Pulsed valve for molecular resonance rotational (MRR) spectroscopy

Abstract

A pulsed valve uses an actuator, such as a solenoid, piezoelectric transducer, or other actuator to inject volatilized sample into the vacuum chamber of a molecular rotational resonance (MRR) spectroscopy system. The valve's sealing components and nozzle are made of materials that can withstand the relatively high temperatures of the volatilized sample, increasing the valve's life and improving its sealing performance. Insulating material shields the vacuum chamber and the actuator from the high-temperature portions of the valve. An optional flexible diaphragm can insulate the actuator from high temperatures and prevent sample material from coating the actuator. An example pulsed valve can operate for millions or billions of cycles at higher temperatures (e.g., 150 °C or higher) than a conventional solenoid valve. It lasts longer, with less frequent maintenance, and can dispense hotter, higher-molecular-weight samples with shorter rise and fall times than conventional solenoid valves, enabling new MRR measurement techniques.

Description

Pulsed Valve for Molecular Resonance Rotational (MRR) SpectroscopyCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the priority benefit, under 35 U.S.C. 119(e), of U.S. Application No. 63 / 572,665, entitled “Pulsed Solenoid Valve for Molecular Resonance Rotational (MRR) Spectroscopy” and filed April 1, 2024, which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] Molecular rotational resonance (MRR) spectroscopy characterizes compounds through their pure rotational angular momentum transitions in the gas phase. A molecule’s rotational energy levels are quantized by the molecule’s three-dimensional mass distribution, which also determines the molecule’s moment of inertia (I). The moment of inertia can be described with a simple formula, I = i r , where m is the mass of atom z in the molecule and is the distance of atom z from the molecule's center of mass. Molecules can be distinguished through their principal moments of inertia in the three spatial axes. Molecules’ rotational spectra are described by a Hamiltonian that depends on these quantities. Rotational spectra typically contain numerous and extremely narrow transition lines, providing a unique fingerprint of molecular structure.

[0003] An MRR spectroscopy measurement involves a sample of neutral molecules isolated in the gas phase, free of solvent and any other associated molecules. The sample is volatilized, e.g., by heating to its boiling point, and injected into a vacuum chamber with a nozzle. A source antenna in the vacuum chamber illuminates the volatilized sample with microwave or millimeter-wave radiation, causing the volatilized sample to emit a free induction decay (FID) pulse that is detected by a target antenna in the vacuum chamber. The spectrum of the FID pulse represents the rotational resonances of the molecules in the volatilized sample.SUMMARY

[0004] An MRR spectroscopy system typically uses a conventional solenoid valve to dispense the volatilized sample into the vacuum chamber via the nozzle. Unfortunately, conventional solenoid valves limit the operation of MRR spectroscopy systems in several ways. First, a conventional solenoid valve relies on a spring whose tension changes over time and must be adjusted manually, often frequently, to provide the proper spring tension for dispensingvolatilized samples. Even when adjusted, though, a conventional solenoid valve may dispense too much sample, resulting in waste. The changing spring tension can also affect the speed with which the valve opens (and closes), affecting the amount of sample dispensed by the valve and the speed with which that sample is dispensed.

[0005] Second, a conventional solenoid valve has a sealing surface that is made of soft material and can wear out quickly, e.g., within a few weeks or months, and so must be maintained or replaced frequently. For example, the conventional solenoid valve typically used in many MRR spectrometers includes a polytetrafluoroethylene (PTFE) poppet that must be replaced every 200,000 pulse cycles or so.

[0006] Third, a conventional solenoid valve typically cannot withstand the higher temperatures (e.g., 150 °C, 200 °C, 250 °C, 300 °C, or higher) used to volatilize certain samples, including those with higher molecular weights (e.g., about 100 amu), and to keep them in the gas phase for injection into the MRR spectroscopy system’s vacuum chamber. In a conventional solenoid valve, thermal contact between the valve’s nozzle and solenoid means that heating the gas path above about 160 °C degrades the valve’s performance. Higher temperatures can also accelerate degradation of soft sealing surfaces and exacerbate changes in spring tension. These shortcomings limit the utility of conventional solenoid valves for MRR spectroscopy.

[0007] The solenoid valves disclosed herein address these shortcomings of conventional solenoid valves. They can operate for more cycles (e.g., billions of cycles) and at higher temperatures (e.g., 150 °C, 200 °C, 250 °C, 300 °C, or higher) than conventional solenoid valves, meaning that they do not have to be replaced or maintained as frequently and can be used to dispense hotter, higher-molecular-weight samples. In addition, they can be actuated much more quickly, with much shorter rise and fall times, than conventional solenoid valves, enabling new MRR measurement techniques. They can also be adjusted, in real time, to open with the desired speed and by the desired amount to dispense a desired amount of sample. Inventive solenoid valves can also support the high gas flow rates desired for MRR spectroscopy.

[0008] An inventive solenoid valve can include a valve body, nozzle, sealing pin, moving armature, actuator, and, optionally, a flexible diaphragm. The valve body defines a cavity to receive a sample. The nozzle, which is in fluid communication with the cavity and may be shaped to allow supersonic expansion of the sample, dispenses the sample, e.g., into the vacuum chamber of an MRR spectroscopy system. The sealing pin extends through the cavityand seals and unseals a connection between the cavity and the nozzle. If desired, there can be a metal sphere disposed at one end of the sealing pin to mate with an opening of the nozzle. The moving armature, which is mechanically coupled to the sealing pin, moves the sealing pin toward and away from the nozzle, e.g., over a travel range of less than about 100 microns. The actuator, which may be solenoid coil or a piezoelectric actuator, actuates the moving armature. If present, the flexible diaphragm is disposed between the moving armature and the valve body and around the sealing pin. The flexible diaphragm seals the cavity, biases the sealing pin toward the nozzle, and / or thermally insulates the cavity from the moving armature and the solenoid coil. The flexible diaphragm can be flat or corrugated, can comprise stainless and / or hardened steel, and may be welded or press-fit to the sealing pin.

[0009] An inventive solenoid valve may also include a heater in thermal communication with the cavity via the valve body. This heater can heat the cavity to a temperature of at least 150 °C, at least 250 °C, or even higher temperatures.

[0010] An inventive solenoid valve may also include a pressure regulator, in fluid communication with the cavity, to regulate pressure within the cavity.

[0011] An inventive solenoid valve can also include one or more second thermal insulators; a first thermal insulator, disposed between the valve body and the solenoid coil, to thermally insulate the solenoid coil from the valve body; and / or a second thermal insulator, disposed between the valve body and a vacuum chamber connected to the nozzle, to thermally insulate the vacuum chamber from the valve body.

[0012] An inventive solenoid valve can also include a spring that is mechanically coupled to the moving armature and at least partially thermally insulated from the cavity by the flexible diaphragm. This spring provides a bias force driving the moving armature toward the nozzle.

[0013] An inventive valve can be part of an MRR spectroscopy system and arranged to dispense the sample into a vacuum chamber of the MRR spectroscopy system. Such an MRR spectroscopy system can also include a mass flow meter, waveform generator, and processor. The mass flow meter is in fluid communication with the valve and measures an amount of the sample dispensed by the valve. The waveform generator is operably coupled to the valve and drives the actuator with a driving waveform that causes the actuator to actuate the valve. And the processor, which is operably coupled to the mass flow meter and the waveform generator, adjusts at least one parameter of the driving waveform based on the amount of sample dispensed by the valve.

[0014] All combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are part of the inventive subject matter disclosed herein. The terminology used herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.BRIEF DESCRIPTIONS OF THE DRAWINGS

[0015] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally and / or structurally similar elements).

[0016] FIGS. 1A and IB are isometric views of an inventive solenoid valve for a molecular rotational resonance (MRR) spectroscopy system.

[0017] FIGS. 2A-2C are cutaway isometric views of an inventive solenoid valve.

[0018] FIG. 2D is a cutaway isometric view of an inventive solenoid valve with a corrugated diaphragm.

[0019] FIG. 3 is a cutaway isometric view of the sealing pin, metal sphere, and nozzle of an inventive solenoid valve.

[0020] FIG. 4 shows a cutaway isometric view of a solenoid valve with a gas port for regulating pressure on the solenoid side of a diaphragm that seals a cavity in the valve body.

[0021] FIGS. 5A and 5B are cutaway views of an inventive solenoid valve coupled to the vacuum chamber of an MRR spectroscopy system.

[0022] FIG. 6 illustrates how an inventive solenoid valve injects a volatized sample into the vacuum chamber of an MRR spectroscopy system.

[0023] FIG. 7A is an oscilloscope trace showing the drive signal and pulsed response of an inventive solenoid valve.

[0024] FIG. 7B illustrates an inventive solenoid valve used with an MRR spectroscopy system in a feedback loop to control valve actuation.

[0025] FIG. 8 shows an inventive solenoid valve without a diaphragm.

[0026] FIG. 9 shows an inventive piezoelectric valve for an MRR spectroscopy system.DETAILED DESCRIPTION

[0027] FIGS. 1 A and IB show isometric views, from different angles, of an inventive pulsed solenoid valve 100 for use in a molecular rotational resonance (MRR) spectroscopy system for chemical analysis. The valve 100 includes a valve body 110 that is coupled to a solenoid 120 via a first thermal insulator 150, which both thermally isolates the valve body 110 and the clamp plate (not shown) that secures the solenoid valve 110 to the MRR spectroscopy system’s vacuum chamber (described below with respect to FIGS. 5 A and 5B) and shields the solenoid 120 from heat given off by the valve body 110. Without the first thermal insulator 150, energy lost via conduction to the clamp plate and vacuum chamber could compromise proper heating of the valve body 110. The valve body 110 can be heated to temperatures of 150 °C or higher (e.g., 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, or 500°C) with an optional cartridge heater 154, which is controlled by an external processor or controller (not shown) via electrical leads 156. The cartridge heater 154 is in the valve body 110 and can heat the valve body 110 and the contents of the cavity formed in the valve body 110.

[0028] The valve 100 includes four gas inlets that pipe different samples (analytes), reference gases, and / or carrier gas from compression fittings 112a-112d (e.g., Valeo 10-32 gas chromatography ports) into a cavity or hollow in the valve body 110. (Other inventive valves may include more or fewer gas inlets and fittings.) A capillary tube or nozzle 136 extends from the cavity along the valve’s longitudinal axis and mates with an input to the vacuum chamber of the MRR spectrometer (not shown). The nozzle 136 may have an internal diameter of about 0.9 mm and minimal dead volume (e.g., less than 10 pL). The nozzle 136 may be shaped to allow for supersonic expansion of the sample being injected into the MRR spectroscopy system’s vacuum chamber and / or so that the sample plume injected into the vacuum chamber has a desired shape, e.g., selected based on the size, shape, and / or arrangement of the microwave antennae in the vacuum chamber. For example, the nozzle 136 may end in a cylindrical channel, a curved channel, or a conical channel 137 as shown in FIGS. 2A-2C.

[0029] A second thermal insulator 152 on the other side of the valve body 110 surrounds the nozzle 136 and shields the MRR spectrometer from the (hot) valve body 110. Bolts 153 or other fasteners fix the second thermal insulator 152 and the nozzle 136 to the valve body 110. The nozzle 136 also be welded or otherwise secured to the valve body 110. One or more O- rings 155 (shown in FIGS. 2A-2D) around the nozzle 136 seal any gaps between the second thermal insulator 152, nozzle 136, and / or valve body 110. One or more of these O-rings 155 can be omitted if the nozzle 136 is welded to or integral with the valve body 110.

[0030] FIGS. 2A-2C are cutaway isometric views of the inventive pulse solenoid valve 100 showing the cavity 111 formed in the valve body 110. The pressure in the cavity 111 be regulated by feeding gas into the cavity 111 through one of the inlet tubes 112. This gas can be supplied by an external gas cylinder (not shown) and regulated by a pressure regulator on the external gas cylinder.

[0031] A gas-tight, flexible diaphragm 140 seals one end of the cavity 111. This flexible diaphragm 140 is a flat ring or annulus that fits around a cylindrical sealing pin 134. The flexible diaphragm 140 can be made of stainless and / or hardened steel (e.g., SAE 304 stainless steel) and can be welded, press-fit, or otherwise attached to the sealing pin 134, which extends through the cavity 111 toward the end of the nozzle 136 that opens into the cavity 111.

[0032] FIG. 2D shows an inventive pulse solenoid valve 100’ with a corrugated flexible diaphragm 140’ instead of the flat flexible diaphragm 140 of FIGS. 2A-2C. The corrugated flexible diaphragm 140’ tends to be stiffer than the flat flexible diaphragm 140. The corrugated flexible diaphragm 140’ can be made by punching a suitably sized and shaped disc or ring out of stainless steel or hardened steel, then forming the corrugations. (In contrast, the flat, flexible diaphragm 140 can be made by simply punching a suitably sized and shaped disc or ring out of stainless steel or hardened steel without any forming.) Like the flat flexible diaphragm 140, the corrugated flexible diaphragm 140’ can be welded, press-fit, or otherwise attached to the sealing pin 134.

[0033] The other end of the sealing pin 134 screws into a cylindrical moving armature 130 contained within an armature tube 132. The moving armature 130 and armature tube 132 extend through the first thermal insulator 150 and into a hollow or cavity extending along the longitudinal axis of the solenoid coil 120. An optional coil spring 138 fits in the armature tube 132, between the armature tube 132 and moving armature 130, and biases the moving armature 130 toward the nozzle 136.

[0034] The coil spring 138 can push against a fixed armature or screw plug 131 that is fixed to the armature tube 132 and acts as a stop or limit on the moving armature’s travel away from the nozzle 136. The screw plug 131 can be rotated (screwed in or out) to adjust the compression of the spring 138. Generally, the screw plug 131 can be set to a certain depth during production of the valve 100 and may not be something that a user could adjust. The back of the screw plug 131 can be tapped for a threaded hole for the screw that holds the solenoid 120 in place with respect to the armature tube 132.

[0035] As shown in FIGS. 2A-2D and 3, a metal sphere 135 (e.g., a ball bearing) affixed to the tip of the sealing pin 134 provides the valve’s sealing surface. The metal sphere 135 fits into the end of the nozzle 136 that opens onto the cavity 111. Alternatively, the tip of the sealing pin 134 could be machined into a hemispherical shape instead of affixing a metal sphere to the tip. Or the valve 100 can have a sealing surface at the tip of the sealing pin 134 that is from a polymer, such as PTFE. Polymer sealing surfaces tend to have lower leak rates than metal sealing surfaces, which tend to be able to operate at higher temperatures than polymer sealing surfaces.

[0036] Together with the first thermal insulator 150, the flexible diaphragm 140 physically and thermally isolates the moving armature 130 solenoid coil 120, and the rest of the valve stem from the cavity 111 in the valve body 110. This isolation allows for the flow volume and wetted surfaces of the valve body 110 to be heated by the cartridge heater 154 while the solenoid coil 120 is kept at a lower temperature for more repeatable operation. This reduces or minimizes the upswept internal volumes in the valve 100 to reduce carryover of sample between valve pulses. It also allows for cooling of the valve stem, including the solenoid coil 120, and moving armature 130, without causing cold trapping and carryover of sample in the cavity 111.

[0037] The flexible diaphragm 140 also acts as a spring that biases the sealing pin 134 toward the nozzle 136, eliminating or reducing the need for a conventional spring (e.g., spring 138) to bias the moving armature 130. In its normal (relaxed) state, the flexible diaphragm 140 can push the sealing pin 134 far enough toward the nozzle 136 that the metal sphere 135 at the end of the sealing pin 134 seals the end of the nozzle that opens into the cavity 111 as shown in FIG. 3. This prevents gas in the cavity 111 from exiting the cavity 111 via the nozzle unless the valve 100 is actuated. When the valve 100 is opened (i.e., when the metal sphere 135 is withdrawn from the end of the nozzle 136), the volatilized sample travels out of the cavity 111 via the nozzle 136 and into the vacuum chamber of the MRR spectrometer. Closing the valve 100 can trap some hot gas in a dead space between the side of the metal sphere 135 pressedagainst the nozzle 136 and the far end of the nozzle 136. This dead space or dead volume should be as small as possible (e.g., less than 10 pL) to minimize the amount of wasted sample and to prevent unused sample from accumulating in the nozzle 136. Keeping this dead space as small as possible provides faster injection of gas into the vacuum chamber. If the dead volume between the nozzle seal and the vacuum chamber is too large, then the leading-edge pressure of the gas pulse injected into the vacuum chamber will rise more slowly and compromise the supersonic expansion and cooling of the injected gas.

[0038] FIG. 4 illustrates how the volume on the moving armature side of the flexible diaphragm 140 can be filled with gas under a second regulated bias pressure. A gas port 160 through the fixed armature 131 connects via an interface 161 and gas line 162 to an external gas cylinder (e.g., air or nitrogen; not shown) or other external gas source. A pressure regulator (not shown) controls the flow of gas from the external gas source to the volume on the moving armature side of the flexible diaphragm 140, regulating the pressure on demand.

[0039] This bias pressure pushes on the flexible diaphragm 140, creating a spring force that pushes the sealing pin 134 toward the nozzle 136, closing the valve. Regulating this bias pressure makes it possible to continuously adjust the spring force exerted by the flexible diaphragm 140 on the sealing pin 134. The bias gas pressure acting on the flexible diaphragm 140 can also be dynamically controlled in a coordinated manner with the actuation of the solenoid coil 120 to allow for an asymmetric spring force on the sealing pin 134, e.g., lower force when the valve 100 is opening and higher force when the valve 110 is closing.

[0040] The valve 100 can be actuated quickly by moving the sealing pin 134 with magnetic force generated by the solenoid electromagnet 120. The flexible diaphragm 140 and optional spring 138 push the sealing pin 134 and metal sphere 135 against the nozzle 136, assuring that the valve 100 is closed when the solenoid electromagnet 120 is off (not actuated). Powering the solenoid electromagnet 120 creates a force that pushes against the flexible diaphragm 140 and spring 138 and forces the valve 100 to open. The valve 100 remains open as long as the solenoid electromagnet 120 is powered on and generates enough force to counteract the force exerted by the flexible diaphragm 140 and spring 138. When the solenoid electromagnet 120 is off, the force exerted on the sealing pin 134 by the flexible diaphragm 140 and spring 138 closes the valve 100.

[0041] The valve’s opening speed is controlled by several factors, including the force exerted by the solenoid electromagnet 120, the mass of the sealing pin 134 and the metal sphere 135,and the force exerted by flexible diaphragm 140 and spring 138. The forces exerted by the solenoid electromagnet 120, flexible diaphragm 140, and spring 138 depend on temperature and tend to be higher at lower temperatures.

[0042] FIGS. 5 A and 5B show the valve 100 connected to an MRR spectrometer. The nozzle 136 connects to a vacuum chamber flange 500 that forms one side of the vacuum chamber 501. The vacuum chamber flange 500 can be made of 6061 aluminum or other suitable material and may have a diameter of about 10 inches and a thickness of about 1.5 inches. The connection between the valve 100 and vacuum chamber flange 500 is surrounded by a vacuum tight seal to prevent the sample from leaking as the valve 100 injects it into the vacuum chamber 501. When no gas is flowing from the valve 100 to the vacuum chamber 501 (when the valve is standing by), a vacuum pump (not shown) keeps the vacuum chamber 501 at a pressure of 107to 108Torr. When gas flows through the valve 100 into the vacuum chamber 501 (when the valve is operating), the pressure inside the vacuum chamber 401 can rise to 2 / I 03to 5 / 105Torr.

[0043] The second thermal insulator 152 prevents heat from flowing from the valve body 110, which may be at a temperature of 150 °C or more, to the vacuum chamber flange 500, which is at ambient temperature (e.g., about 20 °C). Preventing this heat flow reduces thermal loss from the valve body 110. It also prevents higher valve temperatures from increasing the load on the vacuum pump that keeps the vacuum cavity 501 at the desired pressure.

[0044] FIG. 6 illustrates the valve 100 injecting a volatilized sample into the vacuum chamber 501. The volatilized sample forms a sample plume 503 whose size and shape can be adjusted by changing the waveform used to actuate the valve, e.g., based on the size(s), shape(s), and / or position(s) of the antennae for making the MRR spectroscopy measurements in the vacuum chamber 501. More specifically, the valve actuation speed affects the plume shape, with faster actuation generally providing enhanced supersonic expansion and gas cooling. Ideally, the plume should be shaped and size for optimal coupling to the microwave radiation used to excite the sample and for optimal coupling of its microwave emission to the detecting antenna. The plume shape can be optimized in coordination with the design of the MRR spectrometer’s cavity and RF components.

[0045] Each gas inlet 112 can accept neon or nitrogen carrier gas seeded with approximately 0.1% of a sample, which may include high-boiling molecules, into the cavity 111. The valve 100 can accept input gas in a pressure range of about 0-3 bar (gauge) (0-45 psig). The cartridgeheater 154 heats the sample in the cavity 111 to temperatures of at least 150 °C (e.g., 200 °C, 250 °C, 300 °C, 350 °C, 400 °C, 450 °C, 500°C, or higher). The hot sample flows through nozzle 136 into the vacuum cavity 501 of the MRR spectrometer along the valve’s longitudinal axis.

[0046] The valve 100 can inject samples into the vacuum chamber 501 with high molecular density, while limiting the presence of weakly bound complexes, to achieve the desired measurement sensitivity. It can dispense samples as gas pulses with a gas pulse duration of about 1 ms or less and a gas output of about 0.1 mL (at standard temperature and pressure, or 0 °C (273.15 K) and 1 bar (100 kPa, 14.5 psi)) per valve pulse. For instance, gas pulse durations with the inventive solenoid valve 100 may be about 0.4-0.5 ms at room temperature and about 0.6-0.7 ms at 250 °C. These values include some dead time (e.g., around 200 ms), possibly tied to the response time of the electronics. For comparison, a Parker valve can produce gas pulses of about 0.8-1.0 ms at room temperature. Preliminary results indicate that the shorter gas pulse from an inventive solenoid valve increases MRR measurement sensitivity by up to 100%. For a valve pulse repetition rate of 10 Hz, this results in flow rates between 50-100 mL / min. The valve 100 can operate at higher flow rates, e.g., with a higher pulse repetition rate and a gas output of about 0.1 mL per valve pulse.

[0047] For many types of MRR measurements, the MRR spectrometer operates at constant gas pressure, where the quantity of analyte / carrier gas mixture injected into the MRR spectrometer’s vacuum chamber 501 is controlled by opening and closing of the valve 100. The quantity of injected gas depends on how fast the valve 100 opens, how long it stays open for (pulse width), and its frequency of operation (pulse repetition frequency). Ideally, the valve 100 should open instantly and create a well-defined gas pulse into the MRR spectrometer. In practice, the valve 100 opens gradually. For example, the valve 100 may transition from closed to open in about 200 ps or less and can be opened for pulses with durations of 1 ms or less (that is, the valve can transition from closed to open, dispense gas, and transition from open to closed in less than 1 ms).

[0048] As the valve’s sealing surface (metal sphere 135) separates from the capillary tube (nozzle 136), the gas flow through the valve 100 increases as the distance between the two surfaces increases. The gas flow reaches a maximum when the valve is fully open (i.e., when the metal sphere 135 and nozzle 136 are farthest apart). The gas flow stays at its maximum value while the valve 100 is held open and then decreases as the valve starts to close and thevalve sealing surface and the capillary tube are brought back into contact. Unlike the valve opening speed, the valve closing speed has no effect on instrument performance.

[0049] An inventive valve can be opened very quickly, allowing injection of the desired amount of gas (0.1 mL) with a valve pulse width as low as 0.3 ms at room temperature. This allows the pulse width to be increased as desired to optimize gas introduction into the instrument without any negative effect(s) on instrument performance. At room temperature, for example, a valve pulse width of 0.4 ms provides an average flow rate of 40 mL / min, while at 240 °C providing the same average flow rate requires 0.6 ms pulse width. Matching the gas flow rate between two temperature settings (e.g., ambient and 240 °C) also keeps the analyte signal intensity constant within experimental uncertainty.

[0050] FIG. 7A shows oscilloscope traces of the transistor-transistor logic (TTL) signal used to drive an example inventive solenoid valve (TTL IN) and the actual voltage waveform applied to the solenoid valve in response to the drive signal (V VALVE). The voltage waveform is a hit-and-hold pulse with a hit portion with an amplitude of about 280 V (depending on the solenoid) and a duration of about 220 ps and can be adjusted, e.g., from 50 ps to 400 ps. The amplitude drops to 28 V for the hold portion, which can last from about 1 ms to about 5 ms. The valve is typically driven at a pulse repetition frequency of about 10 Hz. The amplitude, duration, shape, and pulse repetition frequency of this hit-and-hold pulse can be adjusted so that the valve dispenses the desired amount of sample with each pulse, e.g., on a pulse-to-pulse basis.

[0051] For reliable instrument performance, the gas mass flow rate should be constant across the MRR spectrometer’s (and valve’s) full range of operating temperatures. MRR spectrometers tend to operate well at low analyte concentrations in neon (less than 0.2%), so the viscosity and density of the gas mixture will typically be very close to that of neon gas. Increasing the temperature from ambient (20 °C) to 300 °C reduces neon gas viscosity by 27% and neon gas density by 48%, reducing the mass flow rate by 55%. While mass flow rate can be increased by increasing the valve’s pulse width (open duration), this is effective only with pulse widths up to 1 ms. Longer pulse widths, while increasing gas flow, can degrade instrument performance due to the sub-optimal shape of the gas pulse.

[0052] The optimum or desired pulse shape is related to supersonic expansion of the gas pulse injected into the vacuum chamber (the sample plume 503 shown in FIG. 6). For efficient cooling by supersonic expansion, the gas pulse should be short, with a sharp rise time (leadingedge). Injecting analyte molecules and neon (carrier gas) atoms causes them to accelerate to supersonic speeds, converting their internal (rotational) energy into kinetic (movement) energy. The better the acceleration, the higher the speed and the lower internal (rotational) energy and temperature. Longer pulse widths reduce the acceleration efficiency as the molecules later in the pulse collide with the molecules in front of them. Reduced acceleration efficiency produces higher rotational temperature, so it’s undesirable in our instruments. Because the MRR spectroscopy signal increases with the amount of injected analyte, but decreases with loss of cooling efficiency, the duration of the injected gas pulse should be long enough for injecting as much analyte as possible into the vacuum chamber and short enough to avoid loss of cooling efficiency.

[0053] An inventive pulsed valve can be operated to dispense the desired / optimal amount of sample with every pulse. For example, the waveform used to actuate an inventive pulsed valve can be chosen to inject smaller amounts of sample (e.g., to conserve the sample) or larger amounts of sample (e.g., to decrease sample characterization and measurement time) with each pulse, even on a pulse-to-pulse basis. The actuation waveform and hence the valve operating characteristics can be based on a variety of different operational parameters, including but not limited to sample characteristics, such as sample composition, molecule size, volatility, potential for clustering, etc., and valve characteristics, such as variations in manufacturing, wear over time, operating temperature, operating pressure, and so on.

[0054] The valve’s operating characteristics can be measured directly, e.g., with thermometers and flow meters, and / or indirectly, e.g., by looking at the signal amplitude or signal -to-noise ratio of the MRR spectrometer measurement. For example, a flow meter or other sensor can measure the quantity of sample that the valve dispenses with each pulse; a computer, controller, or other processor coupled to the flow meter can use these measurements to adjust the waveform (e.g., (peak) amplitude, shape, pulse repetition frequency, etc.) that drives the valve so as to adjust the quantity of sample dispensed with each pulse. This quantity can be adjusted for operational drift. The computer can also store the sensor data for calculating the amount of sample used in the experiment / measurement and for documenting the valve’s performance (e.g., for confirming measurement validity, audit and regulatory purposes, etc.).

[0055] FIG. 7B illustrates the valve 100 and MRR spectrometer 700 in a feedback loop with a waveform generator 702 used to generate the voltage waveform(s) that drive the valve 100. The feedback loop also incorporates a mass flow meter 703, which measures gas flow input into the valve 100, and a control computer 704, which collects data from the MRR spectrometer700 and mass flow meter 703 and provides control parameters for the voltage waveform(s) to the waveform generator 702. The gas flow rate can be controlled by adjusting the valve pulse timing using pre-programmed valve pulse lengths at different temperatures or by using realtime gas flow measurement by the mass flow meter 703. For example, neon gas flow can be measured using the mass flow meter 703, which provides an electronic reading of the gas flow rate to the control computer 704 through a digital interface (an RS-485 interface, for example). Control software executed by the control computer 704 reads the gas flow rate and, if different than the requested gas flow rate, adjust the valve pulse width to compensate. For example, the control computer 704 can increase the pulse width and / or pulse repetition frequency if the gas flow rate is too low or decrease the pulse width and / or pulse repetition frequency if the gas flow rate is too high, possibly using a pre-measured calibration curve to estimate the magnitude of the adjustment. This feature can be used to improve the accuracy and reproducibility of measurements, for example, keeping the measurement gas flow rate consistent across long time periods (e.g., months) where valve mechanical wear could otherwise result in performance differences over time. The voltage waveforms can also be adjusted based on the signal-to- noise ratios and / or other parameters of the MRR spectroscopy measurements made by the MRR spectrometer 700, where control software executed by the control computer 704 could read the signal intensity of the spectroscopic measurement and make voltage adjustments to find a gas flow value where signal intensity (or other spectrometric measurement parameters) is maximized.

[0056] It can be beneficial for the valve to open as fast as possible, i.e., to transition from no gas flow to maximum gas flow instantaneously (a perfectly square leading edge). The shape of the gas pulse can be changed by balancing the spring force holding the valve closed and the solenoid magnetic power. The acceleration of the sealing pin (and the speed with which the valve opens) is proportional to the difference between the spring force and solenoid power. Keeping the spring force at the minimum to keep the valve closed increases the opening speed and produces a gas pulse with the “squarest” leading edge, albeit with a potentially slower valve closing speed. The solenoid power can be controlled by the voltage applied to the solenoid, and the spring force can be adjusted by regulating the pressure on the solenoid side of the diaphragm and / or by adjusting the tension on the (optional) coil spring with the screw Plug.

[0057] Typically, the valve’s closing speed does not affect the performance of the MRR spectroscopy instrument, as by the time the valve closes the MRR detection cycle is alreadyover. But closing the valve slowly increases sample usage, which can be problematic when dealing with small amounts of analyte. In situations where the amount of analyte is limited, it may be preferable to increase the spring force so that the valve closes faster and to shorten the gas pulse to conserve analyte. While this may reduce the sensitivity of detection for each gas pulse, it can reduce sample usage by more than enough to offset any loss in sensitivity. In other words, it may optimize the signal per amount of sample at a cost of increased experimental time.

[0058] An inventive solenoid valve’s ability to emit gas pulses with different shapes and durations means that it can be operated in different regimes, including a maximum signal regime and a minimum sample consumption regime. In the maximum signal regime, the solenoid valve and MRR spectroscopy instrument are operated to produce the highest possible signal in a shorter time at the expense of increased sample consumption — the solenoid valve operates with a lower spring force to increase its opening speed and produces a shorter gas pulse with a sharper leading edge and a longer trailing edge. In the minimum sample consumption regime, the solenoid valve and MRR spectroscopy instrument are operated to use the sample more efficiently but produce less signal per pulse — the solenoid valve’s spring force is higher, so it opens more gradually and closes more quickly than in the maximum signal regime.

[0059] FIG. 8 shows an inventive solenoid valve 800 without a flexible diaphragm. Aside from the lack of a flexible diaphragm, this valve 800 is very similar to the inventive solenoid valve 100 with a flexible diaphragm described above; at most, this valve 800 may have an armature tube 832 without any holes for pressuring the void, space, or cavity between the back of the moving armature 132 and the (absent) flexible diaphragm. Instead, the cavity 111 extends from the nozzle 136 to the back of the moving armature 132. Eliminating the flexible diaphragm makes the valve 800 easier to manufacture and makes the operational tuning of the valve 800 less dependent on temperature, possibly at the cost of shorter valve life due to corrosion and / or build-up of analytes or sample materials on the moving armature 132 and other components that would otherwise be protected by the flexible diaphragm. (FIG. 8 also shows the nozzle 136 and thermal insulator 152 welded, instead of bolted, to the valve body 110, along with fewer O-rings 155.)

[0060] FIG. 9 shows an inventive pulsed valve 900 with a piezoelectric actuator 920 instead of a solenoid coil. The piezoelectric actuator 920 is coupled to one end of a moving armature 930 in an armature tube 932. The other end of the moving armature 932 is coupled to a sealingpin 134 that extends through the cavity 111 in a valve body 110 as described above. A ringshaped, flexible diaphragm 140 is welded, press-fit, or otherwise attached to the sealing pin 134 and the moving armature 130, sealing the end of the cavity 111 closest to the piezoelectric actuator 920 and biasing the sealing pin 134 toward the nozzle 136. When the valve is closed, a metal sphere 135 at the tip of the sealing pin 134 fits into the end of a nozzle 136 as described above.

[0061] The piezo actuator 920 has the advantage of being able to explicitly control the position of the moving armature 932 in time. It therefore allows for explicit control of how far and how quickly the valve 900 is opened and / or closed, enabling more precise control of when and how much sample the valve 900 injects, e.g., into the vacuum chamber of an MRR spectrometer. Driving the piezoelectric actuator 920 with a suitable voltage waveform actuates the valve 900 to provide the desired timing and degree of opening. The voltage waveform causes the piezoelectric actuator 920 to pull the sealing pin 134 away from the nozzle 136, allowing the sample in the cavity 111 to flow through the nozzle 136, for example, into the vacuum chamber of an MRR spectrometer (not shown). The voltage waveform can be adjusted or modified to dispense the desired amount(s) of sample and / or to produce a sample plume with the desired shape and / or size as well to provide the desired timing as described above with respect to FIGS. 7 A and 7B.Conclusion

[0062] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to eachindividual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0063] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0064] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0065] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0066] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0067] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only beinterpreted as indicating exclusive alternatives (i.e., “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0068] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0069] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMS1. A valve comprising: a valve body defining a cavity to receive a sample; a nozzle, in fluid communication with the cavity, to dispense the sample; a sealing pin, extending through the cavity, to seal and unseal a connection between the cavity and the nozzle; a moving armature, mechanically coupled to the sealing pin, to move the sealing pin toward and away from the nozzle; and an actuator, operably coupled to the moving armature, to actuate the moving armature.

2. The valve of claim 1, wherein the nozzle is shaped to allow supersonic expansion of the sample.

3. The valve of claim 1, wherein the moving armature and the actuator are configured to move the sealing pin over a travel range of less than about 100 microns.

4. The valve of claim 1, wherein the actuator comprises a solenoid coil in electromagnetic communication with the moving armature.

5. The valve of claim 1, wherein the actuator comprises a piezoelectric actuator.

6. The valve of claim 1, further comprising: a flexible diaphragm, disposed between the moving armature and the valve body and around the sealing pin, to seal the cavity, to bias the sealing pin toward the nozzle, and to thermally insulate the cavity from the moving armature and the actuator.

7. The valve of claim 6, wherein the flexible diaphragm comprises stainless and / or hardened steel.

8. The valve of claim 6, wherein the flexible diaphragm is corrugated.

9. The valve of claim 6, wherein the flexible diaphragm is welded to the sealing pin.

10. The valve of claim 6, wherein the flexible diaphragm is press-fit to the sealing pin.

11. The valve of claim 1, further comprising:a heater, in thermal communication with the cavity via the valve body, to heat the cavity to a temperature of at least 150 °C.

12. The valve of claim 11, wherein the heater is configured to heat the cavity to a temperature of at least 250 °C.

13. The valve of claim 1, further comprising: a pressure regulator, in fluid communication with the cavity, to regulate pressure within the cavity.

14. The valve of claim 1, further comprising: a metal sphere, disposed at one end of the sealing pin, to mate with an opening of the nozzle.

15. The valve of claim 1, further comprising at least one of: a first thermal insulator, disposed between the valve body and the actuator, to thermally insulate the actuator from the valve body; or a second thermal insulator, disposed between the valve body and a vacuum chamber connected to the nozzle, to thermally insulate the vacuum chamber from the valve body.

16. The valve of claim 1, further comprising: a spring, mechanically coupled to the moving armature and at least partially thermally insulated from the cavity, to bias the moving armature toward the nozzle.

17. A molecular rotational resonance (MRR) spectroscopy system comprising the valve of claim 1 arranged to dispense the sample into a vacuum chamber of the MRR spectroscopy system.

18. The MRR spectroscopy system of claim 17, further comprising: a mass flow meter, in fluid communication with the valve, to measure an amount of the sample dispensed by the valve; a waveform generator, operably coupled to the valve, to drive the actuator with a driving waveform that causes the actuator to actuate the valve; and a processor, operably coupled to the mass flow meter and the waveform generator, to adjust at least one parameter of the driving waveform based on the amount of sample dispensed by the valve.

19. A method of dispensing a sample with a pulsed valve comprising a sealing pin extending through a cavity formed in a valve body to a nozzle, the method comprising: receiving the sample in the cavity; withdrawing the sealing pin from the nozzle so as to unseal a connection between the cavity and the nozzle and to dispense the sample via the nozzle; and moving the sealing pin against the nozzle so as to seal the connection between the cavity and the nozzle.

20. The method of claim 19, wherein the nozzle is shaped to allow supersonic expansion of the sample.

21. The method of claim 19, wherein withdrawing the sealing pin comprises moving the sealing pin over a travel range of less than about 100 microns.

22. The method of claim 19, wherein withdrawing the sealing pin comprises actuating a moving armature coupled to the sealing pin.

23. The method of claim 22, wherein actuating the moving armature comprises running a current through a solenoid coil in electromagnetic communication with the moving armature.

24. The method of claim 22, wherein actuating the moving armature comprises applying a voltage to a piezoelectric actuator coupled to the moving armature.

25. The method of claim 22, further comprising at least one of: measuring an amount of the sample dispensed by the pulsed valve; and adjusting a waveform used to drive the moving armature based on the amount of sample dispensed by the pulsed valve.

26. The method of claim 19, further comprising: sealing the cavity, biasing the sealing pin toward the nozzle, and / or thermally insulating the cavity with a flexible diaphragm disposed around the sealing pin.

27. The method of claim 19, further comprising: heating the cavity to a temperature of at least 150 °C.

28. The method of claim 19, further comprising: heating the cavity to a temperature of at least 250 °C.

29. The method of claim 19, further comprising: regulating pressure within the cavity.

30. The method of claim 19, wherein dispensing the sample comprises injecting the sample into a vacuum chamber of a molecular rotational resonance (MRR) spectroscopy system.

31. The method of claim 30, further comprising at least one of: thermally insulating the vacuum chamber from the valve body.

32. A valve compri sing : a valve body defining a cavity to receive a sample; a nozzle, in fluid communication with the cavity, to dispense the sample; a sealing pin, extending through the cavity, to seal and unseal a connection between the cavity and the nozzle; a moving armature, mechanically coupled to the sealing pin, to move the sealing pin toward and away from the nozzle; a solenoid coil, in electromagnetic communication with the moving armature, to actuate the moving armature; and a flexible diaphragm, disposed between the moving armature and the valve body and around the sealing pin, to seal the cavity, to bias the sealing pin toward the nozzle, and to thermally insulate the cavity from the moving armature and the solenoid coil.

Images