringe  600  may be ejected from the pipette  5 . In this exemplary embodiment, actual ejection of the syringe  600  occurs by first retracting the piston carriage  100  (see  FIG. 21F ) back to its home position, which retractive movement permits the piston head arms  630   a ,  630   b  to clear the rollers  310  of the piston head release elements  305  during ejection. Physical ejection may thereafter occur automatically as a result of gravity in combination with the axially-directed force exerted on the syringe retention element  620  by the spring(s)  300 , and/or the syringe  600  may be removed from the pipette  5  by a user. The ejection movement as well as the return movement of the piston carriage  100  may occur automatically according to ejection operation program commands from the pipette controller  90 . 
     Various states and operations of the exemplary pipette  5  will now be described with respect to  FIGS. 22-24 .  FIG. 22  represents a home position of the exemplary pipette  5 . In the home position, the distal end of the piston carrier  205  essentially resides against the hard stop  225 , with the understanding that residing “against” the hard stop allows for a minimal assembly clearance to exist between the hard stop and the piston carrier. Likewise, in the home position of the pipette  5 , the armature  260  of the dispensing solenoid assembly  250  is at its distal hard stop against the bottom wall of the core  270  and the coil  260  of the dispensing solenoid assembly is not energized. In the home position of the pipette  5 , the piston carriage  100  is distally positioned such that a slight gap  400  exists between the piston carrier  205  and the rollers  310  of the piston head release elements  305 , such that there is no unintended interference between the rollers and the piston head  630  when the syringe is inserted into the pipette  5 . A home position sensor  405  may be provided to indicate to the controller  90  that the piston carriage is in the home position. 
     An aspirating function of an exemplary pipette is represented in  FIGS. 23A-23B  through use of the exemplary pipette  5  and syringe  600  assembly of  FIG. 2 .  FIG. 23A  shows the exemplary pipette  5  in the home position, as described immediately above. It may be further observed that when the pipette  5  is in the home position with the syringe  600  installed thereto, the piston head  630  of the syringe piston  625  is engaged with the piston carrier  205  of the pipette but the piston has not yet been deliberately moved toward the proximal end of the pipette (beyond any incidental axial movement necessary to engage the piston head with the piston carrier). Consequently, the piston  625  still resides substantially against the distal interior of the syringe capillary  605 . 
     The pipette assembly of  FIG. 23B  is depicted in a ready to dispense or fully aspirated position—i.e., the pipette  5  is shown to have performed an aspiration function by which a full syringe volume of a fluid of interest is drawn into the syringe  600 . It is also possible to aspirate less than a full syringe volume of fluid. To aspirate the fluid, the tip  610  of the syringe  600  is placed in the fluid and an aspiration program is initiated via the user interface portion  15  of the pipette or a user manipulates an actuator to energize the motor  45  of the motorized drive assembly  40 , to drive the piston carriage  100  and the associated components coupled thereto some desired distance toward the proximal end of the pipette  5 . This proximally-directed axial movement of the piston carriage  100  produces a like movement of the solenoid body  260  which, in turn, produces a like movement of the armature  260  and the piston carrier  205  that is attached to the armature shaft  265 . Since the head  630  of the syringe piston  625  is engaged with the piston carrier  205 , the syringe piston is also moved proximally an equal distance within the syringe capillary  610 , which draws the fluid of interest into the now evacuated capillary. 
     When the exemplary pipette  5  is in the fully aspirated position such as that shown in  FIG. 23B , various ones of the pipette components will still reside in the same positions relative to other components as when the pipette resides in the home position. For example, the armature  260  of the dispensing solenoid assembly  250  remains at its distal hard stop  275  against the bottom wall of the bore  270  and the coil  260  of the dispensing solenoid assembly is not energized. Likewise, the gap  400  between the piston carrier  205  and the rollers  310  of the piston head release elements  305  is also maintained when the pipette  5  is in an aspirated position. 
     The action of the various pipette components during a dispensing operation are described with reference to  FIGS. 23B and 24 . The specific manner in which the dispensing components of the pipette  5  are activated during a dispensing operation is dependent on the selected dispensing volume. That is, small volume dispensing is preferably performed using the solenoid assembly  250  while large volume dispensing is preferably performed using the motorized drive assembly  40  alone or the motorized drive assembly  40  in combination with the solenoid assembly  250 . 
     The delineation between a small dispensing volume and a large dispensing volume may vary across different pipette embodiments, because the largest volume of fluid that can be dispensed by the solenoid assembly  250  alone is dependent on the maximum stroke of the solenoid armature  260 , which is in turn, determined by the maximum distance the piston carriage  100  may be moved from the fully aspirated position toward the distal end of the pipette  5  before causing an unintended dispensing of fluid from the syringe  600 . For purposes of illustration, and not limitation, the maximum piston carriage displacement that may be produced without causing unintended dispensing is 0.5 mm in this exemplary embodiment of the pipette  5 . 
     Because the solenoid body  255  is coupled to the piston carriage  100 , the solenoid body moves toward the distal end of the pipette  5  during like movements of the piston carriage. However, since the armature  260  of the solenoid floats freely within the bore in the solenoid body  255 , because the solenoid armature is also coupled to the piston carrier  205  by the armature shaft  265 , and because the piston carrier is biased toward the proximal end of the pipette  5  by the pressure of the aspirated fluid in the syringe  600  pushing against the syringe piston  670 , the solenoid armature remains in its current position and does not move with the piston carriage and the solenoid body during the aforementioned movement of the piston carriage. This creates a solenoid stroke gap  280  between the distal face  260   b  of the armature  260  and the bottom wall of the bore  270  in the solenoid body  255  of a distance that is commensurate with the aforementioned distal movement of the piston carriage  100  (up to 0.5 mm in this example). This solenoid stroke gap  280  is the maximum stroke of the solenoid armature  260  and thus, in this exemplary embodiment of the pipette  5 , is also 0.5 mm. 
     A 0.5 mm maximum stroke of the solenoid armature  260  results in a corresponding dispensing volume of approximately 0.01 (1%) of the total volume of the given syringe installed to the pipette. Consequently, for this particular example, a small dispensing volume would be considered to be about 0.001 ml or less of the 0.1 ml volume syringe  500 , about 0.01 ml or less of the 1.0 ml volume syringe  550 , about 0.1 ml or less of the 10 ml volume syringe  600 , about 0.25 ml or less of the 25 ml volume syringe  650 , and about 0.5 ml or less of the 50 ml volume syringe  700 . Dispensing volumes greater than these approximate small volume dispensing volumes would be considered large volume dispensing volumes in this particular example. Note that the smallest deliverable dispensing volume using the motorized drive assembly  40  alone or the motorized drive assembly  40  in combination with the solenoid assembly  250 , is generally the same as the largest deliverable dispensing volume using the solenoid assembly alone (although there may be some overlap). 
     Upon initiation of a small volume dispensing operation, the controller  90  of the pipette  5  instructs the motorized drive assembly  40  to move the piston carriage  100  some distance (less than or equal to 0.5 mm, depending on the selected small volume to be dispensed) toward the distal end of the pipette. The specific distance by which the piston carriage  100  moves is dependent on the selected small volume of fluid to be dispensed. The maximum piston carriage  100  displacement distance and resulting solenoid armature  260  stroke in this exemplary pipette  5  is 0.5 mm. 
     With the piston carriage  100  moved to the small volume dispensing position and the gap  280  in the solenoid assembly resultingly created, the controller  90  temporarily energizes the solenoid body  255  which, as would be understood by one of skill in the art, creates a magnetic field that rapidly and forcefully fires the armature  260  toward the distal end of the pipette  5  and into halting contact with the armature hard stop  275 . This rapid and distally directed movement of the solenoid assembly armature  260  produces a like movement of the piston carrier  205  and the syringe piston  625  that is coupled therewith, which causes the selected dispensing volume of fluid to jet out from the tip  610  of the syringe  600  with sufficient velocity to break any surface tension between the fluid and the inner wall surface of the syringe capillary  610  and to thereby ensure that the last drop of fluid is dispensed without the need to touch off the syringe tip  610  on the receiving vessel. The process of moving the piston carriage  100  and dispensing a small fluid volume by firing the solenoid assembly  250  may be repeated until the aspirated volume is fully dispensed or until a desired number of dispensing operations have been completed. 
     As may be understood from the foregoing description, large volume dispensing in the context of the exemplary pipette, is simply the dispensing of fluid volumes greater than the maximum possible fluid volumes that are dispensable by action of the solenoid assembly alone. Therefore, with respect to the exemplary pipette  5  and the exemplary syringes  500 ,  550 ,  600 ,  650 ,  700  shown and described herein, large volume dispensing encompasses dispensing volumes greater than about 0.001 ml of the 0.1 ml volume syringe  500 , greater than about 0.01 ml of the 1.0 ml volume syringe  550 , greater than about 0.1 ml of the 10 ml volume syringe  600 , greater than about 0.25 ml of the 25 ml volume syringe  650 , and greater than about 0.5 ml of the 50 ml volume syringe  700 . The maximum volume that can be dispensed during a single large volume dispensing operation is the entire volume of the given syringe  500 ,  550 ,  600 ,  650 ,  700 . 
     As mentioned above, two methods of large volume dispensing may be possible. According to a first method, large volume dispensing is performed using the motorized drive assembly  40  alone, while according to a second method, large volume dispensing is performed using the motorized drive assembly  40  in combination with the solenoid assembly  250 . The employed large volume dispensing method may be dependent on the specific construction of the pipette and possibly also on the properties of the fluid to be dispensed. 
     In accordance with the first method of large volume dispensing method mentioned above, it has been found that when dispensing a large fluid volume, or at least when dispensing a fluid volume that falls within some volume range of the overall large volume dispensing range of the exemplary pipette  5 , dispensing may be performed without the need for assistance from the solenoid assembly  250 . More specifically, it has been found that when dispensing large fluid volumes, movement of the piston carriage  100  alone, coupled with an increase in fluid velocity resulting from the fluid in the syringe  600  being forced from the larger diameter capillary  605  through the much smaller diameter tip  610  and orifice  615 , may be sufficient to produce a fluid dispensing velocity that is great enough to overcome any surface tension between the fluid and the inner wall surface of the syringe capillary and to thereby ensure that the last drop of fluid is dispensed from the syringe without the need to touch off the syringe tip on the receiving vessel. 
     Large volume dispensing by movement of the piston carriage  100  alone may be automatically directed by the pipette controller  90  based on the dispensing program selected by a user, the syringe installed to the pipette  5 , the dispensing volume associated with the selected dispensing program, etc. In any event, upon initiation of a large volume dispensing operation by means of piston carriage  100  movement only, the controller  90  determines the displacement of the piston carriage required to eject the selected large volume of fluid to be dispensed. The motorized drive assembly  40  subsequently rotates the drive nut  50  to linearly displace the lead screw  95  and the piston carriage  100  until the gap  400  between the piston carrier  205  and the rollers  310  of the piston head release elements  305  is closed, which produces a like displacement of the piston carrier  205  and the syringe piston  625  that is engaged therewith. Dispensing of the selected large fluid volume is thus accomplished. 
     Alternatively, large volume dispensing may be accomplished by a combination of piston carriage movement and firing of the solenoid assembly  250 . As with the first large volume dispensing method, the second large volume dispensing method may be automatically selected by the pipette controller  90  based on the dispensing program selected by a user, the syringe installed to the pipette  5 , the dispensing volume associated with the selected dispensing program, etc. In any event, upon initiation of the second large volume dispensing operation the controller  90  again determines the displacement of the piston carriage required to eject the selected large volume of fluid to be dispensed. The motorized drive assembly  40  subsequently rotates the drive nut  50  to linearly displace the lead screw  95  and the piston carriage  100  by the required distance, which produces a like displacement of the piston carrier  205  and the syringe piston  625  that is engaged therewith, and a corresponding dispensing of fluid from the syringe 
     Upon completion of piston carriage  100  movement and the corresponding dispensing of fluid from the syringe  600 , the controller  90  temporarily energizes the solenoid body  255 , which fires the armature  260  of the solenoid assembly  250  toward the distal end of the pipette  5  and into halting contact with the armature hard stop  275 . This rapid and distally directed movement of the solenoid assembly armature  260  produces a like movement of the piston carrier  205  and the syringe piston  625 , which will dispense any non-dispensed fluid remaining in the syringe tip  610  due to surface tension between the fluid and the inner wall surface of the syringe capillary  610 . Thus, it can be ensured that the last drop of the fluid volume intended to be dispensed is actually dispensed and not inadvertently retained in the syringe tip  610 . When the volume of fluid dispensed during a large volume fluid dispensing operation is less than the total volume of fluid in the syringe  600 , the dispensing operation may be repeated until a desired number of dispensing operations have been completed, until the fluid volume is exhausted, or until the remaining fluid volume is insufficient to perform another dispensing operation of a desired fluid volume. 
     Dispensing operations using the exemplary pipette  5  may be accomplished via a selected pipetting program that operates the pipette in an automatic (auto) mode or via a manual mode. As briefly mentioned above, a user is able to access and selectively initiate a desired pipetting program through the user interface portion  15  of the pipette  5 . 
     Auto mode dispensing may encompass a number of different and selectable dispensing procedures. One simplistic example of such a dispensing procedure results in aspiration of a full syringe volume of fluid, followed by dispensing of the entirety of the aspirated fluid volume in one dispensing operation. 
     In another auto mode dispensing procedure example, a volume of fluid is aspirated into the syringe  600  as previously described, and is subsequently dispensed in multiple doses of equal volume until a desired number of dispensing operations have been completed, until the fluid volume is exhausted, or until the remaining fluid volume is insufficient to perform another dispensing operation of selected fluid volume. In yet another auto mode dispensing procedure example, a volume of fluid is aspirated into the syringe  600  as previously described, and is subsequently dispensed in multiple doses of variable volume until a desired number of dispensing operations have been completed, until the fluid volume is exhausted, or until the remaining fluid volume is insufficient to perform another dispensing operation of a desired fluid volume. In still another auto mode dispensing procedure example, a volume of fluid is aspirated into the syringe  600  as previously described, and is subsequently dispensed in multiple doses of equal or variable volume until some portion (e.g., 50%) of the aspirated volume has been dispensed. At this point, another aspiration operation is performed to increase the volume of fluid in the syringe  600  and dispensing is performed again. This process may be repeated until a desired number of dispensing operations have been completed, until the fluid volume is exhausted, or until the remaining fluid volume is insufficient to perform another dispensing operation of selected fluid volume. 
     In any of the above-described exemplary auto mode dispensing procedures, the aspirated volume of fluid may be the entire fluid volume of the installed syringe, or some lesser volume. Dispensing of the fluid may be accomplished by firing of the solenoid assembly  250  alone, by movement of the piston carriage  100  alone, or by a combination thereof. As described above, the dispensing method used may be selected based on the pipette construction (e.g., resolution), the installed syringe, the desired dispensing volume, some combination thereof, and/or on other factors. 
     The menu of exemplary procedures that may be performed under the auto mode of an exemplary pipette may further include a titration procedure. As would be understood by one of skill in the art, a titration procedure using the exemplary pipette  5  generally involves adding some amount of a titrant that has been aspirated in to the syringe  600  to a container of analyte and indicator until the indicator changes color or achieves some other observable characteristic, indicating that the reaction has reached a state of neutralization. Since the amount of titrant that will need to be added to the analyte solution to reach neutralization is typically unknown, the titration program may include a titrated volume counter that indicates the volume of titrant that has been dispensed. The counter may be resettable to allow for multiple titration operations from a single aspirated volume of titrant. 
     A dispensing operation may also be performed by a user in a manual mode rather than by the controller  90  of the pipette  5  operating in auto mode. In manual mode, the user operates the motorized drive assembly  40  to produce a fast or slow aspiration and/or dispensing of fluid from the syringe  600 . 
     An exemplary pipette may also be provided with fluid viscosity detection capability. More specifically, the viscosity of a fluid of interest may be determined indirectly such as by providing the pipette with appropriate circuitry  350  (see  FIG. 5B ) or other means for monitoring and analyzing the increased current draw by the drive motor resulting from the increased motor torque required to move the syringe piston relative to the syringe capillary during an aspiration or dispensing operation; through use of a provided load cell  355  (see  FIG. 5B ) that measures the force required to move the syringe piston relative to the syringe capillary during an aspiration or dispensing operation; by way of a mechanical spring; or via another technique that would be understood by one of skill in the art. 
     When utilizing a current draw monitoring technique, the value of the current draw may be used to categorize the viscosity of the fluid, and the pipette controller may adjust the dispensing operation parameters of the pipette based on the identified fluid viscosity category. For example, and without limitation, if the fluid of interest is determined to have a low viscosity, the controller may apply normal dispensing settings during a fluid dispensing operation. If the fluid of interest is determined to have a medium viscosity, the controller may increase the voltage to the drive motor and may also enforce a suck back mode (a retraction of the lead screw that draws air into the syringe capillary) for aliquots that would normally not require suck back during dispensing of fluids of low viscosity. If the fluid of interest is determined to have a high viscosity, the controller may disable the solenoid assembly so dispensing is possible only via movement of the piston carriage, and may also notify a user that syringe tip touch-off will be required to ensure no liquid is left in the syringe tip. 
     An exemplary pipette, such as the exemplary pipette  5 , may also be programmed to performed a discard dispense function. The discard dispense function is preferably a part of pipetting process when using the exemplary pipette  5 , and may be enforced by the controller  90 . Generally speaking, the discard dispense function is operative to remove any backlash and to account for any manufacturing and/or assembly tolerance issues in the drive, solenoid, and overall system, and may also remove any air that is entrapped near the distal end of the syringe tip. The controller  90  may be programmed to initiate a discard dispense function after each aspiration operation. The discard dispense function may also be initiated any time all of the fluid previously aspirated into a syringe is fully dispensed. The discard dispense volume will be variable based on the viscosity of the liquid being worked with and the syringe construction. 
     Another possible exemplary pipette feature that may be provided according to the general inventive concept is automatic syringe identification functionality. Because an exemplary pipette is usable with syringes of many different volumes, it is realized that it would be beneficial if an exemplary pipette could automatically identify the syringe volume when the syringe is installed to the pipette. Such an ability would allow the controller of the pipette to automatically select the appropriate operating parameters for the given syringe volume, thereby simplifying the setup process and possibly eliminating operator error associated with mistakenly identifying the volume of a syringe being used. 
     In one exemplary embodiment, color coding is used as a mechanism for syringe identification. More specifically, each syringe volume is associated with a different color and an area of corresponding color is located on the syringe. 
     Using the exemplary syringes  500 ,  550 ,  600 ,  650 ,  700  depicted in  FIGS. 6A-10B  as examples, a color band  450 ,  455 ,  460 ,  465 ,  470  that corresponds to the volume of each given syringe is placed along an upper shoulder  520   a ,  570   a ,  620   a ,  680   a ,  730   a  of the syringe retention element  520 ,  570 ,  620 ,  680 ,  730 . In some embodiments, the color band of a given syringe may extend only partially around the syringe retention element, while in other embodiments the color band may extend around the entire circumference of the syringe retention element. Color coding may also be provided in the form of a continuous patch of color, a discrete patch of color, or in any other readable form such as without limitation, a collection of dots, segmented lines, etc. Color may also be molded into the material from which a given syringe retention element is made. Further, in alternative embodiments, color coding may be placed on the syringe piston instead of or in addition to, on the syringe retention element of a given syringe. 
     As illustrated in  FIG. 24 , one or more color sensors  475  may reside within the distal end of the exemplary pipette  5 , and may be configured and located to image the color bands on the syringe retention elements  520 ,  570 ,  620 ,  680 ,  730  of the exemplary syringes  500 ,  550 ,  600 ,  650 ,  700 . Upon installation of an exemplary syringe  500 ,  550 ,  600 ,  650 ,  700  to the pipette  5 , the color sensor(s)  475  images the color band  450 ,  455 ,  460 ,  465 ,  470  and transmits a signal to the pipette controller  90  that is indicative of the color of the color band. The controller  90  is provided with the proper data (e.g., a lookup table, etc.)—such as for example through a process of preliminary and offline color recognition and registration operation using the color sensor(s)  475 —to analyze the signals received from the color sensor(s)  475  to identify the color of the color band  450 ,  455 ,  460 ,  465 ,  470  and, thus, the volume of the installed syringe  500 ,  550 ,  600 ,  650 ,  700 . As described above, with the syringe volume identified, the controller  90  may proceed to automatically set any of various pipetting parameters and/or to indicate the syringe volume to a user of the pipette  5 . 
     In the exemplary pipette and syringe embodiments presented herein, the upper shoulders  520   a ,  570   a ,  620   a ,  680   a ,  730   a  of the syringe retention elements  520 ,  570 ,  620 ,  680 ,  730  are preferably chamfered at some angle (e.g., between 30° and 60° relative to the upper face of the retention element). The chamfered upper shoulders  520   a ,  570   a ,  620   a ,  680   a ,  730   a  of the syringe retention elements  520 ,  570 ,  620 ,  680 ,  730  facilitate insertion of the syringe retention elements into the pipette  5 . Additionally, the chamfered upper shoulder  520   a ,  570   a ,  620   a ,  680   a ,  730   a  of each syringe retention elements provide an angled surface from which light emitted by the emitter portion (illumination source)  480  of the color sensor  475  can be reflected toward the detection face  485  of the color sensor  475 , which may be mounted to the pipette at a corresponding angle. Use of such a chamfered shoulder further allows for a color band to be applied using a vertical pad printing process, which is the most efficient way of printing. 
     While color sensing using a color sensor  475  to read color coding on the chamfered upper shoulders  520   a ,  570   a ,  620   a ,  680   a ,  730   a  of the syringe retention elements  520 ,  570 ,  620 ,  680 ,  730  is shown and described herein for purposes of illustration, it is to be understood that exemplary pipette embodiments are not limited to this arrangement. For example, and without limitation a sensor(s) may instead be located to read color coding, printing, etc., on other areas of a syringe. 
     While certain embodiments of the general inventive concept are described in detail above for purposes of illustration, the scope of the general inventive concept is not considered limited by such disclosure, and modifications are possible without departing from the spirit of the general inventive concept as evidenced by the following claims: