Patent Description:
Microcalorimeters are broadly utilized in fields of biochemistry, pharmacology, cell biology, and others. Calorimetry provides a direct method for measuring changes in thermodynamic properties of biological macromolecules. Microcalorimeters are typically two cell instruments in which properties of a dilute solution of test substance in an aqueous buffer in a sample cell are continuously compared to an equal quantity of aqueous buffer in a reference cell. Measured differences between the properties of the two cells, such as temperature or heat flow, are attributed to the presence of the test substance in the sample cell.

One type of microcalorimeter is an isothermal titration calorimeter. The isothermal titration calorimeter (ITC) is a differential device, but operates at a fixed temperature and pressure while the liquid in the sample cell is continuously stirred. The most popular application for titration calorimetry is in the characterization of the thermodynamics of molecular interactions. In this application, a dilute solution of a test substance (e.g., a protein) is placed in the sample cell and, at various times, small volumes of a second dilute solution containing a ligand, which binds to the test substance, are injected into the sample cell. The instrument measures the heat which is evolved or absorbed as a result of the binding of the newly-introduced ligand to the test substance. From results of multiple-injection experiments, properties, such as, the Gibbs energy, the association constant, the enthalpy and entropy changes, and the stoichiometry of binding, may be determined for a particular pairing between the test substance and the ligand.

While currently utilized ITCs provide reliable binding data results, their widespread utilization in the early stages of drug development have been limited by several factors: the relatively high amounts of protein required to perform a binding determination (e.g., about <NUM> milligram (mg) to about <NUM> of a protein), the time required to perform the measurement, and the complexity of using conventional ITCs. Due to the extremely high costs of biological substances used in research, there is a need to reduce the amount of biological substance used for each experiment. A reduction in the amount of the biological substance used in a calorimeter experiment, will require a more accurate, sensitive, and reliable titration calorimeter than what is currently available.

Furthermore, gathering binding data utilizing prior art ITCs require extensive preparation and skill by the practitioner. For example, using prior art ITCs, the reference and sample cells are first filled respectively with the reference substance and sample substance via a corresponding cell stem. Next, a syringe of the ITC is filled with a titrant. Then a needle of the ITC is placed in the sample cell via a cell stem leading to the sample cell while the syringe fits into a holder on the ITC enabling the syringe to rotate around its axis. Subsequently, the syringe is aligned with the sample cell so that the needle does not touch either the cell stem or the sample cell. Then, the syringe is connected to a stirring motor and a linear activator of the ITC, wherein the stirring motor and the linear activator must also be aligned with the sample cell.

As would be appreciated by a reading of the above-described prior art procedure, utilizing prior art ITCs, the quality of binding measurements performed with these prior art ITCs depends heavily of the operator's skills and experience, and involves a considerable amount of preparation time.

More recently developed prior art ITCs have attempted to simplify the preparatory procedures described above. For example, in one such prior art ITC, which is partly shown in <FIG> as ITC <NUM>, a syringe <NUM>, a syringe holder <NUM>, and a linear actuator <NUM>, which actuates syringe <NUM>'s plunger, are integrated into a single unit referred to as an automatic pipette. ITC <NUM> further comprises a stirring mechanism comprising a stirring motor <NUM>, which is attached to calorimeter body <NUM>. ITC <NUM> also comprises an inner magnet couple <NUM> located around syringe <NUM>, and an outer magnet couple <NUM> located on calorimeter body <NUM> in close proximity to stirring motor <NUM>. The rotation from stirring motor <NUM> to syringe <NUM> is transferred via magnet couplings <NUM> and <NUM>. Attached to syringe <NUM> is a needle <NUM> and a paddle <NUM>. The needle <NUM> is arranged to be inserted into a sample cell <NUM> via a cell stem <NUM> for performing ITC experiments. For reference purposes, ITC <NUM>, also comprises a reference cell, not shown, in communication with the ambient atmosphere via a reference cell stem.

The prior art design discussed above and depicted in <FIG> has certain limitations. For example, since the magnet coupling is a soft/flexible transmission, it is prone to resonant vibration of the stirrer at certain rotation speeds and accelerations, which negatively affects the instrument's sensitivity. The resonant vibration can be reduced by either employing a less sensitive feedback mechanism controlling the rotation speed (which leads to less stable rotation speed), or by lowering the rotation speed. However, less stable rotation speed also reduces the ITC's sensitivity, while lower rotation speed impedes proper mixing of reagents which reduces the ITC's accuracy.

Another limitation of the prior art design is that the stirring motor and the magnet coupling are placed closely to the sensitive measuring unit of the instrument and generates a substantial alternating magnetic field that produces electric noise which negatively affects the operation of the ITC's sensitive electronic circuitry. Since the ITC's sensors process signals of approximately <NUM>-<NUM> volts, and the noise generated by the motor and the magnetic coupling is a reciprocal of the distance between the sensor and the source of the noise, further improvements in the performance characteristics of this ITC design become increasingly challenging. As stated earlier, one of the underlying factors affecting the design of new microcalorimeters is the need to reduce the amount of biological substance used for each experiment. This requires smaller sample cells and shorter cell stems which in turn leads to, smaller distances between the cell sensor and the motor and magnetic coupling (source of electric noise), which limits the instrument's sensitivity.

<NPL>" discloses a titration microcalorimeter with an active feedback system for determining reaction heats. A sample cell is disclosed, fitted with a rotating syringe that acts as titrant delivery device and stirrer. The sample cell and a reference cell are both suspended in an adiabatic chamber.

<CIT> discloses a random access microbiological analyser for performing AST and ID tests on samples using on board inventories of different AST test arrays and different ID test rotors within separate AST and ID incubation and analysis chambers. Optical properties of the sample are the basis for both AST and ID tests.

<CIT> discloses an automatic analyser that can be used by an inexperienced operator to execute all necessary setup works for performing immunoassay. Various buttons are displayed on a viewing screen. The colours of the buttons changes in response to the status of the analyser. Photometry is used to monitor concentration on an analysis object or test object.

The invention described herein is aimed to improve the aforementioned characteristics and use of prior art ITCs such that the sensitivity of the ITC is improved, the amount of biological substance necessary for testing is reduced, the reliability of the results generated by the ITC is improved, and use of the ITC is eased.

The object of the invention is to provide a new automatic pipette assembly for an isothermal titration micro calorimetry system and an ITC system, which pipette assembly and ITC system overcomes one or more drawbacks of the prior art. This is achieved by the pipette assembly and the ITC system as defined in the independent claim.

One advantage with the present pipette assembly and the associated ITC system is that it makes it possible to reduce the cell compartment volume by about a factor of seven as compared to prior art ITCs, without a reduction in sensitivity, and with a significantly faster response time. Such an ITC system permits the performance of experiments with about <NUM> times less protein sample, and with only a total of about <NUM> to about <NUM> titrations per hour.

In addition to reducing the costs associated with running the ITC experiment, a smaller cell volume also extends the number of ITC applications. For example, the range of binding affinities that can be measured by ITC is dictated by a parameter called "c value," which is equal to the product of the binding affinity (Ka) and the total concentration (Mtotal) of macromolecule (c = [Mtotal]Ka). For accurate affinity determination, the c value must be between <NUM> and <NUM>,<NUM>. A decrease in the cell volume by a factor of ten results in a similar increase in c value if the same amount of protein is used, and, consequently, the ability to measure weak binders. This ability is especially important in the early stages of drug discovery, in which binding affinities are weak, especially in conjunction with a fully automated instrument.

<FIG> schematically shows one embodiment of an ITC system <NUM> according to the present invention. The ITC system <NUM> comprises a micro calorimeter <NUM> and an automatic pipette assembly <NUM>. The micro calorimeter <NUM> comprises a reference cell <NUM> and a sample cell <NUM> which are designed to be essentially identical in heat capacity and volume. The cells <NUM> and <NUM> are comprised of a suitable chemically inert and heat conductive material, such as gold, Platinum, tantalum, hastelloy or the like. The cells <NUM> and <NUM> may be of essentially any suitable shape, but it is desirable that they are of the same shape, that they are possible to arrange in a fully symmetric arrangement, and that efficient mixing of the titrant with the sample may be achieved. In the disclosed embodiment, the cross-section of the cells <NUM> and <NUM> is rectangular, and the cross-section in the transverse horizontal direction may be circular, resulting in coin shaped cells with circular facing surfaces.

In order to reduce any external thermal influences to a minimum, the, reference cell <NUM> and the sample cell <NUM> are both enclosed by a first thermal shield <NUM> which in turn is enclosed by a second thermal shield <NUM>. The thermal shields <NUM>, <NUM> may be comprised of any suitable thermally conductive material such as silver, aluminum, cupper or the like. The shields <NUM>, <NUM> may further be comprised of one or more thermally interconnected sub shields (not shown, to provide even further stable temperature conditions for the calorimetric cells <NUM>, <NUM>.

In order to control the temperature of the shields <NUM>, <NUM>, thermal control means may be arranged to control the temperature thereof. In an ITC system said thermal control means are mainly used to set the "isothermal" temperature of the calorimeter, ie. of the thermal shields <NUM>, <NUM>, before the titration experiments are initiated. But as will be disclosed in greater detail below, said thermal control means may also be used to improve the adiabatic behavior of the calorimeter. According to one embodiment, the thermal control means are comprised of one or more heat pump unit, such as a thermoelectric heat pump device based on the peltier effect or the like. Other types of thermal control means include thermostatically controlled liquid baths, mechanical heat pumps, chemical heating or cooling systems or the like.

In the disclosed embodiment a first heat pump unit <NUM> is arranged to transfer heat energy between the first <NUM> and second thermal shields <NUM>, a second heat pump unit <NUM> is arranged to transfer heat energy between the second thermal shield <NUM> and a heat sink <NUM> in thermal contact with the ambient temperature. A temperature controller <NUM> is arranged to control the first and second heat pump units <NUM>, <NUM> so that the desired temperature conditions are achieved. The temperature controller <NUM> and associated sensors will be disclosed in more detail below.

A reference cell stem <NUM> and a sample cell stem <NUM> provides access to the reference cell <NUM> and sample cell <NUM>, respectively, for supplying reference and sample fluids, titration fluid, washing of the cells etc. In the disclosed embodiment, the cell stems <NUM> and <NUM> both extends essentially vertically through both thermal shields and the heat sink to provide direct communication with cells <NUM> and <NUM> and the cell stems <NUM> and <NUM> each support their respective cell <NUM> and <NUM> in the cavity of the first thermal shield <NUM>.

The automatic pipette assembly <NUM> comprises a pipette housing <NUM>, a syringe <NUM> with a titration needle <NUM> arranged to be inserted into the sample cell <NUM> for supplying titrant, and a linear activator <NUM> for driving a plunger <NUM> in the syringe <NUM>. The titration needle <NUM> is rotatable with respect to the housing <NUM> and is provided with a stirring paddle <NUM> arranged to stir sample fluid in the sample cell <NUM> in order to achieve efficient mixing of titrant and sample fluid. The automatic pipette assembly <NUM> further comprises a stirring motor <NUM> for driving the rotation of the titration needle <NUM>.

In the embodiment disclosed in <FIG> the stirring motor <NUM> is a direct drive motor with a hollow rotor <NUM> arranged concentric with the syringe <NUM> and the titration needle <NUM>. The syringe <NUM> is at its upper end supported for rotation by the stirring motor <NUM> and at the lower end by a bearing <NUM>. Both the stirring motor <NUM> and the bearing <NUM> are schematically disclosed as comprising ball bearings, but any other type of bearing, bushings or the like capable of providing smooth and low friction rotation of the titration needle <NUM> may be used.

In the embodiment disclosed in <FIG>, the syringe <NUM> is arranged to be rotatable with respect to the housing <NUM> and the titration needle <NUM> is non-rotatably attached to the syringe <NUM>. In an alternative embodiment (not shown in figs. ), the needle <NUM> is rotatable with respect to the syringe <NUM> and the syringe <NUM> static with respect to the pipette housing <NUM>. <FIG> shows an alternative embodiment, wherein the syringe <NUM> is detachably arranged in a rotation frame <NUM> within the pipette housing <NUM>, the rotation frame <NUM> being rotably supported by the motor <NUM> and bearing <NUM>. In the disclosed embodiment, the syringe <NUM> is retained in the rotation frame <NUM> by a cap <NUM> that is detachably attached to the rotation frame <NUM> by threads or the like. By removing the cap <NUM>, the syringe <NUM> with the titration needle <NUM> can be replaced.

In an alternative embodiment, not shown in the figures, the stirring motor <NUM> drives the titration needle for rotation by a rotation transmission arrangement, such as a drive belt arrangement, a drive wheel arrangement or the like. In such an arrangement, the drive motor may be placed at an ever greater distance from the calorimetric cells.

The stirring motor is controlled by a stir controller <NUM> of the ITC system. The stir controller be a conventional BLDC. The linear actuator is controlled by a titration controller <NUM> of the ITC system. The stir and titration controllers <NUM>, <NUM> may be arranged in the pipette assembly <NUM>, and in turn connected to the ITC control system (not shown in detail), or they may be an integrated part of the ITC control system.

In the disclosed embodiment, the linear activator <NUM> comprises a stepper motor <NUM> arranged to drive a threaded plunger <NUM> that extends coaxially through the hole of a hollow rotor <NUM> and into the syringe <NUM> wherein it is rotatably attached to a pipette tip <NUM> that seals against the inner wall of the syringe <NUM> to allow displacing a precise volume of titration liquid from syringe <NUM>. The pipette assembly further comprises position sensors 500a, 500b for detecting two predetermined positions of the threaded plunger <NUM>. The linear activator <NUM> may be of any other type capable of perform controlled linear motion with sufficient precision. This design allows syringe to be rotated independently of the main body <NUM> of the pipette assembly <NUM>; at the same time, the linear activator <NUM> can drive the threaded plunger <NUM>.

In the ITC system the titration <NUM> controller is arranged to control the linear activator of the pipette assembly <NUM>. According to one embodiment, titration controller <NUM> uses the position sensors 500a, 500b for detecting two predetermined positions of the threaded plunger, and the titration controller <NUM> is arranged to register the two predetermined positions of the threaded plunger <NUM> and to determine the pitch of the threads of the plunger <NUM> from the number of steps performed by the stepper motor <NUM> to move the threaded plunger <NUM> between said positions. The so determined pitch of the threaded plunger is thereafter used by the pipette controller to increase the accuracy of the titration pipette, when displacing small volumes of titrant.

In the disclosed embodiments, the pipette assembly housing <NUM> serves as mounting base for the stators of the stirring motor <NUM> and the linear activator <NUM>. The housing <NUM> may further comprise an attachment section for precise positioning of the pipette assembly with respect to the sample cell stem.

The automatic pipette assembly <NUM> with an integrated stirring motor <NUM> arranged at the upper end of, or above the syringe <NUM> not only increases the distance between the stirring motor <NUM> (i.e., the source of an alternating electro-magnetic field) and the sensitive electronic circuitry, which is located at and/or nearby the thermal core of the calorimeter, but it also allows for the reduction in the amount of power needed to operate the stirring motor <NUM>. That is, due to the placement of the stirring motor <NUM> on the pipette assembly <NUM>, the size of the stirring motor <NUM> is not determined by the space between the sample cell and the reference cell as it is determined by prior art ITCs that place the stirring motor on the calorimeter housing (<FIG>). In the prior art, then, the cell stems protrude through the center of rotation of the magnetically coupled stirrer. Therefore, the lower limit of size for the stirrer mechanism is determined by the spacing between the cell stems. Accordingly, the size of the stirring motor of the present invention can be significantly reduced, e.g., by a factor of about <NUM> times that of stirring motors found in prior art ITCs, thereby resulting in a significant reduction in the amount of power needed to operate the ITC, e.g., about <NUM> watts versus the <NUM> watts used to power conventionally known ITCs.

The reduction in size of the stirring motor to a size of about five times less than stirring motors of prior art ITCs, and the placement of the stirring motor on the pipette such that the stirring motor is at a distance of about <NUM> millimeters or more away from the sensitive electronic circuitry of the calorimeter, and the removal of the magnetic coupling, closes the magnetic field that exists in conventionally used ITCs. Accordingly, the sensitivity of the inventive ITC is raised by the lower power, the lower heat, the lower electricity, and the lower noise and vibration caused by the placement of the stirring motor as disclosed herein. Furthermore, the disclosed embodiments also exclude magnetic coupling which is an additional source of alternating electro-magnetic field.

These improvements reduce the electrical noise induced in the sensitive electronic circuitry which, in turn, helps improve the calorimeter's sensitivity, whereby the volume of the sample and reference cells may be significantly reduced. Reducing the size of the sample cell and its corresponding cell stem, in turn, reduces the amount of biological substance used for each experiment.

The following Table <NUM> represents certain key dimensions of the cell stems and test and reference cells of both the prior art ITC and the ITC of the present invention. As shown in Table <NUM>, the inventive ITC, which places the stirring motor directly on the pipette subassembly, rather than positioning it on the calorimeter body, allows a smaller volume of test substance to be used, thereby reducing the costs associated with conducting calorimeter experiments.

According to the invention, the micro titration calorimetry system <NUM> is provided with a pipette guiding mechanism <NUM> arranged to guide the pipette assembly <NUM> between and into at least two positions of operation. The first position of operation is a pipette washing position <NUM> wherein the titration needle <NUM> is inserted in a washing apparatus (see <FIG>), and the second position of operation is a titration position <NUM> wherein the syringe is inserted into the sample cell <NUM> for calorimetric measurements. In the embodiment of <FIG>, the guiding mechanism <NUM> is comprised of a pipette arm <NUM> that supports the pipette assembly <NUM>, and an essentially vertical guide rod <NUM>. The pipette arm <NUM> is moveably attached by a sleeve <NUM> to the guide rod <NUM>, but its motion about the guide rod is restricted by a guide groove <NUM> in the guide rod <NUM> and a guide pin <NUM> that protrudes from the inner surface of the sleeve <NUM> and which fits into the guide groove <NUM>. The disclosed guiding mechanism <NUM> is of rotational type, and the positions of operation are arranged at equal distance about the centre of rotation of the guide assembly but at different angular positions, wherein movement of the pipette assembly <NUM> in the vertical direction is restricted to the angular positions of the positions of operation, and wherein rotational movement of the pipette assembly <NUM> between the angular positions only is permitted when the titration needle <NUM> is fully retracted from respective positions of operation. <FIG> shows the guide mechanism <NUM> in a position wherein the pipette assembly <NUM> is fully retracted from the titration position, i.e. from the sample cell <NUM>. At this position the guiding mechanism <NUM> restricts the possible movement of the pipette arm <NUM> to a vertical movement down into the titration position, or a rotational movement to reach another position of operation. In a micro titration calorimetry system <NUM> with two positions of operation, the washing apparatus <NUM> may be arranged to allow filling of titrant to the pipette assembly <NUM> after washing of the pipette assembly is completed. Alternatively, filling of the pipette may be performed through other means, such as a specific filling port in the syringe or the like.

<FIG> show a schematic perspective view of one embodiment of a micro titration calorimetry system <NUM> with a pipette guiding mechanism <NUM>, arranged to guide the pipette assembly <NUM> to and from three different positions of operation <NUM>, <NUM>, <NUM>. According to one embodiment, the third position of operation is a titrant filling position <NUM>, wherein the titration needle <NUM> is inserted in a titrant source <NUM>. <FIG> shows the guiding mechanism <NUM> in a state wherein the pipette assembly <NUM> is in the titration position <NUM>. <FIG> shows the guiding mechanism <NUM> in a state intermediate the titration position <NUM> and the filling position <NUM>. <FIG> shows the guiding mechanism <NUM> in a state wherein the titration needle <NUM> of the pipette assembly <NUM> is in the filling position <NUM>. As is disclosed in figs, 4a to 5c, the vertical guide grooves <NUM> associated with a specific position of operation <NUM>, <NUM>, <NUM> may be arranged to position the pipette assembly <NUM> at a predetermined height with respect to the operation to be performed.

<FIG> shows another embodiment of the guide mechanism <NUM>, wherein the guide groove in the guide rod <NUM> is replaced by a coaxial external guide sleeve <NUM> with corresponding guide paths <NUM> for the guide arm <NUM>.

According to one embodiment, the micro titration calorimetry system <NUM> comprises one or more position sensors, not shown, arranged to register when the pipette assembly <NUM> is positioned at one or more of the positions of operation <NUM>,<NUM>,<NUM>, and wherein the associated operation is restricted by the state of the position sensor. A sensor may, e.g. be arranged to register when the pipette assembly <NUM> is in correct position for titration <NUM>, and the calorimetry system <NUM> may be arranged to prevent start of a titration operation unless said sensor confirms that the pipette assembly <NUM> is in correct position.

Again referring to the figures, the guiding mechanism <NUM> ensures proper alignment and positioning of pipette assembly <NUM> in the sample cell <NUM> etc. All elements of the pipette assembly <NUM> (syringe, needle, paddle, plunger, linear activator, hollow rotor) and the guiding mechanism <NUM> are preferably precisely aligned during the manufacturing process and do not require any additional alignment during the use of the instrument. The pre-set factory alignment significantly improves usability and reliability of the instrument, considerably reduces the amount of preparatory time for an experiment, and makes the quality of measurements independent of the user skills. The guiding mechanism <NUM> also enables proper positioning of the pipette assembly <NUM> in the washing apparatus <NUM> for cleaning and drying of the syringe and e.g. for filling the syringe with titrant.

An exemplary method for utilizing the ITC apparatus disclosed herein comprises the non-manual alignment, both in depth and in breadth, of the syringe for filling titrant, washing the pipette, and delivering the titrant to the syringe.

An exemplary method for operating the inventive ITC apparatus comprises using the guiding mechanism <NUM> to position the pipette for filling the syringe with titrant (see <FIG>). In this position, the end of the needle with the paddle is placed in the titrant. The plunger of the syringe is moved from its lower position to its upper position thereby filling the syringe with the titrant. The sample cell is filled with the sample solution via the cell stem using an auxiliary syringe. Using the guiding mechanism, the pipette is moved to a position for performing an experiment (see <FIG>). The program for performing the experiment is activated. Consistent with the program used for the experiment, the rotor of the stirring motor rotates the syringe, needle, and paddle with the assigned speed enabling proper mixing of the reagents. Consistent with the program used for the experiment (e.g., when a certain temperature and/or equilibrium are reached), the linear activator moves the plunger and injects the titrant into the sample solution. The injection can be done discretely (step-by-step) or continuously, depending on the program settings. The calorimeter continuously measures and records the heat release/absorption versus time associated with the interaction of reagents. The analysis of the results is done according to the established algorithm.

Referring again to <FIG>, the temperature controller <NUM> is arranged to control the first and second heat pump units <NUM>, <NUM> in accordance with predetermined control-modes. The temperature controller <NUM> is schematically disclosed by functional blocks, and it may either be designed as an electronic circuit, as a software in a CPU based controller, or as a combination thereof. In the disclosed embodiment, the thermal controller <NUM> may be switched between two modes of operation:.

In the isothermal mode the thermal controller <NUM> is arranged to control the first heat pump <NUM> to minimize the temperature difference between the sample cell <NUM> and the first thermal shield <NUM>. The temperature difference between the sample cell <NUM> and the first thermal shield <NUM> is registered by a temperature sensor arrangement <NUM> in communication with the temperature controller <NUM>. In the disclosed embodiment, the temperature sensor arrangement <NUM> is a differential thermocouple that gives a non-zero signal when there is a temperature difference between the two points of registration, and the output from the thermocouple is connected to a preamplifier block <NUM> in the temperature controller <NUM>. The out-put from the preamplifier <NUM> is directed by the mode select block <NUM> to a first heat pump controller block <NUM> that controls the first heat pump <NUM> in response to the signal from the preamplifier <NUM>. By this arrangement, the first heat pump controller <NUM> will strive to compensate for any thermal difference between the sample cell <NUM> and the first thermal shield <NUM>, whereby a compensated adiabatic state is achieved in the calorimeter <NUM>. In order to compensate for minor systematic drifts in adiabatic behavior, an offset parameter <NUM> may be applied on the signal from the preamplifier <NUM>. The offset parameter <NUM> may be set during calibration of the calorimeter <NUM>. In the isothermal mode, the temperature controller <NUM> is arranged to control the second heat pump <NUM> to keep the second thermal shield <NUM> at a predetermined temperature, as is defined by a parameter Tshield. The control of the second heat pump <NUM> is performed by a second heat pump controller block <NUM> that receives an output from a second comparator block <NUM> wherein Tshield is compared with the present temperature of the second shield registered by a second shield thermal sensor <NUM>,.

In the temperature set mode the temperature controller <NUM> is arranged to control the first and second heat pump <NUM>, <NUM> to bring the first and second thermal shields <NUM>, <NUM> to a predetermined temperature, defined by the temperature Tshield. This mode is mainly used to bring the calorimeter <NUM> to the temperature at which the ITC experiments are to be run. In this mode, a first comparator block <NUM> compares Tshield with the present temperature of the first shield registered by a first shield thermal sensor <NUM>, and the output from the first comparator block <NUM> is directed by the mode select block <NUM> to the first heat pump controller <NUM>. The second heat pump <NUM> is controlled in the same manner as in the isothermal mode. The thermal set mode may further be used as a stand by mode in order to keep a constant temperature in the calorimeter <NUM>.

The temperature controller <NUM> may further comprise a cell temperature controller block <NUM> for controlling cell heating elements <NUM> arranged to heat the sample and the reference cells <NUM>, <NUM> in accordance with a predetermined temperature set by a parameter Tcell. The cell heating elements <NUM>, are mainly used for fine tuning of the temperature of the cells <NUM>, <NUM>.

The parameters Tshield, Tcell and offset may be set via a dedicated user interface of the thermal controller, not shown, or e.g. via a calorimeter user interface run on a computer <NUM> or the like. Calorimetric sensors <NUM> for sensing the temperature difference between the sample cell <NUM> and reference cell <NUM> during the ITC experiments may be connected to the computer <NUM>, e.g. via a preamplifier <NUM>.

Claim 1:
A micro titration calorimetry system (<NUM>) comprising:
a sample cell (<NUM>) and a sample cell stem (<NUM>) providing access to the sample cell (<NUM>);
an automatic pipette assembly (<NUM>) with a titration needle (<NUM>) arranged to be inserted into the sample cell (<NUM>) for supplying titrant; and
a pipette guiding mechanism (<NUM>) arranged to guide the pipette assembly (<NUM>) between and into at least two positions of operation;
wherein: a first position of operation is a pipette washing position (<NUM>) wherein the titration needle (<NUM>) is inserted in a washing apparatus (<NUM>), and a second position of operation is a titration position (<NUM>) wherein the titration needle (<NUM>) is inserted into the sample cell (<NUM>) for calorimetric measurements;
the pipette assembly (<NUM>) comprises a housing (<NUM>) having an attachment section for precise positioning of the pipette assembly (<NUM>) with respect to the sample cell stem (<NUM>);
the guiding mechanism (<NUM>) comprises a pipette arm (<NUM>) that supports the pipette assembly (<NUM>), an essentially vertical guide rod (<NUM>), and an alignment means for receiving the attachment section in the titration position (<NUM>);
wherein the pipette assembly comprises a chamfer on the attachment section.