Heated rotary valve for chromotography

A heated rotary valve for use in connection with a sample to be separated in a column for heating the sample to temperature within the valve. The heated rotary valve permits introduction of compounds, having a wide boiling range, into a gas chromatograph with improved precision of area and retention time. The valve includes a stator, an elongate body, a rotor seal, a drive shaft, and an internal element for generating heat. The rotor seal may be laterally captured by a ring to prevent movement or creep due to heat absorption during operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

BACKGROUND

The present disclosure pertains to valves and systems for use in chromatography. More particularly, the present disclosure pertains to a heated rotary valve for use in connection with a sample to be separated in a column for heating the sample to temperature within the ports of the valve. The heated rotary valve permits introduction of a wide boiling range compounds into a gas chromatograph with improved precision of area and retention time.

2. Description of the Related Art

Gas chromatography (GC) is generally performed on a sample using a column positioned within and heated by an oven or other heating device, wherein the sample is heated before introduction to the column. The separated sample is then introduced to a detector for identification of compounds. Chromotagraphy ovens may be operated at elevated temperatures in the range of 40′ C to 400′ C. Because the column is typically a coil of thin tube, such as of metal or fused silica, with an internal polymer coating, the column rapidly reaches the ambient temperature within the oven or applied by an external heating element, which permits movement of the sample through the column. Problematically, the sample needs to be heated to the elevated temperature of the column. This is sometimes accomplished using a heated injection port where the sample size is sufficiently small, such that the injection can be accomplished using a syringe which peirces a septum—a thick, rubber disk. Heated injection ports are sufficiently hot that the sample boils and is carried into the column as a gas by helium or another carrier.

Historically, liquid injection for gas chromatography has included liquid injection by a syringe, whether split on column, but which, while simple, suffered from issues of septum lifetime and an automation system more complex that associated with a valve. The historic alternative was injection by valve, whether a one zone system such as standard liquid sample valves) or two zone injection systems, in which a sampe is moved from a cool zone, such as a sample supply, to a hot zone, such as the column. While more easily controlled and repeatable, these valve systems suffered the difficulty of ensuring the sample was at the temperature of the hot zone when reached.

Additionally, because of the large internal volumes of the valves known in the art, not only was heating unfeasible, but recycling of samples through columns repeatedly for high separation was largely only theoretical as those valves, typically using releatively large fitting adapters ( 1/16 inch or 1/32 inch, for example) introduced peak broadening in each switch, as those fittings were incompatible with small bore columns. Alternatives have included use of Dean's switching and other pressure differential methods using external solenoid valves to control the carrier gas direction. None have been highly effective for column switching.

It would be desirable to incorporate a sample which may be introduced according to a mechanically controlled system and which would be at temperature for processing through the chromatography system, but otherwise would not transfer heat or suffer from heat soak.

Additionally, in chromatography systems, it is typical that the sample may be flowed through a valve during times when no analysis is desired or ongoing. Providing a valve at an elevated temperature during those off-analyzing periods in contact with a flowing sample could be detrimental to the sample, as it could result is repeated vaporization of the sample prior to analysis.

It would therefore be desirable to provide a valve for communication with a sample source, where the valve would permit sample to flow to the column while simultaneously heating the sample to temperature for during the analysis period, but which would otherwise not introduce heat into the surrounding system or to the sample.

It would therefore be desirable to provide a valve having an internal volume of only a few nanoliters which could be used for column switching at an elevated temperature without undesirable cooling or unnecessary additional heating equipment.

SUMMARY

The present disclosure therefore meets the above needs and overcomes one or more deficiencies in the prior art by providing a heated rotary valve for use in connection with one or more heated columns so that a sample, heated to, or maintained at, temperature in the valve may then be separated in a column heated to the same temperature.

The present disclosure provides a heated rotary valve which includes a stator, an elongate body, a rotor seal, a drive shaft and an element for generating heat. The stator has a stator first surface and a stator second surface, where the stator first surface has a plurality of stator connectors while the stator second surface includes a flat plate. The stator has a plurality of stator ports, each extending from a connector to the flat plate of the stator second surface.

The elongate body has an internal bore from a body first end to a body second end in which a drive shaft is positioned so as to free rotate. The stator is affixed at its second surface to the body at the body first end, so as to form an integral unit in which the rotor seal may be rotated. The rotor seal is a polymeric disk that makes a high pressure seal against the stator and therefore has a rotor seal first surface which is positioned adjacent the stator second surface. The rotor seal has at least one channel in its first surface to connect two stator ports when desired. The drive shaft, which extends beyond the second end of the body, is affixed to the rotor seal so that an actuator may switch the valve to connect particular parts when desired. The element for generating heat is affixed to the body in or at the body first end proximate the rotor seal's first surface and the stator's second surface, or in the stator head so that heat is transmitted to stator ports by the body, and/or the stator, which are composed of a material to transmit heat from said element for generating heat to said stator ports.

In an alternative embodiment, the valve is part of a rotary valve system which further incorporates a controller which is adapted to receive a start instruction and to activate the element for generating heat upon receipt of that start instruction.

In a further embodiment, the rotary valve system may be incorporated into a chromatography system wherein the controller is further adapted to receive an oven temperature from a temperature sensor in the oven so that the valve may be heated by the element for generating heat to the oven temperature, together with a chromatography column, a sample supply, an oven, and a temperature sensor. In the chromotography system, the valve is in communication with the chromatography column at a column inlet and with a sample supply at a supply outlet. The column, the sample supply and the temperature sensor are positioned within the oven, while the valve is positioned through the oven wall, so that the rear of the oven-side body section contact the oven wall while the oven-external body section is positioned external the oven.

Additional aspects, advantages, and embodiments of the disclosure will become apparent to those skilled in the art from the following description of the various embodiments and related drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIGS. 1-7, a heated rotary valve100is provided for use in connection with a sample to be separated in a column704, heated by an oven712or other heating systems, for heating the sample within the ports of the valve to the temperature of the column during periods of analysis, but not otherwise heating the sample. The valve100may be placed so that the first surface104and stator connectors108of the stator102are exposed in a chromatography oven712in communication with a sample source708, so that a sample to be introduced to the column704is heated within the valve100body first end100to the temperature of the associated chromatography column704, but which otherwise does not introduce excess heat into the surroundings of the valve100. Referring toFIG. 8, the heated rotary valve100may be positioned adjacent a column804which is heated by direct or indirect heat transfer, such as by a heating element bound to the column804. The valve100includes a stator102, an elongate body112, a rotor seal230, a drive shaft134, all of which may be composed of stainless steel, and a element for generating heat236, internal or external to the body112of the valve100.

Referring toFIG. 7, the stator102is made integral to the elongate body112and provides the point of connection for the valve100to the sample supply708and the column704. Referring toFIGS. 1-6, the stator102has a stator first surface104and a stator second surface106. The stator first surface104has a plurality of stator connectors108which provide the point of communication with the sample supply708and the column704. The stator second surface106includes a flat plate502which provides a portion of the flow path for the sample in operation of the valve100. The stator102has a plurality of stator ports210, each extending from a connector108to the flat plate502of the stator second surface106. Preferably each stator port210is constructed for use with 360 micrometer fittings, which reduces the volume of sample in the stator102, and therefore further increases the heat transfer rate from the stator102.

Referring toFIGS. 1-7, the elongate body112has sections intended to permit heat transfer to the stator, but not to the second end118wherein the drive shaft134is connected to an actuator718, which permits control of the valve100and control over the flowpaths used. Referring toFIGS. 2 and 6, the body112has an internal bore214which extends from the body first end116to the body second end118. The drive shaft134is positioned within the internal bore214of the elongate body112so as to freely rotate when activated by the actuator718. Heating is desirable only in the body first end116.

Referring toFIGS. 1-6, the stator102is therefore affixed at the stator second surface106to the body112at the body first end116. As it is desirable that the stator102heat rapidly, while it is desirable the body112not retain any conducted heat, the body112is sized to be smaller in diameter than the stator102such that heat will not readily be conducted toward the body second end118and any conducted heat will be readily shed. The elongate body112may therefore have a body diameter140which is less than seventy-five percent (75%) of the stator diameter504of the stator102.

Referring toFIGS. 2 and 6, the rotor seal230completes the flow path through the valve100depending on its position. The rotor seal230has a rotor seal first surface232, which when the valve100is assembled, is adjacent the stator second surface106. The rotor seal230has at least one channel606on or in the rotor seal first surface232which provides, when positioned, the connection of two of the stator ports210. Referring toFIG. 7, the rotor seal230may be positioned to permit flow of a sample from the sample supply708through the valve100and to the column704, or may be positioned to preclude such flow, may be positioned to cause the sample to enter a loop, or may be positioned for other desired flowpaths. Referring toFIG. 6, the rotor seal230is maintained in contact with the stator second surface106by driving the drive shaft134forward, such as by use of a spring608and end cap610in conjunction with the body112.

As the heat into the valve100from the element for generating heat236may also be conducted to the rotor seal230, a rotor ring634may be provided about the rotor seal230to contain the rotor seal230and prevent movement, such as creep, during heating. This is particularly true for seals provided of polymeric material, which may become more pliable, and more likely to move, when heated.

Referring toFIGS. 2 and 6, the drive shaft134is affixed to, or may be formed integral with the rotor seal230. Referring toFIGS. 1-7, the drive shaft134extends from the rotor seal230to beyond the body second end118so that an actuator718may be affixed thereto which may control the position of the rotor seal230and therefore the flowpath through the valve100.

Referring toFIGS. 2 and 6, the valve100includes an element for generating heat236which may be affixed, internally or externally, to the body112at the body first end116proximate the rotor seal first surface232and the stator second surface206or may be affixed, internally or externally, to the stator102. Referring toFIG. 6, the element for generating heat236may be positioned in an external groove602about a body first end side surface604. The element for generating heat236may be any of several heating elements known in the art, whether chemically or electrical, but whose temperature is controllable externally. Thus, in one embodiment, the element for generating heat236is an electrically-driven heating element with leads250,252for connection to provide electrical energy to the element for generating heat236, which becomes hotter due to application of electricity and which may be temperature controlled, such as by measurement of power, current, voltage and/or resistance, or which may include a thermocouple, thermistor, resistance temperature detector (RTD), or other temperature detecting device. The element for generating heat236may be connected to a power supply for provision of electrical energy, which may be incorporated into a controller or which may be external to the controller.

The small sizes of the components associated with chromatography ensure low mass and therefore high heat transfer rates. Maintaining the size only as necessary to permit operation minimizes mass. In particular, the stator connectors108and associated stator ports210and the rotor seal channels606are sized for 360 micrometer fittings. The resulting low mass may be heated directly, even by an air bath oven. As a result, the internal volume of the valve100is also ultra low, which speeds the heat transfer to the sample while the sample passes through the stator102. As a result, the valve100may have a high maximum operating temperature, such as around 400 degrees Celcius and, because the small rotary distances, may provide fast switching between positions, such as around 125, or 250, milliseconds. Moreover, the low mass of the valve100provides for heating at 200 degress Celcius per minute and also provides for rapid cooling. As result, there is minimum sample vaporization during injection and low carry over. Additionally, this may provide for a sample size of a few nanoliters, up to 40 nanoliters, and beyond.

The relative small size and mass, and associated rapid heating and switching, of the valve100provide an improved choice for liquid injection in gas chromatography. The ease of operation of the valve100eliminates the issue associated with syringe injection while providing an improve valve injection.

When activated, such as a by a start signal in connection with sample introduction to a column704,804, the element for generating heat236provides heat to the valve100, whether the stator102, the drive shaft134, or the body112, which is composed of a material to transmit heat from the element for generating heat236, to the stator ports210, such as metal, such as stainless steel. Thus, the element for generating heat236is used to indirectly heat the stator ports210, though other components are directly heated to provide the heat transfer to the stator ports210, and therefore to the sample flowing through the stator port210, which are sufficient small to ensure rapid heat transfer to the sample. In operation, the element for generating heat236is activated when needed to heat a sample, which quickly vaporizes the sample at the temperature of the column704. When not needed, particularly when no analysis is on-going, the element for generating heat236is deactivated and the valve100begins to cool, to the ambient temperature of the oven712in the case of the body first end116.

Referring toFIGS. 1-3, to reduce the heat soak through the body112, the body112may include a plurality of lateral vents138radially through the body112from the internal bore214distant the stator102.

Referring toFIG. 7, the valve100may be integrated into a heated rotary valve system together with a controller702. The controller702may adapted to receive a start instruction, such as when analysis using the column704is to be permited, to simultaneously activate the element for generating heat236and to cause the valve actuator718to position the valve100to permit the flow to the column704.

Referring toFIG. 7, the heated valve system may be coupled with an improved controller702, a chromatography column704, which may be connected to a detector, a sample supply708, and oven712, and a temperature sensor716to provide a chromotagraphy system. In the chromotagraphy system, the controller702may further be adapted to receive an oven temperature from a temperature sensor716in the oven712. The chromography column704, also positioned in the oven712, such as by suspension lines720, is attached for communication with the valve100at a column inlet706while the sample supply708, which may also be in the oven712, is attached for communication with the valve100at a supply outlet710. The valve100may be positioned through the oven wall714, so that only the stator first surface104and stator connectors108are exposed to the interior722of the oven712, while the body second end118and the end of the driveshaft134are sufficient external the oven wall714to permit connection with the valve actuator718.

Referring toFIG. 8, the heated valve100may be coupled with an improved controller802, a chromatography column804, which may be connected to a detector, and a sample supply808to provide an alternative chromotagraphy system. In the alternative chromotagraphy system, the controller802may further be adapted to control the temperature of a column804which may be heated by direct contact, or indirect contact, with a heating element. The chromography column804is attached for communication with the valve100at a column inlet806while the sample supply808is attached for communication with the valve100at a supply outlet810. Thus, the valve100and column804may be adapted for a portable chromatography system.

The construction of the valve100permits rapid column switching which may be useful in complex separations or in two-dimensional gas chromatography separations.

Moreover, the valve100permits two column recycling, such as illustrated inFIG. 9to achieve improved separation of compounds in a gas chromatography system. The ultra low internal volume and the rapid heating of the stator ports210to permit cycling of sample constituents, from a sample supply908, back and forth through a first column902and a second column904multiple times, producing extremely high plate numbers and resulting in improbable separations, not possible with microfluidics or Dean's switching. Additionally, any peak broadening may be reduced, and peak capacity increased, by using negative temperature programming on the downstream column904connected to the detector906.

Additionally, with its low mass, ultra-low internal volume, fast switching and high temperature limit, the valve100may be utilized as a comprehensive two-dimensional gas chromatography (GCxGC) modulator. As can be appreciated, the valve100provides better performance than a diaphragm valve, has faster switching time and longer secondary duration time that a microfluidic device, and allows use of a lower secondary flow rate and use of a microbore secondary column.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof.