Abstract:
A coaxial-drive centrifuge provides for contactless regulation of sample temperature. The sample is contained in a multi-station chemical-processing circuit that has a metal receptor at each station. On demand, a stationary inductor induces eddy currents in the receptor as it spins by. Dissipation of the eddy current heats the receptor and the surrounding sample. The receptor has a thermal sensor that provides an optical indication of the sample temperature. A stationary contactless reader reads the optical indication. A controller activates the inductor when the reading indicates an actual temperature below a predetermined target temperature. When heating is required, the inductor is pulsed as the receptor is aligned with a gap in the inductor. 
     The chemical-processing circuit is designed for a specific series of chemical reactions, in this case, a polymerase chain reaction (PCR) is implement as an iterated series of three steps. To this end, the chemical-processing circuit has three stations arranged in a closed loop with interconnecting channels. When a treatment is completed, the chemical-processing circuit tilts so that the sample to the next station for the next treatment. Each station has its own receptor and thermo-sensor so that each treatment can be performed at its respective optimal temperature. The centrifuge system thus provides for automating a sequence of chemical processes using contactless regulation of temperature.

Description:
This is a continuation-in-part application of U.S. patent application Ser. No. 09/514,975, filed Feb. 29, 2000, now U.S Pat. No. 6,309,875, and a continuation-in-part application of U.S. patent application Ser. No. 09/576,690, filed May 23, 2000, now U.S. Pat. No. 6,491,804. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to analytical chemistry and, more particularly, to centrifuge-based automated sample treatment systems. A major objective of the present invention is to provide rapid and fine temperature control during a series of sample treatments in a centrifuge-induced supergravity field. 
     The standard of living in modern societies has been greatly enhanced by advances in chemical, biological, and medical sciences. These fields all involve the separation of samples into constituent components that may then be processed to aid in their identification and/or quantification. The centrifuge is an important instance of instrumentation used to separate sample components. 
     A simple centrifuge has a centrifuge rotor that is spun, e.g., by a motor. Typically, a liquid chemical sample spins with the rotor. The spinning liquid sample components are subjected to a centrifugal force (F=mω 2 r) proportional to their mass, their distance from the centrifuge spin axis, and the square of the spin rate. The effect of the centrifugal force is much like the effect of gravity-liquid components are separated according to their relative densities. However, unlike gravity, the centrifugal force is readily controlled, e.g., by controlling the spin rate. Thus, a centrifuge can generate centrifugal forces orders of magnitude greater than gravity at the earth&#39;s surface. Generally, the “supergravity” conditions of a centrifuge are much more effective than gravity in separating sample components. 
     In addition, the supergravity conditions afforded by a centrifuge can be used to overcome liquid surface effects that might otherwise impede sample movement. Accordingly, centrifuges that can control the tilt of a chemical-processing unit relative to the centrifugal force can be used for pouring, mixing, filtering, and facilitating chemical reactions. Furthermore, tilting can be used to control liquid movement among multiple processing stations of a chemical-processing circuit so that a series of processes can be implemented without manual intervention. Thus, a centrifuge with tilt control can automate sample processing conventionally performed manually by chemists. 
     Independent control of centrifuge spin rate and tilt action is disclosed in U.S. Pat. No. 4,814,282 to Holen et al. Tilt of a chemical-processing circuit is used to transfer liquid from one station to another under the influence of centrifugal force. A tilt-drive assembly, including motor and drive chain, is attached to the centrifuge rotor so that it rotates therewith. Power is delivered to the tilt-drive motor via slip rings, which tend to wear out as they are not generally designed to operate at centrifuge speeds. In this approach, any sensors used to track tilt would also rotate at high speeds, further complicating operation. In addition, centrifuge forces are applied to the tilt motor and the drive train. For example, a 1-pound motor must withstand 1000-pound forces in a readily achievable 1000 G supergravity field. Thus, there are a number of robustness issues that can only be addressed with additional complexity and expense. 
     These robustness issues are mitigated in the centrifuge disclosed in U.S. Pat. No. 5,089,417 to Wogoman. In the Wogoman centrifuge, a holder for a chemical-processing circuit snaps from a first tilt orientation to a second tilt orientation when the centrifuge exceeds a predetermined rotation rate. Similarly, the first tilt orientation is resumed when the centrifuge spin rate falls below the threshold rate. Thus by increasing and decreasing the centrifuge spin rate, sample movement between reaction stations of the chemical-processing circuit can be controlled. However, this approach provides little flexibility in selecting the centrifuge spin rate or tilt angles relative to the centrifugal force. It would be preferable to control the centrifuge rotation and the tilt actions independently. 
     U.S. Pat. No. 4,776,832 to Martin et al. avoids the need for physical connections to drive a tilt rotor by using inductive motors. The inductive motors include induction rotors that are physically coupled to holders, e.g., for reaction cells, and stationary stators, which are located beneath the centrifuge rotor (wheel). The stators induce eddy currents in the induction rotors, causing them to rotate. No physical connection is required between the stators and the induction rotors, eliminating the need to deliver power through slip rings. On the other hand, the non-physical coupling of drive and induction rotor does not ensure precise and flexible control of sample-container orientation relative to the supergravity field. 
     Parent U.S. patent application Ser. No. 09/576,690 discloses a coaxial-drive centrifuge in which part of the drive assembly for the tilt motion is coaxial with the centrifuge axis. This arrangement overcomes the robustness limitations of Holen et al., the flexibility limitations of Wogoman, and the precision limitations of Martin et al. A tilt-drive motor provides complete control over tilt without restricting centrifuge rotation rates. The tilt-drive motor is stationary, so electrical coupling is not required to a rotating element. The coupling between the tilt-drive motor and the chemical-processing circuit is mechanical, so there is no problem of precision in tilt control. 
     The coaxial-drive centrifuge holds the promise for rapid and fully automated sample processing through a series of treatment steps. For example, a polymerase chain reaction (PCR) technique requires many iterations of a series of steps. PCR is used to copy small fragments of doxyribonucleic acid (DNA); the procedure can be iterated so that the amount of DNA grows exponentially. Thus, a limitless amount of DNA sample can be “amplified” from a single DNA fragment. This can allow, for example, multiple parallel destructive analyses to be performed. PCR techniques have accelerated the study of gene functions and gene mappings (e.g., in the Human Genome Project). Generally, PCR is useful in biology, clinical medice, and forensic science. 
     One variant of PCR , begins with heating a DNA solution (e.g., to 90° C.) so that individual strands separate. Then the DNA solution is cooled (e.g., to 50-60° C.), allowing oligonucleotide primers to bind to the separated DNA. Then the temperature is raised (e.g., to 70° C.) so that polymerase can copy the DNA rapidly. These three phases, melting, annealing, and extension, can be iterated so that the amount of DNA grows exponentially. Typically, the DNA sample remains in a container that is heated and cooled by using temperature controlled baths. The time for the temperature to transfer through the sample container wall is a limiting factor in the rate at which the PCR reaction can be iterated. 
     Tilt-capable centrifuges with multi-chamber chemical-processing circuits could be used so that each PCR step can be conducted in a dedicated station. Each station can be kept at the temperature associated with one step, e.g., melting, annealing, and extension. Changes in container orientation between steps can be used to move the sample from station to station to automate the processing. 
     However, the promise for rapid and fully automated chemical-sample processing faces a challenge in temperature control. Typically, different temperatures are required for different sample treatments. The entire centrifuge can be temperature controlled, but then it is difficult to change temperatures rapidly. At best, slow temperature changes delay processing throughput; at worst, slow temperature changes can be incompatible with certain treatment requirements. Local resistive heaters can provide rapid heating. However, delivering electrical power to a rotating chemical-processing circuit for heat control faces linkage challenges as discussed above with respect to Holen et al. 
     Moreover, sample temperature should be monitored to provide precise closed-loop control thereof. Once again, electrical connections to rotating elements are preferably avoided. What is needed is a system that provides for rapid and precise temperature control to a chemical-processing circuit in the context of a centrifuge. 
     SUMMARY OF THE INVENTION 
     The present invention provides a centrifuge with inductive temperature control of a tiltable chemical-processing circuit. The centrifuge has a centrifuge rotor, a centrifuge-drive assembly, a chemical-processing unit, a tilt-drive assembly, and an inductor. The tilt-drive assembly is mechanically coupled to the chemical-processing unit to provide for precise and flexible control of tilt relative to the centrifugal force provided by the centrifuge. The chemical-processing unit includes a receptor in which eddy currents are generated when exposed to the alternating magnetic field generated by the inductor. The eddy-current energy is dissipated as heat due to resistance in the receptor. 
     Energy transfer between the inductor and the receptor is contactless. Accordingly, the inductor can be “stationary” in the sense that it does not rotate with the centrifuge rotor or the chemical-processing circuit. Thus, electrical power can be supplied to the inductor through standard cabling. So that power is not wasted, and more tightly directed to a small zone on the rotor, the alternating magnetic field can be preferably generated only at times that are at least in part a function of the centrifuge rotor orientation. 
     The chemical-processing unit can include an optical temperature sensor. This can be read by a stationary optical reader as the chemical-processing circuit rotates by. The optical reader can be powered via standard electrical cabling and its signal output can be provided to a controller that regulates the temperature of the sample. The temperature at which the sample is to be maintained depends on the treatment, which can correspond to the station or container location of the sample. Thus, the maintained temperature can be determined as a function of the tilt orientation of the chemical-processing circuit relative to the centrifugal force applied by the centrifuge. 
     The basic method provided for by the present invention involves spinning a chemical-processing unit about a centrifuge axis so that a centrifugal force is applied to the chemical sample. Movement of the sample within the chemical-processing unit is effected by titling the chemical-processing unit relative to the centrifugal force. Heating of the sample is achieved by inducing eddy currents in the chemical-processing unit using an inductor. Preferably, the inductor generates the eddy currents only when a receptor is aligned with the inductor, as determined by the centrifuge orientation. Regulation of sample temperature can be achieved by contactlessly reading a thermo-sensor included with the chemical-processing unit. 
     If a chemical-processing circuit (a multi-station chemical-processing unit with channels permitting sample flow between stations) is used, the method of the invention provides for automated processing sequences. The chemical-processing circuit can be oriented relative to the centrifugal force so that the chemical sample is maintained at the first processing station. Once the first treatment is complete, the chemical-processing circuit can be tilted so that the sample flows to a second station for a second treatment. 
     Where the different treatments require different temperatures, each station can include its own thermo-sensor. The contactless optical reader can read whichever thermo-sensor corresponds to the present location of the sample. A controller can vary inductor pulse widths to control the rate of heating as appropriate to minimize deviations of the actual sample temperature from the target sample temperature. 
     In a more specific method of the invention, a sample is inserted into a multi-station chemical-processing circuit. Centrifugal force is applied with the chemical-processing circuit oriented so that the sample is held in the first station. In the meantime, the temperature of the sample is regulated using a sensor in the container so that a first temperature is maintained. When the first treatment is completed, the orientation of the chemical-processing circuit relative to the centrifugal force is changed so that the sample moves to the second station. Then the sample is maintained in the second station while the second treatment is applied at a second temperature maintained through regulation response to the sensor. 
     In the context of PCR, the present invention permits rapid amplification of DNA fragments. For example, each of three stations of a chemical-processing circuit can be dedicated to one of the three phases, melting, annealing, and extension, of the PCR procedure. The chemical-processing circuit can be tilted to pour the DNA sample from station to station. Each station can be kept at the appropriate temperature for the corresponding phase of the PCR procedure. The chemical-processing circuit can be rocked back and forth to agitate the DNA sample to facilitate uniform temperature changes. Thus, the invention provides for rapid automated PCR reactions. Reactions with similar requirements for temperature changes and agitation are similarly facilitated by the present invention. 
     The present invention provides for rapid and fully automated multi-treatment sample processing with rapid and precise contactless sample temperature control. The chemical-processing circuit is not encumbered either by cables to supply heat or to power a temperature sensor, or to provide feedback to a controller. These and other features and advantages of the invention are apparent from the description below with reference to the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially isometric schematic view of a centrifuge system in accordance with the present invention. 
     FIGS. 2A,  2 B, and  2 C are bottom plan views of a chemical-processing circuit (as used in the centrifuge system of FIG. 1) at three different temperatures. 
     FIG. 3 is a block diagram of the centrifuge system of FIG.  1 . In FIG. 3, signal lines are solid and functional lines are dashed. 
     FIG. 4 is a flow chart of a method of the invention practiced in the context of the centrifuge system of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the present invention, a centrifuge system AP 1  comprises a centrifuge rotor  11 , a centrifuge-drive assembly  13 , three chemical-processing circuits  15 , a tilt-drive assembly  17 , an inductor  19 , an optical reader  21 , and a controller  23  as shown in FIG.  1 . Centrifuge drive assembly  13  includes a centrifuge motor  25 , and tilt-drive assembly  17  includes a tilt-motor  27 , both motors are mounted to a stationary centrifuge housing (not shown). Inductor  19  and optical reader  21  are stationary components fixed to the housing. Inductor  19  provides for contactless heating of chemical-processing circuits  15 , while optical reader  21  provides for contactless monitoring of sample temperature. 
     Centrifuge-drive assembly  13  comprises centrifuge motor  25  that includes a centrifuge-motor shaft  31 , a centrifuge-motor pulley  33 , a centrifuge drive belt  35 , a centrifuge-rotor pulley  37 , and a hollow centrifuge shaft  39 . Centrifuge rotor  11 , centrifuge shaft  39 , and centrifuge-rotor pulley  37  rotate together about a centrifuge axis  41 . Likewise, centrifuge-motor-pulley  33  is rigidly attached to centrifuge-motor shaft  31  so that they turn together. Pulleys  33  and  37  are geared, as is drive belt  35  that connects them. The gear ratio between pulleys  33  and  37  is 1:1 so that centrifuge rotor  11  turns at the same rate as centrifuge motor shaft  31 . 
     Centrifuge motor  25  includes a position encoder  43  so that the orientation of centrifuge motor shaft  39  can be precisely tracked. This allows the rotation rate of servo-controlled motor  25  to be precisely controlled. In addition, the orientations of centrifuge rotor  11  and centrifuge motor shaft  31  are initialized so that the centrifuge rotor orientation is known from the centrifuge motor-shaft orientation. The centrifuge-motor orientation is used by controller  23  to determine when to activate inductor  19  to heat a sample. 
     Tilt-drive assembly  17  comprises tilt-drive motor  27  with a tilt-motor shaft  51 , a tilt-motor pulley  53 , a tilt-drive belt  55 , a tilt-shaft pulley  57 , a tilt-drive shaft  59 , and a tilt-drive pinion  61 . Tilt-motor pulley  53  is mounted on tilt-drive motor shaft  51  so that they turn together. Toothed tilt-drive belt  55  links geared pulleys  53  and  57  so that they turn based on a 3:1 ratio. Tilt-drive shaft  59  extends through the hollow of centrifuge shaft  39  and thus rotates about centrifuge axis  41 . Tilt-shaft pulley  57  and pinion  61  are rigidly coupled to tilt-drive shaft  59  so that the three rotate together. Pinion  61  is engaged with chemical-processing circuits  15  so that they rotate on a 1:3 ratio with pinion  61  and thus on a 1:1 ratio with tilt-motor shaft  51 . 
     Tilt motor  27  is essentially identical to centrifuge motor  25 . It includes a position encoder  63  that permits the orientations of chemical-processing circuits  15  to be tracked to 1000 parts per circle (about ⅓°). Tilt-motor encoder  63  is coupled to controller  23  so that the tilts of chemical-processing circuits  15  relative to the centrifugal force can be controlled precisely. 
     Inductor  19  includes a cable  71  wound on a spool. Cable  81  is coupled to an alternating current source with an adjustable frequency from 10 khz to 1 MHz. Cable  71  serves as a primary winding that is transformer coupled to a coil  73  that includes a gap  75 . Coil  73  is a copper laminate structure. AC excitation of coil  73  generates alternating magnetic field to be generated in gap  75 . This alternating magnetic field induces eddy currents in metal that is disposed in gap  75 . 
     Each chemical-processing circuit  15  includes three processing stations  81 ,  82 , and  83  coupled by channels  85 . During centrifuging, sample tends to accumulate in the radially outward station. Movement of sample from one station to another can be effected by rotating the chemical-processing circuit so that the succeeding station is radially outward (“down” in the supergravity field associated with the centrifugal force). Specifically, this relative orientation determines which station is “outward”; the outward station in general holds the sample. 
     Chemical-processing circuits  15  each include a base  87  and a cover  88  (not all covers are shown). These ate made of transparent acrylic. Circular bases  87  and covers  88  have 6 cm diameters. Covers  88  are 1 mm thick, while bases have a maximum 3 mm thickness with 2 mm deep molded stations  81 ,  82 , and  83  and channels  85 . These leave a 3 cm center barrier  91  that defines radially inward walls for channels  85  and stations  81 ,  82 , and  83 . The outer walls of stations  81 ,  82 , and  83  are formed as arcs with 2 cm radii and centers 3.5 cm from the centers of chemical-processing circuits  15 . 
     One stainless steel receptor  93  is loosely fitted in each station  15 . Receptors  93  conform to the station shape, but have smaller dimensions than the stations. The receptor thickness is 1 mm. When inductor  19  generates an alternating magnetic field while a receptor  93  is in its gap  75 , the receptor heats. The amount of heating is determined by the amount of time the alternating magnetic field is generated while the receptor  93  is in gap  75 . 
     A thermo sensor  95  is formed on the bottom of each receptor  93 . Sensor  95  includes an elongated strip that of material that changes color and reflectance when heated. The length of the strip that changes color depends indicates the receptor temperature. This technology is used in Duracell batteries with “PowerCheck™ available from Duracell USA, a division of Duracell, Inc., Berkshire Corporate Park, Bethel, Conn. 06801. 
     Optical reader  21  is arranged to read thermo-sensors  95 . Optical reader  21  includes a Xenon flash lamp  96 , lens  97 , lens  98 , and a photo-diode  99 . Controller  23  triggers Xenon flash lamp  96  when, based on motor orientation inputs, a receptor  93  is aligned with reader  21 . Lens  97  collimates the resulting flash; lens  98  causes the reflection to converge at photo-diode  99 . Photodiode  99  provides an output signal corresponding to the intensity of incident light, which in turn corresponds to the length of sensor  95  that has changed color. Alternatively, an array (e.g., photo-diode or CCD) can be used as the optical reader to provide an image of the sensor. In that case, CCD-pixels corresponding to the heated length of the sensor can be counted to provide a temperature indication. 
     In system AP 1 , receptors  15  have identical thermo-sensors  95 . Alternatively, thermo-sensors with different ranges can be used depending on the target temperature for the associated station. This reduces the dynamic range required of the sensors and permit greater precision in controlling temperature. Alternatively, more sophisticated sensors can be used to provide range and precision. At one extreme, digital readout thermometers can be included in the receptors. An imaging optical reader with optical-character recognition (OCR) capabilities can be used to monitor sample temperature. 
     Signal flow for system AP 1  is shown in FIG.  3 . Controller  23  controls centrifuge motor  25  and tilt motor  27 , and thus the centrifuge rotation rate and the orientation of each chemical-processing circuit relative to the centrifugal force. Centrifuge-motor encoder  43  monitors the orientation of centrifuge motor shaft  39  and, indirectly, the orientation of centrifuge rotor  11 . The actual orientation of centrifuge motor shaft  25  can be compared to the intended orientation; any error can be used to adjust the centrifuge rotation rate. Likewise, tilt-motor encoder  63  monitors the orientation of tilt-motor shaft  51  and, indirectly, the orientation of each chemcial-processing circuit  15  relative to the local centrifugal force. Controller  23  controls the spin rates of motors  25  and  27  to minimize deviations from expected centrifuge rates and tilts. 
     Controller  23  also uses the orientation information to determine when a station  81 ,  82 ,  83  is within inductor gap  75 , and thus when to fire inductor  19  if additional heating is required. If a temperature increase is required, inductor  19  generates an alternating magnetic field so that eddy currents yield heat in the receptor in gap  75 . The temperature of the receptor  93  is continuously indicated by the thermo-sensor  95  on each receptor  93 . 
     Since controller  23  knows the orientation of centrifuge rotor  11 , it knows when a thermo-sensor  95  is aligned with optical reader  21 , and thus when to fire Xenon flash lamp  96  to get a sample-temperature reading. The resulting reading is provided to controller  23 . Controller  23  coordinates the temperature reading with centrifuge orientation information to determine which chemical-processing circuit  15  is involved; controller  23  coordinates the temperature reading and centrifuge orientation with the tilt information to determine which station  81 ,  82 ,  83  is involved. 
     The actual temperature information for a given chemcial-processing station  81 ,  82 ,  83  is compared with a target temperature; if the actual temperature falls below the target temperature, controller  23  fires inductor when next the station is in gap  75 . The length of time inductor  19  is activated can be adjusted to determine the amount of energy supplied for heating per cycle of rotor  11 . 
     A method M 1  of the invention practiced in the context of system AP 1  is flow-charted in FIG.  4 . At step S 1 , sample is inserted into a chemical-processing circuit  15 . More specifically, sample is injected via a syringe through a membrane-covered via  101  of the cover of chemical-processing circuit  15 . The membrane serves as a septa, sealing the sample circuit interior once the syringe is removed. Via  101  is located over a radially inward portion of the first station  71  that is not contacted by sample during centrifuging. (Each chemical-processing circuit  15  can also have a well for collecting sample upon completion of processing to facilitate sample removal.) 
     At step S 2 , centrifuging is begun. Controller  23  activates centrifuge motor  25 . 3000 rpm is a typical centrifuge spin rate; it achieves a centrifugal force of 1000 G at 10 cm from the centrifuge axis  41 . In general, step S 2  is begun with first station  81  down in the centrifugal force field so that the sample remains in the first station  81 . 
     The first sample treatment is conducted at step S 3 , which includes three generally concurrent substeps S 3 A, S 3 B, and S 3 C. Substep S 3 A involves controlling sample-circuit orientation so that the sample remains in the first station  71 . This can mean rotating the chemcial-processing circuit  15  at the centrifuge rate so that its orientation relative to centrifuge rotor  11  does not change. However, if some agitation is required, the tilt rate can oscillate above and below the centrifuge rate. 
     Substep S 3 B involves sensing sample temperature using thermo-sensors  95  built into receptors  93 , and contactless reading of thermo-sensors  95  using optical reader  21 . Readings can be taken of each chemcial-processing circuit  15  as it passes reader  21 . However, to accommodate charge-time requirements for Xenon flash lamp  96 , readings do not need to occur every pass of every circuit. Likewise, if a CCD-ased reader is used, readings can be spaced to allow time for CCD data to be read out and processed. 
     Substep S 3 C involves regulating sample temperature to a first temperature using the readings obtained in substep S 3 B. If a reading indicates the sample temperature is below the target first temperature, controller  23  controls inductor  19  so that it generates eddy currents in the appropriate receptor  93  when that receptor is in the inductor gap  75 . The length of time the eddy currents are induced can be adjusted to correspond to the magnitude of the temperature deviation. The first temperature need not be a constant; the temperature can be regulated to match a desired temperature- versus-time function. 
     Step S 3  continues until the first sample treatment is completed. Step S 4  involves changing circuit orientation relative to the centrifugal force so that the sample is urged through an inter-station channel  85  to the second station  82 . Step S 5  parallels step S 3 , and has the corresponding substeps S 5 A, S 5 B, and S 5 C. 
     If more than two treatments are required, step S 5  can be iterated, in which case, reference is to an Nth station, an Nth receptor, and an Nth temperature. Note that the Nth station can be the same as an earlier station. In the illustrated case, the third station is different from the second and first stations, but the fourth station would be the same as the first station and the fifth station would be the same as the sixth station, and so on. Once processing is complete, method M 1  ends at step S 6 . 
     In the context of PCR, the sample can be a DNA fragment. The three stations  81 ,  82 ,  83  can be heated respectively to 90° C., 60° C. and 70° C. The DNA sample can be introduced into first station  81  and the centrifuge accelerated to 3000 rpm. Chemical-processing circuit  15  can be rocked back and forth +/1 6d at 5 Hz to facilitate rapid and uniform heating of the DNA sample solution. Melting is likely to be complete by the time the full centrifuge rate is achieved. 
     The orientation of chemical-processing circuit  15  can be changed 120° so that the DNA sample pours into second station  82 , which is maintained at 60° C. Chemical-processing circuit  15  can be rocked back and forth to agitate the DNA sample so that the new temperature is achieved uniformly and rapidly. Once the annealing step is complete, chemical-processing circuit  15  can be reoriented so that the DNA sample pours into station  83 , which is at 70° C., optimized for the extension reaction. Again, chemical-processing circuit  15  can be agitated to facilitate a rapid and uniform temperature change. Once the extension reaction is complete, chemical-processing circuit  15  can be reoriented so that the DNA sample pours into first station  81 , to begin the next iteration of the PCR procedure. 
     The present invention has industrial applicability in any field where chemical processes can take advantages of supergravity conditions offered by a centrifuge. A wide variety of chemical processing sequences can be accommodated using different chemical-processing circuit designs. The illustrated chemical-processing circuits  15  have three stations  81 ,  82 , and  83  arranged in a closed loop for automated three-step PCR procedures. Alternatively, there can be two stations or more than three. The stations can be arranged in a closed loop or in an open loop. An open loop can be suited for non-iterated procedures in which a return to a first station is not needed or desired. These and other variations upon and modifications to the described embodiments are provided by the present invention, the scope of which is defined by the following claims.