JP3065100B2 - Sample pipetting method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention is a continuation-in-part of co-pending US patent application Ser. No. 07 / 612,160.

The present invention relates generally to non-intrusive automatic pipetting methods, and more particularly to a method for determining the level of a fluid level in a test sample. Level sensing is performed by moving the pipettor toward the sample while aspirating air and monitoring changes in pressure inside the pipettor. Next, the fluid sample is aspirated under control.

Automatic pipetting systems for contacting an electrode with a liquid test sample are known. For example, an electrical signal is generated when a conductive pipette tip or an electrode adjacent to the pipette tip contacts a conductive fluid surface such as a buffer or serum, plasma or urine sample. Because these methods involve manipulation of the fluid, there is a risk of cross-contamination between the test samples. When a portion of the first sample adheres to the pipette tip or electrode and the pipette tip or electrode contacts the second sample, the pipetting sample becomes contaminated with the first sample. This cross-contamination or carry-over can also occur between assay reagents and between assay reagents and samples. The risk of cross-contamination or carryover can be reduced by extensively cleaning the pipette tips or electrodes after each pipetting, but such a cleaning step reduces the processing time with automated equipment.

For accurate pipetting of fluid, sensing of the fluid surface is very important. By determining the fluid surface, the penetration of the pipette tip into the fluid can be controlled. By controlling the depth of penetration of the pipette tip into the fluid, the amount of fluid adhering to the outside of the tip becomes constant, thereby increasing the consistency of the total volume dispensed by pipetting. The use of non-invasive fluid sample surface sensing and a device coupled with a disposable polymer pipette tip increases controllability and consistency. Thus, two advantages are provided from sensing a fluid surface non-invasively. First, instrument processing time is increased because cleaning of the pipette tip between samplings is not required. Second, non-intrusive surface probing removes the possibility of sample carryover.

Non-intrusive fluid surface sensing systems are described in U.S. Patent Nos. 3,347,902 and 3,349,191. The non-intrusive fluid surface sensing system senses fluid surface levels using a method that includes blowing air with a stepper motor controlled syringe. This level sensing method can be used for automatic pipetting of biological samples. However, air is frequently blown to the test sample and foaming often occurs, which may generate aerosol. To minimize the formation of air bubbles, move the pipettor very slowly towards the sample until the sample surface is detected, then quickly pull it back to the end of its travel range. The syringe is then dispensed and all remaining air is exhausted completely from the syringe. Finally, return the pipettor to the fluid surface,
Start suction. It is an object of the present invention to provide non-invasive level sensing of a fluid sample without blowing air through the pipette tip. It is another object of the present invention to aspirate a fluid sample by penetrating the sample at a controlled minimum depth with the pipette tip to minimize the amount of sample adhering to the outside of the pipette tip. Yet another object of the present invention is to detect inhomogeneities such as clumps, air bubbles, foams, etc. in a fluid sample. Still other objects of the present invention will be apparent to those skilled in the art.

The present invention offers advantages over known level sensing and fluid sample aspiration methods. By using a non-intrusive method without contact between the level sensing means, such as a pressure transducer, and the test sample, carryover or cross-contamination between the sample and the reagent is eliminated. The present invention also has advantages over positive pressure (air blast) level sensing.
The invention eliminates the possibility of air bubbles and aerosols. Also, instrument processing time is increased because the direction reversal of the syringe pump between the level sensing step and the suction step is not required. Furthermore, the present invention eliminates the need to withdraw the pipettor from the sample to empty the syringe prior to aspiration, and improves instrument processing time by reducing steps in the method without generating bubbles or aerosols.

SUMMARY OF THE INVENTION The present invention provides an apparatus and method for pipetting a fluid from a container, wherein (a) (i) measuring the ambient air pressure inside the pipettor as a reference pressure reading, and (ii) connecting the pipettor to the container. Aspirating air into the pipettor while moving toward the fluid sample in the (iii) determining the fluid level by monitoring the change in air pressure in the pipettor and indicating the surface level of the fluid in the vessel; (B) aspirating fluid from the container into the pipettor in controlled steps while penetrating the fluid and aspirating the incremental volume; (c) monitoring the pressure change after each incremental aspiration step; d) moving the pipettor tip from the sample in such a way as to tear off the droplets. The pipettor tip may be disposable or reusable.

The present invention further provides devices and methods for detecting heterogeneity in a fluid sample, such as the presence of bubbles or bubbles on the sample surface and / or the presence of clumps on or within the test sample. This method involves (a) measuring the ambient air pressure in the pipettor as a reference pressure reading, (b) drawing air into the pipettor while moving the pipetter toward the fluid sample in the container, and (c) measuring the air pressure in the pipettor. Determining the level of the fluid by monitoring the change in air pressure of the vessel and indicating the surface level of the fluid in the vessel, (d) allowing the pipettor to penetrate the fluid, drawing the fluid from the vessel into the pipettor, and (e) Monitoring the pressure change after suction in the suction step (d),
(F) comparing the measured pressure change with a predetermined normal suction pressure frame, and then (g) observing a pressure value deviating from the pressure frame.

BRIEF DESCRIPTION OF THE FIGURES The figure is a graph of a typical sample of normal bovine serum using the level sensing method of the present invention, with pressure (+1 psi to -1 psi).
Is represented as a 10 digit binary number) versus the serial number of pressure readings taken at intermittent intervals. A pressure change occurs when the pipette tip contacts the surface of the sample and the aspiration of air is stopped immediately.

FIG. 2 is a graph of a typical pressure change during aspiration of a sample of normal bovine serum using the level sensing and aspiration methods of the present invention, wherein the pressure (+1 psi to -1 psi expressed as a 10 digit binary number). Are plotted against aspiration data points. All measured pressures are within a predetermined suction pressure window indicating sample homogeneity.

FIG. 3 is a graph of a typical sample of normal bovine serum with foam on the surface, where a 1000 μl sample was aspirated using the level sensing and aspiration methods of the present invention and the pressure (+
1 psi to -1 psi expressed as a 10 digit binary number) is plotted against the aspiration data point. At least one of the measured pressure values is outside a predetermined suction pressure window indicating the homogeneity of the sample, meaning the presence of a foam.

FIG. 4 is a graph of a typical sample of normal bovine serum with large air bubbles on the surface where a 1000 μl sample was aspirated using the level sensing and aspiration methods of the present invention, and the pressure (+1 psi to −1 psi was increased by 10 orders of magnitude 2). (Expressed in base) is plotted against the aspiration data point. At least one of the measured pressure values is outside of a predetermined suction pressure window indicating the homogeneity of the sample, meaning the presence of bubbles.

FIG. 5 is a graph of a water sample containing a non-dairy cream mimicking a mass in the sample, wherein a 1000 μl sample was aspirated using the level sensing and aspiration methods of the present invention, and the pressure (+1 psi to −−). 1 psi expressed as a 10 digit binary number) is plotted against aspiration data points. At least one of the measured pressure values is outside a predetermined suction pressure window indicating the homogeneity of the sample, meaning the presence of a mass.

FIG. 6 depicts a device that senses levels in two samples simultaneously, aspirates, and then dispenses the two samples to a sample reaction dish.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel level sensing and suction device and method of the present invention is based on a measurable pressure change in the pipettor during the level sensing and suction step. Compared to prior level sensing and aspiration devices and methods, the present invention surprisingly finds more rapid and accurate level sensing and aspiration of fluid samples.

As shown in FIG. 6, the pipettor apparatus of the present invention is airtightly connected to a pipette tip holding means (12) having an inner hole capable of airtightly connecting the tube (16) and the pipettor and a tube connecting means (14). It consists of a disposable pipette tip (10) that can be connected, through which air can be sucked through the disposable pipette tip (10) into the pipette tip holding means (12) and then into the tube (16). Tube (16)
Is connected to a pressure measuring means (18) and a means for sucking air through the pipettor (20), said connection being airtight. Finally, the pipette tip holding means (12)
Comes with means (not shown) for vertical movement along the axis.

Pipette tip holding means (12) are known. For example, manual and automatic pipettors having a tip probe that can form an airtight seal between the pipettor and the disposable pipette tip while simultaneously removing the disposable pipette tip are readily available. Furthermore, the presence or absence of the pipette tip of the pipette probe can be detected by incorporating a limiter switch. One skilled in the art can manufacture such a pipettor without reproducibility testing. Tube connection means (14) such as luer-locks, compression mounting tube adapters, etc. are also known to those skilled in the art and can be readily applied by the skilled artisan to use in the present invention without repetitive testing. Things.

Standard disposable pipette tips (10) such as polypropylene and Tygon®, vinyl,
Standard tubes (16) of polypropylene, polyethylene, metal, etc. can be used in the present invention and are readily available. Disposable pipette tips (10)
Can be stored on a shelf accessible to the pipettor.

In the method of the present invention, the pressure measuring means (18) measures the air pressure in the pipettor either continuously or intermittently. A preferred pressure measuring means is a pressure transducer (electrode). The pressure transducer is a Detem dcm300 digital I / O board (made by Detem Limited, Ontario, Canada)
Through the main computer system. A 10 digit binary (0 to 1023) output is provided by the pressure transducer and the ambient air pressure is measured at approximately the center of the range (512). Full scale positive pressure (+1 psi) translates to 0 and full scale vacuum (-1) translates to 1023.

The means (20) for sucking air into the pipettor must be able to precisely control its operation. For example, during level sensing, the suction means (20) must be able to stop immediately after the pipette tip reaches the fluid surface. The preferred suction means (20) is mechanically connected to a stepper motor and home limit switch that allows control of the movement of the syringe piston and allows the syringe to draw and dispense air through the tube (16). Syringe (preferably a 1500 μl syringe).
The stepper motor and home limit switch are connected to the main computer through a Daytem dcm340 Stepper Motor Control (made by Daytem Limited, Ontario, Canada).

Means for moving the pipettor vertically along the Z axis are:
The pipettor can move (vertically) at least along the Z-axis with respect to the XY plane of the sample container (22), and can move the X-axis and the Y-axis.
An electromechanical assembly that also allows movement of the pipettor along an axis. Preferably, a stepper motor and home limit switch are used to position the pipettor along the Z axis. Once again, connect the stepper motor and home limit switch to the main computer through the Datum dcm340 stepper motor control. Preferably, a Magnon XY table (manufactured by Magnon Engineering, Fontana, Calif.) Is used for positioning the pipettor. The Magnon XY table has both the mechanical hardware and electrical control needed to position the pipettor. The XY table controller is connected to the main computer through a bit bus communication port (Intel, Santa Clara, CA).

To pipet many samples at the same time,
Multiple pipettor assemblies can be connected.
For example, FIG. 6 illustrates a dual pipettor assembly. Each pipettor part is disposable pipette tip (10), pressure measurement means (18) through tube (16)
A pipette tip holding means (12) and a suction means (20) are connected to the device. The two pipettor parts are 2
It is connected to a means for moving both pipetters vertically along the Z-axis so that they can level sense and aspirate one sample simultaneously or sequentially. These dual pipettor assemblies allow the dispensing of two samples into a reaction dish (24) having dual reaction wells.

Sample Pipetting Method The sample pipetting method of the present invention comprises a level sensing of a fluid surface of a sample and a sample suctioning step. The detailed outline of the present invention using the pipettor apparatus shown in FIG. 6 is as follows.

Level Sensing 1. Place the syringe in its fully dispensed position, position the pipettor at the top of its stroke in the Z-axis, and measure the ambient air pressure in the pipettor with a pressure transducer. That value is the basis for comparing all other pressure readings. By using this value as a reference value, any influence on the pressure measurement due to changes in the ambient air pressure is eliminated.

2. Lower the pipettor towards the test sample until the pipette tip is flush with the top of the test sample tube.

3. Next, lower the pipettor toward the sample fluid surface. Simultaneously with the downward movement of the pipettor descending toward the sample fluid surface, air is drawn into the pipettor by drawing air into the syringe and the pressure inside the pipetter is measured with a pressure transducer. In the process of drawing air into the pipettor, the pressure in the pipettor will be somewhat lower than the ambient pressure.

4. When the pressure inside the pipettor drops suddenly, the tip of the pipettor is in contact with the surface of the sample (see Figure 1). Immediately stop both syringe and pipettor operation. Preferably, the pipettor should be stopped so that the tip of the pipettor does not go below the sample surface by more than 0.125 or 1/8 inch. By stopping within 0.125 inches, the amount of sample fluid adhering to the outside of the pipette tip can be easily minimized.

The continuous pressure measurement is actually recorded as a series of intermittent measurements rather than as one continuous measurement (see FIG. 1). In a pressure measurement system as described herein, the recording of the value essentially requires the measured pressure value to be processed in binary output, and such data processing requires minimal processing. It is known to take place in time. Thus, immediately after each data processing cycle, the pressure is recorded.

Sample Pipetting 5. Lower the pipettor a small distance (approximately 0.055 inches) into the sample so that the pipetter does not break the sample during sample aspiration.

6. By pulling the syringe down a suitable distance, at least about 100 μl of sample is aspirated into the pipettor. The pressure in the pipettor is measured immediately after stopping the movement of the syringe (see FIG. 2, aspiration data point 1). After the pressure has reached equilibrium, ie a steady state pressure (about 0.2 seconds), the pressure is measured again (FIG. 2, aspiration data point 2).
reference).

7. Next, compare the two pressure measurements to the suction pressure window. If either or both pressure values are outside the box, the sample is heterogeneous and pipetting is stopped (see FIGS. 3-5). If both values are within the box, continue pipetting and go to step 8.

The suction pressure window is calculated from the ambient pressure measurements by adding the empirically determined pressure to the ambient pressure measurements obtained in step 1 above (see Table 1 below). Empirical determinations are obtained using known standard laboratory techniques, such as pipetting various normal, homogeneous samples with various pressure transducers using the sample pipetting method described herein. It is known that there are differences in the individual performance characteristics of pressure transducers, and by setting a standard range such as a suction pressure frame, sample pipetting can be performed between different transducers or between different normal samples. Can be excluded from one of the factors in the law. A heterogeneous sample is a sample that has at least one pressure measurement that falls outside the suction pressure window within which the normal homogeneous sample pressure measurement should be contained.

An empirical determination is easily obtained by subtracting the ambient pressure (as at the normal sample pressure measurement) from the highest and lowest pipettor pressure measurements obtained during sample pipetting of a normal sample. Thus, adding these empirical values to ambient pressure in future sample pipetting will automatically adapt to any changes in ambient pressure.

8. Next, lower the pipettor a small distance (approximately 0.055 inches) into the sample so that the pipetter does not break the sample during sample aspiration.

9.Approximately 150μ by lowering the syringe a suitable distance
1 sample is aspirated into the pipettor. After the pressure has reached equilibrium, ie a steady state pressure (about 0.2 seconds),
Measure the pressure in the pipettor (see FIG. 2, aspiration data point 3).

10. Next, compare the pressure measurement to the suction pressure frame. If at least one of the pressure values is outside the box, the sample is heterogeneous and pipetting is stopped. If the value is within the frame, continue pipetting and go to step 11.

11. Step 8 if necessary until the desired total volume (about 100 μl to about 1000 μl) of sample has been aspirated into the pipettor
~ 10 suction cycles (Figure 2, suction data points 4-8)
Repeat).

12. Raise the pipettor slightly (about 0.055 inches) so that the pipettor tip is at the surface of the sample at this point. Dispense about 50 μl of sample to the sample to prevent backlash in the syringe before dispensing the test sample to the reaction vessel. It is well known that this back crash occurs in mechanical systems due to loose parts or poor gear engagement. Therefore,
When moving the mechanical system in the opposite direction to move the syringe in the opposite direction, one must take up any backlash or looseness in the mechanical system before starting to move the syringe. By returning about 50 μl of sample to the sample tube, backlash is prevented and sample distribution to the reaction vessel becomes more accurate.

13. Next, slowly raise the pipettor by about 0.5 inch to prevent a small amount of sample from being stripped from the inside of the pipettor tip. Next, return the pipettor to its original position where the pipettor can move to the dispensing position and be ready to dispense the correct aliquot of the sample into the reaction vessel.

In the level sensing method, air is sucked into the pipettor while lowering the pipetter toward the surface of the fluid sample. The syringe used in this method is preferably a 1500 μl syringe. When aspirating 1000 μl using a 1500 μl syringe, only 500 μl can be used for level sensing. Therefore, the movement of the pipettor descending towards the surface of the sample must cooperate with 500 μl of air suction.
The preferred syringe aspiration rate for the level sensing method is 160 μl / sec, and the pipettor travel speed reaches the end of its stroke as soon as the syringe completes aspirating 500 μl of air if no sample surface is detected. (Ie, the limit of pipettor descent). However, it is preferred that the lowering speed of the pipettor be slower than the maximum speed so that the pipettor can be stopped so that the tip of the pipette tip is only 0.125 (1/8) inch below the surface of the sample. The syringe begins to aspirate before the pipettor descends from a position where the pipette tip is flush with the top of the sample container. The delay in pipettor operation (preferably about 0.2 seconds) provides air compression time to reach a standstill.

After the level on the sample surface is sensed and the pipette tip is located only 0.125 inches below the sample surface, the aspiration procedure is started. Both the syringe and the pipettor are stationary. Allow the pipettor to descend a short distance (preferably 0.055 inches) so that the pipetter does not break the sample during sample aspiration. If the sample breaks in the pipettor, air will be aspirated in addition to the sample, and the wrong amount of sample will be aspirated. Then aspirate at least 100 μl of sample (first aspiration).
Approximately 100 μl of sample appears to be the minimum that can be accurately aspirated by this protocol using the device shown in FIG. This sample volume is the basis for comparing various samples that contain inhomogeneities in the sample, such as air bubbles, foam, and other system problems such as air leaks in the device. A pressure reading is taken immediately after the syringe stops at the first sample aspiration (aspiration data point 1). If this pressure reading is outside the suction pressure window at suction data point 1, the sample is heterogeneous. For example, high viscosity samples, such as clumps or thick foams, create a higher vacuum inside a pipetter than a normal homogeneous sample. Samples with air bubbles or leaks in the system may have a lower vacuum inside the pipettor than normal homogeneous samples and may be at ambient pressure. The second suction pressure reading (suction data point 2) is slightly delayed (preferably at least about 0.
2 seconds) This is done inside the pipettor, but this delay is enough time for the pressure inside the pipettor to reach a standstill. With respect to the first pressure reading, a pressure reading outside the suction pressure window corresponding to suction data point 2 indicates a heterogeneity or system problem. The suction process is automatically stopped whenever any pressure reading is outside the corresponding suction pressure window.

The remaining sample to be aspirated into the pipettor
A sample aspiration cycle in which a fixed volume (or less if all needed to obtain the desired total sample volume to be aspirated) (preferably at least 100 μl) is aspirated in each aspiration cycle Is sucked in. More preferably, a volume of about 150 μl is aspirated in each aspiration cycle. Therefore, seven aspiration cycles are required to completely aspirate a total of 1000 μl of sample. The suction cycle is as follows:
(1) To prevent the sample from being cut off by the pipettor,
The pipettor is lowered a short distance (preferably about 0.055 inches) through the sample, (2) aliquots the sample (preferably about 150 μl) into the pipettor, and (3) with a slight delay (at least about 0.2 seconds). Read the pressure in the pipettor (preferred) (aspiration data points 3 to 3)
8). Again, if the pressure reading is outside the corresponding suction pressure window, the sample is heterogeneous and suction is stopped.

The suction pressure window is an empirically derived value. A large number of normal homogenous fluid samples are aspirated using the method of the present invention using a wide variety of pressure measurement means. Thus, normal fluctuations in pressure readings (aspiration data points) due to changes in the sample or the pressure measurement means create a normal range of pressure values that would be observed when a normal homogeneous sample is aspirated. The range at each aspiration data point extends from the lowest pressure reading obtained when a normal homogeneous sample is aspirated to the highest pressure reading.
Subtract ambient pressure (at the time of aspiration) from the minimum and maximum pressure readings obtained at each aspiration data point to eliminate the effects of atmospheric pressure fluctuations. For example,
The difference values for each aspirated data point from ten samples of normal bovine serum are shown in Table 1 below. The suction pressure window for future suction can then be calculated from these difference values by adding the ambient pressure measured at the start of the level sensing step (step 1 above). The accuracy of these ranges (ie, the difference values) will depend on the number of normal samples used to create the suction pressure window. Preferably at least 10 samples should be used to create the suction pressure frame.

If any of the pressure readings (aspiration data points) taken during the aspiration of the sample are outside the corresponding aspiration pressure window, the sample is heterogeneous and the aspiration is stopped. For example, at the sixth pressure reading, if the ambient pressure is 512, the value of the suction pressure frame according to the values in Table 1 will be 752 (512 + 240) to 882 (512 + 370). Pressure readings for samples below 752 or above 882 indicate that the sample is heterogeneous.

After aspirating the desired total sample volume, raise the pipettor a short distance (preferably 0.055 inches) so that the end of the pipette tip is within 0.125 inches below the sample surface. This allows some samples (about 50μ
1 is preferred) in the sample. Because the mechanical system has slack in the coupling of the machine, such as to slip between gears or the like, backlash is observed when the mechanism that drives the syringe piston reverses its previous motion. For example, when approximately 50 μl of sample is returned to the sample, some of the mechanical operations readjust the tension between the parts before the syringe piston begins to move. Therefore, less than 50 μl of sample is accurately returned to the sample.

After returning the aspirated sample to the sample, a small delay (preferably at least 0.5 seconds) causes most of the sample liquid attached to the outside of the pipette tip to flow out. The pipettor is then raised a short distance (preferably 0.05 inches) at a very slow speed (preferably 2.88 inches / second). This allows a small amount of sample to be stripped or released from inside the pipette tip end,
The pipette tip is removed from the sample. The pipettor can then be returned to its original position at normal speed. Move the pipettor from the original position to a new position to dispense the aspirated sample. Alternatively, the reaction dish may be moved instead of the sample vessel and the pipettor lowered again.

The sample must be at least partially liquid so that it can be aspirated. Therefore, blood, serum, plasma,
The sample can be urine, spinal fluid, ascites fluid, cell culture media, tissue and swab extracts, biological fluids such as fluids obtained from sample processing in a DNA cyclizer, and the like. Biological samples also include particles such as cells. Microparticles or other small particles used in assay operations are also included in the particles. A non-biological fluid, such as a water sample or a chemical or at least a solid that can be dispersed in a suspension, can also be a sample.

The examples described below are specific examples of the present invention, but the scope of the present invention defined by the claims is not limited thereto. It will be appreciated that those skilled in the art can envision many other instruments and methods of use to which the concepts of the present invention may be applied.

Example 1 Sample Detection by Vacuum According to the method of the invention described above, the surface of a sample is detected (level sensing). As the pipettor moves towards the surface of the sample, drawing air (with a syringe) into the pipetter creates a vacuum inside the pipettor shown in FIG. During this process, the pressure is monitored by a pressure transducer and the data is stored in a variable named "p_column". The pipettor control software runs under the control of a Soft-Scope 286 debugger program (Concurrent Sciences, Inc., Mosco, Idaho). This software package has the ability to monitor program execution and examine the value of variables during processing. After level sensing is complete, the first 30 pressure readings are determined by examining the values stored in the "p_column". Due to the data processing by the computer, there is a slight delay between each pressure reading. The length of this delay depends on software and computer hardware.
If longer delays are needed, they can be incorporated into the software. The reading numbers and resulting pressures are tabulated in Table 2.

The values in Table 2 are 10-digit binary numbers, and full-scale vacuum (-
The value of 1 psi is expressed as 1023, and full scale positive pressure (+1 ps)
The value of i) is represented by 0. The change in pressure at read number 14 indicates that the surface has been reached, ie, the tip of the pipettor has contacted the surface of the sample.
Immediately, the movement of the pipettor is stopped and the suction is stopped. The pressure inside the pipettor is then brought back into equilibrium with the ambient pressure. These data demonstrate the ability of the system to detect the surface of the sample while vacuuming (ie, air suctioning). The pressure value is stored during level sensing. When contacting the sample, a vacuum spike occurs. Graph the data, pressure (+1 psi to -1p expressed as a 10 digit binary number)
FIG. 1 shows si) plotted against the pressure reading.

Example 2 Suction pressure test of normal calf serum The suction pressure frame is demonstrated using normal calf serum. Aspirate 10 normal calf serum samples individually and store pipettor suction pressure data. Visually confirm that all ten samples are free of foam, air bubbles, fines or other inhomogeneities. All ten samples are level sensed within 0.125 (1/8) inch from the surface of the sample, and thus are within a tolerance of 0.125 inches from the sample surface. Table 3 summarizes the suction data from all ten samples. A representative sample is graphed and the pressure (+1 psi to -1 psi expressed as a 10 digit binary number) is plotted against the aspiration data point in FIG. One calf serum sample is plotted and shown as a solid line connecting ■. The lower limit frame is indicated by a solid line connecting x, and the upper limit frame is indicated by a solid line connecting *.

Example 3 Detection of foam during aspiration The effect of foam on the sample surface is tested as follows. Three normal calf serum samples are pipetted into separate containers. All three samples are foam,
Visually check for the absence of air bubbles, fines or other inhomogeneities. Shake each test sample vigorously to create a foam. Sensing the fluid level according to the method of the invention described above. All three samples containing foam on the surface of the sample are detected on the foam surface. However, these samples are later rejected based on suction pressure data. Table 4 summarizes the suction data of all three samples. Graph data from one of the calf serum samples containing foam (indicated by the solid line connecting ■), and plot the pressure (+1 psi to -1 psi expressed as a 10 digit binary number) against the aspiration data points. FIG. 3 is a plot. The lower limit frame is indicated by a solid line connecting x, and the upper limit frame is indicated by a solid line connecting *.

Example 4 Detection of Bubbles During Aspiration The effect of large bubbles on the sample surface is tested as follows. Three normal calf serum samples are pipetted into separate containers. Visually confirm that all three samples are free of foam, air bubbles, fines or other inhomogeneities. Using a Pasteur pipette and a spoid sphere, air is blown into the surface of the sample to create large bubbles in each test sample. Sensing the fluid level according to the method of the invention described above. Table 5 summarizes the suction data of all three samples. The first two samples with bubbles are accurately level sensed. That is, the bubbles present in each of these two samples had no effect on level sensing. As the pipettor moves toward the surface of the sample, the pipette tip appears to break air bubbles.

Bubbles in the third sample prevent level sensing on the sample surface. When bubbles come into contact with the pipettor, bubbles and non-sample surfaces are detected. This sample is rejected based on suction pressure data. FIG. 4 is a graph of the data of the third sample (shown by the solid line connecting ■) and plotting the pressure (+1 psi to −1 psi expressed as a 10 digit binary number) against the aspiration data point. The lower limit frame is indicated by a solid line connecting x, and the upper limit frame is indicated by a solid line connecting *.

Example 5 Detection of lump during aspiration A test is performed to demonstrate the ability of the method of the present invention to detect lump in a test sample. The non-dairy cream is partially mixed with water to form small chunks, forming simulated chunks. The mixture is aspirated three times using the method of the invention described above. Table 6 summarizes the suction pressure data.

All three samples are rejected based on the aspiration data. The first and third samples are also out of limits at resting pressure following the desired aspiration. FIG. 5 is a graph of the data of a typical sample (shown as a solid line connecting ■) and plotting the pressure (+1 psi to −1 psi expressed as a 10 digit binary number) against the aspiration data point. Also,
The lower limit frame is shown by a solid line connecting x, and the upper limit frame is shown by a solid line connecting *.

The above examples and alternatives suggested are not limiting, but rather are intended as illustrations. Therefore, the present invention is not limited to these, and any modifications are included in the present invention without departing from the scope of the invention described in the claims.

Continuation of the front page (56) References JP-A-2-243962 (JP, A) JP-A-2-17448 (JP, A) JP-A-2-243960 (JP, A) JP-A-61-292557 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 35/00-35/10 G01N 1/00 101

Claims (5)

(57) [Claims] (A) measuring the ambient air pressure in the pipettor as a reference pressure reading; (b) sucking air into the pipettor while moving the pipetter toward the fluid sample in the container; Determining the fluid level by monitoring the change in air pressure in the pipettor and indicating the surface level of the fluid in the vessel; (d) allowing the pipettor to penetrate the fluid, drawing the fluid from the vessel into the pipettor;
(E) monitoring the pressure change after suction in step (d), (f) comparing the measured pressure change with a predetermined normal suction pressure frame, and then (g) the pressure deviating from the pressure frame. A method for detecting heterogeneity in a fluid sample, characterized by observing a value. 2. The method according to claim 1, wherein the heterogeneity of the sample is bubbles.
The described method. 3. The method of claim 1, wherein the heterogeneity of the sample is a foamy layer. 4. The method of claim 1, wherein the heterogeneity of the sample is a lump. 5. A method comprising: (a) measuring the ambient air pressure in a pipettor as a reference pressure reading; (b) allowing the pipetter to penetrate the fluid, drawing the fluid from the container into the pipettor;
(C) monitoring the pressure change after suction in step (d), (d) comparing the measured pressure change with a predetermined normal suction pressure frame, and then (e) the pressure deviating from the pressure frame. A method for detecting heterogeneity in a fluid sample, characterized by observing a value.