Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR WASHING A
I .1 .1 I t PROBE
FIELD OF THE INVENTION
The present invention provides an apparatus and a method for
cleansing liquid dispensers and has particular utility in cleansing pipetting
probes, such as the type of pipettes commonly used in automated analyzers.
BACKGROUND OF THE INVENTION
When a pipeKe or the like is used to dispense fluids, the fluid being
dispensed will tend to contaminate the interior of the tube or other structure
through which the fluid is dispensed. When fluids are transferred using
pipettes, an end of the pipette is commonly immersed in the fluid to aspirate
the fluid into the pipette. Accordingly, both the interior and the exterior of
the pipette will become contaminated with the fluid being dispensed.
In those situations where a pipette or the like is dedicated to
dispensing a single fluid, this contamination generally is not a problem.
Likewise, if cross-contamination between two or more fluids is not a concern
in the particular application for which the pipette is used, there is generally no
need to remove any previously dispensed fluid from the interior and exterior
of the pipette.
In many situations in which pipettes are used, though, cross-
contamination of fluids is a major concern. For example, in conducting
chemical analyses of medical samples, such as assays for a particular
constituent in a patient's blood, care must be taken not to introduce any of
the patients' samples into the reagent supplies or to intermingle one patient's
sample with that of another patient.
When manually processing such patient samples with pipettes, one will
commonly employ disposable pipette tips. These tips are typically thrown
away after they are used to aspirate and dispense a single patient sample,
effectively preventing cross-contamination of the different samples. In
automated analyzers of the type commonly used for clinical laboratory
analysis of such samples, though, disposable pipette tips generally are not
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deemed to be ~r~Lical and the pipette probes used in such analyzers must
typically be cleansed after each dispensing operation to maintain integrity of
both the patients' samples and the reagent supplies used to conduct the
tests.
A number of different approaches to washin~ pipette probes have been
developed. In each case, the function of the pipette washing apparatus is to
clean the pipette sufficiently to avoid any deleterious cross-contamination of
the fluids b2ing handled. In most cases, this means that the wash station
must efficiently and relatively thoroughly wash both the exterior and interior
surfaces of the probe to remove any contaminating fluids.
One common way to clean probes in automated pipettors is to
dispense a wash fluid through the pipette probe from a dedicated wash fluid
supply and to spray the outside of the probe with wash fluid supplied through
a separate washinç~ element. Contaminated wash fluid will typically be
withdrawn from a collectin~ cup positioned below the probe and transferred
to a waste fluid collector. This construction provides an efficient cleansing ofthe probe. Unfortunately, it also requires a relatively large volume of wash
fluid and requires separate pumping mechanisms and fluid supply systems for
both the pipette probe and the separate external washing hardware,
increasing both the cost and complexity of the device and generating more
biohazardous waste.
Another approach known in the art for cleansing pipette probes in
automated analyzers is to dispense wash fluid through the probe into a
relatively shallow receiving cup and to use the same fluid to rinse both the
interior and exterior surfaces of the probe. At first blush, this would appear
to provide a superior washing station in that only one wash fluid supply
system - i.e. the one connected to the probe - need be provided and it seems
that the quantity of wash fluid needed to cleanse the probe would be
minimized since the same fluid is used to wash the entire pipette.
In practice, however, this has proven to be a somewhat inefficient way
to cleanse pipette probes. The problem arises from the fact that the interior
of the pipette probe tends to carry the highest concentrations of
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contaminated fluids since the fluids being transferred are received in the
interior of the probe. When wash fluid is first passed through the probe, it
will carry with it the bulk of the contaminated fluid with it into the small
receiving cup and this contaminated fluid is flushed around the outside of the
5 probe. In order to cleanse the probe, one must pump further fluid through the
probe both to increase turbulence in the receiving cup and to dilute to
contaminated wash fluid with more fresh wash fluid. If low levels of possible
cross-contamination are required, as is the case for most automated chemical
analyzers used in the medical field, it takes a fair amount of wash fluid to~0 sufficiently clean the pipette probe and yield reliable results.
SUMMARY OF THE INVENTION
The present invention provides a method for cleaning pipette probes
and the like and an apparatus for carrying out this method. In accordance
with the method, a pipette probe is positioned in or adjacent to a receiving
15 cup. Initially, fluid is dispensed through the probe and simultaneously drained
from the receiving cup at least as fast as it is dispensed into the cup. Once a
sufficient volume of fluid has been passed through the probe to remove the
majority of the contaminants from the interior of the probe, the flow rate is
increased or the rate of evacuation of fluid from the receiving cup is
20 decreased, or both, to build up a level of fluid in the receiving cup. This fluid
is allowed to contact and wash the exterior of the probe and fluid is desirably
continuously flushed through the probe until is has been sufficiently cleaned.
The apparatus of the invention provides a receiving cup having a drain
therein. In one embodiment, the drain is designed to remove fluid at a
25 relatively constant rate, such as by simply having an open port in the cup
through which spent wash fluid is allowed to pass under gravity. Wash fluid
is passed through the probe at an initial rate which is slow enough to allow allof the fluid to exit the receiving cup through the drain. After the majority of
the contaminant in the probe is dispensed into and drained out of the cup, the
30 flow rate of wash fluid through the probe is increased so that it is greater
than the rate at which it will drain from the cup. In this device, it may be
desirable to have a larger wash basin around the receiving cup to catch
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overflow from the receiving cup during the washing of the exterior of the
probe.
In another embodiment of the present apparatus, a selectively
controllable pump is attached to the drain in the receiving cup. Initially, the
pump will aspirate fluid from the receiving cup at least as rapidly as it is
dispensed. Once the majority of the contaminating fluid within the probe is
washed into the receiving cup and pumped out, the drainage rate of the pump
will be slowed to allow fluid to build up in the receiving cup and cover a
portion of the exterior of the probe to wash it. The pump is then operated to
withdraw fluid from the receiving cup rapidly enough to prevent it from
overflowing, but slowly enough to permit the exterior of the pump to be
washed. When washing is complete, flow through the probe may be
terminated and the remaining fluid in the receiving cup can be withdrawn
through the drain.
BRIEF DESCRIPTIOI~I OF THE DRAWINGS
Figure 1 is a schematic cross sectional view of a washing system in
accordance with the present invention; and
Figure 2 is a schematic cross sectional view of an alternative
embodiment of a washing system of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 schematically illustrates one embodiment of a washing system
10 in accordance with the present invention. The system includes a receiving
cup 20 positioned within a wash basin 30. The receiving cup 20 of Figure 1
has a generally cylindrical side wall 22 and a bottom 24, with a drain 26
positioned adjacent the bottom for draining fluid out of the receiving cup.
Although the drain may take any desired form, in the illustrated embodiment
the drain simply comprises a port which extends generally horizontally
through the wall 22 of the cup adjacent the lower end of the wall. This
permits any fluid within the receiving cup 20 to drain into the wash basin 30
for removal.
The wash basin 30 is desirably larger than the receiving cup. The
wash basin, not unlike the receiving cup, may have a generally cylindrical wall
,
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32 and a bottom 34, with a drain 36 positioned adjacent the bottom to allow
fluid to be drained from the wash basin. The drain 36 of the wash basin is
desirably connected, e.g. by flexible tubing, to a waste container (not shown)
so that spent wash fluid can be collected to later disposal.
If so desired, the receiving cup can be positioned generally
concentrically with respect to the wash basin, but this is not necessary. It
may be desirable, though, to maintain at least some space between the wall
22 of the receiving cup and the wall 32 of the wash basin at all points so that
fluid overflowing from the receiving cup can flow into the wash basin without
fear of spilling over into other parts of the apparatus with which the wash
system 10 is used. In order to minimize any problems associated with
splashing of wash fluid out of the receiving cup 20, it may be advantageous
to have the wall 32 of the wash basin extend higher than the top of the wall
22 of the receiving cup, as shown.
The absolute and relative sizes of the receiving cup 20 and the wash
basin 30 can be varied to accommodate the equipment with which it is to be
used. In order to reduce the amount of wash fluid necessary to wash the
outside of a pipette probe 15 received in the receiving cup, the inner diameter
of the receiving cup is desirably relatively small. However, care should be
20 taken to ensure that there is enough clearance between the exterior of the
probe and the interior of the receiving cup to both allow turbulent flow within
the receiving cup and to avoid undue splashing of wash fluid out of the
receiving cup.
It may be desirable to position the probe 15 toward a side of the
25 receiving cup rather than having it aligned with the axis of the cup, as
illustrated in Figure 1. This tends to increase turbulence in the cup, further
aiding in washing the exterior of the pipette. Much the same effect could
also be achieved by changing the shape of the bottom 24 of the receiving
cup from the relatively flat shape shown in Figure 1 to either an irregular
30 shape or a shape which is asymmetrical with respect to the axis of the probe.As noted above, the wash basin is desirably larger than the receiving
cup. So long as the wash basin can readily capture and drain away the wash
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fluid coming out of the receiving cup durinç1 the washinçl operation, though,
the relative sizes of these two components is not believed to be critical. For
example, if drainage of fluid from the wash basin through the drain 36 were
enhanced with a pump, the wash basin would not need to be larger than the
wash basin and, as a matter of fact, the wash basin could have a smaller ~,
volume than that of the receiving cup.
Figure 2 shows an alternative design of a washing system 10' in
accordance with the invention. This system 10' has a receiving cup 20
which is directly analogous to the receiving cup of Figure 1. However, this
design eliminates the wash basin and instead employs a pump 40 to control
the rate of drainage from the receiving cup during operation.
The pump 40 should be selectively controllable to allow an operator or
a computer-based automated controller (not shown) to control the pump and
the rate at which it removes fluid from the receiving cup. Although Figure 2
schematically shows a pump to be used for selectively controlling drainage of
the receiving cup, it should be understood that other functional equivalents of
a pump could instead be employed, such as providing a vacuum line with a
valve to control the rate of aspiration of fluid from the receiving cup. The
operation of the pump or aspiration line in a washing operation is described
below.
Another aspect of the present invention provides a method for washing
a fluid dispensing tube, such as a manual pipette or an automated pipette
probe used in an automated analyzer. Before the probe or other fluid
dispensing tube needs to be washed, it will generally be used to transfer a
fluid which raises a possible cross-contamination risk, such as a sample of a
patient's bodily fluid or a reagent used to carry out a specific chemical
reaction.
When such fluids are transferred or dispensed with a pipette or
automated pipette probe, the tip of the probe is usually inserted a relatively
short distance into a supply of the fluid to be transferred. Once at least the
tip of the pipette is immersed in the fluid, a predetermined quantity of the
fluid will be aspirated into the interior of the probe. The fluid will be held in
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the probe until it is positioned over the vessel into which it is to be dispensed
and is then forced out of the interior of the tube. At the end of this transfer
process, some fluid will usually cling to or wet both the interior of the tube
and the exterior of the tube where it was immersed in the fluid.
Once a fluid has been transferred with a fluid dispensing tube, the tube
can be washed in accordance with the present invention, such as with a
washing system 10 or 10' described above. The probe or other dispensing
tube is positioned adjacent, and desirably within, a receiving cup 20. As
discussed above, it may be desirable to position the probe within the
receiving cup so that the probe axis is spaced away from the axis of the
generally cylindrical receiving cup to increase turbulence in the cup when
washing the exterior of the probe. A wash fluid is dispensed through the
pipette to flush contaminants from the interior of the tube and the
contaminated wash fluid is simultaneously drained from the receiving cup.
This draining desirably takes place at least as fast as the fluid is dispensed
from the probe.
Once a majority of the contaminants in the interior of the tube have
been removed, wash fluid is dispensed through the probe at a rate faster than
it is drained from the receiving cup so that the level of fluid in the cup will
rise to cover a portion of the exterior of the probe. In particular, the wash
fluid in the receiving cup in this stage of washing should be deep enough to
cover at least that length of the probe which was immersed in the
contaminating fluid. Wash fluid can then be delivered through the probe to
carry away, or at least greatly dilute, the contaminants in the cup and this
can be continued until the exterior and interior of the probe are as clean as
the system's requirements dictate.
The particulars of this method will vary somewhat on the nature of the
wash system employed to carry out the invention. If the wash system 10
shown in Figure 1 is used, the first, initial cleansing of the interior of the tube
desirably takes place at a relatively slow flow rate, while the second stage of
washing where the exterior is also cleaned takes place at a higher flow rate.
For example, the flow rate of wash fluid in the first stage of washing can be
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on the order of 400-450 microliters per second while the second stage of
washinçl ernploys a significantly faster flow rate, such as on the order of
1700-1800 rnicroliters per second. The exact flow rate employed in any
0iven situation will depend on a number of factors, including the dimensions
of the probe, the dimensions of the receiving cup, the viscosity and solubility
of the contaminant, and other factors which will be readily recognized by one
skilled in the art.
Employing two different flow rates in the wash system 10 of Figure 1
permits the present method of washing to be carried out without requiring
10 any complex equipment. In the first stage of washing at the lower flow rates,the fluid will drain out of the receiving cup through the drain 26 and simply
flow into the wash basin 30 for disposal. When the flow rate is increased
beyond the rate through which the fluid will exit through the drain 26, the
fluid level will inherently rise in the receiving cup. In a preferred embodiment,
15 the rate at which wash fluid flows through the probe is significantly higher
than the rate at which it can exit through the drain, causing the wash fluid to
flow over the top of the wall 22 of the receiving cup. If the flow rate and
dimensions of the receiving cup are properly chosen, this will also tend to
provide good turbulence in the receiving cup to help wash the exterior of the
20 probe.
If the washing system 10' of Figure 2 is instead employed, the rate at
which the fluid is drained by the pump 40 (or other functionally equivalent
component) can remain substantially constant and the wash fluid's flow rate
through the probe can be varied in much the same manner as that described
25 above for the system 10 of Figure 1. Care should be taken, however, not to
allow any of the contaminated wash fluid to spill out of the washing system
10'.
In a preferred embodiment, though, the washing system 10' is
operated somewhat differently, with the selectively controllable pump 40
30 controlling the rate at which waste fluid is drained and the pipette probe
delivering a relatively constant flow of wash fluid. In the first washing stage,the pump is operated so that the wash fluid is drained relatively rapidly,
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preventing the wash fluid from building up in the receiving cup and contacting
the exterior of the probe. Once a majority of the more concenllaLeJ fluid
from the interior of the probe has been flushed and drained through the drain
26, the rate at which the pump withdraws fluid can be reduced, or even
5 temporarily terminated, to allow fluid to build up in the receiving cup. The
pump can then be operated to withdraw fluid from the receiving cup at the
same rate at which it is delivered through the probe to prevent it from
overflowing.
Hence, the present invention provides an effective method and
10 apparatus for washing pipette probes and the like. This method and
apparatus are believed to simplify the equipment necessary to cleanse a
pipette probe and, at least in some circumstances, provide the possibility of
reducing the volume of wash fluid necessary to reach the necessary level of
cleaning.
