Method and apparatus for evaporating liquid components from a liquid sample in a container - Patents.com

Abstract

A method and apparatus (2) for performing an evaporation procedure to evaporate a liquid component from a liquid sample in a container, the method including the steps of heating the container to a target temperature using a heat source (32) having an automatic temperature control mechanism (42), repeatedly determining with a controller (30) a value of a heat flow parameter, determining with the controller that the value of the heat flow parameter has decreased a predetermined amount from a peak value, and outputting a control signal from the controller in response to said determination, the control signal causing further steps in the evaporation procedure to be performed.

Description

[Technical field]

[0001] The present disclosure relates to methods and apparatus for evaporating liquid components from a liquid sample in a container, and more particularly to determining the endpoint of the evaporation process. [Background technology]

[0002] Sample evaporators are used to evaporate liquid components from a sample to dry the sample. It is desirable to automatically identify when the evaporation process is complete, eliminating the need for a human operator to continue to monitor the process. Furthermore, it is preferable to complete the evaporation process as quickly as possible to minimize the time required. Also, some samples may be affected by heat, and therefore it may be advantageous to minimize the heating time to avoid damaging the sample.

[0003] In some existing evaporators, the endpoint of the evaporation process is determined relative to the temperature of the sample vessel. Summary of the Invention [Means for solving the problem]

[0004] The present disclosure provides a method for performing an evaporation procedure using an evaporator to evaporate liquid components from a liquid sample in a container, the method comprising: heating the container to a target temperature using a heat source having a thermostatic control mechanism; repeatedly identifying, by the controller, a value of a heat flow parameter, the heat flow parameter relating to an amount of thermal energy output by the heat source during an immediately preceding time period; detecting, by a controller, a peak in the value of the heat flow parameter; determining, by the controller, that the value of the heat flow parameter has decreased by a predetermined amount from its peak value; outputting a control signal from a controller based on said determination, the control signal causing a further step in an evaporation procedure to be performed; Includes.

[0005] The controller may be a controller of the evaporator. The further steps may be process steps performed by components of the evaporator or by equipment coupled to the evaporator in response to control signals output by the controller. For example, the further steps may be stopping the process of heating the container by the heat source to hold the target temperature, triggering a next stage in the evaporation procedure, which may have different parameter settings such as different pressure and / or temperature levels, performing a draining process to remove condensed solvent from a condenser coupled to the evaporator, and / or performing a defrosting procedure to remove frost from a condensing element of a condenser coupled to the evaporator.

[0006] By determining the end point of the evaporation process in relation to the heat flow parameter, it is possible to determine with greater certainty that evaporation is complete. In particular, it has been found that determining the end point in relation to the peak value of the detected heat flow parameter allows for more reliable control.

[0007] Heating of the vessel by the heat source may be stopped, for example, when the value of the heat flow parameter drops to a particular fraction or percentage of its peak value.

[0008] In some preferred embodiments, the method includes monitoring a temperature indicative of the sample container, and the advance period begins only when or after the monitored temperature has been raised to a threshold temperature by a heat source during the current evaporation procedure. This can be advantageous for many processes, since the amount of thermal energy required to raise the temperature of the sample container and associated holder to a target temperature can substantially exceed the energy required for evaporation. By starting the period used to determine the heat flow parameter only after the threshold temperature has been reached, the monitoring of the heat flow parameter can be made more sensitive to the amount of thermal energy used in evaporating the solvent, since a peak in the value of the heat flow parameter can then be detected and used as an indication of the time when the peak evaporation rate was reached.

[0009] The threshold temperature can be equal to or a predetermined range below the target temperature (eg, about 3-5° C.).

[0010] The heat flow parameter may depend on the percentage of the preceding period during which the heat source was on.

[0011] The heat flow parameter may depend on the proportion of the set of time points during the preceding period that the heat source was on. For example, these time points may be equally spaced apart over the period.

[0012] The advance period may have a predetermined length or may correspond to the time that has elapsed since the evaporation procedure began if that time is less than this predetermined length of time.

[0013] The controller may identify when the value of the heat flow parameter has dropped to a predetermined percentage of its peak value.

[0014] Identification of the end point of the evaporation process can also be performed in conjunction with a signal relating to the pressure in the evaporator housing and / or a signal relating to the sample temperature.

[0015] The present disclosure further provides an evaporator configured to perform an evaporation procedure for evaporating a liquid component from a liquid sample in a container as described herein, the evaporator comprising: a heat source having a thermostatic control mechanism for heating the vessel; a controller communicatively coupled to the heat source and configured to determine a heat flow parameter, detect peaks in a value of the heat flow parameter, determine when the value of the heat flow parameter has dropped a predetermined amount from its peak value, and output a control signal in response to said determination, the control signal causing a further step in an evaporation procedure to be performed; Includes.

[0016] The evaporation method described herein can be deployed in various types of evaporators, for example, it can be used in centrifugal evaporators, rotary evaporators, and static evaporators.

[0017] Examples of the present disclosure will now be described with reference to the accompanying schematic drawings, as follows: [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of a centrifugal evaporator according to an example of the present disclosure. [Diagram 2] 1 is a graphical illustration of evaporation processes and their control using techniques according to the present disclosure and techniques outside the scope of the present disclosure. [Diagram 3] 1 is a graphical illustration of evaporation processes and their control using techniques according to the present disclosure and techniques outside the scope of the present disclosure. [Figure 4] 1 is a graphical illustration of evaporation processes and their control using techniques according to the present disclosure and techniques outside the scope of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] 1 shows a centrifugal evaporator 2 having an evaporation chamber 10. The chamber houses a rotor assembly 12 carried by a central shaft 14 that is rotatably connected to the chamber via bearings 4. An electric drive 16 is coupled to the shaft to rotate it relative to the chamber.

[0020] Two sample holders 20 and 22 are pivotally mounted to rotor 6 of rotor assembly 12 by respective pivots 24, 26. When the rotor is stationary, each holder is upright as shown by holder 22 in Figure 1. When the rotor spins at high speed, the holders swing outward to assume the pivoted orientation of holder 20 in Figure 1. Sample containers can be inserted into the sample holders through openings in the top of the evaporator, which are closed by lid 18 until the evaporation process is initiated.

[0021] A vacuum pump 27 is connected to the chamber by a tube 28. The pressure in the tube is monitored by a pressure sensor 38.

[0022] A heat source 32 is configured to heat the interior of the evaporation chamber. This may be, for example, an infrared source. Alternatively, a resistive heater may be used to heat the chamber. A temperature sensor 40 is provided to sense the temperature of the sample holders 20 and 22. A thermostatic control mechanism 42 is coupled to the heat source 32 and is operable to turn the heat source on and off in relation to the temperature signal generated by the temperature sensor 40. The thermostatic control mechanism is configured to leave the heat source on until a target temperature is reached, and then turn the heat source off and on as needed to keep the measured temperature at or near the target temperature.

[0023] The evaporator is controlled by a controller 30, which is communicatively coupled to the electric drive 16, the vacuum pump 27, a temperature sensor 40, and a thermostatic control mechanism 42. The controller may actually be implemented by multiple separate control devices.

[0024] During the evaporation procedure, the rotor spins at high speed, oscillating radially outwardly the holders 20 and 22. The lower surfaces 20A and 22A of the holders are then sequentially brought against the heat source 32, thereby heating the holders and their contents.

[0025] The controller is configured to determine when to terminate the evaporation process with respect to an input signal responsive to operation of the heat source. The signal is used by the controller to determine a heat flow parameter indicative of the percentage of the immediately preceding period during which the heat source was energized. Evaporating solvent from the sample draws thermal energy from its container, which in turn cools the sample holder supporting the container. A temperature sensor 40 is used to monitor the temperature of the sample holder and generate a corresponding signal that is provided to a thermostatic control mechanism 42. In response to detecting that the temperature of the sample holder has fallen below a target temperature, the thermostatic control mechanism turns on the heat source until the desired temperature of the sample holder is restored.

[0026] As the evaporation process approaches its end point, the amount of solvent remaining decreases, and therefore the evaporation rate. As a result, the amount of thermal energy required to maintain the temperature of the sample holder decreases as well, which is reflected in a shortening of the "on" periods of the heat source, and generally an increase in the length of the "off" intervals between them. The progress of the evaporation procedure can therefore be monitored in terms of the amount of thermal energy emitted by the heat source during the immediately preceding period (which may be, for example, in the range of about 5 to 15 minutes). The end point can be calculated as the time when the heat flow parameter has fallen to a predefined percentage of its maximum value, which corresponds to the continuous use of the heat source during the monitored preceding period.

[0027] However, the inventors have determined that the accuracy of such an approach can be significantly reduced in some circumstances, for example when the amount of solvent to be evaporated from the sample is relatively low. This is because the thermal energy required to raise the sample holder and container to the desired temperature (e.g., 90 W) is then significantly greater than that required to evaporate the solvent (e.g., 10 W), thereby somewhat reducing the sensitivity of the heat flow monitor. The present disclosure seeks to address this issue.

[0028] The controller of the evaporator 30 is configured to terminate the evaporation process when the heat flow parameter has fallen a predetermined amount from its peak value measured during the current evaporation procedure, rather than on a maximum achievable value, which may provide more reliable endpoint detection.

[0029] In a preferred example, the controller is configured to begin calculating the value of the heat flow parameter only once a threshold temperature has been reached, which serves to mitigate the effect on the heat flow parameter of using a relatively large amount of thermal energy to heat the sample holder and vessel.

[0030] Examples of evaporation parameters using the techniques described herein are described below with respect to FIGS.

[0031] In Figures 2-4, time is plotted along the horizontal axis. The lower portion of the vertical axis shows a plot of temperature along with plots showing the on / off periods of the heat source. The upper portion of each vertical axis shows a plot of a heat flow parameter, which represents the proportion of a set of times (e.g., 1 second intervals) that the heat source was on during the preceding period (5 minutes in these examples), as a percentage.

[0032] "Swing temperature" refers to the temperature of the sample holder.

[0033] The plot labeled "Heat Flow" corresponds to heat flow parameter data generated without a threshold temperature to indicate the start of the heat flow parameter calculation. The plot labeled "New Heat Flow" corresponds to heat flow parameter data generated using a threshold temperature to initiate the heat flow parameter calculation process.

[0034] The heat flow parameter threshold is labeled "Arm" in each figure. This represents the minimum level of heat flow that must be measured before the controller begins monitoring for the evaporation process endpoint. Since the endpoint corresponds to a calculated heat flow value, the threshold level of heat flow must be achieved at the beginning of the process higher than the expected endpoint value to ensure that the detected endpoint is valid.

[0035] The calculated end point level of the heat flow for the plot labeled "Heat Flow" is indicated in the figure by the term "Trigger" and the calculated end point level of the heat flow for the plot labeled "New Flow" is indicated by the term "New Trigger."

[0036] In the evaporation process of Figure 2, the flow rate value reaches its maximum value when the swing is at its target temperature. The trigger is calculated as a predefined percentage of this maximum value, which is taken as the level of heat flow typically reached at the completion of the evaporation process, and may be, for example, about 20% of the maximum value.

[0037] In FIG. 2, the calculation of the new heat flow value begins only after the swing temperature reaches a predefined threshold (e.g., about 3-5° C. below the target temperature). As a result, the plot of “New Heat Flow” then rises to a peak value, indicated in the figure as “New Heat Flow Peak”. This provides a more pronounced indication or indication as to when the evaporation rate is likely to be at its highest value. The “New Trigger” is calculated relative to this peak value rather than the maximum heat flow value. The “New Trigger” may be calculated, for example, as corresponding to 5% of the peak value. Because the detected peak value provides a more reliable reference point during the evaporation process, the new trigger may be set to a relatively low percentage of the peak value to more accurately indicate the actual end point of the evaporation procedure.

[0038] In the example of FIG. 2, the trigger obtains an endpoint that is too early, before the sample dries (denoted "Old End"), while the "New Trigger" displays an endpoint that is somewhat later and corresponds more accurately to the completion of the evaporation process, which occurs shortly after the sample dries (denoted "New End").

[0039] An evaporation process similar to that of Figure 2 is shown in Figure 3. In this example, the sample is relatively small. As a result, the amount of heat energy required for evaporation is much less than that required to bring the sample holder to the desired temperature. This causes the new heat flow plot to rise to a lower peak than in Figure 2. Therefore, the "trigger" value is the same in Figure 3 as in Figure 2, but the "new trigger" is lower in Figure 3 than in Figure 2 (because the "new heat flow peak" value is lower in Figure 3 than in Figure 2). As a result, the new method thus allows the evaporation process to run longer until it reaches completion, thereby producing a dry sample.

[0040] FIG. 4 relates to a scenario involving a relatively small sample, where the temperature of the sample holder is relatively close to the target temperature at the beginning of the process. As a result, the "old arm" level typically used in the "old method" (e.g., about 20-25% of the maximum heat flow value) is not reached, so an end point is not identified for the "heat flow" and the procedure ends only when the default maximum evaporation period defined by the controller 30 has elapsed. Due to the higher sensitivity of the "new method", a "new arm" level lower than the typical "old arm" level can be used (the new arm level is, for example, about 10% of the maximum heat flow value). Therefore, the "new heat flow" only reaches a relatively low value, which is sufficient to exceed the "new arm" level and thereby initiate the end point monitoring process. The peak value of the new heat flow is then detected and used to set a "new trigger" level (which may, for example, be about 5% of the peak value). When the "new heat flow" falls to the "new trigger level", the evaporation process ends at a much earlier time than with the "old method". This significantly shortens the time during which the evaporation process takes place, allowing the next stage of sample processing to begin sooner, as well as reducing the risk of damaging the sample due to overheating.

Claims

1. 1. A method for performing an evaporation procedure using an evaporator to evaporate a liquid component from a liquid sample in a container, comprising: heating the vessel to a target temperature using a heat source having a thermostatic control mechanism; repeatedly identifying, by a controller, a value of a heat flow parameter, said heat flow parameter relating to an amount of thermal energy output by said heat source during an immediately preceding time period; detecting, by the controller, a peak in the value of the heat flow parameter; determining, by the controller, that the value of the heat flow parameter has decreased by a predetermined amount from its peak value; outputting a control signal from the controller based on the determination, the control signal causing further steps within the evaporation procedure to be performed; A method comprising:

2. monitoring a temperature indicative of the container; The method of claim 1 , wherein the advance period begins only when or after the monitored temperature is raised to a threshold temperature by the heat source.

3. The method of claim 2 , wherein the threshold temperature is equal to or a predetermined range below the target temperature.

4. A method according to any one of claims 1 to 3, wherein the heat flow parameter depends on the proportion of the advance time during which the heat source was on.

5. The method of any one of claims 1 to 3, wherein the heat flow parameter depends on the proportion of a set of times during the preceding period that the heat source was on.

6. A method according to any one of claims 1 to 3, wherein the controller determines when the value of the heat flow parameter has fallen to a predetermined percentage of its peak value.

7. An evaporator configured to perform an evaporation procedure for evaporating a liquid component from a liquid sample in a container according to the method of any one of claims 1 to 3, comprising: a heat source having a thermostatic control mechanism for heating the vessel; a controller communicatively coupled to the heat source and configured to identify a heat flow parameter, detect peaks in a value of the heat flow parameter, identify when the value of the heat flow parameter has decreased by a predetermined amount from its peak value, and output a control signal in response to the identification, the control signal causing further steps in the evaporation procedure to be performed; An evaporator including:

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