Abstract:
This invention relates generally to a volumetric pipet used to make a volumetric measurement and transfer a measured amount of liquid. More specifically the invention relates to a pipet that fills from the top, works well with automated systems because it does not require positioning devices or a supply of suction, is easy to rinse and rinses upon filling, and meets the precision requirements of class A volumetric glassware. The pipette of the invention may include a chamber for manipulation of the liquid before pipetting. The pipet is capable of delivering a repeatable predetermined volume of fluid, fills from the top and dispenses from the bottom, which eliminates a need for suction to fill the pipet. The pipet does not trap air in the measuring chamber and works without any valves making contact the sample liquid in the measuring chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of copending U.S. patent application Ser. No. 10/208,420 entitled FLOW THROUGH PIPET filed Jul. 30, 2002. 

   FIELD OF THE INVENTION 
   This invention relates generally to a volumetric pipet used to make a volumetric measurement and transfer a measured amount of liquid. More specifically the invention relates to a pipet that fills from the top, works well with automated systems because it does not require positioning devices or a supply of suction, is easy to rinse and rinses upon filling, and meets the precision requirements of class A volumetric glassware. The pipette of the invention may also include a chamber for manipulation of the liquid before pipetting. 
   BACKGROUND OF THE INVENTION 
   Pipets are used to extract, measure and transfer a volume of liquid. A common pipet design is a cylindrical vessel open at both ends, like a drinking straw, with a mark to indicate a predefined volume and a means to apply suction and pressure to one end of the cylinder. In use, suction is applied to draw liquid into the pipet from a reservoir. The pipet is then moved to a receiving vessel and pressure or gravity empties measured volume. 
   An important concept in volumetric measurement of liquid is that precision can be increased by reducing the diameter of the cylinder at the upper limit of the liquid. This is seen in volumetric flasks, which have a large diameter base and a smaller diameter neck at the top. Volumetric pipets are usually cylindrical, as previously stated. However, volumetric pipets may have a large diameter section, e.g., in the middle, so that the pipet can hold more volume, although the area of the pipet corresponding to the limiting point for the liquid is typically narrowed again. Stated another way, reducing the surface area of the meniscus increases the accuracy. 
   Most pipets fill from the bottom end, while pressure and suction are applied at the upper end. This configuration has the advantage of minimizing the surface area of the boundary between the liquid and the air, thereby maintaining precision. Another advantage of this simple yet effective device is that the liquid to be measured does not contact any valves. The liquid is suspended in the pipet with suction. A disadvantage associated with the use of valves is that valves have mating surfaces, seats, and fittings having irregular surfaces that are likely to retain the liquid, reduce precision and make the device more difficult to rinse. 
   One disadvantage of the bottom fill pipet described above is that the pipet must be moved with each cycle of operation from the fill location to the dispense location. Another disadvantage is that the pressure and suction must be carefully controlled. 
   In addition to manual pipets, automated pipet systems have been developed. An example automated pipet system may include a syringe, a stepper motor, a three-way valve to select between intake and dispense functions, and equipment necessary to move the pipet vertically in and out of a fluid as well as equipment necessary to move the pipe horizontally from an intake location to a dispense location. Although a means to apply pressure and suction has been automated and the movement of the pipet in the x and y directions has been automated, typically the same basic design is used, wherein a cylindrical vessel is opened at both ends. Examples of typical “glass straw” pipet vessels may be found in U.S. Pat. Nos. 3,992,947, 4,476,095, 4,624,147, 5,090,255, 5,271,902, 5,679,575, 5,820,824, and 6,253,628. 
   Other known pipette designs include the unitary filter-pipette taught in U.S. Pat. No. 3,415,380 to Ellis. The Ellis pipette fills from the top and has the advantage of a measuring chamber that, by its design, holds a limited amount of liquid, making the volumetric measurement automatic. Ellis teaches a manual pipet. 
   One drawback associated with Ellis is that liquid may continue to enter the measuring chamber from the filter and its funnel while the pipet is emptying, which will compromise the accuracy. Additionally, liquid is supported by a valve at the bottom of the measuring chamber, which will reduce precision and complicate rinsing. Rinsing requires either moving the device or replacing the receiving vessel after rinsing because the rinse media exits the device through the same port as measured liquid. 
   The above described accuracy limitations make the Ellis device inappropriate for high precision applications. Having to position the device for rinsing makes the Ellis device less suitable for automation. 
   U.S. Pat. No. 2,434,723 to Shook describes a Means for Measuring Volumetric Samples in that has the feature of isolating measure liquid between two valves. Shook teaches a manual rather than automated pipet. 
   Shook&#39;s device does not provide a clear or separate path for displaced air to evacuate when filled from the top. Rinsing is required between the fill and dispense operations. Otherwise, liquid will continue to enter the measuring chamber from the vessel above the uppermost valve while the measured liquid is emptying. Rinsing requires either moving the device or replacing the receiving vessel after rinsing, or turning a valve to select a separate passage for the rinse media. This device has a valve below and another above the measuring chamber. These valves will reduce precision and complicated rinsing. 
   German Patent No. 929,333 to Altmann describes a buret. The Altmann device fills from the top, using pressure or suction to fill from a supply reservoir that is at a lower elevation than the full mark of the buret. Altmann teaches that the buret is filled with excess fluid, then gravity and a siphon effect return the excess to a supply reservoir. 
   The Altmann device has a valve at the lower boundary of the measuring chamber, which will reduce precision and complicate rinsing. The use of pressure or suction requires that a source of pressure or suction be available. The Altmann device delivers the rinse media and the measured liquid through the same opening requiring that the rinse vessel and the sample vessel be moved back and forth. Only one opening is provided in the top of the measuring chamber through which air must evacuate and liquid enter, which limits accuracy. The Altmann buret is shown having a straight cylinder wall. Altmann shows the upper limit of the liquid to be at point D, the delivery tip. Further, Altmann&#39;s device requires that air must evacuate the measuring area of the buret and escape through opening H. 
   U.S. Pat. No. 4,476,095 to Scott describes an automated pipet that includes a motor driven syringe to supply suction, pressure and volumetric measurement, and a device to position the pipet in two locations, i.e., one location for filling the pipet and a second location for delivering the measured liquid. Scott teaches a “drinking straw” style pipet that has been automated and has many limitations. The Scott device is difficult to rinse and rinsing may require disassembly. It is complex because it has a motor driven syringe supplying pressure and suction, and a positioning device. Position devices and motor driven syringes require control circuits, motors, gears and maintenance. 
   Moon describes a Flow-thru-Pipet in U.S. patent application Ser. No. 10/208,420. The Moon device includes a fill chamber where sample preparation can occur. It uses compressed air to empty the measuring chamber. The Moon pipet fills from the top. The measuring chamber has separate passages to simultaneously fill with liquid and evacuate air. To rinse the device, the receiving vessel must be replaced because the rinse media and measured liquid are dispensed through the same port. The device also has a valve at the lower end of the measuring chamber, which compromises precision and complicates rinsing. 
   A drawback with bottom fill manual and automated pipets is that fluid is drawn into the pipet and dispensed from the pipet through the same orifice, which is usually located at the lower end of the pipet. Filling and dispensing of fluid from the same orifice in the pipet necessitates locating the pipet in a fluid source to fill the pipet and then relocating the pipet at a dispensing location every time it is desired to dispense a sample of fluid. Consequently, automated pipet systems require complex systems to relocate the pipet from the fluid source to the dispensing location. 
   Therefore, a pipet is desirable that is capable of delivering a repeatable predetermined volume of fluid, wherein the pipet fills from the top and dispenses from the bottom, i.e., a “flow through” pipet, which would eliminate the need for positioning devices. It is further desirable to provide a top fill pipet that does not trap air in the measuring chamber. Such a pipet could be provided in an automated pipetting system wherein the pipet would not have to be repositioned to a fill location after dispensing a fluid sample, thereby greatly simplifying an automated pipetting system. 
   It is further desirable to have a system that automates titrations that use volumetric measurement of the sample. There are many titration methods that are specific to a sample and chemical species being measured. Generally a titration method is comprised of four steps: 1) Sample preparation, which may be a chemical addition or physical manipulation of the sample; 2) Sample measurement by weight or volume; 3) Titration, which is the addition of a chemical of known concentration until a desired reaction occurs; and 4) Calculation of the concentration of the sample. Sample preparation may include more than one step and may occur before or after the sample measurement. To summarize, it is desirable to have a system that automates all four steps above and does not require any human input during the sample preparation step through the calculation steps described above. 
   Therefore, it is desirable to accomplish sample measurement by volume, and to provide a vessel where sample preparation can occur when necessary and prior to sample measurement. Until now, volumetric measurement has been manually accomplished with volumetric pipets, volumetric flasks, and in a limited number of situations with automated pipets. 
   It is additionally desirable to provide a pipet that includes a vessel or chamber for sample preparation wherein the pipet is capable of dispensing a measured volume that meets the precision requirements of a class A volumetric pipet as specified in ASTM E969-02, which is plus or minus 0.08 milliliters for a 100 ml pipet. One drop of liquid is usually about 0.05 ml. Therefore, the device is accurate to approximately a single drop of fluid. 
   It is further desirous to eliminate the need for any positioning devices including both devices for moving the pipet and devices for moving the sample vessel or rinse media vessel. Positioning devices are expensive and complex. Therefore it is beneficial to fill the pipet from the top so that gravity can be used to move the liquid to different locations. 
   It is desirous to eliminate the need for suction to fill the pipet, eliminating the need for an expensive vacuum supply or a suction pump. Therefore, it is beneficial to fill the pipet from the top allowing gravity to fill the pipet. Additionally, it is desirable that the device be configured for effective rinsing, thereby eliminating contamination of one sample by the previous sample. Also, rinsing should be simple and quick for minimizing operator time and skill. The device should be inexpensive to build, maintain and operate. 
   It is desirous to eliminate valves that contact the sample liquid in the measuring chamber. The “straw” style pipet does not have any valves in contact with the measured liquid. It is desirable to emulate this feature because it will benefit precision. 
   SUMMARY OF THE INVENTION 
   In one embodiment, the invention is directed to a flow through pipet for fluid measurement. The pipet of the invention has a body defining an interior space for receiving a fluid. The drain line is provided to drain fluid in the interior space above a drain line inlet, thereby establishing a repeatable upper fluid level in the body. A dispense valve on the lower end of the body selectively permits dispensing of the fluid from the body. 
   A restriction member may be located in the interior space of the body for defining a passageway. The drain line inlet preferably communicates with the passageway. By locating the drain line inlet in the restriction member passageway, a smaller surface area of an upper surface of the fluid is exposed, thereby minimizing inconsistencies in the fluid level. The drain line inlet establishes an upper end of a measuring chamber and also establishes a lower end of an overflow chamber. 
   The flow through pipet may further include a vent line that communicates the overflow chamber with the measuring chamber, which allows trapped gas to escape from the measuring chamber during filling of a fluid. A fill valve may be provided in the interior space, wherein the fill valve defines an upper end of an overflow chamber and a lower end of a fill chamber. The fill valve selectively permits fluid to pass from the fill chamber to the overflow chamber. 
   A compressed gas line may be provided that is in communication with the overflow chamber for delivering compressed gas to the interior space. A junction for separating the body into an upper segment and a lower segment is provided so that the body can be disassembled, thereby permitting the attachment of a lower segment of a desired volume to be affixed to the upper segment. 
   In use, a fluid is delivered into a measuring chamber through an upper end of a pipet body to fill the measuring chamber with a fluid. Fluid in excess of a predetermined amount is drained out of the drain line. The draining of excess fluid establishes an upper fluid level in the measuring chamber so that a predetermined volume of sample fluid may be established in the measuring chamber. During delivery of the fluid into the measuring chamber, gas may be vented from the measuring chamber via a separate pathway simultaneous to the filling of the measuring chamber with fluid. 
   Fluid may be delivered into the measuring chamber through an upper end of the body from an attached supply source, which may be desirable in an automated process. Preferably, the filling and delivering steps are achieved without moving the body in an X or Y direction. Compressed gas may be delivered into the body above the sample chamber to force the fluid out of the body or the fluid may be delivered by gravity feed. 
   In a second embodiment of the invention, a pipet is provided that includes a vessel or chamber for sample preparation. In the pipet of the invention, rinsing is simplified, automation is easier to accomplish and precision is improved. The pipet is accurate to within approximately one drop of fluid. One drop is generally considered to be 0.05 ml. The operation and rinsing of this device is preferably automated, requiring as little operator input as possible. 
   The device is configured for effective rinsing, thereby eliminating contamination of one sample by the previous sample. Also, rinsing is simple and quick for minimizing operator time and skill. The device is further inexpensive to build, maintain and operate. 
   The pipet of the second embodiment of the invention is comprised of two, three or four chambers positioned so that the first is elevated above the second, the second above the third, and the third above the fourth. 
   The first or uppermost chamber is optional and shall be referred to herein as the fill chamber. The fill chamber is defined by a fill valve at its lower boundary and is configured so that liquid can be introduced to the pipet through this chamber. If a fill chamber is not provided, then liquid may be introduced directly through the fill valve. The fill chamber is available for sample preparation before the volumetric measurement when required. 
   The second chamber shall be referred to herein as the funnel chamber. The funnel chamber is provided to direct liquid into the third chamber. The upper end of the funnel chamber is defined by the fill valve, which permits selective communication of chamber  1  (fill chamber) with chamber  2  (funnel chamber). The lowest point in chamber  2  communicates with a liquid passage. The liquid passage is exclusively for liquid when filling the pipet. At some elevation in the funnel chamber is an imaginary line, i.e., the maximum liquid level line. When the funnel chamber is filled from the first chamber (fill chamber) the liquid settles below the maximum liquid level line. An air vent communicates with the funnel chamber. The air vent is used exclusively for air. The air vent communicates some point above the maximum liquid line in the funnel chamber with the third chamber (measuring chamber). 
   The third chamber or measuring chamber defines the volume of liquid to be measured. The uppermost point in the measuring chamber communicates with the air vent. The liquid passage enters the measuring chamber at some point below the uppermost point and communicates the measuring chamber with the second or funnel chamber. The liquid passage may be offset. The liquid passage preferably communicates with a drain line. The lowest point in the measuring chamber communicates with a measuring chamber drain passage to the fourth or trap chamber if provided or, alternatively, to a trap valve. 
   The fourth chamber or trap chamber is optional. The uppermost point in the trap chamber communicates with a dispense tube. The liquid passage from the third chamber or measuring chamber communicates with a location in the trap chamber below the uppermost point of the trap chamber. The lowest point in the trap chamber communicates with a trap valve. The trap chamber can be omitted and the two-way trap valve replaced with a three-way trap valve having a common valve port in communication with the measuring chamber and a second port in communication with the dispense line and third port. 
   A drain line and valve is provided for selectively communicating the liquid passage, which is between the funnel chamber and the measuring chamber, with some point outside the instrument. A gas valve and line selectively communicates with a location in the second or funnel chamber, above the maximum liquid level, providing gas pressure inside the pipet. The trap valve selectively communicates the trap chamber with a location outside of the instrument. The dispense tube communicates the uppermost point in the trap chamber with some location outside the instrument and delivers the measured volume. 
   The second embodiment provides several improvements over the first embodiment. For example, the location of the air vent and liquid passage in the top of the second or measuring chamber has been changed so that the air vent is at the highest elevation within the measuring chamber. This reduces the mixing of the evacuating air with the incoming liquid, reducing the chance of entraining air bubbles within the measured liquid. The result is improved precision. 
   The optional fourth or trap chamber and dispense tube have been added, and the dispense valve replaced with the trap valve. The filling of this device is substantially a ‘first in, first out’ process, i.e., the first liquid into the second chamber is the first into the third chamber and the first into the fourth chamber. Additionally, it is common industry practice to use the next liquid to be measured as a rinse media. So, with an excess of liquid to be measured and ‘first in, first out’ filling, the trap provides a chamber to isolate excess liquid that has been used to rinse the pipet. Optionally, another port can be added to the trap valve and the chamber eliminated, providing the same function. This feature provides a rinsing of the pipet with the perfect rinse media without any additional user input. 
   Further, the addition of the trap chamber allows the measuring chamber to function without a valve in contact with the measured liquid, thereby improving precision. That is, the addition of the trap chamber creates a measuring chamber wherein the measured liquid is supported by an excess of the same liquid rather than by a valve. 
   Another option is to offset segments of the liquid passage, i.e., the segment of the liquid passage exiting the funnel chamber may be offset from the segment of liquid passage entering into the measuring chamber, and connect the liquid passage with the drain line. This creates a trap, or small chamber. Once the trap is filled, additional liquid moves on to the measuring chamber. This improves both rinsing and precision. Rinsing is improved because the first liquid into the funnel chamber rinses the funnel chamber where it is contaminated and then caught in the trap. The contaminated liquid in the funnel chamber never gets into the measuring chamber. The drain valve may be opened to eliminate the excess liquid and to empty the liquid passage trap. Further, as the measured volume is being delivered from the device, residual liquid in the funnel chamber drips into the liquid passage trap. Without the trap the liquid would go directly to the measuring chamber and compromise the volumetric measurement. Again, both rinsing and accuracy are improved. 
   In operation the above changes reduce the steps required for operation of the device. The original device required replacing the rinse vessel with the receiving vessel after rinsing because the rinse liquid and measured liquid were dispensed at the same opening. Additionally, the improved design increases the precision and the effectiveness of rinsing. 
   The device is suitable for meeting or exceeding the precision requirements of class A volumetric glassware. The measuring chamber with separate passages for air and liquid is believed to be unique and provides a superior means of filling with liquid from the top and simultaneously evacuating the displaced air. Offsetting the liquid passages is also believed to be novel and increases the precision and the effectiveness of rinsing. 
   The need for positioning devices is eliminated with this automated pipet. The need for suction supply is also eliminated with this automated pipet, because separate openings for filling and dispensing are provided. The present invention has a measuring chamber with three openings. 
   This device is easier to rinse than known prior art devices in two ways. First, the default or home position of the valves and trap line allow the device to be rinsed without any positioning, movement of valves or any other manipulation. Simply pour the rinse media into the fill chamber and it passes through the device, rinsing as it goes. Second, the trap valve and optional trap chamber cause the device to rinse as it is filled. This unique feature is created by the presence of the trap valve and optional trap chamber. 
   The relation of the funnel chamber to the measuring chamber and the passages that allow communication between the two chambers allows for a small diameter liquid passage. With the present invention, liquid flows into the funnel chamber then into the measuring chamber. The funnel chamber allows for a smaller diameter liquid passage, thereby increasing precision. 
   The present invention is the only known top filling pipet that has a measuring chamber without a valve, and which successfully emulates the “drinking straw” style pipet. 
   A better understanding of the present invention, its several aspects, and its advantages will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the attached drawings, wherein there is shown and described the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements retain the same numerical designation in the several figures. 
       FIG. 1  is a schematic view of a pipet of the invention for sample or reagent measuring; 
       FIG. 2  is a schematic view of a pipet of the invention having a remote fluid supply, a pump, and a recirculation line for recirculating excess fluid; 
       FIG. 3  is a schematic view of a pipet of the invention having a continuous supply source; 
       FIG. 4  is a schematic view of a pipet of the invention suitable for use with small volumes of fluid; 
       FIG. 5  is a schematic view of another embodiment of a pipet of the invention suitable for use with small volumes of fluid. 
       FIG. 6  is a schematic view of the pipet of the invention incorporated into a multi-pipet assembly. 
       FIG. 7  is a schematic view of a second embodiment of a pipet of the invention in a default or home position; 
       FIG. 8  is a schematic view of the pipet of  FIG. 7  shown in a simple preparation configuration. 
       FIG. 9  is a schematic view of the pipet of  FIG. 7  shown in a fill configuration. 
       FIG. 10  is a schematic view of the second embodiment of the pipet of the invention shown in an excess liquid elimination configuration. 
       FIG. 11  is a schematic view of the pipet of the invention shown in a fill valve closed configuration. 
       FIG. 12  is a schematic view of the pipet shown in  FIG. 7  shown in an excess liquid eliminated configuration. 
       FIG. 13  is a schematic view of the pipet of  FIG. 7  shown in a sample dispense configuration. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the embodiments and steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. 
   Referring now to  FIGS. 1-6  shown are embodiments of a flow through pipet designated generally  10 . Pipet  10  has a body  12 . Body  12  has an upper end  14 , a lower end  16  and defines an interior space  18 . Supplied fluid is delivered to interior space  18  through or proximate to upper end  14 . 
   In one embodiment, shown in  FIG. 2 , a fill line  20  is provided that communicates a remote fluid supply source  22  to interior space  18 . Remote fluid supply source  22  may be a supply pump reservoir or other fluid supply source. Fill line  20  preferably communicates with interior space  18  proximate upper end  14  of body  12 . A fill line valve  24  is preferably provided to control fluid flow from the fluid supply source  22 . 
   In another embodiment, shown in  FIG. 3 , the upper end  14  of body  12  communicates with a continuous supply source  26 . Examples of a continuous supply source  26  include a process pipe, tank or other source. As shown in  FIG. 3 , a measured volume of fluid may be collected from process pipe  28 . Still referring to  FIG. 3 , an isolation valve  30  is preferably provided to selectively allow supplied fluid into interior space  18  from the continuous supply source  26 . 
   Referring back to  FIGS. 1-3 , a restriction member  32  may be provided in interior space  18  of body  12 . Restriction member  32  has a lower surface  34 , which may be conically shaped. Restriction member  32  additionally has an upper surface  36  which is preferably conical to assist in directing fluid toward a reduced area passageway  38 . Reduced area passageway  38  is defined by inner walls  40  located between upper surface  36  and lower surface  34 . 
   Still referring to  FIGS. 1-3 , drain line  42  has an inlet  44  that communicates with passageway  38  in interior space  18 . When a restriction member  32  is used, drain line  42  preferably communicates with passageway  38 . Placing inlet  44  in passageway  38  is advantageous because passageway  38  has a reduced diameter as compared to a diameter of body  12 . The reduced diameter passageway  38  results in a reduced diameter of an upper surface of the fluid, thereby yielding a greater accuracy with respect to the fluid volume. A drain line valve  46  is provided to selectively open or close drain line  42 . 
     FIGS. 4 and 5  disclose pipets suitable for use with small volumes of fluid. Additionally, the pipets of  FIGS. 4 and 5  could be used with any volume of fluid when less precision is required. The pipets of  FIGS. 4 and 5  have no restriction members therein. Therefore, inlet  44  of drain line  42  communicates with interior space  18 . 
   Inlet  44  defines an upper end of a measuring chamber  54  in interior space  18 . Additionally, inlet  44  defines a lower end of an overflow chamber  56  in the interior space  18  ( FIGS. 1-3 ). In all embodiments, drain line  42  defines a repeatable upper fluid level of the interior space  18  of pipet  10 . 
   In one embodiment, shown in  FIG. 2 , drain line  42  communicates with a pump  48 , which is used to draw excess fluid from interior space  18 . The excess fluid may then be pumped through recirculation line  49  back to remote fluid supply source  22  or discarded as desired. Still referring to  FIG. 2 , if a drain line pump  48  is used to suck excess fluid from the interior space  18 , then it is desirable to provide a pressure equalization line  50  with a pressure equalization valve  52  to allow gas to enter interior space  18  when drain line pump  48  is activated. 
   Referring now to FIGS.  1  and  3 - 5 , a fill valve  58  is located in body  12  to isolate a fluid supply from a measured fluid that is located in measuring chamber  54 . Fill valve  58  defines an upper end of overflow chamber  56  and defines a lower end of fill chamber  60  (FIGS.  1  and  3 - 5 ). Fill valve  58  selectively permits fluid to pass from fill chamber  60  to overflow chamber  56 . 
   Referring now to  FIGS. 1 ,  2  and  4 , a vent line  62  is provided that communicates the overflow chamber  56  with measuring chamber  54 . As shown in  FIGS. 1 ,  2  and  4 , vent line  62  is located in the interior space  18  of body  12 . It is desirable to provide a weather cap  64  ( FIGS. 1 ,  2  and  4 ) on an upper end of vent line  62  so that when fluids are delivered to interior space  18 , fluids are prevented from entering an upper end of the vent line  62 . 
   In other embodiments, as shown in  FIGS. 3 and 5 , vent line  62  communicates with an exterior of body  12 . In embodiments having an exterior vent line  62 , it may be desirable to provide a vent valve  66  ( FIGS. 3 and 5 ). 
   A compressed gas line  68  may be provided for communicating a compressed gas source with interior space  18  ( FIGS. 1-6 ). A compressed gas valve  70  may be provided to control access of compressed gas to the body  12 . Compressed gas may be useful in forcing fluids out of lower end of  16  the pipet  10 . However, compressed gas may be substituted by the use of gravity to dispense fluids from the body  12  with the pipet  10  of the invention. 
   A dispense valve  72  is provided on lower end  16  of body  12 . Dispense valve  72  allows for selective dispensing of a fluid from measuring chamber  54 . Dispense valve  72  may be any type of suitable valve known in the art. However, in a preferred embodiment, dispense valve  72  is pressure actuated. Additionally, dispense valve  72  may be manually actuated, electronically actuated, or actuated by other means. 
   A junction  74  may be provided so that body  12  is separatable into an upper segment  76  and a lower segment  78 . Upper segment  76  and lower segment  78  may be connected at junction  74  by threads, cooperating detents and protrusions, clips or other means. 
     FIG. 6  shows a multi-pipet assembly  80  having a fill line  20  that has multiple branches that communicate a remote fluid supply source  22  to interior space  18   a  and  18   b  of bodies  12   a  and  12   b , respectively. Although only two pipet bodies,  12   a  and  12   b , are shown for purposes of example, it should be noted that any number of pipet bodies  12   a ,  12   b ,  12   c  . . . may be incorporated into the multi-pipet assembly  80  of the invention. It should also be noted that like elements of multi-pipet assembly  80  to elements of embodiments shown in  FIGS. 1-5  have retained the same numerical designation in  FIG. 6 , with the exception that “a” or “b” has been appended to some of the numbers to designate to which of the pipet bodies  12   a, b  that the numeral designations refer. For example, in a manner similar to that of the embodiment of  FIG. 2 , drain line pump  48  draws excess fluid from interior space  18   a  and  18   b  through drain line branches  42   a  and  42   b . The excess fluid may then be directed through recirculation line  49  back to remote fluid supply source  22  or discarded as desired. A single pressure equalization line  50  and compressed gas line  68  may be provided, which are capable of acting upon interior spaces  18   a ,  18   b , etc., since interior spaces  18   a ,  18   b , etc. communicate with one another via passageway  82 . Alternatively, pressure equalization line  50  and compressed gas line  68  may provide individual branches for communicating with each of interior spaces  18   a ,  18   b , etc. 
   In use, a fluid is delivered into measuring chamber  54  through an upper end  14  of body  12 . Fluid in excess of a desired amount drains out of drain line  42 . By draining fluid out of drain line  42 , an upper fluid level is established in interior space  18 . The upper fluid level defines a predetermined volume of fluid in measuring chamber  54 . The predetermined volume of fluid may then be dispensed out of lower end  16  of body  12  through dispense valve  72 . The dispense valve  72  may be electronically actuated, manually actuated or actuated by other methods. 
   In one embodiment, e.g., as shown in  FIGS. 1-3  and  6 , the surface area of the fluid may be restricted or reduced in size as compared to the dimensions of the interior space  18  by providing a restriction member  32 . For example, the drain line  42  may be located to communicate with an inner wall  40  of a restriction member  32 , thereby establishing an upper fluid level having a reduced or restricted service area. Minimizing the surface area of the fluid surface minimizes measurement error of the pipet. 
   To prevent gas from being trapped in the measuring chamber  54 , a vent line  62  ( FIGS. 1-6 ) may be provided. By separating the vent line  62  from the passageway  38  ( FIGS. 1-3  and  6 ), gas may simultaneously escape from measuring chamber  54  while measuring chamber  54  is being filled with the fluid. 
   The delivery of fluid into interior space  18  may be accomplished via a fill line  20  ( FIGS. 2 and 6 ), which delivers fluid to an area proximate upper end  14  of the body  12 . Additionally, fluid may be delivered directly into upper end  14  of body  12  via manual delivery or delivery from a remote fluid supply source  22  ( FIGS. 2 and 6 ) or a continuous supply source  26  ( FIG. 3 ). 
   Referring back to  FIGS. 2 and 6 , it may be desirable to provide a pump  48  for sucking excess fluid from the interior space  18 . To minimize waste of the fluid, a recirculation line  49  may be provided to route excess fluid back to a remote fluid supply source  22  where the fluid can be reintroduced into the interior space  18  via fill line  20 . 
   Dispensing the predetermined volume of fluid may be achieved by gravity feed or, alternatively, by delivering compressed gas into the interior space  18  to force the fluid out of lower end  16  of body  12 . To deliver compressed gas to interior space  18 , compressed gas valve  70  is opened and gas is delivered through line  68  into interior space  18  at a location above the drain line  42 . 
   Referring now to  FIGS. 4 and 5 , for dispensing very small amounts of a predetermined volume of fluid, it may be unnecessary to provide a restriction member  32 , as shown in  FIGS. 1-3 , in the interior space  18  of the body  12 . However, it may still be desirable to provide a structure for venting gas from measuring chamber  54  when fluid is delivered to the measuring chamber  54 . In particular, for a very small diameter of body  12 , incoming fluid may not readily permit trapped gas to escape. Therefore, in one embodiment, vent line  62  may be provided within interior space  18 , where the vent line  62  has a lower opening at a location below the inlet  44  of drain line  42  and has an upper opening at a location above the inlet  44  of drain line  42 . Weather cap  64  is preferably provided above the vent line  62  of  FIG. 4  to prevent fluid from entering the upper opening of vent line  62 . In another embodiment, as shown in  FIG. 5 , the vent line  62  may be provided externally to the body  12 . A vent valve  66  may be provided on vent line  62 . 
   Referring back to  FIG. 3 , delivery from a continuous supply source  26  may be desirable to provide a sampling device for a process stream. In this embodiment, isolation valve  30  is selectively opened to admit fluid from process pipe  28 . The fluid then fills the fill chamber  60 . Fill valve  58  may then be opened to allow the fluid to pass from the fill chamber  60  through overflow chamber  56 , through passageway  38  and into measuring chamber  54 . As the fluid fills measuring chamber  54 , displaced gas is vented out through vent line  62 . In this embodiment, the vented gas is vented to an exterior of body  12  through vent line  62 . Once the fluid level in the measuring chamber  54  rises to the inlet  44  of level of the drain line  42 , any excess fluid is drained out of interior space  18 , e.g., any fluid rising into overflow chamber  56  will be drained out of interior space  18 , thereby establishing a maximum volume of fluid in the measuring chamber  54 . 
   If it is desired to use a pipet  10  having a fill valve  58 , a drain valve  46  on a drain line  42 , a gas valve  70  on a compressed gas line  68  and a dispense valve, then a prescribed sequence of opening and closing various valves  58 ,  46 ,  70  and  72  is desirable for operating the pipet. Below is an example sequence of valve operation. The valve operation may be varied without adversely affecting the accuracy and precision of the inventive pipet. 
   Description of steps:
         0. Start with valves  46 ,  58 ,  70  and  72  closed.   1. Fluid is delivered through the fill valve  58 . The fluid flows through the passageway  38  through the restriction member  32  and into the measuring chamber  54 .   2. The drain valve  46  is opened and excess liquid drained out of the manifold.   3. The fill valve  58  is closed.   4. Gas valve  70  is opened briefly to ensure that excess liquid drains through the drain valve  46  and into drain line  42 .   5. The drain valve  46  is closed.   6. The compressed gas valve  70  is opened. The increased pressure inside interior space  18  activates a pressure actuated dispense valve  72  to allow the measured liquid within measuring chamber  54  to exit via the open dispense valve  72 .   7. The compressed gas valve  70  is closed.   8. The drain valve  46  is opened to relieve pressure.   9. Step 5 is repeated   10. Step 6 is repeated   11. Step 7 is repeated   12. Step 8 is repeated   13. Step 9 is repeated       

   Alternatively, step 9 could comprise “close drain valve  46 ” and steps 10-13 could be eliminated. Steps 10-13 are cautionary to ensure that all measured liquid has been discharged. 
   Steps for one method of operation are presented in the below Table. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
             
             
                 
                 
                 
                 
               Dispense Valve 
             
             
               Step 
               Fill Valve 58 
               Drain Valve 46 
               Gas Valve 70 
               72 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               0 
               Close 
               Close 
               Close 
               Close 
             
             
               1 
               Open 
               Close 
               Close 
               Close 
             
             
               2 
               Open 
               Open 
               Close 
               Close 
             
             
               3 
               Close 
               Open 
               Close 
               Close 
             
             
               4 
               Close 
               Open 
               Pulse 
               Close 
             
             
               5 
               Close 
               Close 
               Close 
               Close 
             
             
               6 
               Close 
               Close 
               Open 
               Open 
             
             
               7 
               Close 
               Close 
               Close 
               Close 
             
             
               8 
               Close 
               Open 
               Close 
               Close 
             
             
               9 
               Close 
               Close 
               Close 
               Close 
             
             
               10 
               Close 
               Close 
               Open 
               Open 
             
             
               11 
               Close 
               Close 
               Close 
               Close 
             
             
               12 
               Close 
               Open 
               Close 
               Close 
             
             
               13 
               Close 
               Close 
               Close 
               Close 
             
             
                 
             
           
        
       
     
   
   As described above, a novel pipet is taught for automatically and inexpensively extracting an aliquot of liquid from one source, measuring a predetermined volume of the liquid and transferring the volume of liquid to a different vessel. Benefits of the novel pipet include simplicity and therefore low expense to manufacture, ease of automation, minimization of the volume of liquid that must be used to rinse the apparatus, elimination of a need to reposition the pipet after liquid has been introduced into the pipet, elimination of expensive syringe pumps that are used in typical automated pipetting systems, elimination of the use of suction to fill the pipet with liquid, and use of gravity and overflow rather than a syringe pump to measure volume. 
   Referring now to  FIGS. 7-13 , shown is a second embodiment of the pipet of the invention which will be referred to as pipet  100 . Pipet  100  has four chambers: a fill chamber  102 , a funnel chamber  104 , measuring chamber  106  and a trap chamber  108 . A first barrier  110  separates funnel chamber  104  from measuring chamber  106 . A second barrier  112  separates the measuring chamber  106  from the trap chamber  108 . A third barrier  114  may be provided to define a lower surface of trap chamber  108 . 
   Fill chamber  102  is preferably defined at a lower end by fill valve  116 . Funnel chamber  104  is defined at an upper end by fill valve  116  and a lower end by first barrier  110 . A maximum liquid level  118  inside funnel chamber  104  is offset some distance from fill valve  116 . Space between maximum liquid level  118  and fill valve  116  defines air space  120 . Funnel chamber  104  defines a low point  122 . Low point  122  communicates with liquid passage  124  which passes through first barrier  110 . 
   Measuring chamber  106  is defined on an upper end by first barrier  110  and a lower end by second barrier  112 . Measuring chamber  106  defines an upper point  126  and a low point  128 . Liquid passage  124  communicates with measuring chamber  106  at a location below upper region  126 . A measuring channel outlet line  130  preferably communicates with low point  128  of measuring chamber  106 . Measuring chamber outlet line  130  passes through second barrier  112 . 
   Trap chamber  108  is defined at an upper end by second barrier  112  and at a lower end by third barrier  114 . Trap chamber  108  defines an upper point  134  and a lower point  136 . Measuring chamber outlet line  130  preferably communicates with trap chamber  108  at a location below upper point  134  of trap chamber  108 . Trap drain line  138  preferably communicates with low point  136  of trap chamber  108 . Trap valve  140  is provided on trap drain line  138 . 
   A pressurized gas line  150  is provided for communicating a compressed gas source with air space  120  in funnel chamber  104 . Gas line valve  152  is provided for selectively opening and closing gas line  150 . 
   Air vent line  154  passes through first barrier  110  and communicates upper point  126  of measuring chamber  106  with air space  120 , i.e., with a location above maximum liquid level  118  in funnel chamber  104 . 
   Drain line  156  is provided to communicate an interior of pipet  100  with a location external to pipet  100 . Drain line  156  preferably communicates with liquid passage  124 . In a preferred embodiment, liquid passage  124  is made up of an upper segment  124   a  which is offset from lower segment  124   b  as is shown in  FIGS. 7-13 . In a preferred embodiment, drain line  156  is offset from horizontal so that excess liquid passing through the upper leg of liquid passage  124  must first fill drain line  156  before spilling into measuring chamber  106 . Drain line  156  is provided with a drain line valve  158  for selectively opening or closing drain line  156 . 
   A dispense tube  160  preferably communicates upper region  134  of trap chamber  108  with an exterior of pipet  100 . Dispense tube  160  passes through first barrier  110  and exits pipet  100  at a location proximate air space  120 . Dispense tube  160  delivers fluid to sample receptacle  162 . 
   Referring now particularly to  FIG. 7 , shown is the default or home configuration of pipet  100 , i.e., a configuration where fill valve  116  is open, drain valve  158  is closed, trap valve  140  is open and gas valve  152  is closed. In this configuration, pipet  100  is ready for rinsing. Rinse media is first poured into fill chamber  102 . The rinse media then passes through funnel chamber  104 , measuring chamber  106  and into trap chamber  108 . The rinse media is then released through trap drain line  138 . 
   Referring now to  FIG. 8 , pipet  100  is shown in a sample preparation configuration, i.e., a configuration where fill valve  116  is closed, drain valve  158  is closed, trap valve  140  is closed and gas valve  152  is closed. In this step, liquid  164  is delivered to fill chamber  102  where it remains since fill valve  116  is closed. Sample preparation can now be executed. 
   Referring now to  FIG. 9 , pipet  100  is shown in a fill configuration, i.e., a configuration where fill valve  116  is open, drain valve  158  is closed, trap valve  140  is closed and gas valve  152  is closed. Fill valve  116  is opened allowing liquid  164  to pass into funnel chamber  104  and to travel through liquid passage  124 , through measuring chamber  106 , to trap chamber  108 . As trap chamber  108  fills, along with measuring chamber  106 , air evacuates through air vent line  154 . Once both trap chamber  108  and measuring chamber  106  is full, funnel chamber  104  holds any excess liquid. This can be seen in  FIG. 9  where the upper surface of liquid  164  is constant through the lower portion of funnel chamber  104 , the air vent line  154  and dispense tube  160 . The design of the pipet results in impressive precision, which is largely the result of the unique measuring chamber design: separate passages for air and liquid that provide a superior means of filling, i.e., liquid fills from the top while simultaneously evacuating the displaced air. 
   Referring now to  FIG. 10 , wherein pipet  100  is shown in an excess liquid elimination configuration, i.e., a configuration where fill valve  116  is open, drain valve  158  is open, trap valve  140  is closed and gas valve  152  is closed. At this time, drain line valve  158  is opened so that all liquid above the upper drain point  157  of drain line  156  is evacuated out of pipet  100 . It is noted that any liquid remaining in funnel chamber  104  is now unable to enter measuring chamber  106  due to the bifurcated liquid passage  124  and angled drain line  156 . The ability to prevent additional liquid from dropping into the measuring chamber  106  once a measured amount is achieved enables the precision of this device to meet or exceed the precision requirements of class A volumetric glassware as specified in ASTM E969-02. ASTM E969-02 specifies that the tolerance of a class A 100 ml pipet be less than +/−0.08 ml. Applicant has observed accuracy in repeated samples to be between −0.05 milliliters and the +0.02 milliliters, which is well within the limits of class A tolerance for a 100 ml pipet. 
   Referring now to  FIG. 12 , pipet  100  is shown in a fill valve closed configuration, i.e., a configuration where fill valve  116  is closed, drain valve  158  is closed, trap valve  140  is closed and gas valve  152  is closed. In this configuration, pressure may be applied through compressed gas line  150 . Gas line valve  152  is opened so that compressed gas may be delivered through compressed gas line  150  and into pipet  100 . The pressurized gas forces the level of liquid  164  level down until the upper liquid level drops into trap chamber  108 . Therefore, the repeatable measured volume delivered into a sample reservoir  162  is the amount of liquid present in measurement chamber  106  plus the amount present in liquid passage  124   b , in dispense tube  160 , chamber outlet line  130  and a portion of trap chamber  108  as shown in  FIGS. 12 and 13 . 
   The table below summarizes the position of valves in the various configurations: 
   
     
       
             
             
             
             
             
           
         
             
                 
             
             
               Step 
               Fill Valve 
               Drain Valve 
               Gas Valve 
               Trap Valve 
             
             
                 
             
           
           
             
               0 
               Open 
               Closed 
               Closed 
               Open 
             
             
               1 
               Closed 
               Closed 
               Closed 
               Closed 
             
             
               2 
               Open 
               Closed 
               Closed 
               Closed 
             
             
               3 
               Open 
               Open 
               Closed 
               Closed 
             
             
               4 
               Closed 
               Open 
               Closed 
               Closed 
             
             
               5 
               Closed 
               Closed 
               Closed 
               Closed 
             
             
               6 
               Closed 
               Closed 
               Open 
               Closed 
             
             
                 
             
           
        
       
     
   
   Description of steps from table above:
         Step 0, as shown in  FIG. 7  Pipet  100  is shown in a default or home position. Pipet  100  is ready for rinsing; rinse media is poured into fill chamber  102 , the uppermost chamber, passes through chambers  104 ,  106  &amp;  108 , and exits through trap valve  140 .       

   Step 1, as shown in  FIG. 8  Liquid  164  is delivered to fill chamber  102 . Sample preparation can be executed at this step.
         Step 2, as shown in  FIG. 9  Liquid  164  fills funnel chamber  104 , travels through the liquid passage  124 , through the measuring chamber  106 , fills trap chamber  108 . After the trap fills, measuring chamber  106  fills, and air evacuates through the air vent  154 . After measuring chamber  106  fills, funnel chamber  104  holds excess liquid.   Step 3, as shown in  FIG. 10  Excess liquid  164  is eliminated through the drain line.   Step 4, as shown in  FIG. 11  Close fill valve  116 .   Step 5, as shown in  FIG. 12  Excess liquid has been eliminated.   Step 6, as shown in  FIG. 13  Pressure administered through gas line  150  causes liquid to exit through the only opening, i.e., dispense tube  160 ; until liquid level drops below the end of the dispense tube  160 , i.e., into trap chamber  108 .       

   While the invention has been described with a certain degree of particularity, it is understood that the invention is not limited to the embodiment(s) set for herein for purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled. 
   Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the appended claims.