Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: PIPETTE TUBE
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a heatable pipette tube with a controlled
electric heater.
Description of the Related Art
A heatable pipette tube, such as the one described in German patent
specification 26 26 332, permits regulatable heating extending over the
pipette tube, with the exception of the tip end. A drawback of this design is
that temperature control of samples is difficult. For example, if the heating
and
the regulation (control) is adjusted in order to temper larger volumes, there
is
a danger that smaller volumes may become overheated. Likewise, if the
pipette is adjusted for small volumes, large samples may not become heated
enough. There also exists a controllable heater for a centrifuge, into which a
pipette tube may be inserted. However, temperature control with this
arrangement is also problematic. That is, it is difficult to temper different
volumes of pipette fluid quickly to a desired temperature without overheating
the fluid.
EP-0 192 957 B1 describes an analysis device with a slide which
transports via a pipette, fluid samples from a rotating plate to a tempered
cuvette. The slide is provided with a controllable heater. This temperature
controller pretempers the sample fluid to the temperature of the cuvette.
German Offenlegungsschrift 38 38 626 discloses a pipette tube that is
heated by electrically heated water. However, this heater lacks sufficient
responsiveness because the water supply together with other structural parts
must first be heated by the water to the desired temperature.
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SUMMARY OF THE INVENTION
An aspect of the present invention is to provide a heatable pipette tube
in which different volumes can be brought very quickly to the desired
temperature.
This aspect is attained by providing a pipette tube with two zones,
namely a first zone containing the tip of the pipette tube and comprising a
relatively small pipette volume, and a second zone with a comparatively larger
pipette volume. Both zones are provided with separate heaters each with its
own regulator. The regulator provided for heating of the first zone works with
greater corrective action of manipulated value while the regulator of the
second zone works with smaller corrective action of manipulated value. In
other words, the temperature of the contents in the first zone may be changed
more quickly and accurately than the temperature of the liquid in the second
zone which has a larger area of heat transmission.
If a small volume is pipetted, it is quickly heated to the desired
temperature. If a larger volume is pipetted, the pipette fluid is sucked into
the
second zone above the first zone, wherein the first zone acts as pretempering
for the second zone. However, these volumes arrive in the second zone at
temperatures that depend on pretempering that occurs in the first zone.
Generally, there will be a relatively low temperature differences of some
degrees between the zones.
Due to the different structure of the two zones, temperature regulation
of the second zone is more sluggish and is distinguished by small
temperature fluctuations and by a larger area of heat transmission, in order
to
be able to temper larger volumes in a short period of time.
It is preferable for the tube of the first zone to be relatively straight and
for the tube of the second zone to be twisted or wound, for example, in either
a spiral or in a meander configuration. This structure facilitates the smaller
heat capacity of the first zone and the larger heat capacity of the second
zone.
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1t is also beneficial if the tube in the area of the second zone abuts a
heat conductor, such as a metal block having an aperture for receiving the
tube.
According to a preferred embodiment of the invention, the electrical
heater of the first zone is a PTC (positive temperature coefficient) heater
wherein the heating wire has a varying resistance. Thus, if the tube in the
first
zone is only partly filled with the pipette fluid, the temperature of the PTC
resistance wire in the unfilled part increases, which results in increased
electrical resistance, so that the part that does not contact the fluid is
heated
less. Due to this feature, a very even tempering may be obtained
independent of the filling condition of the tube in the first zone.
A temperature sensor is provided at the entrance of the second zone
so that the first temperature at the side of the entrance is measured.
Additionally, a similar temperature sensor also can be provided at the
egress of the second zone, which is beneficial for example for cleaning
purposes, when the tube is filled in the reverse direction. For this reason,
throughout the present application the zones are not referred to as lower and
upper pipetting zones, but rather are referred to as a first and a second
pipetting zone. Generally, the pipetting fluid is sucked through the tip to
the
first, lower zone, and then arrives in the second, upper zone, if a sufficient
volume is present.
In a preferred embodiment, in the second zone, the temperature
sensor, and the heating element are identical.
The pipette tube according to the invention may also be used for
cooling. For this, the invention may include Pettier elements instead of the
heating elements described above. Pettier elements, which are known, are
used for both cooling or heating.
In a further preferred embodiment, the nominal temperature in the
second zone is somewhat lower, preferably between 0.5 and 5° C lower
than
in the first zone.
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BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing, which is incorporated in and constitutes a
part of this specification, illustrates one embodiment of the invention, and
together with the description, seeks to explain the principles of the
invention.
FIG. 1 is a schematic diagram of a preferred embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the invention will now be described with
further detail. FIG. 1 schematically illustrates a pipette tube according to
the
invention. The pipette tube includes a lower area 1 and a subsequent upper
area 2. The lower area includes a pipette tip, and is characterized by a
substantially linearly extending tube portion.
In the upper area 2, the tube may be spirally wound or may be wound
in other manners such as meander configurations. The tube of upper area 2
abuts a body 3, constructed of material with good heat conducting properties,
so that the heat capacity is increased.
At least the largest length of the lower area 1 is heated by means of a
first electrical heater 4 to which a regulator 5 is connected. Similarly, the
upper area 2 of the tube is also heated by means of a second electrical heater
6, to which a regulator 7 is connected.
Thus, the total length 1, 2 of the tube is heated by two separate heaters
4, 6, wherein two different regulators 5, 7 with different regulating
characteristics are utilized. The regulator 5 works with a strong corrective
action of manipulated value and the regulator 7 has a smaller corrective
action of manipulated value. In other words, the first heater has a superior
ability than the second heater to quickly and accurately alter the temperature
of the fluid in the tube to reach a predetermined temperature. There is a
difference in the range of adjustments between the heaters due to differences
in the temperature changing magnitude of the regulators.
The first heater 4 heats the substantially linear portion of the tube up to,
for example 15 mm before the tip. The second heater 6 includes an aluminum
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cylinder (body 3) with a large heat capacity. The greatest part of the tube in
respect to its length is wound around the cylinder.
The regulating circuit 5 of the lower heater 4 regulates, without delay,
the temperature of the quantity of fluid in the lower area 1. This means that
5 great fluctuations in the nominal size are regulated very quickly. If cold
fluid is
received, it is heated near the desired temperature when passing the lower
part of the tube (area 1 ). If it is received in the upper part 2 of the tube
which
is tempered by the upper heater 6, the temperature is adapted quickly and
without great fluctuations because of the smaller heat capacity of the fluid
compared to the aluminum cylinder 3 and because of the small difference in
temperature of the fluid to the temperature of the cylinder. Thus, a
regulating
circuit with very small corrective action of manipulated value is used.
The advantage of the described regulation is a very small fluctuation
(change) of the temperature at the nominal value. The disadvantage of the
longer regulation time for strong flucuation of the nominal value thereby is
not
effective.
Tests have shown that with the pipette tube according to the invention,
pipette fluids of, for example, 20 pm up to 600 p1 can be pipetted wherein the
different areas 1, 2 of the tube were utilized. In this case, the pipette
fluid was
heated within a few seconds to 37.3 +/- 0.3°C. The wall temperature of
the
tube should not exceed a temperature of 4°C in order to avoid damage to
the
pipette fluid.
FIG. 1 also shows a temperature sensor 8 at the inlet of the second
zone. A further temperature sensor 9 may also be provided at the outlet of
zone 2. The temperature sensors 8, 9 are part of the regulating circuit of
regulator 7.
In a preferred embodiment of the invention, the lower area 1 has a
volume of 100 ~I and the upper area 2 has a volume of 500 p1. However,
volumetric relationships other than a 1:5 ratio of the volume of the lower
area
to the upper area are possible.
Other embodiments of the invention will be apparent to those skilled in
the art from consideration of the specification and practice of the invention
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disclosed herein. It is intended that the specification and examples be
considered as exemplary only, with a true scope and spirit of the invention
being indicated by the following claims.
