Apparatus for supercritical fluid extraction

Abstract: An apparatus for supercritical fluid extraction incorporates a removable extraction cartridge which in operation has insignificant pressure difference between its inside and outside walls. In one embodiment, the extractor includes a fraction collector for extractants, an automatic sample changer and an automatic cartridge transfer mechanism which provide completely automated extractions. To automatically perform extraction, valves for the fluids are automatically opened and closed in synchronism with the insertion and removal of the cartridges. These valves force a hard valve element into a softer valve seat with a valve stem that does not rotate significantly under the control of a rotary motor.

Description: This invention relates to supercritical fluid extraction. In supercritical fluid extraction, an extraction vessel is held at a temperature above the critical point and is supplied with fluid at a pressure above the critical pressure. Under these conditions, the fluid within the extraction vessel is a supercritical fluid. In one type of apparatus for supercritical extraction, there is a specially constructed extraction vessel within a source of heat. A prior art apparatus for supercritical extraction of this type is described by B.W. Wright, et . al ., in ANAL. CHEM. 59 , 38-44 (January 1987) using a glass-lined extraction chamber within a bolted stainless steel extraction vessel heated in an oven. This type of extraction apparatus has the disadvantages of: (1) requiring time consuming steps to open the pressurized extraction vessel before use to insert the sample and again to open it after use to remove the spent sample; and (2) under some circumstances, requiring the handling of a hot extraction vessel. Supercritical fluid extraction apparatus are also known from EP-A-0466291. In such apparatus, an extraction vessel is held at a temperature above the critical point and is supplied with fluid at a pressure above the critical pressure. Under these conditions, the fluid within the extraction vessel is a supercritical fluid. In this apparatus for supercritical extraction, there is a specially constructed extraction vessel within a source of heat. To control the flow of supercritical fluids for an automatic supercritical fluid extractor, automatic valves are needed. Preferably, the valves are of economical construction and contain all other features of being able to handle high pressure, high temperature and have long life. Prior art inexpensive automatically programmable valves do not contain all of these features and thus suffer from one or more of the disadvantages of short life, inability to handle high temperature, high cost or inability to handle high pressure. The object of this invention is to provide a novel inexpensive valve capable of handling high temperatures, high pressures, and of having long life in supercritical extraction apparatuses. To accomplish this object, apparatus for supercritical fluid extraction includes a plurality of extraction cartridges having an interior for containing material to be extracted. A plurality of fluid lines that may be brought into fluid contact with a cartridge interior, a first line of said plurality of fluid lines capable of supplying supercritical fluid at high pressure to said cartridge interior and a second line of said fluid lines capable of depressurizing fluid carrying extractant from said interior to a pressure lower than said high pressure. At least one of the plurality of fluid lines incorporates a programmable valve having a valve body, said valve being disposed to regulate fluid flow in said one of the fluid lines, and said valve further comprising a linear actuator. This apparatus is characterized by a plurality of samples in sample containers located on a first transport means and a programmable timer that causes the first transport means to move a selected sample container and sample to the location of a second transport. The programmable timer also causes the second transport means to move a selected container and sample from the first transport means to a place of extraction and activates a motor to rotate a shaft engaging fixed threads in the valve body to cause linear motion driving a reciprocally mounted nonrotating stem linearly without rotation through an antirotation ball and curved shaft surface wherein the stem moves a valve element without rotation against a valve seat to seal the container and resist the extraction pressure at the extraction temperature. The nonrotating stem has a first curved face contacting antirotating ball to form a low friction contact point and a second flat face contacting value element thereby forming a conformal seal and stopping flow between said inlet and said outlet ports. Advantageously, a programmable timer signals the second transport means to provide for movement of the said selected container out of the place of extraction and back to the the first transport means after said extracting of analyte. The direction of motion of the said second transport means is vertical. The direction of motion of the said first transport means is horizontal. Another sample container and sample is selected from the first transport means after a previous sample has been extracted. The above noted and other features of the invention will be better understood from the following detailed description when considered with reference to the accompanying drawings in which: FIG. 1 is a schematic diagram illustrating the operation of a single supercritical fluid extraction system according to the invention; FIG. 2 is an exploded perspective view of an extraction cartridge used in the embodiment of FIG. 1 according to the invention; FIG. 3 is an elevational view of the extraction cartridge of FIG. 2 clipped into a breech plug used in the embodiment of FIG. 1; FIG. 4 is a fragmentary sectional view of the extraction cartridge, breech plug pressure vessel and heating block; FIG. 5 is a perspective view of another embodiment of the invention capable of automatic extraction of a series of samples; FIG. 6 is a sectional view taken through lines 6-6 of FIG. 5; FIG. 7 is a sectional view taken through lines 7-7 of FIG. 6; FIG. 8 is a sectional view taken through lines 8-8 of FIG. 6; FIG. 9 is a cross-sectional elevational view of a valve useful in the embodiment of FIGS. 1-8; FIG. 10 is an elevational view of a fitting for the connecting tubing used with the valve of FIG. 9; FIG. 11 is an elevational side exterior view of the valve of FIG. 9; FIG. 12 is an elevational top exterior view of the valve of FIG. 9; and FIG. 13 is a block diagram of the circuitry for operating the valves; FIG. 14 is a schematic circuit diagram of a portion of the block diagram of FIG. 13; FIG. 15 is a schematic circuit diagram of another portion of the block diagram of FIG. 13. In FIG. 1, there is shown a schematic fluidic diagram of one channel of a dual-channel supercritical fluid extraction system 10 having a pumping system 12, a valve system 14, a collector system 16 and a pressure vessel and fluid-extraction assembly 18. The pumping system 12 communicates with two extraction cartridges within the pressure vessel and fluid-extraction assembly 18 and for this purpose is connected through a tee joint 20 to two identical valve systems, one of which is shown at 14. Each valve system communicates with a different one of two inlets for the corresponding one of two extraction cartridges. The pumping system 12 itself is not part of the invention except insofar as it cooperates with the collector system 16, valve system 14 and pressure-vessel and fluid-extraction assembly 18. Any pumping system capable of providing the flow rates and pressures described herein is suitable and one such system is sold by Isco, Inc., P.O. Box 5347, Lincoln, NE 68504, under the designation Isco Model 260D Pump. The valve system 14 and a second valve system (not shown in FIG. 1) which is connected to the other branch of the tee joint 20 are each connected to two different collector systems 16, one of which is shown in FIG. 1, and to different ones of the two extraction cartridges in the pressure-vessel and fluid-extraction assembly 18 so that, two extraction operations can be performed at the same time using the same pumping system 12. With this arrangement, the valve system 14 causes: (1) supercritical fluid to flow from the pumping system 12 into a space between a cartridge and the interior of the pressure vessel of the pressure-vessel and fluid-extraction assembly 18 for purging the outside of the cartridge and the inside of the pressure vessel; and (2) applies supercritical fluid through the cartridge for extraction of a sample 134 therein. Because the fluid is applied both to the interior of the cartridge and the exterior, the cartridge does not have to withstand a high pressure difference between its interior and exterior and can be made economically. In addition to controlling the flow of fluid into the pressure-vessel and fluid-extraction assembly 18, the valve system 14 controls the flow of: (1) purging supercritical fluid from the space between the cartridge and interior of the vessel to the collector system 16 or to a vent; and (2) the extractant from the interior of the cartridge to the collector system 16 for separate collection. To hold sample 134 during an extraction process, the pressure-vessel and fluid-extraction assembly 18 includes a heating block 22, a pressure vessel 24 and a cartridge and plug assembly 26 with the cartridge and plug assembly 26 extending into the pressure vessel 24. The pressure vessel 24 fits within the heating block 22 for easy assembly and disassembly. With this arrangement, the heating block 22 maintains the fluids within the pressure-vessel and fluid-extraction assembly 18 at supercritical fluid temperature and pressure for proper extraction. The cartridge and plug assembly 26 includes an extraction cartridge assembly 30, a breech plug 32 and a knob 34 which are connected together so that: (1) the pressure vessel 24 is easily sealed with the breech plug 32; (2) the extraction cartridge assembly 30 snaps onto the breech plug 32 and the assembly may be carried by the knob 34; and (3) the knob 34 serves as a handle to insert and fasten the assembly to the tube pressure vessel with the extraction tube communicating with an outlet aligned with its axis and an inlet for the space between the internal walls of the pressure vessel 24 and the exterior of the extraction cartridge 30 and for the interior of the extraction cartridge 30 being provided through a groove circumscribing the assembly inside the pressure vessel 24. With this arrangement the extraction cartridge assembly 30 may be easily sealed in the pressure vessel 24 by threading the breech plug 32 into it and may be easily removed by unthreading the breech plug 32 and lifting the knob 34. The extraction cartridge assembly 30 contains a hollow interior, an inlet and an outlet so that a sample to be extracted may be placed in the hollow interior and supercritical fluid passed through the inlet, the hollow interior and to the outlet to a collector. The extraction cartridge assembly 30 serves as an extraction chamber or tube, the pressure vessel 24 serves as an extraction vessel and the heating block 22 serves as an oven as these terms are commonly used in the prior art. In the preferred embodiment, the knob 34 is of a low heat conductivity material and it should include in all embodiments at least a heat insulative thermal barrier located to reduce heating of the handle portion of the knob 34. It extends outside of the pressure vessel 24 and is adapted to aid in the sealing of the pressure vessel 24 and the breech plug 32 together so that the extraction cartridge assembly 30 is within the pressure vessel 24 for maintaining it at the appropriate temperature and the knob 34 is outside the pressure vessel 24 so as to remain cool enough to handle. Although in the preferred embodiment the knob 34 is a heat insulative material, it only needs to be insulated against heat conducted from the interior of the pressure vessel 24 and this may also be done by a thermal barrier separating the pressure vessel 24 from the knob 34 such as an insulative disc having a width of at least 1 millimeter and extending across the cross-section of the knob 34 to the extent of at least 80 percent of the cross-section to effectively block any considerable amount of transfer of heat between the cartridge and the knob 34. It should have a heat conductivity no greater than .20 joules/cm. sec. degree C at 30 degrees Celsius (0.05 calories/cm. sec. degree C at 30 degrees Celcius). The extraction cartridge assembly 30 has an opening which permits some supercritical fluid to enter the pressure vessel 24 to follow one path passing into the extraction tube and out through an outlet of the extraction tube into a conduit leading to a collector. Other supercritical fluid follows a second path around the outside of the cartridge to remove contaminants from the pressure vessel 24, equalize pressure and flow from another outlet. One of the inlet and outlet of the extraction cartridge assembly 30 enters along the central axis of the extraction cartridge assembly 30 and the other from the side to permit rotation of parts with respect to each other during seating of the pressure vessel 24 and yet permit communication of the extraction cartridge assembly 30 with the fluid source and with the collector. To reduce wasted heat and fluid, the space between the outside of the cartridge and the inside walls of the pressure vessel 24 is only large enough to accommodate the flow of purging fluid and to equalize pressure between the inside and outside of the cartridge. The volume between the outside of the cartridge and the inside of the pressure vessel 24 is less than 10 cubic centimeters. In the preferred embodiment, the inlet opens into an annular space between the internal wall of the pressure vessel 24 and the cartridge and plug assembly 26. The fluid follows two paths from the annular space, both of which include an annular manifold with narrow holes and a passageway that communicates with the recess in the breech plug 32. One path opens into the extraction cartridge assembly 30. The other passes along the narrow space outside the extraction cartridge assembly 30. Thus, supercritical fluid enters the extraction tube through a labrythian like path and at the same time passes outside the extraction tube so that the pressure inside the extraction tube is always substantially the same as that inside the pressure vessel 24. Because the pressures are substantially the same, the tube itself may be formed of relatively inexpensive plastics notwithstanding that a high pressure is desirable for extraction from the sample within the extraction tube. The pressure vessel 24 is generally formed of strong material such as metal and is shaped as a container with an open top, an inlet opening and two outlet openings. The inlet opening is sized to receive an inlet fitting 42, the inlet fitting 42 being shown in FIG. 1 connected in series with check valve 60A to corresponding heat exchanger 40. Each of the two outlet openings are sized to receive a different one of a corresponding purge valve fitting 44, and a corresponding extractant fluid fitting 46. With these fittings, the pressure vessel 24 is able to receive the cartridge and plug assembly 26 in its open end and permit communication between the cartridge and the extractant fluid fittings such as shown at 46. The inlet fittings such as shown at 42 and purge valve fitting, such as 44, permit communication with the inside of the pressure vessel 24. To control the flow of fluids to and from the pressure vessel and fluid-extraction assembly 18, the valve system 14 includes an extractant valve 50, a purge fluid valve 52 and an extracting fluid valve 54. To introduce extracting fluid into the pressure-vessel and fluid-extraction assembly 18, the extracting fluid valve 54 communicates with one branch of the tee joint 20 through tube 56 and with one end of the heat exchanger 40 through tube 58, the other end of the heat exchanger 40 communicating with the inlet fitting 42 through tube 60, check valve 60A and tube 60B. With these connections, the extracting fluid valve 54 controls the flow of fluid from the pumping system 12 through the heat exchanger 40 and the pressure vessel 24 through the inlet fitting 42. To remove purge fluid from the pressure vessel 24, the purge fluid valve 52 communicates at one port with the purge valve fitting 44 through tube 62 and with its other port through tube 64 (not shown in Fig. 1) with the collector system 16 or with a vent (not shown) to remove fluid containing contaminants from the exterior of fluid extraction cartridge assembly 30 and the interior of the pressure vessel 24. To remove extractant from the extraction cartridge assembly 30, the extractant valve 50 communicates at one of its ports through tube 66 with the extractant fluid fitting 46 and through its other port with the collector system 16 through tube 68 for the collecting of the extracted material, sometimes referred to as analyte or extractant, from the sample within the pressure vessel and fluid-extraction assembly 18. For convenience, the valves 52 and 54 are mounted to be operated by a single manual control knob 70. To supply fluid to the valve system 14: (1) the tube 56 carries pressurized fluid from the pumping system 12 to tee joint 20; (2) tube 76 is connected to one arm of tee joint 20 to carry pressurized fluid to another liquid extraction system unit not shown on FIG. 1; and (3) the remaining arm of the tee joint 20 is connected through the tube 56 to an inlet fitting 74 of extracting fluid valve 54. The valves 50, 52 and 54 are, in the preferred embodiment, SSi type 02-0120. The extracting fluid valve 54 has a rotary control shaft 80 that is rotated to open and close its internal port. This shaft is operated by hand control knob 70 and carries spur gear 82 pinned to the control shaft 80. Spur gear 84, which is pinned to control shaft 107 of purge fluid valve 52, meshes with spur gear 82 so that when control knob 70 is rotated clockwise, extracting fluid valve 54 is closed, but since the control shaft 107 of purge fluid valve 52 is geared to turn in the opposite direction, the clockwise rotation of knob 70 opens purge fluid valve 52. The relative locations of the two gears on the two shafts are such that, in the first (clockwise) position of the knob 70, the extracting fluid valve 54 is shut and the purge fluid valve 52 is open. Turning the control knob 70 counterclockwise 130 degrees from this first position opens extracting fluid valve 54 while allowing purge fluid valve 52 to remain open. Thus, both valves are open when the knob 70 is rotated 130 degrees counterclockwise from the first position. When the knob 70 is rotated 260 degrees counterclockwise from the first position, extraction fluid valve 54 is open and purge fluid valve 52 is shut. Thus, there are three definable positions for control knob 70: (1) clockwise with valve 54 shut and valve 52 open; (2) mid position with both valves open; and (3) full counterclockwise with valve 54 open and valve 52 shut. The extractant valve 50 includes an inlet fitting 120, outlet fitting 122, manual control knob 132 and control shaft 126. The rotary control shaft 126 is attached to control knob 132. When the extractant valve 50 is opened by turning the control knob 132 counterclockwise from its closed position, fluid flows from the extraction cartridge assembly 30, through the extractant fluid fitting 46, the conduit 66, the valve inlet fitting 120, the outlet fitting 122, through the tube 68 and into the collector system 16. The collector system 16 includes a purge coupling 90, a purge fluid collector 92, an extractant coupling 94, an analyzing instrument 96, and an extractant fluid collector 98. The purge fluid flowing through the valve 52, flows through purge coupling 90 into the capillary tube 110 and from there into the purge fluid collector 92 where it flows into a solvent 100. Similarly, the extractant flowing through valve 50 flows through tube 68 to the extractant coupling 94 and from there to the capillary tube 128 and extractant fluid collector 98 which contains an appropriate solvent 104 in the preferred embodiment. The analyzing instrument 96 may be coupled to the capillary tube 128 through an optical coupling 102 in a manner known in the art. The optical coupling 102 is a photodetector and light source on opposite sides of a portion of the capillary tube 128, which portion has been modified to pass light. This instrument 96 monitors extractant and may provide an indication of its passing into the extractant fluid collector 98 and information about its light absorbance. Other analytical instruments may also be used to identify or indicate other characteristics of the extractant. In FIG. 2, there is shown an exploded perspective view of the supercritical fluid extraction cartridge assembly 30, having a substantially cylindrical tubular body portion 140, a bottom porous means 142 such as a filter, frit or other means for confining sample, a bottom cap 144, and a top porous means 146 such as a filter, frit, or means for confining sample and a top cap 148. In one embodiment, the tubular body portion 140 is a cylindrical plastic tube adapted to hold within it the sample 134 (FIG. 1) having shoulders on each end with reduced diameter externally threaded top and bottom end portions 154 and 156. A central opening 158 passes along its axis for receiving sample. However, the tube may take other shapes and be formed of other suitable materials. To confine the sample, the bottom and top porous means 142 and 146 each include stainless steel porous frit members 160 and 162 held within different ones of two sealing rings 164 and 166 respectively. The frit members 160 and 162 have the same diameter and are arranged to be aligned with the central opening 158 and the sealing rings 164 and 166 have the same internal and external diameter as the end portions 154 and 156 of the tube 152 to lie flat over the tubular body portion 140 with the frit members 160 and 162 closing their ends. The sealing rings 164 and 166 are preferrably made of Teflon or Kel-F (trademarks of E.I. DuPont de Nemours Co., Wilmington, Delaware, United States of America for tetrafluoroethylene and other fluorocarbon plastics). The top and bottom caps 144 and 148 include internal threads such as the threads 168 in the bottom cap 144 that engage with corresponding external threaded end portions 156 and 154 of the tube 152 to hold the top and bottom caps 148 and 144 in place. The bottom cap 144 is sized so that when threaded against the shoulder of the body portion 140, it sealingly forces the ring 164 against the bottom face of the tubular body portion 140 to form a seal and hold the frit member 160 in place. Similarly, the top cap 148 is sized to compress the ring 166 against an annular face 170 of the top end portion 154 of the tubular body portion 140 to form a seal. The bottom cap 144 has an inwardly turned annular flange 175 for engaging the ring 164 with a conical central opening 210 (FIG. 4) for an outlet fitting and a similar flange is in the top cap 148. Within the flanges are corresponding circular appertures substantially the same size as the porous means 142 and 146 and of the central opening 158 and aligned therewith for the passage of fluid. The upper cap 148 includes lateral sides 174 having internal threads for compressing the frit member 162 in place and an engaging nipple 176 having an open end 177. The extraction tube 152 may be machined of 303 stainless steel for a permanent cartridge or molded of polyphenylene sulfide, polyetherimide or polyethersulfone plastic for a disposable cartridge. This cartridge has an internal volume for sample of 2.5 cubic centimeters in the preferred embodiment, but may be as large as 1000 cubic centimeters. The top and bottom caps 148 and 144 may be machined from polyetherketone plastic for a permanent cartridge or molded of polyetherimide or polyphenylene sulfide ("Fortron," Celanese Chemical Co., 1211 Avenue of Americas, New York, New York 10036) plastic for a disposable cartridge. If the cartridge is intended for use at temperatures greater than 100 degrees C it is advantageous to make the caps 144 and 148 and the tubular body 140 from stainless steel. In FIG. 3, there is shown an assembled cartridge and plug assembly 26 having a breech plug 32, an extraction cartridge assembly 30 and a knob 34. The breech plug 32 is made of high strength, corrosion resistant, stainless steel (Nitronic 50) and includes cylindrical recess 180, sealing surface 186, engaging thread 188 and annular stop flange 190. The cylindrical recess 180 is positioned to receive engaging nipple 176 on one side and the knob 34 on the other with the external threads 188 between them for forming a closure with the pressure vessel. Near the outer end of the recess 180 is located a retaining groove 182. Within this groove 182 is located a garter spring 184. The garter spring 184 is a helical coil of stainless steel wire bent into the shape of a circle and welded closed at the ends to form a torus. The turns of the helix are inclined to the helix axis so that they deflect rather than buckle when a circular member of outside diameter greater than the inside diameter of the torus is pressed through the center of the torus while the outside diameter of the torus is constrained by means such as the groove 182. Therefore, upon pressing the extraction cartridge assembly 30 into the recess 180 so that the major diameter of its engaging nipple 176 pops past the garter spring 184, the extraction cartridge assembly 30 is retained in breech plug 32. The strength of retention depends upon the strength of the garter spring 184. The garter spring 184 is chosen so that the cartridge is retained against gravity and other relatively light forces but still is easy to remove manually by pulling it from the breech plug 32. The knob 34 is fastened to the top of breech plug 32 by any conventional means. In the preferred embodiment, knob 34 is fabricated of temperature-resistant insulating material, such as phenolic plastic and fastened in place. In FIG. 4, there is shown a sectional view of the clipped-together extraction cartridge 26, knob 34 and breech plug 32 replaceably installed in pressure vessel 24 which in turn has previously been permanently force fit into heating block 22. The pressure vessel 24 is fabricated of type 303 stainless steel for good machinability and corrosion resistance and has within it a cylindrical central opening sized to receive the extraction cartridge 26, two openings for outlet fittings in its bottom end, an opening in its cylindrical side wall to receive an inlet fitting and an open top with internal threads sized to engage the external threads 188 of the breech plug 32. The heating block 22 is fabricated from aluminum for good thermal conductivity and includes a cylindrical opening sized to tightly receive the pressure vessel 24. The breech plug 32 and the extraction cartridge assembly 30 are a slip fit within the pressure vessel 24. External threads 188 on breech plug 32 engage in internal threads 200 within pressure vessel 24. An annular self-acting high pressure seal 202 cooperates with a sealing surface 186 to seal high pressure supercritical fluid from the atmosphere and an annular low pressure seal 204 spaced from the annular high pressure seal 202 prevents contaminated supercritical fluid in the space between the interior of the pressure vessel 24 and the exterior of the extraction cartridge assembly 30 from getting back to the supercritical fluid supply. These two annular seals 202 and 204 form between them a torroidal inlet chamber into which the outlet of the fluid inlet 42 extends to introduce fluid. Contamination may arise from fingerprints or other foreign material on the outside wall of extraction cartridge assembly 30 and the low pressure seal 204 protects against this contamination. Seals 202 and 204 are Bal-Seal type 504MB-118-GFP. Supercritical fluid is supplied to fluid inlet 42 and circulates in the annular space between high pressure seal 202 and low pressure seal 204, and then follows two paths into the pressure vessel 24 and extraction cartridge 30: one path for purging and one path for extraction. An annular spacer 206 within the torroidal opening between seals 202 and 204 has an hour-glass shaped cross section with radial holes through it and distributes incoming supercritical fluid from the inlet of fitting 42 to the opposite side of the spacer 206 from which it flows to passageway 208 drilled in breech plug 32. Because the passageway 208 extends radially from the recess 180 in the breech plug 32 to the annular ring, it provides an open path for fluid between the two regardless of the orientation of passageway 208. The passageway 208 opens at an uncontrolled angular location with respect to the inlet fixture 42 (inner side). Fluid flows from one side of the inwardly curved portion of the hour glass shaped spacer 206 that communicates with the outlet of fitting 42 to the other side of the inwardly curved portion and from there to the passageway 208. When the cartridge and plug assembly 26 shown in FIG. 3 are inserted into the pressure vessel 24 as shown in FIG. 4, the knob 34 is rotated and the external threads 188 of the breech plug 32 which form an eight thread per inch connector engage internal threads 200 in the pressure vessel 24, screwing the breech plug 32 and attached cartridge and plug assembly 26 down into the pressure vessel 24. When conical recess 210 in the bottom cap 144 reaches the external conical tip 212 of fitting adapter 214, the cartridge and plug assembly 26 is prevented from moving further down. Screwing the breech plug 32 in further after the cartridge and plug assembly 26 has bottomed causes the upper flat annular surface of fitting nipple 176 to bear upon the flat lower surface of a hat-shaped washer 216. At this time, the hat-shaped washer 216 is residing against the upper surface of the head of a shoulder screw 218 which is threaded into cylindrical hole 222 in breech plug 32. Further screwing of the breech plug 32 into the pressure vessel 24 causes the nipple 176 to lift the washer 216 off of the screw head and compress a coil spring 201 between annular surface 205 and the ridge of the washer 216. Continued screwing of the breech plug 32 into the pressure vessel 24 causes annular flange 190 of breech plug 32 to bear upon the upper surface of the pressure vessel 24. This provides a limit stop with the coil spring 201 compressed, as shown in FIG. 4. The force of the compression spring 201 is enough to provide a low pressure seal between the hat-shaped washer 216 and the upper annular surface 203 of the fitting nipple 176. More importantly, this force also provides a low pressure seal on the mating concical surfaces of the recess 210 of lower cap 144 and the external conical tip 212 of the fitting adapter 214. The sealing surface 186 acts as a pilot during the initial part of insertion to insure that the internal threads 188 do not get cross-threaded. A taper 189 at the end of the cylindrical sealing surface 186 pilots the breech plug 32 past seals 202 and 204 so that they are not damaged during insertion of the breech plug 32. The locations of recess 224, passageway 208, high pressure seal 202 and the engaging threads 188 and 200 are chosen such that if the breech plug 32 is inadvertently removed when the interior of the pressure vessel 24 is pressurized, fluid within the pressure vessel 24 leaks past high pressure seal 202 and runs up the flights of the engaging screw threads 188 and 200, and depressurizes the system while there is still adequate screw engagement to ensure safety at the maximum rated operating pressure. The maximum rated operating pressure of the embodiment shown in FIG. 4 is 6.89·10 7 Pa (10,000 psi). The maximum operating temperature is 150 degrees Celcius. The equipment need not be designed for operating temperatures above 300 degrees Celsius and pressure above 2.07·10 8 Pa (30,000 pounds per square inch). After the breech plug 32 and the cartridge and plug assembly 26 are assembled into the pressure vessel 24 as described above, but before an extraction, the space between the cartridge and plug assembly 26 and the pressure vessel 24 is purged of contaminants. During such a purge or cleaning cycle supercritical fluid enters fluid inlet 42, is distributed by the annular spacer 206 and goes through passageway 208. It passes between the outer diameter of hat-shaped washer 216 and the inside cylindrical diameter 230 of the recess within breech plug 32. Fluid then continues down and passes the annular space between the outside diameter of engaging nipple 176 and inside diameter 230 of the recess 180 in breech plug 32. The fluid passes garter spring 184 and circulates with even circumferential distribution around the outside of top cap 148, the extraction tube 152, and the bottom cap 144. The flow is collected in the annular space below the bottom cap 144 and above the bottom 240 of pressure vessel 24 and exits through vent discharge fitting 44, carrying contaminants with it. Contaminated fluid between the exterior of extraction cartridge 26 and the interior of high pressure vessel 24 does not make its way into the interior of the extraction vessel. Low pressure seal 204 prevents contaminated fluid from reaching passageway 208. A labyrinth seal consisting of the narrow gaps between the major diameter of fitting nipple 176 and the inside diameter 230 of recess 180, and between inside diameter 230 and the outside diameter of the hat-shaped washer 216, prevents contaminants from reaching the space above the hat-shaped washer 216 by diffusion. During a purge or cleaning cycle, there is downward flow of supercritical fluid through these gaps, and since the gaps are small, this downward fluid flow prevents eddies of contaminated fluid from passing up through the gaps. These gaps are only a few millimeters (thousandths of an inch). Because the top of nipple 176 and the conical recess 210 at the bottom of the extraction cartridge are sealed by spring pressure, contamination cannot enter in these ways. For extraction, supercritical fluid entering fitting 42 is distributed in the space occupied by spacer ring 206, flows through passageway 208 and flows down the few millimeters (thousandths of an inch) radial gap between the shoulder of shoulder screw 218 and the inside diameter of washer 216. The fluid continues to flow down and flows through passageway 250, porous frit 162 and into extraction volume 254 where it passes through material to be extracted. Extraction volume 254 is shown sized in FIG. 4 for a 10 cubic centimeter volume to receive sample. After passing the extraction volume fluid, it is exhausted for sample collection through frit 160, passageway 260, fitting adapter 214 and out through fitting 46. All tubing, except tubing designated as capillary tubing, in this disclosure is 300 series stainless steel with an outside diameter of .15 cm (1/16 inch) and inside diameter .05 cm (0.02 inch). In operation after assembly, the fluid flow associated directly with the pure fluid valve 54 (FIG. 1) exiting its port 114 (Fig. 1) flows through tube 58 through the heat exchanger 40, which is formed by coiling a contiguous segment of tubing into a helix, through the check valve 60A and through the tube 60B to the inlet fitting 42 of pressure vessel 24. The heat exchanger 40 actually resides in a longitudinal bore through heating block 22 so that the heat exchanger is at the same temperature as pressure vessel 24 and extraction tube 30. This preheats any fluid flowing into inlet fitting 42 to essentially the same temperature as the extraction cartridge assembly 30. This temperature is above the critical temperature for the fluid. Assuming that the pump 12 is set to produce a constant fluid pressure greater than the critical pressure, fluid entering the pressure vessel 24 will be a supercritical fluid. The check valve 60A prevents backflow of supercritical fluid out of the pressure vessel 24 and extraction cartridge 26 of a first channel of a dual channel supercritical extraction system if there is a momentary drop in pressure of the supercritical fluid at the location of the tee 20. Such a pressure fluctuation could occur if the second channel of a dual channel extraction system is suddenly purged while the first channel is extracting. Each channel requires such a check valve. During a purge cycle, contaminated supercritical fluid leaves fitting 44, flows through a tube 62 and enters the inlet fitting 116 of the purge fluid valve 52. Then it exits the outlet fitting 118 and passes through the tube 64 to the coupling 90 (Fig. 1). The coupling 90 couples the quartz capillary tube 110 so that contaminated purge gas exits through it. The bore of the capillary tube is small enough, such as 75 micrometers, and its length long enough, on the order of a few centimeters (inches), to provide enough fluid resistance to limit the flow to a convenient rate: for example 5 milliliters per minute with respect to displacement of pump 12, at a pressure of 2.07·10 7 Pa (3,000 psi). Pump 12 is a constant pressure pump so this fluid flow does not affect the pressure within pressure vessel 24 once the flow stabilizes. The outer end of capillary 110 may be immersed a purge fluid collector 92 (Fig. 1) containing an appropriate solvent 100 such as isopropyl alcohol to serve as a collector. Bubbles through this solvent indicate proper flow and the solvent tends to prevent the end of the capillary tube 110 from being plugged by the exhausted contaminants. A solvent is chosen in a manner known in the art to dissolve contaminants so the end of the capillary tube 110 does not plug and so the solvent may later be analyzed if desired to determine whether there was any contaminants on the exterior of the extraction cartridge. During an extraction cycle, extractant exits fitting 46 on pressure vessel 24 and passes through tube 66. This tubing extends to inlet fitting 120 of extractant valve 50 which has rotary control shaft 126 attached to control knob 132. When the extractant valve 50 is opened by turning it counterclockwise from its closed position, fluid exits from its fitting 122, through tube 68 to fitting 94. Fitting 94 couples to quartz capillary tube 128. Capillary tube 128 has a small enough bore, such as 50 micrometers, and a long enough length, on the order of several inches, to produce a flow rate, relative to the displacement of constant pressure pump 12, of a conveninent amount. For example, this may be two milliliters per minute. The end of the capillary tube 128 dips into solvent 104 in the extractant collector 98. Isopropyl alcohol is under some circumstances used for solvent 104. This solvent 104 must be a good solvent for the extractant since it must trap the extractant by dissolving it from the gas bubbling through it and must prevent plugging at the end of the capillary tube 128. The solvent 104 is removed after extraction and is analyzed to determine the composition and amount of the extractant. Because of the pressure and temperature drop along the length of capillary 128 (and also capillary 110) fluid entering the capillary as a supercritical fluid (or a liquid if fitting 90 or fitting 94 is not heated) changes to a gas by the time it reaches the far end where it dips into the solvent which is at room temperature. In FIG. 5, there is shown a simplified perspective view of another embodiment 10A of supercritical fluid extraction system having a cabinet 400 containing a drive section in its lower portion (not shown in FIG. 5), an extraction section in the upper portion of the cabinet (not shown in FIG. 5), a sample injection section 406 and a fraction collection section 408. The supercritical liquid extraction system 10A is controlled from a panel 410 on the front of the cabinet 400 and the drive section operates the extraction section, the sample injection section 406, and the fraction collection section 408, which cooperate together to extract a plurality of samples sequentially and collect the extractant from the samples in separate containers with minimum intervention by an operator. The liquid extraction system in the embodiment 10A operates in a manner similar to that of the embodiment of FIG. 1 but is adapted to cooperate with the novel sample injector and fraction collector. With this arrangement, a series of samples to be extracted are preloaded into a means for holding the samples and the samples are automatically injected one at a time into the extractor. In the extractor, supercritical fluid is supplied to the samples and an extractant is removed from the samples one by one. To aid in correlating the embodiment 10 and the embodiment 10A, similar parts have the same reference numerals but in the embodiment of FIG. 10A, the numerals include the suffix "A". The extractant is supplied to individual containers or individual compartments of one container in a fraction collector. Thus, a plurality of extractions are performed on a plurality of different preloaded samples without the need for manually loading samples or initiating the flow of the supercritical fluid for each individual sample. The samples are automatically mechanically moved one by one into the extractor for extraction instead of being individually physically injected by an operator. The cabinet 400 has a lower portion 412 generally shaped as a right regular parallelopiped with an angled control panel 410 and upstanding upper portion 414 which is another right regular parallelopiped extending upwardly to create a profile substantially shaped as an "L" having a common back portion or rear panel 416 which may contain fans and connections for supplementary pumps and the like. A fluid fitting 420 extends from one side to permit near supercritical fluids to be introduced into the cabinet 400. The L-profiled cabinet 400 has an angled front panel 410 for convenient use of controls and a top surface on the foot of the "L" for manipulation of samples to be injected and extractants that are collected. To permit access to the interior of the cabinet 400, the upper portion 414 includes a hinged front access panel 422 having hinges 426 at its top so that it can be pivoted upwardly. It includes an opening 424 near its bottom to permit the entrance of fraction collector receptacles that are relatively tall. It extends downwardly to a point spaced from the top surface of the lower portion 412 of the cabinet 400 a sufficient distance to permit the entrance of normal receptacles used in the sample injector and the fraction collector. The sample injection section 406 includes a sample reel 430 which is formed of upper and lower rotatable plates 432 and 434 spaced vertically from each other and containing holes in the upper plate 432 and openings in the lower plate 434 which receive cylindrical tubular sleeves 436 having vertical longitudinal axes and open ends. The upper open end 438 permits samples to be received and to be removed as the sample reel 430 is rotated into the extractor. With this arrangement, the sample reel 430 may be rotated to move samples one by one into the extractor for processing. The sample reel 430 is horizontal and extends into the upper portion 414 of the cabinet 400 and into the extractor assembly with its vertical center of rotation being outside of the upper portion 414 to permit ready access to a number of the sleeves 436 by users and yet to permit sequential rotation by automatic means into the extractor. In the preferred embodiment, there are 24 sleeves for containing 24 distinctly different samples which can, without human intervention, be moved into the extractor. To receive extractant, the fraction collection section 408 includes a horizontal fraction collector reel 440 mounted concentrically with the sample reel 430 but having a smaller diameter to be inside the sample reel 430 having a plurality of openings 442 circularly arranged in spaced apart relationship with each other about the periphery of a top plate 446 of the fraction collector reel 440 and having in its center a knob 444 by which the fraction collector reel 440 may be lifted and removed from the cabinet 400. With this arrangement, the fraction collector reel 440 may be lifted and removed or reinserted after the hinged access panel 422 is pivoted upwardly about the hinges 426. When the fraction collector reel 440 is in place, it is rotated automatically through the opening 424 into a location in which one or more individual containers 442 may receive extractant. The fraction collector reel 440 is moved alternately with the sample reel 430 and independently of it so that, after a sample injection and extraction, one or more of the openings 442 are moved into position to receive the extractant prior to the injection of another sample for extraction. Because the reels 430 and 440 rotate within the upper portion 414 of the cabinet 400 with a portion of its periphery outside of the cabinet 400, the collected extractant may be removed and new sample added during operation of the equipment. For this purpose, the receptacles for the fractions and the receptacles for the samples have upward open ends and are mounted with their axes vertical. In FIG. 6, there is shown a longitudinal sectional view through lines 6-6 of FIG. 5 showing the cabinet 400, the drive section 402 within the cabinet 400, the extraction section 404, the sample injection section 406 and the fraction collection section 408. The drive section 402 includes a control system 450, a sample-and-extractant container reel drive assembly 452, a sample injector drive 454 and a fluid drive or pump 456. The control system 450 receives information from the control panel 410 and conveys information to it through a cable 458. It also controls the pump 456, the sample-and-extractant container reel drive assembly 452 and the sample injector drive 454, which cooperate together to move samples into position, inject them into the extractor, pump fluids through the extractor to extract the samples and collect the samples in sequence one by one. To inject samples into the extraction section 404, the sample injection section 406 includes the sample-and-extractant container reel drive assembly 452, the sample reel assembly 430, and a cartridge injector assembly 460. The sample-and-extractant container reel drive assembly 452 drives the sample reel assembly 430 to carry a cartridge assembly 30A onto the cartridge injector assembly 460 which lifts it under the control of the sample injector drive 454 upwardly into a pressure vessel 24A for the purpose of extracting a sample within the cartridge assembly 30A. The cartridge assembly 30A and the pressure vessel 24A are similar to the cartridge assembly 30 and pressure vessel 24 of the embodiment of FIGS. 1-14 and are only adapted such as by having their top and bottom sides reversed to permit the cartridge assembly 30A to be inserted from the bottom into the pressure vessel 24A and be more easily sealed therein for extraction and removed by gravity after extraction. To drive the sample reel assembly 430, the sample-and-extractant container reel drive assembly 452 includes a central transmission and motors on each side that drive the transmission under the control of the control system 450 to drive either one or both the sample injector reel assembly 430 and the fraction collector reel 440. The sample injector reel assembly 430 includes the top plate 432, the bottom plate 434, both of which are rotatable together to carry a plurality of sleeves 436 sequentially, one at a time, into position for the repeated injecting of cartridges one by one into the pressure vessel 24A and the removal of the cartridges from the pressure vessel 24A and the return of them to the reel assembly 430 one by one so that only one cartridge is in the pressure vessel 24A at a time. Within the extraction section 404, a stationary bottom plate 462 has a hole 464, with the hole being aligned with the open-bottom end of the pressure vessel 24A and the upper end of the cartridge injector assembly 460. Consequently, the cartridge assemblies such as 30A are rotated one by one above the open end 464 in the bottom plate 462 for movement upwardly into the pressure vessel assembly 24A by the cartridge injector assembly 460 under the control of the sample injector drive 454 for extraction of the sample therein. With this arrangement, a stationary plate 462 holds the cartridge assemblies 30A in place as they are rotated by the upper and lower plates 432 and 434 until they are sequentially brought over the opening 464 through the stationary plate 462 for elevation into the pressure vessel 24A. To inject cartridges into the pressure vessel 24A, the cartridge injector assembly 460 includes the sample injector drive 454, a pinion 470, a gear 472, a multi-threaded, fast action nut 474, a corresponding screw 476, and piston or plug 32A. The pinion 470 is mounted to the output shaft of the drive gear motor 454 and engages the teeth of gear 472. The gear 472 is fastened to or integrally formed with the drive nut 474 which, as it rotates, moves the screw 476 upwardly or downwardly. The support platform 475, piston or plug 32A and sample container 30A are carried by the top of the screw 476 and are moved upwardly and downwardly. The top surface of the plug 32A, which is supported by the screw 476 in its lower position is flush with the bottom of the opening 464 in the fixed plate 462 to support a cartridge such as 30A therein and in its top position positions the piston or plug 32A at the bottom of the pressure vessel 24A. Plug 32A carries self-actuated, spring-biased, cylinder seals, such as those made by the Bal-Seal Corporation. These seals provide a high pressure fluid-tight seal between the plug 32A and the inner wall of the pressure vessel 24A. With this arrangement, the piston or plug 32A is sealable against the walls of the pressure vessel 24A during the extraction process after moving the cartridge assembly 30A upwardly into the pressure vessel 24A, and after extraction, can move the cartridge assembly 30A downwardly back to the sample reel assembly 430 for rotation out of the upper injector housing 414 as a new cartridge is moved into position for injecting into the pressure vessel 24A. A bearing mount rotatably supports the nut 474 while maintaining it in the same vertical position so as to move the rapid-advance screw or other screw 476 upwardly and downwardly. The plug 32A serves a function similar to the breech plug 32 in the embodiment of FIGS. 1-4 and contains within it an opening supporting a spring 201A and a support block 482 so that the support block 482 is biased inwardly against the cartridge end 148A to move the cartridge 30A into place against fittings for supercritical fluid. To extract the sample in the cartridge 30A after it has been moved into position and the breech plug 32A fastened in place for a seal, extracting fluid is applied through the fitting 42A in a manner similar to the embodiment of FIG. 1, so that the extracting fluid flows through one path into the cartridge 30A and through another path over the outside of the cartridge 30A into the fitting 44A and from there to a purge collector or vent. The extractant, after passing through the cartridge and the sample, exits from a fitting 46A and proceeds to the sample collector in a manner to be described hereinafter. To pump fluid such as carbon dioxide into the pressure vessel 24A at a temperature proper for supercritical extraction: (1) the pump 456 includes a pump head 490 and an electrical motor 492; and (2) the pressure vessel 24A has an aluminum heating block 22A over it, an opening 278A in the aluminum heating block, a rod-shaped heating element 274A in the aperture 278A, the extracting fluid fitting 42A and a heat exchanger 40A entering the aluminum heating block 22A at aperture 270A. The motor 492 drives the pump mechanism 490 to pump fluid into the aperture 270A, through the heat exchanger 40A within the aperture 270A, through the connecting tubing 60A and the fitting 42A and into the cartridge 30A and the pressure vessel 24A. The aluminum block 22A controls the temperature of the fluid, which may be carbon dioxide or any other useful extracting fluid to keep it above the supercritical temperature for that fluid and for that purpose, the heating rod 274A within the aperature 278A is used when necessary to heat the aluminum block 22A. The pump 456 may be any suitable pump, but an appropriate pump for carbon dioxide is the pump used in the Isco model 2350 HPLC Pumping System sold by Isco, Inc., Lincoln, Nebraska. However, for best results when using carbon dioxide, the stroke of this pump is modified from ten millimeters to fifteen millimeters, and smaller, lower trapped-volume check valves are used. These modifications increase the compression ratio of the pump from 1.7:1 to 2.6:1 and increase the displacement by a multiple of 1.5. An additional change is to use Carpenter Technologies 182FM stainless steel in the pump head, instead of type 316, for better thermal conducting. To collect extractants, the fraction collector section 408 includes the fraction collection reel 440, the sample-and-extractant container reel drive assembly 452, a purge fluid outlet system 520 and an extractant fluid outlet system 522. The fraction collection reel 440 moves receptacles such as 98A into position within the housing 414 where the extractant fluid outlet system 522 to be described in greater detail hereinafter causes fluid from the fitting 46A in the pressure vessel 24A to flow outwardly and into the receptacle 98A after piercing a seal therein. The purge fluid system 520 causes purge fluid to flow from the purge fluid fitting 44A to a pressure control unit and finally to an exhaust or collection unit. To move the collection receptacles 98A into position, the fraction collection reel 440 includes a knob 444, an intermediate plate 448, an upper plate 446, a lower disk plate 530 and a drive rod 532. The drive rod 532 rotates within the fixed disk 530 and carries above them the upper and lower plates 446 and 448. The upper and lower plates 446 and 448 have aligned circumferentially spaced holes through them, each of which can receive a collection vial such as 98A. The lower disk 530 does not have holes and supports the plates as they are moved. The knob 444 may be used to lift the fraction collector reel 440 from the center of the sample injector reel 430 after the hinged front access panel 422 has been opened about its hinge 426. The sample-and-extractant container reel drive assembly 452 moves the collection vials one by one inside the upper portion of the housing 414 to receive extractant. One or more such vessels 98A may be moved in place each time a sample cartridge 30A is extracted so that the receptacles 98A are moved alternatively with the sample cartridges 30A, although several receptacles 98A may be moved in the time between moving one of the sample cartridges 30A into a pressure vessel 24A and the time the sample cartridge is removed from the pressure vessel 24A. The extractant passes through fitting 46A and into the fraction collector receptacles 98A in a manner to be described hereinafter. The purge fitting 44A communicates with the extraction volume in the cartridge 30A and is connected to a Tee-joint tube 542 through tubing 62A. A second arm of the Tee-joint tube 542 is connected to an over-pressure safety diaphram 540 calibrated to burst at 8.62·10 7 Pa (12,500 pounds per square inch). This is an excess of the maximum rated working pressure of 6.89·10 7 Pa (10,000 pounds per square inch) for pressure vessel 24A. The remaining arm of the Tee-joint tube 542 is connected to the purge valve 52A. The other side of the purge valve 52A is connected to the first side of a second Tee-joint tube 544 through the tube 64A. The second side of the Tee-joint tube 544 is connected to an exterior vent port 546 through a tube 548. The third arm of the Tee-joint tube 544 is connected to the exhaust tube 110A which vents the fraction collection vial 98A. With this arrangement, the purge fluid flowing through fitting 44A is removed and a tube connected to the vent port 546 is also used to vent the sample receptacle 98A in a manner to be described hereinafter. In FIG. 7, there is shown a simplified sectional elevational view of the embodiment 10A of supercritical fluid extractor taken through lines 7-7 of FIG. 6 having the sample-and-extractant container reel drive assembly 452, the pump 456 and the extractant fluid outlet system 522. The sample-and-extractant container reel drive assembly 452 may selectively move either the sample reel 430 or the fraction collection reel 440 under the control of the controller 450 (FIG. 6). To selectively drive the fraction collection reel 440, the sample-and-extractant container reel drive assembly 452 includes a fraction collection spindle 532, a tubular shaft 580, a bevel gear 582, a bevel gear 584 and a gear motor 586. The controller 450 controls the gear motor 586 to rotate the fraction collection reel 440. For this purpose, the spindle 532 is held by the tubular shaft 580. The bevel gear 582 is fastened at the end of the spindle 532 and meshes with the bevel gear 584 on gear motor 586. The controller 450 moves these gears into meshing position and causes the motor 586 to rotate its output shaft so as to drive the collection reel 440 (FIGS. 5 and 6) and not the sample injector reel 430 (FIGS. 5 and 6). To move the sample injector reel 430, the sample-and-extractant container reel drive assembly 452 includes the tubular shaft 580 supported by bearing block 590, fraction collection spindle 532, bevel gear 588, bevel gear 592 and gear motor 594. The controller 450 actuates gear motor 594 to cause the bevel gear 592 to rotate. The bevel gear 592 meshes with the bevel gear 588 which is attached to the bottom end of the fraction collection spindle 532. To cause extractant to flow into the fraction collection vial 98A, the extractant fluid outlet system 522 includes a gear motor 552, a pinion 554, a gear 556, a lead screw 558, an arm 560, and a restrictor tube 66A. The vials 98A have a seal 550 over the top, which seal can be pierced. To cause the seal 550 to be pierced and extractant to flow into the vial 98A, the controller 450 starts the gear motor 552 which rotates its pinion 554 which is in engagement with the gear 556. The pinion 554 rotates the gear 556, which engages and is fastened to the rotating lead screw 558. The arm 560 is mounted for movement by the lead screw 558 and lowers it into a position where the restrictor tube 66A pierces the cap 550 on the collection vial 98A and moves its tip below the surface 564 of the collection fluid within the vial 98A. As the extractant flows into the tube, exhaust is removed from the tube through an exhaust tube 110A (FIG. 6 in addition to FIG. 7). If either the tube 66A or the tube 110A are stiff or otherwise inconvenient to bend, it is advantageous to raise the collecting vial 98A up to tubes 66A and 110A, instead of lowering the tubes into the collecting vial. This alternate arrangement does not pose any difficulty as the collecting vial 98A may be raised by a support similar to plug 32A, which support is connected directly to plug 32A so that it moves synchronously with plug 32A. With either arrangement, extractant flows through the fitting 46A (FIG. 6) from the sample cartridge 30A (FIG. 6) through the tubing 522 (FIG. 6), the valve 50A and the restrictor tube 66A. Extractant residing in bubbles from the tube are captured through trapping fluid 104A whereby extractant is trapped in the trapping fluid 104 in the vial 98A and extracting fluid passes out through the exhaust tube 110A, Tee-joint tube 544 (FIG. 6), tube 66A and exhaust port 546 (FIG. 6). After collection of the extractant, the motor 552 moves in the reverse direction and raises arm 560 which removes the restrictor tube 66A and exhaust tube 110A from the vial 98A. Because the pump head 490 is heated by pumping at high compression, both the pump head 490 and incoming fluid line are preferably cooled. In the preferred embodiment, they are cooled thermoelectrically (Peltier effect) and the pump head 490, the inlet check valve housing 494 are formed of Carpenter 182FM stainless steel rather than type 316 stainless steel to increase their thermal conductivity. In pumping, the pump drive motor 492 (FIG. 6) drives a cam within cam housing 495 through appropriate gear train within the gear housing 496. The rotating cam within the cam housing 495 operates a pump plunger which cooperates with the pump head 490 (FIG. 7) to draw liquid carbon dioxide through inlet check valve assembly 494 and discharge it through outlet check valve assembly 436. The Peltier cooling plate 500 is mounted to the flat face of the pump head 490 (FIG. 7) with cooling fins 502 mounted for good thermal contact to the opposite side of the Peltier cooling plate 500. When an electric current is passed in the proper direction through the Peltier cooling plate 500, heat is withdrawn from the pump head 490 (FIG. 7) and rejected into the cooling fins 502. A fan 504 driven by an electric motor 493 (FIG. 6) withdraws heat from the fins 502. Another Peltier-effect cooled heat exchanger is also utilized in the inlet line. To control the speed of the motor 492 (FIG. 6), a tachometer wheel 505 is mounted to the shaft of motor 492 (FIG. 6) with a photoelectric tachometer sensor 510 mounted to provide signals reading indicia on the wheel. The signals from the photoelectric tachometer 510 indicate the speed of motor 492 and thus the pumping speed of pump 456. These signals are compared in the controller 450 and utilized to control the speed of the motor 492. To control the pressure on the outlet line 512 from the pump, a pressure transducer 514 (FIG. 8) generates a signal indicating the pressure. This signal is used as a feedback signal to control the pumping speed. This structure is provided by existing pumps such as the Isco model 260D pump. In FIG. 8, there is shown a sectional view, partly simplified, taken through lines 8-8 of FIG. 6 having a locking mechanism 614 for locking plug 32A into the pressure vessel 24A and a control mechanism 616 for controlling the extraction fluid. As best shown in this view, the locking mechanism 614 includes a gear motor 600, a pinion 602, a rack 604, a locking pin 606, a hole 609 in the pressure vessel 24A and a hole 610 in the piston or end piece or breach plug 32A and a hole 612 through the other side of the pressure vessel 24A. Instead of a pin 606, a yoke of the type conventionally used as a Winchester 94 rifle locking mechanism advantageously may be used. This type of locking mechanism is a yoke mounted to a pinion 602 and rack 604 as shown in FIG. 8. In this mechanism, a plate with a slot cut out of it to form a yoke is moved by the rack and pinion to pass under the plug 32A to hold it against pressure and provide strong support therewith by further engaging slots in the pressure vessel 24A. The aforementioned slot in the plate provides clearance for the screw 476. In operation, the gear motor 600 is caused by the control system 450 (FIG. 6) to drive locking pin 606 through the opening 609 in the pressure vessel 24A, through the opening 610 in the piston 32A and through the opening 612 in the pressure vessel 24A by rotating the pinion 602 to drive the rack 604 that carries the locking pin 606, thus locking the cartridge 30A (FIG. 6) in place within the pressure vessel 24A. To control the flow of extracting fluid from the pump 12 (FIG. 1) into the pressure vessel 24A and cartridge 30A, the control mechanism for extracting fluid includes the gear motor 570 and valve 54A that is connected at one end to the conduit 58A that extends from line 512 and pressure transducer 514 to the conduit 58 which passes into the heat exchanger 40 (FIG. 1). In operation, the gear motor 570 under the control of the control system 450 opens the valve 54A to permit the flow of extracting fluid into the cartridge 30A and pressure vessel 24A during an extraction operation. It also rotates in the opposite direction after extraction is complete to close the valve 54A. The sample cartridge 30A (FIG. 6) is composed of a tubular sleeve or body portion 140A (FIG. 6) and end pieces 144A (FIG. 16) and 464A (FIG. 6). The end pieces 144A and 464A are made of stainless steel or an inert plastic and carry a stainless steel frit or filter disk centered in the interior of each. The flat, narrowed ends of the tubular sleeve 140A seal against PTFE washers around the frits which seal against the end pieces at the location between the diameters of the filter disks and the inside diameters of the end pieces 144A or 464A respectively. In FIG. 9, there is shown a cross-sectional view of a valve 54B usable in the embodiments of FIGS. 1-8, having a valve body 1001, female fittings 1002 and 1003, a ball valve assembly 702 and a valve stem assembly 700. The female fitting 1003 is adapted to communicate with the pump 12 (FIG. 1) to receive supercritical fluid therefrom and the fitting 1002 is adapted to communicate with the pressure vessel and fluid assembly 18. The fitting 1003 and 1002, each communicating with each other through the ball valve assembly 702. The valve stem assembly 700 is positioned to hold the ball valve assembly 702 closed in one position, thus blocking flow between the fitting 1003 and the fitting 1002 and in another position to release the valve ball assembly 702 so the fluid may flow from the pumping system 12 (FIG. 1) through the valve 54B and into the pressure-vessel and fluid-extraction assembly 18 (FIG. 1). The ball valve assembly 702 includes passageways 1006, 1007, 1008, 1009 and 1010, a valve seat 1013, a valve element 1014 and a cavity 1015. The valve seat 1013 is initially machined as a female cone. The valve element 1014 is spherical and lies conformingly in the seat 1013 when it is forced into the seat as the valve is tightly closed, thereby forming a seal. When the valve is opened, the valve element 1014 may be lifted from the seat to permit communication between the fitting 1002 and 1003. For this purpose, the valve seat 1013 communicates through the passageway 1008 at the bottom of the valve as a valve outlet and through the successively larger passageways 1007 and 1006 to the inlet female fitting 1003 to receive fluid underneath the valve seat capable of lifting the valve element 1004. The cavity 1015 is located above the valve element to communicate with the passageway 1008 when the valve element 1014 is lifted but to be sealed from it when it is closed at its bottom-most location. The cavity 1015 communicates through the successively larger passageways 1009 and 1010 with the outlet female fitting 1002 to permit fluid to flow from the female inlet fitting 1003 through the female outlet fitting 1002 when the valve element 1014 is permitted to rise into the cavity 1015 by the valve stem assembly 700. The valve element 1014 must be harder on its surface and have a higher yield point than the valve seat 1013 and should be at least three times as hard as the seat 1013 on its surface. It should have a yield point of more than three times that of the seat and at least 1.38·10 8 Pa (20,000 psi) since it must retain complete spheri-city even though it rotates when it is lifted from the valve seat 1013 and is compressed by the stem into the valve seat 1013 when the valve 54A is closed by the stem assembly 700. The valve element 1014 must form a relatively large area of the seat to provide Hertzian line contact in order to form an adequate seal. The valve seat 1013 is formed of the same material as the valve body 1001 and has a yield strength of at least 1.38·10 8 Pa (20,000 psi) and preferably of about 5.86·10 8 Pa (85,000 psi). It is made of 316 stainless steel bar stock, hardened to about 5.86·10 8 Pa (85,000 psi) yield strength by cold working to a 20 percent reduction in area. With this method of forming, the valve itself and the valve body 1001 is as small as one and .32 cm (one-eighth inch square) by 3.04 cm (one-half inch) thick. In this embodiment, the valve element 1014 is approximately eight times as hard as the seat 1013 so that the seat 1013 deforms to fit the valve element 1014 rather than the valve element 1014 deforming. In this specification, hardness means compression yield point so that expressions such as eight times as hard mean that it has a yield point eight times higher. Because the materials are hardened throughout in this embodiment rather than having only a surface hardening, the surface hardness is proportional to the yield point. Because the valve element 1014 is substantially harder than the seat, one or several tight closures of the valve force the valve element into the seat, thereby causing the seat to conform to the spherical surface of the valve element. The valve element is not deformed because it is too hard to do so. To form a sufficiently strong valve element 1014, it is formed in this embodiment of tungsten carbide with six percent cobalt. Brittle balls, such as balls of monocrystalline sapphire and polycrystalline aluminum oxide ceramic, are generally less desirable and do not have the most useful hardness characteristics that permit sealing in the valve seat without leakage and resistance to scratching or breaking when lifted from the seat in a manner that causes rotation. The valve element 1014 is .32 cm (one-eighth inch) in diameter with a diametral tolerance of 254 micrometers (100 micro-inches) and a sphericity tolerance of 0.16 micrometers (16 micro-inches). The close sphericity tolerance is desirable so that, after the ball rotates for more or less random reasons when the valve 54A is open, the sealing surface that is superimposed onto the conical seat 1013 by cold flow of the 316 stainless steel (due to the contact pressure or force of the ball 1014) continues to conform to the surface of the ball 1014. This conformance in shape with the contact surfaces prevents leaks when the valve 54A is closed. In this embodiment, the cemented tungsten carbide ball 1014 has a hardness of 4.83·10 9 Pa (700,000 psi). Fittings for conducting fluids through the valve 54A are threaded into the female fittings 1002 and 1003 in a manner to be described hereinafter. Tapered sections or cones of the female fittings 1002 and 1003, shown respectively at 1011 and 1005, receive sealing ferrules to seal the connecting tubings protruding from the ferrules in the passageways 1010 and 1006. The internal threads are shown at 1012 and 1004, respectively, to engage the external threads on the corresponding male fittings. The valve stem assembly 700 includes an outer stem 1030B, an inner stem 1027, a hard anti-friction device 1035, a captivating element 1034, a spring 1016, a stepped bushing 1022B and a threaded bushing 1045B. The outer stem 1030B fits rotatably within the threaded bushing 1045B with external threads on the outer stem 1030B engaging internal threads on the threaded bushing 1045B. Beneath the outer stem 1030B is the captivating element 1034 which holds an upper part of the inner stem 1027. Between the inner stem 1027 at its top point and the outer stem 1030B is the anti-friction device 1035 which is a hard ball that contacts the inner stem at a relatively small location and the top of the outer stem 1030B over a wider area to provide a connection capable of pushing the inner stem 1027 downwardly but unlikely to transmit rotating forces between the outer stem 1030B and the inner tem 1027. The spring 1016 biases the inner packing support upwardly, compressing washer-shaped packing 1018 against the stem 1027. The inner stem 1027 is supported for up and down movement within the stepped bushing 1022B. With this arrangement, rotation of the outer stem 1030B causes it to move downwardly within the threaded bushing 1045B to cause the anti-friction device 1035 to press the inner stem 1027 downwardly through tightly fitting packing 1018. The inner stem 1027, as it moves downwardly, presses the valve element 1014 into the valve seat 1013 and when it moves upwardly, releases the valve element 1014. The larger opening of the conical seat 1013 is large enough in diameter and the recess 1019 is small enough in diameter and the recess 1019 is small enough in diameter so that the ball, when pressed by the face 1023 of stem 1027, will find its way into the seat regardless of fluid flowing outwardly from the larger opening of the seat and regardless of the orientation of the valve with respect to gravity. Above the cavity 1015, is a larger, .54 cm (one-fourth inch) diameter, cylindrical recess 1019. In recess 1019, is the Bellville stainless steel spring 1016 made of highly work-hardened type 302 stainless steel (Associated Spring Company part number B-0250-013-S), washer-shaped packing support washer 1017 and semi-hard packing or seal 1018. Bellville spring 1016 is sized to fit loosely within the .64 cm (one-fourth inch) diameter recess 1019 and to fit loosely around the .32 cm (one-eighth inch) diameter internal stem 1027. The spring 016 bears upwardly on the packing support washer 1017 and downwardly on the wall of the recess 1019. Packing support washer 1017 is made of Armco Nicronic R 60 stainless steel to prevent galling due to moving contact with the internal stem 1027. The annularly-shaped semi-hard seal 1018 is positioned between the packing support washer 1017 and the bottom of the stepped bushing 1021. It is dimensioned to sealingly fit the cylindrical wall of recess 1019 and is annularly shaped with its central hole dimensioned to sealingly fit the circumference of the .32 cm (one-eighth inch) diameter inner stem 1027. The semi-hard stem seal 1018 is made of DuPont Vespel type SP-211. Vespel is a trademark of DuPont for a temperature-resistant thermosetting polyimide resin reinforced with carbon and internally lubricated with Teflon polytetrafluorethylene powder (Teflon is a trademark of DuPont). Various softer seals made of plain and reinforced polytetrafluorethylene (PTFE) were tried, but had inadequate life at high temperatures and pressures. A seal with a hardness greater than 2.76·10 7 Pa (4000 psi), and which retains its hardness better than PTFE at high temperature, such as Vespel SP-211, is necessary. The internal stem 1027 is made of age-hardened Type 17-4 PH stainless steel. Internal stem 1027 is guided by stepped bushing 1022 made of Nitronic 60 stainless steel. Nitronic 60 is used to prevent galling due to the motion of the contacting internal stem 1027. There is a distinct relationship between the compressive yield strengths or hardnesses of the internal stem 1027, the very hard ball 1014 and the conical seat 1013. The ball 1014 must be substantially harder than the face 1023 of stem 1027, and the stem 1027 must be substantially harder than the seat 1013. This is because when the valve closes tightly the ball 1014 must deform a relatively large area of the seat (a so-called Hertzian line contact) in order to seal, but the ball 1014 is in contact with a smaller area on the stem 1027 (a so-called Hertzian point contact). The ball's contact pressure on the stem 1027 is higher than its contact pressure on the seat 1013 because its contact area on the seat 1013 is larger. Nevertheless, the ball 1014 must not too greatly deform into (press too large a dimple into) the face 1023 of the stem 1027, or stem 1027 will swage outwards and interfere with or rub hard on washer 1017. Hence, stem 1027 must have a significantly higher yield point than conical seat 1013. Furthermore, ball 1014 should have a significantly higher yield point than stem 1027 so that the permanent contact dimple is on the stem face 1023 and not on the ball 1014. Ball 1014 must retain almost perfect sphericity, as it is free to rotate when the valve is open and if it has a contact dimple it can produce a leak at the seat 1013 when the valve is closed. The internal stem 1027 has a neck 1029 and a head 1033 which cooperates with captivating element 1034 of outer stem 1030. Head 1033 resides in cylindrical recess 1070 of outer stem 1030. The anti-friction device or hard ball 1035 transmits thrust from the female conical face 1036 of outer stem 1030 to the flat surface 1038 at the end of head 1033. Before assembly of the head 1033 of inner stem 1027 and hard ball 1035 into outer stem 1030, captivating element 1034 is straight rather than curved and extends as a hollow cylinder with its extended interior diameter being part of the cylindrical recess or cavity 1070. At the final part of its assembly process, captivating element 1034 is bent, as shown in the figure, by a spinning or rotary swaging process. Outer stem 1030 is made of Type 17-4 PH age-hardened stainless but it not as hard as the interior stem 1027. The 17-4 PH stainless stem 1027 and its face 1023 has a hardness of 1.17·10 9 Pa (170,000 psi). The face 1023 of stem 1027 should have a yield point and hardness at least 1.3 times higher than the seat 1013 and no more than 0.5 times as high as the yield point and hardness of the ball 1014. Screwing the stem 1030 counterclockwise relieves the force between the stem face 1023 and the ball 1014 and the ball 1014 is dislodged by any excess pressure present in fluid entering the location 1003, said fluid then exits through location 1002 and is prevented from leaking up through the valve stem area by the spring and fluid pressure loaded semi-hard seal 1018. Because the yield strength of the 17-4 PH stainless steel at the face 1023 of the inner stem 1027 is only about 1.77·10 9 Pa (170,000 psi) and the yield strength of the cobalt-cemented tungsten carbide ball 1014 is about 4.83·10 9 Pa (700,000 psi), the rotation of the stem 1027 would be expected not to have a detrimental effect on the very hard ball or element 1014. Nevertheless, rotation of the stem 1027 surprisingly puts microscopic scars on the ball 1014 at the location of the interface between the ball 1014 and the stem end 1023. When the ball 1014 rotates later for semi-random reasons when the valve is opened, and the valve is closed again, these microscopic scars interfere with sealing at the interface between the ball 1027 and the conical seat 1013. To avoid these scars, the inner stem 1027 is provided with an anti-rotation element such as the ball 1035. In FIG. 10, there is shown conventional tubing fitting for connecting .16 cm (one-sixteenth inch) outside diameter or other diameter stainless steel tubing to the ports 1002 and 1003 (FIG. 9) of the valve having a fitting body 1107, hexagonal wrench flats 1040 on the outer surface of the body, integrally formed with unthreaded stem 1106 which in turn is integral with threaded section 1105. Further inward from threaded section 1105 is integral unthreaded section 1104. In use, tubing 1100-1100A is passed through the fitting body 1107 and bored-through stainless steel conical ferrule 1102 which is slipped over the end of the unthreaded section 1104. The fitting, thus assembled, is threaded finger-tight into port 1003 (or port 1002) and the tubing 1100 is pushed in so that its distal end bottoms out at the inner end of tubing passageway 1006 (FIG. 9). The fitting is then wrenched tight causing the ferrule 1102 to be pressed against interior cone 1005 (FIG. 9). This radially compresses the ferrule sufficiently so that it yields diametrically and forms a permanent sealing fit with the tubing passing through it. Its outer conical surface also forms a sealing fit with the female cone 1005. In FIG. 11, there is shown an elevational side view of the valve body 1001, connected to tubings 1100 and 1101 by fittings 1107 and 1108, respectively. Screws 1043 and 1044 hold the valve body 1001, through the two tubular spacers 1054 (FIG. 12) and 1054A (not shown), to mounting plate 1055. The screws 1043 and 1044 pass through mounting holes 1042 and 1041 of the valve body 1001 (FIG. 9), respectively. Mounting plate 1055 is screwed to base 1058 and electric gear motor 570 with screws 1056 and 1057. The rotary output shaft 1051 of gear motor 570 is coupled with flexible coupling 1070 to the outer stem 1030 of the valve 54A (FIG. 9). A coupling between the motor and valve includes coupling member 1050 connected to the output shaft of the motor and coupling member 1049 of the valve. They each have a base to which shafts are pinned and alternately positioned arms extending in the direction of the other member. They are spaced in such a way as to allow relative axial motion of the couplings as well as to allow displacement and angular misalignment. Axial motion is necessary because the outer stem 1030 of the valve 54A can move as much as one millimeter in the axial direction due to movement imparted by the threaded region 1032 (FIG. 9). An elastomeric member 800 fits between the coupling members 1050 and 1049 as a single piece. The coupling including members 1050, 1049 and 800 are made by Love Joy, Inc., under the part number G35-A, and are obtainable from Nicholson Industrial Supply, 2909 North 27th Street, Lincoln, Nebraska 68521, U.S.A. Although only one-tenth of this distance is actually needed to open and close the valve by motion of the very hard ball 1014 within the conical seat 1013 (FIG. 9), it is deemed prudent to allow for a larger movement. An additional distance is useful for overtravel and for the initial cold flow of the conical seat 1013 as the valve is "broken in" and the ball-to-cone conformal seal formed in early operation. The ball 1014 moves further into the seat 1013 as torque is applied to outer stem 1030 (FIG. 9) during the first closures of the valve 54A after its assembly. The coupling parts 1049 and 1050 are each held to their respective valve and motor shafts by a spring pins 1047 and 1067 with C-shaped cross sections. A suitable gear motor for use as gear motor 570 is a Pittman series 9413 direct current permanent-magnetic-field motor having a gear box with a torque rating of 34.56 kg-cm (kilogram-centimeters) (30 pound inches), a nominal supply voltage of 24 volts DC, an output shaft speed of about 16 rpm at 15 volts DC and a current of about one-half ampere at a torque of 16.13 kg-cm (14 pound inches). In FIG. 12, there is shown a top view of the valve 1001 connected to the gear motor 570 of the direct current, permanent magnet field type. The direction of rotation of this type of motor is controlled by reversal of the polarity of the direct current supply voltage applied to its terminals. The torque produced by this type of motor is fairly closely proportional to the current through it. The motor has two electrical terminals 1059 and 1060, with terminal 1060 being located directly under terminal 1059 in FIG. 12. All of the gear motors coupled to valves in this disclosure are of the direct current, permanent magnet field type. To ready the valve for operation, locknut 1026 is screwed back along the outer threads 1025 (FIG. 9) of threaded bushing 1045. The threaded bushing 1045 is wrenched further into the valve body 1001 than shown in FIG. 9 by applying a wrench to the flats 1037 (FIG. 9) and rotating the bushing 1045 clockwise. The threaded bushing 1045, as it screws into the valve body, presses on the stepped bushing 1021, compressing the seal 1018 against the washer 1017 and flattening the Bellville spring 1016. This tightening and compression is continued until seal 1018 (FIG. 9) flattens outwards so that its inside diameter is sealingly compressed against the cylindrical surface of inner stem 1027 (FIG. 9) and its outside diameter is sealingly pressed against the cylindrical wall of recess 1019 (FIG. 9). A typical tightening torque applied to bushing 1045 is 46.8 kg-cm (40 pound inches). At this torque, Bellville spring 1016 (FIG. 9) has flattened. It is sized so that when flat it is capable of providing 6.89·10 6 Pa (1000 psi) residual compression within the seal 1018 (FIG. 9) to provide sealing force against the inner stem 1027 (FIG. 9) even after minor creepage of the spring 1016 (FIG. 9) due to its compression at the maximum operating temperature of 150°C. The seal 1018 is additionally self-activated by the fluid pressure due to the spring 1016. Compression within the seal 1018 due to spring 1016 prevents the seal 1018 from relaxing its leak-tightness when the fluid pressure is low. After the threaded bushing 1045 is tightened, the locknut 1026 is screwed down against the valve body 1001, securing the threaded bushing 1045 in place. In operation, the outer valve stem 1030 may be rotated by any means which may be conveniently coupled to the outer stem 1030 by a pin through hole 1046. Clockwise rotation of the stem 1030 causes it to move into the valve because of the external threads on outer stem 1030 in contact with internal threads in threaded bushing 1045 which meet in the face of stem 1032. Fine-series one-fourth by 28 threads are satisfactory. The threaded face of stem 1032 is lubricated with DuPont Krytox R 217 high temperature, high pressure lubricant which is composed of perfluoronated polyether oil, low molecular weight powdered polytetrafluorethylene thickener and powdered molybdenum disulfide high pressure solid lubricant. This lubricant was found to have the best high temperature resistance of six high pressure, high temperature lubricants tested. The threaded bushing 1045 is made of Nitronic 60 to prevent galling due to the pressure and motion of the threads 1032 of outer stem 1030. As the outer stem 1030 moves inward, so does the inner stem 1027 (FIG. 9) because of force transmitted by ball 1035 (FIG. 9). Although outer stem 1030 rotates, inner stem 1027 does not rotate because of the weakness of the rotary frictional force due to the small diameter of the contact area between the ball 1035 and the top 1038 of the head 1033 (FIG. 9) of the inner stem 1027. This weak friction force is not sufficient to overcome the anti-rotation frictional force of the tightly compressed seal 1018 (FIG. 9) against the cylindrical surface of the inner stem 1027. As clockwise rotation of outer stem 1030 continues, eventually the inner stem 1027 is pushed in enough so that its flat end or stem face 1023 contacts the very hard valve ball 1014. Further clockwise rotation of the outer stem 1030 forces very hard ball 1014 into seat 1013, conformally deforming seat 1013 to fit the ball 1014 and providing a tight seal against flow of fluid entering the female fitting 1003 (FIG. 9). Fourteen pound inches of torque on stem 1030 provide a tight seal. Conversely, when outer stem 1030 is rotated counterclockwise, outer stem 1030 moves outwardly by action of its threads. Captivating element 1034 of outer stem 1030 pulls outwardly on the head 1033 of inner stem 1027, disengaging the boss 1023 of inner stem 1027 from tight contract with valve element or ball 1014. This allows fluid to flow from port 1003 to port 1002 in the valve. In FIG. 13, there is shown a block circuit diagram of the control circuitry 2200 for gear motor 570 (FIGS. 8, 11 and 12) which operates supercritical fluid supply valve 54A (FIG. 8), gear motor 574 (FIG. 7) which operates extraction valve 50A (FIG. 7), and gear motor 573 (FIG. 6) which then operates valve 52A (FIG. 6). The control circuitry 2200 includes a programmer or other computer 2100, controlling a supply motor circuit 710, an extract motor circuit 712 and a vent motor circuit 714 to control the valves 54A (FIG. 8), 50A (FIG. 7) and 52A (FIG. 6), respectively, a reversing switch 716, a drive circuit 720 and a reverse motor torque circuit 718. The computer 2100 is electrically connected to the supply motor circuit 710, the extract motor circuit 712 and the vent motor circuit 714 through conductors 2118, 2119 and 2120 electrically connected to output terminals of the computer 2100. The drive circuit 720 supplies power to a reversing switch 716 that is also electrically connected to the supply motor circuit 710, the extract motor circuit 712 and the vent motor circuit 714 to apply power to the selected one of those motors with a polarity that controls the direction of movement of the motors to open a valve or close a valve. The reversing switch 716 is electrically connected to conductor 2122 from a port 2022 in the computer to activate the reverse direction for closing the valve. This port is electrically connected to the reverse motor torque circuit 718 which controls the amount of torque in opening the valve and is for that purpose electrically connected to the drive circuit 720. A feedback circuit on conductor 2057 is electrically connected to the supply motor circuit 710, extract motor circuit 712 and vent motor circuit 714 to provide a feedback signal to the controller which controls the stopping of the motor when the valves close fully. The stop motor signal comes from conductor 2121 from the port 2021 in the computer or programmer 2100. In the preferred embodiment, a programmable computer with timing circuits is utilized. It is the same computer used to operate the embodiment of FIG. 5. However, a manual switch can be used instead which switch is connected to a positive voltage supply to energize the corresponding motor when closed. The control circuit 2200 includes a supply motor circuit 710, an extract motor circuit 712, a vent motor circuit 714, a computer or programmer 2100, a reversing switch 716, a drive circuit 720 and a reverse motor torque circuit 718. The supply motor circuit 710, extract motor circuit 712 and vent motor circuit 714 open and close corresponding ones of the valves 54A, 50A and 52A. To control the valves, the computer or programmer 2100 has a plurality of output conductors that determine which valve is to be moved and the direction in which it is to be moved. This, in the preferred embodiment, is the computer which operates the extractor 10A (FIG. 5) but may be any timing device or indeed, instead of a programmer, manual switches may be used to close circuits to 15-volt DC voltages to open and close the valves as desired by an operator. In the preferred embodiment, conductors 2118, 2119 and 2120 are connected to outputs 2018, 2019 and 2020, respectively, of the computer or programmer 2100 and to corresponding ones of the supply motor circuit 710, extract motor circuit 712 and vent motor circuit 714 to select those valves for opening or closing. A low-level signal on lead 2127 attached to computer output port 2021 is electrically connected through inverter 2026 to the drive circuit 720 to cause it to supply power to the selected valve through the reversing switch 716 which is electrically connected to the port 2023 through conductor 2123 to the reversing switch 716 and drive circuit 712. The reversing switch 716 is electrically connected through conductors 2053 and 2051 to each of the supply motor circuits 710, extract motor circuit 712 and vent motor circuit 714 to supply the drive power thereto with the proper polarity for opening or closing the valves. The reverse motor port 2022 of the computer 2100 is electrically connected through conductor 2122 to the reverse motor torque circuit 718 and to the reversing switch 716 to select the polarity of electrical power to supply through conductors 2053 and 2051 to the selected one of the supply motor circuit 710, extract motor circuit 712 and vent motor circuit 714 to cause the motor to move the valve into the open position or closed position. A torque adjustment feedback circuit connected to each of the motor circuits 710, 712 and 714 generates a potential which is fed back through conductor 2057 to the drive circuit 720, and in conjunction with the current sense signal on lead 2123 and the stop motor conductor 2121 from the computer 2100, determines when the motor should stop at the close valve position. The reverse motor torque circuit increases the power supplied to the drive circuit 720 when the motors are moving in the direction that opens the valve to overcome overtightening due to differential expansion due to a temperature change since the valve was last closed, which may tend to keep the valve closed and to ensure opening of the valve on command. In FIG. 14, there is shown a schematic circuit diagram of the supply motor circuit 710, extract motor circuit 712 and vent motor circuit 714 having gear motor 570, gear motor 574 and gear motor 573, respectively. Gear motor 570 is electrically selected by relay 2000, gear motor 574 is electrically selected by relay 2001 and gear motor 573 is electrically selected by relay 2002. Gear motor 570 controls or regulates the position (in this case, open or closed) of valve 54A (FIG. 8), gear motor 574 similarly controls valve 50A (FIG. 7) and gear motor 573 similarly controls valve 52A (FIG. 6). The computer or programmable controller 2100 is the same computer controller or programmable controller that automates the other functions of the automatic extraction apparatus shown in FIG. 5. This conventional computer or programmable controller 2100 may be conventionally programmed to carry out any one of a variety of extraction protocols, including control of the valves. Computer 2100 has output ports 2018, 2019, 2020, 2021 and 2022 shown in FIG. 13. It also has input port 2023. Output port 2018 controls relay 2000 through inverter 2015. All of the inverters used in FIG. 13 are Type 2803 devices with open collector outputs. Output port 2019 controls relay 2001 through inverter 2016. Output port 2020 controls relay 2002 through inverter 2017. In FIG. 15, there is shown a schematic circuit diagram of the reversing switch 716, reverse motor torque circuit 718 and drive circuit 720 of the control circuitry 2200. As best shown in this circuit, the output port 2022 controls relay 2003, of the reversing switch 716, through inverter 2027. Relay 2003 has its contacts wired in a conventional double-pole double-throw reversing circuit. It is used to reverse the voltage applied to whichever of the three gear motors is selected by relays 2000, 2001 or 2002 (FIG. 14). To control torque, the control circuitry 2200 includes an operational amplifier 2036 and a power field effect transistor 2029 that provide current control (and therefore torque control) of the selected gear motor. Operational amplifier 2036 is a type 324 and power FET 2029 is a Type MTP12N06. Contacts 2024 of relay 2003 connect the drain 2050 of the power FET 2029 to one of the electrical terminals of the three gear motors 570 (FIG. 8), 574 (FIG. 7) and 573 (FIG. 6), and the motor selected by relay 2000, 2001 or 2002 (FIG. 14). Therefore, motor current flows through power FET 2029 and through current sensing resistor 2030 to circuit common. The voltage drop across current sensing resistor 2030 is applied to the inverting input 2045 of operational amplifier 2036. The output 2043 of the operational amplifier 2036 is led through resistor 2034 to the gate 2048 of the power FET 2029. Resistors 2030 and 2032, the operational amplifier 2036 and the power FET 2029 provide a negative feedback or servo loop which is used to set the maximum current (and therefore the maximum torque or torque limit) of the gear motors. Resistor 2033 is connected between the output 2043 of the operational amplifier 2036 and sets the gain or proportional band of the servo loop. The current setpoint is established by the voltage at the noninverting input 2044 of the operational amplifier 2036. A positive 2.5 volts reference voltage is applied to terminal 2042 and is led to the noninverting input through resistor 2040. The same relays 2000, 2001 and 2002 that select one of the three gear motors 570, 574 and 573 (FIG. 14) also simultaneously select an adjustable resistor corresponding to each gear motor. Adjustable resistor 2018 corresponds to gear motor 570, adjustable resistor 2019 corresponds to gear motor 574, and adjustable resistor 2020 corresponds to gear motor 573. Different nominally similar gear motors have somewhat different current-to-torque characteristics and the torque limit must be set separately for each gear motor. Variable resistances 2018, 2019 and 2020 corresponding respectively to gear motors 570, 574 and 573 are respectively selected by relay contacts 2006, 2009 or 2011. The contacts 2006, 2009 and 2011 connect the selected variable resistance to conductor 2057 which is connected to the resistor 2040 and the noninverting terminal 2044 of the amplifier 2036. The voltage at inverting input 2045 equals the voltage at noninverting input 2044 when current or torque limiting is taking place. The voltage across resistor 2030 is nearly the same as the voltage at the inverting input 2045, so changing the resistance of the variable resistances 2018, 2019 or 2020 during current limiting, varies the voltage across resistor 2030, and varies the limiting current through resistor 2030, which is the same as the current through the selected gear motor. The output port 2022 of the computer 2100 (FIG. 13) is also connected to the gate electrode 2046 of field effect transistor 2038. The source 2060 of the field effect transistor 2038 is connected to circuit common and its drain is connected to the inverting input 2045 of the operational amplifier 2036 through resistor 2037. When the computer operates a selected motor in the reverse (valve-opening) direction, the voltage level at output port 2022 (FIG. 13) goes high, turning on field effect transistor 2038 through its gate 2046. This effectively connects the resistor 2037 between circuit common and the inverting input 2045 of the operational amplifier 2036. Resistor 2037 is approximately twice the value of resistor 2032, so it requires 1.5 times as much voltage across (and current through) resistor 2030 and the selected gear motor to bring the voltage at inverting input 2045 up to the voltage at noninverting input 2044. The effect is to increase the torque limit by a factor of about 1.5 when the valve is opening as compared to when the valve is closing. This ensures that the valve does not stick if the opening torque is greater than the closing torque. It is surprising that such a jam can occur as it is known from experience that it takes less torque to reopen a valve than to close it. However, it is believed the reason for high opening torque is differential thermal contraction occurring when the valve is closed at a high temperature and then later opened at a significantly lower temperature. It is desirable to shut off and turn on power to the gear motors 570, 574 and 573 (FIG. 14) by means other than the selector relays 2000, 2001 and 2002, and also to shut off power during a change of state of reversing relay 2003. It is desirable because these relays have longer life if their contacts switch (change state) at a time when no current is going through their contacts and because solid state power switching generates less electrical noise. To this end the output port 2021 of computer 2100 (FIG. 13) provides a logic high level to shut off power FET 2029 through inverter 2026. A high level signal at output port 2021 (FIG. 13) is inverted by inverter 2026 and the resulting low level voltage is applied to the gate 2048 of power FET 2029, turning off the power FET 2029 and interrupting power to contacts 2024 and 2025 of relay 2003, contacts 2005 of relay 2000, contacts 2008 of relay 2001 and contacts 2010 of relay 2002. The computer 2100 (FIG. 9) is programmed so that the voltage level at output port 2021 (FIG. 13) goes high (power off) before the change of state of every relay and then goes low (power on) after a relay change of state. When a valve is closing, the torque impressed on its gear motor starts to rise and the current through the gear motor starts to rise when the ball 1014 (FIG. 9) is forced into the conformal seat 1013. When the torque and current rise to the limit point described earlier, the voltage at the output 2043 of operational amplifier 2036 decreases. This decreased voltage is applied to gate 2048 of power FET 2029, and therefore the power FET 2029 starts to turn off. When this happens, the voltage at its drain 2050 and on the conductor 2055 starts to rise, causing current to flow through resistor 2035. Resistor 2041 forms a voltage divider with resistor 2035. The voltage division ratio is selected to indicate a torque limiting condition when the voltage on conductor 2055 produces a voltage at input port 2023 of computer 2100 (FIG. 13) which is equal to the logic level at that input port. This signals the computer 2100 that the valve has been closed. In FIG. 9, there is shown a valve 54B which has a life of greater than 100,000 cycles at a temperature of greater than 150 degrees Celsius and turns off and on flow of a non-corrosive fluid at a differential pressure of 6.89·10 7 Pa (10,000 psi) at a temperature of greater than 150 degrees Celcius and when operational life in excess of 35,000 cycles is required, a valve constructed in a manner of the valve 54B may be subject to several disadvantages if the stem 1027 is made of a 17-4 PH (ASTM no. A564 or Carpenter type 630) stainless steel, such as: (1) the stem 1027 may break at the small diameter neck 1029; (2) the stem 1027 may swage out at the stem face 1023 when it contacts the valve element ball 1014; (3) the valve element ball 1014 may erode in a patchy manner after long term operation of many cycles which makes it impossible to close the valve completely leak tight; and (4) the seal packing 1018 may extrude. To reduce the effects of or prevent these problems from occurring, the internal stem 1027 of the valve 54B and valve element ball 1014 are made of special materials. The material for internal stem 1027 is hard drawn 17-7 PH stainless steel, precipitation hardened according to CH900 (cold worked, hardened and heat treated to 900 degrees Fahrenheit). This produces a yield strength of about 1.83·10 9 Pa (265,000 psi). The material for the valve element ball 1014 in this embodiment is silicon nitride which has a hardness of 3.93·10 9 Pa (570,000 psi). With these new materials, the inner stem 1027 retains its ability to resist rotation while having a greater yield strength and the silicon nitride unexpectedly provides the valve element ball 1014 with an extremely long life even though it is not as hard as the tungsten carbide ball which has a hardness of 5.17·10 9 Pa (750,000 psi). It was originally believed that silicon nitride was too brittle for good reliability, but in use, it is tough enough not to crack and its uniform chemical composition, unlike the cemented tungsten carbide, discourages erosion of its inert surface. Moreover, the face 1023 of inner stem 1027 has a yield point and hardness at least 1.3 times larger than the yield point and hardness of the seat 1013, and no more than 0.8 times as large as the yield point and hardness of the ball 1014. The ball 1014 has a hardness at least twice as great as the seat 1013. To further provide a longer life of the valve 54B at a higher temperature, the material for the anti-friction device ball 1035, in this embodiment, is either cemented tungsten carbide or silicon nitride. In the valve 54A, the anti-friction device ball 1035 was made of any reasonable choice of hard material. To reduce the load on the threads of outer stem 1030B and threaded bushing 1045 so they do not fail during the life of the valve, the external threads on outer stem 1030B and the internal threads on threaded bushing 1045B are lengthened by extending the internal threads of threaded bushing 1045B completely out to the outer end of the bushing 1045B, and the external threads of outer stem 1030B are extended outwardly to a location beyond the outer end of threaded bushing 1045B. To prevent extrusion of the seal packing 1018 into the annular space between bushing 1022B and stem 1027 at high temperatures and high pressures: (1) a step is formed in the internal diameter of bushing 1022B so that the lower or inner part of its internal diameter holds inner stem 1027 comparatively closely with a diametral clearance of about .003 cm (0.001 inch); and (2) the upper part of the internal diameter of bushing 1022B is bored out to a larger diameter to provide a looser diametral clearance of about .06 cm (0.022 inch) to the outside diameter of internal stem 1027. The length along which the step in the diameter of bushing 1022B closely holds internal stem 1027 is .15 cm (0.06 inch). The lower or inner face of bushing 1022B and the region of snug diametral clearance is tightly adjacent to washer shaped packing 1018 when assembly is completed by screwing threaded bushing 1045 into the valve body. The annular space 1080 between the internal diameter of bushing 1022B and the stem 1027 is .06 cm (0.022 inch) and the annular space between the top portion of the bushing 1022B and the stem 1027 is .48 cm (0.19 inch). This allows the stem 1027 to be displaced a sufficient distance to permit self-alignment. With the changes in the bushing 1022B: (1) the close diametral clearance of .003 cm (0.001 inch) between the internal diameter step of bushing 1022B and the outside diameter of internal stem 1027 prevents material from the seal packing 1018 from extruding into the annular space between bushing 1022B and stem 1027; (2) the large .06 cm (0.022 inch) diametral clearance between the inside diameter of bushing 1022B and the outside diameter of stem 1027, above or outside the region of close clearance at the location of the step, prevents binding of the stem 1027 within the bushing 1022B; and (3) angular misalignment of stem 1027 with respect to the bushing 1022B can be tolerated without undue friction and binding because of the larger amount of clearance of the annular space 1080 and the smaller amount of clearance of the rest of the bushing 1022B. Operation for a simple extraction procedure under programmable control is as follows with either valves 54A (FIG. 8) or 54B (FIG. 16), 50A (FIG. 7) and 52A (FIG. 6) closed. Under computer control, gear motor 454 (FIG. 6) rotates high speed screw 476, elevating cartridge 30A into the extraction chamber within pressure vessel 24A (FIG. 6). The cartridge 30A positioned within the extraction chamber is shown in FIG. 8. Gear motor 600 drives locking mechanism 606 under computer control, effectively locking the extraction cartridge 30A within the extraction chamber (FIG. 8). The logic level at output port 2021 of computer 2100 (FIG. 13) has been high, shutting off power to all relay contacts. Then the logic level at port 2018 of computer 2100 (FIG. 13) goes high, turning on the coil of relay 2000 by action of the inverter 2015 (FIG. 14). Simultaneously, output port 2022 (FIG. 13) goes high activating relay 2003 (FIG. 15) through inverter 2027. This places the contacts 2024 and 2025 of relay 2003 (FIG. 15) in the opposite position from that shown in FIG. 13. This is the reverse or valve-opening position. Simultaneously, the gate 2046 of FET 2038 goes high, turning on FET 2038. After a fraction of a second, the logic level at port 2021 (FIG. 13) goes low, enabling the relay contact circuits by allowing power FET 2029 to turn on. A positive 15 volts at terminal 2070 is applied through contacts 2025 to place positive voltage on the bottom terminals (FIG. 13) of the gear motors 570, 574 and 573 (FIG. 14) which enables them to operate in reverse or in the direction which opens their associated valves. Positive voltage applied to the top terminals of these three motors enables closing of their respective valves. Relay 2000 then selects the upper terminal of gear motor 570 through conductor 2052, contacts 2005 and conductors 2054 and 2053 (FIG. 14). Lead 2053 is connected to conductor 2055 through contacts 2024 since relay 2003 is activated. Lead 2055 is connected to the drain of power FET 2029 in the current limiting circuit. Since the motor requires less than the limiting current to open, it runs in the reverse (valve-opening) direction at a continuous speed of about 16 rpm, opening valve 54A (FIG. 8) or valve 54B (FIG. 9. After three seconds of such running and the corresponding opening of valve 54A or 54B, the computer 2100 causes output port 2021 (FIG. 13) to go high putting a low on the gate of power field effect resistor 2029 through inverter 2026 (FIG. 15). This stops current through the relay contacts and motor 570 (FIG. 14), and valve 54A (FIG. 9) or 54B (FIG. 9) remains open with the motor stopped. After a fraction of a second, port 2018 (FIG. 13) goes low turning off the relay 2000 which had selected motor 570 (FIG. 14). The computer 2100 (FIG. 13) is programmed so a signal at its output port 2021 (FIG. 13) always shuts off the power FET current source transistor 2029 (FIG. 15) a fraction of a second before any of the relays 2000, 2001, 2002 (FIG. 14) or 2003 FIG. 15) change state. The computer 2100 is also programmed so that a signal at port 2021 re-enables the power FET 2029 a fraction of a second after a single or a group of simultaneous relay state changes, if power is needed at that time. Thus, none of these relays are required to switch any active current or power and their life is thereby prolonged. The operation of this protective feature is performed each time before and after each change of state of any of the relays. In accordance with the above, gear motor 570 (FIG. 14) has opened valve 54A or 54B. This valve supplies supercritical fluid through fluid leads, lines or tubings 58A (FIG. 8) and 60A (FIGS. 1 and 7) to the interior of the extraction chamber 24 (FIGS. 1, 4, 5 and 14) and extraction cartridge 30A (FIG. 8). Then, computer output port 2019 (FIG. 13) goes high selecting relay 2001 through inverter 2016 (FIG. 14). Relay 2003 (FIG. 15) is still activated. Contacts 2008 of relay 2001 (FIG. 14) connect the upper conductor of motor 574 (FIG. 14) to conductor 2055 through contacts 2024 of relay 2003 (FIG. 15). This causes gear motor 574 to open valve 50A (FIG. 7). Valve 50A connects the outlet of the extraction cartridge 30A (FIG. 8) to restrictor tube 66A (FIG. 7) which leads to extractant collection vessel 98A. Three seconds after valve 50A starts to open, the computer 2100 causes the level at port 2019 (FIG. 13) to go low and motor 574 stops opening valve 50A, leaving valve 50A open. Restrictor 66A (FIGS. 6 and 7) depressurizes supercritical fluid from the high pressure in extraction cartridge 30A (FIG. 8) to the lower pressure in collection vessel 98A (FIG. 6). The pressure in collection vessel 98A is usually comparatively close to atmospheric pressure and the supercritical fluid carrying dissolved sample usually has changed to a gas carrying entrained sample as it exits the restrictor 66A. Supercritical extraction of the contents of extraction cartridge 30A takes place as previously described. A programmable timer within computer 2100 (FIG. 13) is set to the desired duration of the supercritical extraction. If the timer is set for ten minutes, then ten minutes after valve 50A (FIG. 7) opens, the extraction is complete. Output port 2022 of computer 2100 (FIG. 13) goes low, de-energizing relay 2003 through inverter 2027 (FIG. 15). De-energized contacts 2024 and 2025 of relay 2003 (FIG. 15) reverse the voltage to the gear motors 570, 574 and 573 (FIG. 14), enabling the gear motors to turn in the forward (valve-closing) direction. Field effect transistor 2038 turns off because of the low voltage on its gate 2046 (FIG. 15). Simultaneously, the computer causes its output port 2018 (FIG. 13) to go high, energizing relay 2000 through inverter 2015 (FIG. 14). Relay 2000 connects the upper terminal of gear motor 570 through conductor 2052, the relay contacts 2005, conductor 2054, conductor 2053 (FIG. 14), contacts 2025 of relay 2003 (FIG. 15) and to a positive 15 volt source at terminal 2070 (FIG. 14). The lower terminal of gear motor 570 is connected through conductor 2051 (FIG. 14) to contacts 2024, conductor 2055 and drain 2050 of field effect transistor 2029 (FIG. 15) and from the source of the field effect transistor 2029 to resistor 2030. Contacts 2006 of relay 2000 connect variable resistance 2018 to conductor 2057 (FIG. 14) and then to noninverting input 2044 of operational amplifier 2036 (FIG. 15). Gear motor 507 now runs in the forward (valve-closing) direction with a current or torque limit set by variable resistance 2018 (FIG. 14). As the valve closes tightly, pressing ball 1014 into conformal seat 1013 (FIG. 9 ), the motor torque and motor current increases, increasing the voltage across current sensing resistor 2030 (FIG. 15). As the torque and current increase a preset amount, the voltage on conductor 2055 (FIG. 15) becomes sufficiently high to reach the logic level of computer input port 2023 (FIG. 13) through the voltage divider composed of resistors 2035 and 2041 (FIG. 15). This causes the computer 2100 (FIG. 13) to bring the voltage at its output port 2018 low, de-energizing relay 2000 (FIG. 14). Then the computer brings the voltage at output port 2019 high. This energizes relay 2001 through inverter 2016, selecting gear motor 574 (which is coupled to valve 50A) and variable resistance 2014. Motor 574 rotates in the forward (valve-closing) direction closing the valve 50A (FIG. 7). When the valve 50A (FIG. 7) is closed, the motor current increases until the voltage across current sensing resistor 2030 is approximately equal to the voltage at inverting input terminal 2045 of operational amplifier 2036 (FIG. 15), which is set by variable resistance 2019 associated with motor 574 (FIG. 14). This causes current and torque limiting which also causes the voltage of conductor 2055 (FIG. 15) to rise, in turn causing the voltage at current sensing input port 2023 (FIG. 13) to rise through the voltage divider comprised of resistors 2035 and 2041 (FIG. 15). When the voltage at input port 2023 was the logic level of the computer 2100 (FIG. 13), the computer 2100 shuts off motor 574 (FIG. 14) at its predetermined torque limit. The voltage at output port 2019 goes low, de-energizing relay 2003 (FIG. 15) through inverter 2016 (FIG. 14). Output port 2022 (FIG. 13) goes high, energizing relay 2003 through inverter 2027 (FIG. 15). Energized contacts 2024 and 2025 (FIG. 15) enable gear motor 573 to open its high energizing relay 2002 through inverter 2017 (FIG. 14). Contacts 2010 and 2011 of relay 2002 select gear motor 573 connected to valve 52A (FIG. 6) and select variable resistance 2020 (FIG. 14) which sets the torque and current limit for gear motor 573. Gear motor 573 runs in the reverse (valve-opening) direction for three seconds opening valve 52A, which vents or discharges the pressure in the interior pressure vessel 24A and in extraction cartridge 30A (FIGS. 16 and 18). After a suitable delay time to allow the pressure to reach a near-atmospheric value, gear motor 600 (FIG. 8) operates in reverse, unlocking the locking mechanism 606 (FIG. 8) under computer control. The gear motor 454 (FIG. 6) then rotates in reverse, causing high speed screw 476 to lower cartridge 30A from the extraction chamber within extraction vessel 24A. Controlling the closing of the valves so that the valve stem motion stops when a torque limit is reached at the gear motor, is more desirable than closing the valve until a position limit is reached. This torque feedback limit control provides just enough force to close the valve. On the other hand, position control tends to either underclose the valve so that it leaks or overclose the valve so that excess unnecessary force causes unneeded wear of the seat. The algorithm used to control the gear motor and open and close the corresponding valve is particularly useful as it is self-adjusting regardless of how far the inner stem 1027 forces the ball 1014 into seat 1013 (FIG. 9). Since the valve-opening torque is greater than the closing torque, the valve cannot stick closed and cause an erroneous "valve-open" condition within the computer or programmer. With repeated operation, the ball 1014 may be forced further and further into conical seat 1013 as the ball 1014 deforms a larger and larger area of the conical seat 1013 into a shape that conforms with the ball 1014. In closing the valve 54A or 54B, the gear motor always also forces the ball 1014 tightly into the seat 1013, shutting off the flow since the gear motor continues to run until attaining the torque limit which indiates leak tight seating of the ball 1014. During opening of the valve 54A or 54B, the motor runs for a predetermined time which is equivalent to a predetermined angular rotation. This is because the motor runs in reverse at constant speed after the first fraction of one-thousandth of an inch of stroke of the inner stem 1027 (FIG. 9) while the stem 1027 is still applying force to the ball 1014 (FIG. 9). During all this time the motor runs with excess torque and is not unduly slowed down because the high logic level at computer output port 2022 (FIG. 13) is applied to the gate 2046 turning on field effect transistor 2038 (FIG. 15). As described previously, this sets a torque limit considerably higher than that necessary to loosen the ball 1014 from its seat 1013. In operation, a program is entered into the control panel 410 (FIG. 6). This program is then stored in controller 450 (FIG. 6) and controls sample changing, fraction collection, static and/or dynamic extractions, fluid pressure, the steps or ramps of pressure, the supercritical fluid temperature, the elevation of the sample cartridge from the sampler reel up to the extraction chamber and return back to the sampler reel after extraction, locking and unlocking of the extraction chamber and operation of the three motor-operated valves in the manner described above to automatically duplicate the hand-operated functions of the embodiment of FIGS. 1-4. In the alternative, the operations may be initiated from the keyboard by manually closing circuits to the motors as required to perform the desired sequence. At the start of an extraction cycle, the extraction fluid valve 54A or 54B (FIGS. 8 and 9), purge valve 50A (FIG. 7), and the extractant valve 52A (FIG. 6) are closed. The sample reel 430 (FIG. 5) brings a selected extraction cartridge 30A into position under the extraction chamber 618 (FIG. 6). The extraction sample cartridge 30A within a sleeve 436 (FIG. 5) on reel 430 is positioned above the single hole 464 in the disk 462 (FIG. 6) and is supported on a spring-loaded support block 482 within the top of the piston 32A (FIG. 6). To move the sample cartridge 30A (FIGS. 6 and 8) into the extraction chamber 618 (FIG. 6), the gear motor 454 (FIG. 6) causes the screw 476, piston 32A and cartridge 30A (FIGS. 6 and 8) to rise to the position shown in FIG. 8, inserting cartridge 30A and piston 32A into the pressure vessel 24A. To lock the sample cartridge 30A in position, the gear motor 600 drives the pin 606 through the hole 609 in the pressure vessel 24A through the hole 610 in the piston 32A and through the hole 612 in the pressure vessel 24A (FIG. 8). This locks the piston into position within the pressure vessel 24A. To remove extractant, the spring 201A under the block 482 (FIGS. 6 and 8) forces the block 482 to push the sample cartridge 30A up against the bottom of the fitting 46A (FIG. 6). The gear motor 552 lowers the arm 560 carrying the restrictor tube 66A and the rack 406 (FIG. 5) into the position shown in FIG. 7, puncturing the cap 550 on the collection tube 98A. Alternatively, the collection tube 98A may be automatically raised to the restrictor tube 98A. The gear motor 570 (FIGS. 11, 12 and 14) rotates, opening the extraction fluid valve 54A (FIG. 8), admitting extraction fluid through the heat exchanger 40A, tube 60A and the fitting 42A (FIG. 6). The extraction fluid flowing through the fitting 42A enters the bottom of the extraction cartridge 30A (FIG. 6) and permeates the sample within it. If it is suspected that the outside cartridge 30A may be contaminated, the purge valve 52A is opened at this time under the control of the gear motor 573 (FIG. 6). This purges or flushes the space between the outer wall of the sample cartridge 30A and the inner wall of the pressure vessel 24A. Flushing fluid leaves the extraction chamber 618 outside of the cartridge 30A through the purge fitting 44A, tube 62A, Tee-joint tube 542, tube 620 (FIG. 6), Tee-joint tube 544, tube 548 and vent port 546 (FIG. 6). After purging, the gear motor 573 closes the purge valve 52A (FIG. 6), terminating the purge operation. At this time, the controller 450 (FIG. 5) activates the gear motor 574 (FIG. 7) which opens the extractant valve 50A. Extractant fluid flows through the cartridge 30A, extracts material from the sample within the cartridge 30A, flows through the fitting 46A (FIG. 6), tubing 62A (FIG. 6), extractant valve 50A (FIG. 7), and to the restrictor tube 66A (FIG. 6). The restrictor tube 66A has a capillary bore of a small enough diameter to maintain the desired extraction pressure at the desired extraction fluid flow rate. In case the extraction cartridge 30A (FIGS. 6 and 8) is not completely full of sample, it is beneficial to flow the extractant fluid downward through the cartridge 30A instead of upwards as in the foregoing example. Downward flow of extractant is accomplished by permitting the extractant to flow into the cartridge 30A through fitting 46A (FIG. 6) and from the cartridge 30A through fitting plug 32A (FIGS. 6 and 8) and the fitting 42A (FIG. 6). After extraction is complete and the extractant is collected in the trapping fluid 104A within the vial 98A (FIG. 7), the gear motor 570 (FIG. 8) shuts the extraction fluid valve 54A or 54B (FIG. 8 or FIG. 9). The gear motor 573 opens the purge valve 52A rapidly discharging the pressure and the extraction chamber 618 (FIG. 6). The gear motor 574 closes the extractant valve 50A and the gear motor 552 raises the arm 560 and restrictor tubing 66A and exhaust tubing 110A (FIG. 7). The gear motor 600 withdraws pin 606 from the holes 609, 610 and 612 in the pressure vessel 24A and the piston 32A (FIG. 8). After the piston 32A has been unlocked, the gear motor 573 (FIG. 6) lowers the piston and sample cartridge 30A so that the sample cartridge 30A is lowered from being within the extraction volume 618 (FIG. 6) to being within the sleeve 436 of the sample reel 430 (FIG. 5). The gear motor 570 closes the purge valve 54A or 54B (FIG. 8 or FIG. 9). After the valves have been closed and the sample cartridge 30A (FIGS. 6 and 8) returned to the sample reel, the sample reel 430 and the fraction collector reel 440 (FIGS. 5) advance to bring another sample cartridge in another fraction collector vial into position. Alternatively, multiple extractions on the same cartridge may be made by leaving the sample cartridge 30A in place and advancing only the collection reel. The cycle of opening the valves and extracting is then repeated until the number of extractions from the single sample cartridge 30A have been made and the extractant deposited in a number of successive collection vials. As can be understood from the above description, the supercritical extraction technique has several advantages: (1) it is more convenient than prior art extractors; (2) it includes a self-cleaning feature; (3) it has, as one component, a disposable inexpensive cartridge; and (4) in one embodiment, a series of samples can be extracted with minimum human intervention and the extractant collected in a fraction collector. The valve arrangement for applying supercritical fluid automatically has the advantages of: (1) providing positive closing independent of valve wear because of the torque limiting mode of closure; (2) reducing leakage from scratches in valve elements by selective choice of the relative hardness of the valve element, valve seat and actuator for the valve element; and (3) providing positive opening of the valve by increasing the force at the time it has been discovered to be necessary.

Claims: Apparatus (10) for supercritical fluid extraction including a plurality of extraction cartridges (30) having an interior (254) for containing material (134) to be extracted, a plurality of fluid lines (58, 62, 66) that may be brought into fluid contact with a cartridge interior, a first line (58) of said plurality of fluid lines capable of supplying supercritical fluid at high pressure to said cartridge interior and a second line (66) of said fluid lines capable of depressurizing fluid carrying extractant from said interior to a pressure lower than said high pressure and at least one of the plurality of fluid lines incorporating a programmable valve (54) having a valve body (1001), said valve (54) being disposed to regulate fluid flow in said one of the fluid lines, said valve further comprising a linear actuator (1030); characterized by a plurality of samples in sample containers (30A) located on a first transport means (432, 434, 436); a programmable timer (2100, 410) that causes the first transport means (432, 434, 436) to move a selected sample container (30A) and sample to the location of a second transport means (472, 474, 475, 476); said programmable timer (2100, 410) also causing said second transport means (472, 474, 475, 476) to move a selected container and sample from the first transport means to a place of extraction (22A) and activating a motor (574) to rotate a shaft (1030) engaging fixed threads (1037) in the valve body to cause linear motion driving a reciprocally mounted nonrotating stem (1027) linearly without rotation through an antirotation ball (1035) and curved shaft surface (1038) wherein the stem (1027) moves a valve element (1014) without rotation against a valve seat to seal the container and resist the extraction pressure at the extraction temperature; the nonrotating stem (1027) having a first curved face (1038) contacting antirotating ball (1035) to form a low friction contact point and a second flat face (1023) contacting valve element (1014) thereby forming a conformal seal and stopping flow between said inlet and said outlet ports. The apparatus of claim 1 characterized by a programmable timer (2100) that signals said second transport means (472, 474, 475, 476) to provide for movement of the said selected container out of the said place of extraction and back to the said first transport means (432, 434, 436) after said extracting of analyte. The apparatus of claims 1 or 2 characterized in that the direction of motion of the said second transport means (472, 474, 475, 476) is vertical. The apparatus of claims 1, 2 or 3 characterized in that the direction of motion of the said first transport means (432, 434, 436) is horizontal. The apparatus of claims 1 or 2 characterized by another sample container and sample is selected from the said first transport means (432, 434, 436) after a previous sample has been extracted.

Inventors: ALLINGTON ROBERT WILLIAM, CLAY DALE LEE, JAMESON DANIEL GENE, WINTER ROBIN RANDALL, ALLINGTON, ROBERT WILLIAM, CLAY, DALE LEE, JAMESON, DANIEL GENE, WINTER, ROBIN RANDALL
Applicants: ISCO INC, ISCO, INC.
Application year: 1992
Main classification: B01D11
IPC codes: B01D11, G01N30