The present teachings generally relate to mass spectrometry, and more particularly to sampling probes and sampling interfaces for mass spectrometry systems and methods.
Mass spectrometry (MS) is an analytical technique for determining the elemental composition of test substances with both qualitative and quantitative applications. MS can be useful for identifying unknown compounds, determining the isotopic composition of elements in a molecule, determining the structure of a particular compound by observing its fragmentation, and quantifying the amount of a particular compound in a sample. Given its sensitivity and selectivity, MS is particularly important in life science applications.
In the analysis of complex sample matrices (e.g., biological, environmental, and food samples), many current MS techniques require extensive pre-treatment steps to be performed on the sample prior to MS detection/analysis of the analyte of interest. Such pre-analytical steps can include sampling (i.e., sample collection) and sample preparation (separation from the matrix, concentration, fractionation and, if necessary, derivatization). It has been estimated, for example, that more than 80% of the overall analytical process can be spent on sample collection and preparation in order to enable the analyte's detection via MS or to remove potential sources of interference contained within the sample matrix, while nonetheless increasing potential sources of dilution and/or error at each sample preparation stage.
Ideally, sample preparation techniques for MS should be fast, reliable, reproducible, inexpensive, and in some aspects, amenable to automation. One recent example of an improved sample preparation technique is solid-phase microextraction (SPME), which essentially integrates sampling, sample preparation, and extraction into a single solvent-free step. Generally, SPME devices utilize a fiber or other surface (e.g., blades, micro-tips, pins, or mesh) coated with an extracting phase to which analytes within the sample can be preferentially adsorbed when the device is inserted into the sample. Because extraction can take place in situ by inserting a biocompatible device directly into tissue, blood, or other biological matrix for a short period of time, SPME does not require any additional sample collection. Alternatively, SPME devices can be used for ex vivo analysis using a small amount of a collected sample (e.g., a sample aliquot).
Though SPME is generally considered to be accurate and simple and can result in decreased sample preparation time and disposal costs, the MS-based analysis of SPME-prepared samples may nonetheless require additional equipment and/or time-consuming steps in order to ionize the analyte from the SPME device directly or to desorb the analytes from the SPME device prior to ionization as required for MS. By way of example, various ionization methods have been developed that can desorb/ionize analytes from condensed-phase samples with minimal sample handling (e.g., desorption electrospray ionization (DESI) and direct analysis in real time (DART), which “wipe-off” analytes from the samples by exposing their surfaces to an ionizing medium such as a gas or an aerosol). However, such techniques can also require sophisticated and costly equipment. In addition, the ionization efficiency of large molecules (e.g., proteins) are generally not as good as small molecules for these ionization techniques.
Alternatively, additional desorption steps have been utilized to extract the analytes from the SPME device prior to ionization via ionization techniques other than DESI or DART. For example, because electrospray ionization (ESI) is one of the most common ionization methods and requires the analyte to be in solution, some users have utilized liquid desorption and subsequent purification/separation of the extracted/enriched analytes via high-performance liquid chromatography (HPLC) prior to MS analysis. However, liquid desorption prior to HPLC may require several minutes to transfer the analyte from the SPME coating to the liquid phase due to requirements imposed on the HPLC mobile phase (weak solvent strength). Typically, high organic solvent has the best elution efficiency, but it cannot be injected directly to the typically-used reverse-phase LC columns. In order to compensate, either an elution solvent having less efficacy (e.g., a mixture of organic solvent and water) is typically utilized, or a follow-up dilution step with water prior to the LC injection is alternatively provided. Both options, however, can reduce sensitivity. Such conventional workflows of elution and LC-MS ejection also generally require a relatively high volume of liquid to be used in the elution step, which leads to additional dilution. Moreover, as discussed above, these increased sample preparation/separation steps can decrease throughput, introduce potential sources of error, increase dilution, and cannot be easily automated. Alternatively, some groups have proposed substantial modifications to the standard electrospray ion source. Typically in ESI, a liquid sample is continuously discharged into an ionization chamber from within an electrically conductive capillary, while an electric potential difference between the capillary and a counter electrode generates a strong electric field within the ionization chamber that electrically charges the liquid sample. This electric field causes the liquid discharged from the capillary to disperse into a plurality of charged micro-droplets drawn toward the counter electrode if the charge imposed on the liquid's surface is strong enough to overcome the surface tension of the liquid (i.e., the particles attempt to disperse the charge and return to a lower energy state). As solvent within the micro-droplets evaporates during desolvation in the ionization chamber, charged analyte ions can then enter a sampling orifice of the counter electrode for subsequent mass spectrometric analysis. PCT Pub. No. WO2015188282 entitled “A Probe For Extraction Of Molecules Of Interest From A Sample,” which is incorporated by reference herein in its entirety, for example, thus purports to provide for electrospray ionization from an SPME device by applying the ionizing electric potential to the conductive SPME device itself (to which a discrete amount of a desorption solution is applied) such that ions are generated directly from the edges of the wetted substrate.
There remains a need for improved and/or reduced-cost systems that enable fast-coupling of SPME devices to MS systems with minimal alterations to the front-end while maintaining sensitivity, simplicity, selectivity, speed, and throughput.
There also remains a need for the efficient coupling of liquid samples (whether undergoing pre-sampling purification or otherwise to the ion source of a mass spectrometer system).
Devices, methods, and systems for delivering a liquid sample to an ion source for the generation of ions and subsequent analysis by mass spectrometry are provided herein. In accordance with various aspects of the present teachings, MS-based systems and methods are provided in which a desorption solvent utilized in a sampling interface to desorb one or more analyte species from a substrate is fluidly coupled to an ion source for ionizing the one or more analyte species desorbed into the desorption solvent for subsequent MS analysis (e.g., without a liquid chromatography (LC) column between the sampling interface and the ion source). In accordance with various aspects of the devices, methods, and systems described herein, the configuration of the sampling substrate (e.g., a SPME device to which extracted analytes are adsorbed) and/or the sampling interface can be optimized so as to increase the surface area of the substrate coated with the extraction phase subject to desorption within a minimal volume of desorption solvent within the fluid chamber of the sampling interface so as to provide for increased concentrations of the one or more analyte species desorbed from the substrate in the desorption solvent delivered to the ion source of the MS system. In some aspects, for example, the substrate can be configured such that the substrate occupies at least 20 percent of the fluid volume in the device-receiving port (i.e., less than 80% of the volume of the device-receiving port is occupied by desorption solvent). By way of non-limiting example, in some aspects, the substrate can occupy at least 30%, at least 40%, or at least 50% of the distal fluid chamber.
In accordance with various exemplary aspects of the present teachings, a substrate for sampling a specimen is provided, the substrate comprising an elongate member extending from a first end to a second end spaced apart from the first end by an outer surface and a bore extending from the second end at least partially through the elongate member. The second end of the elongate member can be sized and configured to be inserted within a substrate sampling probe (e.g., within a port of an open port probe). In various exemplary aspects, the substrate sampling probe can comprise an outer capillary tube extending from a proximal end to a distal end and an inner capillary tube extending from a proximal end to a distal end and disposed within said outer capillary tube (e.g., coaxially), with the distal end of the inner capillary tube being recessed relative to the distal end of the outer capillary tube so as to define a distal fluid chamber between the distal end of the inner capillary tube and the distal end of the outer capillary tube. In such a manner, the inner and outer capillary tubes of the substrate sampling probe can define a desorption solvent conduit and a sampling conduit in fluid communication with one another via the distal fluid chamber. In various aspects, the bore defines an inner surface of the elongate member that is sized and configured to at least partially surround the distal end of the inner capillary tube, for example, when the substrate is inserted into the distal fluid chamber. Further, at least a portion of the elongate member's outer surface, the bore's inner surface, and the second end of the elongate member can comprise a surface coated with an extraction phase to which one or more analytes in a sample can be preferentially adsorbed when the device is inserted into the sample. Additionally, the cross-sectional shape of the elongate member at the coated surface portion can comprise a plurality of protrusions on at least one of the inner and outer surfaces such that desorption solvent flowing from the desorption solvent conduit into the sampling conduit through the distal fluid chamber can flow around said protrusions to desorb analytes adsorbed thereto.
The inner and outer surfaces of the sampling substrate can have a variety of configurations for increasing the surface area to which analytes can be adsorbed during extraction and from which analytes can be desorbed for delivery to the ion source in the sampling interface. By way of example, the inner surface of the bore at the coated surface portion can comprise a circular cross-sectional shape, while for example, the cross-sectional shape of the outer surface comprises a star-like shape (e.g., like a plurality of baffles). In some aspects, the maximum outer dimension of the outer surface at the coated surface portion comprising protrusions is less than the inner dimension of the outer capillary tube, while the minimum inner diameter of the circular bore can be greater than the outer diameter of the inner capillary tube. Alternatively, in some aspects, the outer surface of the elongate member at the coated surface portion can comprise a circular cross-sectional shape and the plurality of protrusions can be formed in the inner surface, for example, as inwardly extending baffles. For example, the minimum inner dimension of the inner protrusions of the non-circular bore can be greater than the outer diameter of the inner capillary tube to allow the inner capillary to be disposed therein, while the diameter of the circular outer surface of the elongate member can be less than the inner dimension of the outer capillary tube.
In various aspects, the elongate member extends along a longitudinal axis from its first end to its second end, and at least a portion of the elongate member can be axially symmetric thereabout (e.g., at the coated surface portion). In some aspects, the entire elongate member can be axially symmetric.
In certain aspects, the coated surface of the sampling substrate (e.g., SPME device) comprises a solid phase extraction medium such as HLB-PAN, C18-PAN, antibodies, etc., all by way of non-limiting example.
In various aspects, the substrate can be configured to rotate within the sample and/or desorption solvent so as to improve mass transfer (e.g., increase extraction or desorption speed). In addition to an actuation mechanism of a sample holder, for example, the first end of the elongate member can comprise a plurality of magnets, for example, that together serve as rotors when energized by an alternating current.
In accordance with various exemplary aspects of the present teachings, a system for analyzing the chemical composition of one or more analytes adsorbed to a sampling substrate as discussed otherwise herein is provided. In various aspects, the desorption solvent conduit and the sampling conduit can be in fluid communication with one another via the distal fluid chamber within which the substrate can be inserted. In various aspects, the desorption solvent conduit can extend from an inlet end configured to fluidly couple to a desorption solvent source to an outlet end in fluid communication with the distal fluid chamber, and said sampling conduit can extend from an inlet end in fluid communication with the distal fluid chamber to an outlet end configured to fluidly couple to an ion source probe for discharging desorption solvent received at the inlet end of the sampling conduit into an ionization chamber in fluid communication with a sampling orifice of a mass spectrometer.
In various related aspects, the system can further comprise a desorption solvent source fluidly coupled to the inlet end of the desorption solvent conduit and a pump mechanism for delivering the desorption solvent from the desorption solvent source to the inlet end of the desorption solvent conduit. In further aspects, the system can further comprise a controller for adjusting a fluid flow rate of the desorption solvent flowing through one or more of the desorption solvent conduit, the sampling conduit, and the ion source probe. Additionally or alternatively, the system can further comprise an ion source probe, an ionization chamber, and a mass spectrometer system, wherein the ion source probe is in fluid communication with the outlet end of the sampling conduit and comprises a distal end disposed in the ionization chamber, wherein analytes contained within said desorption solvent are configured to ionize as the desorption solvent is discharged into the ionization chamber.
In various aspects, the system can additionally include a sample holder that can enable SPME-MS analysis in an automated fashion. In various aspects, for example, the sample holder can be configured to insert the substrate within the sampling probe such that the coated surface portion is disposed within the distal fluid chamber. Additionally, in certain aspects, the sample holder can include an actuation mechanism to rotate the elongate member about its longitudinal axis when the coated surface portion is disposed within the distal fluid chamber to increase desorption therefrom. Additionally or alternatively, an actuation mechanism coupled to the sample holder can be configured to insert the substrate into the distal end of the outer capillary tube such that the coated surface portion of said substrate is in contact with the desorption solvent. In such a manner, various steps of the chemical analysis procedures performed by the exemplary systems described herein can be automated (e.g., performed by a robotic system). In some aspects, for example, the system can comprise a specimen stage configured to support a plurality of substrates, wherein the actuation mechanism is configured to sequentially insert each of said plurality of substrates into the distal end of the outer capillary tube. In some related aspects, though the desorption process and MS-sampling may be performed sequentially, the actuation mechanism can be configured to pre-treat a plurality of substrates simultaneously to increase throughput (e.g., pre-conditioning of the SPME substrate, sampling, and rinsing steps).
In accordance with various aspects of the present teachings, systems for analyzing a chemical composition of a specimen are provided comprising a substrate sampling probe configured to be directly coupled to an ion source of a mass spectrometer system.
In accordance with various exemplary aspects of the present teachings, a method for performing chemical analysis is provided, the method comprising providing a system for analyzing the chemical composition of one or more analytes adsorbed to a sampling substrate as discussed otherwise herein. The method can also include inserting the second end of the elongate member into the distal fluid chamber of the substrate sampling probe such that at least a portion of the inner capillary tube is disposed within the bore of the elongate member and flowing a desorption solvent through the desorption fluid pathway such that at least a portion of the one or more analyte species is desorbed from the coated surface portion and delivered to the ion source probe within the desorption solvent via the sampling conduit. The desorption solvent containing the portion of the one or more analyte species can then be discharged from the ion source probe so as to ionize the one or more analyte species and mass spectrometric analysis can be performed on the one or more ionized analyte species. In some related aspects, the method can additionally include interacting the coated surface portion with a sample so as to adsorb the one or more analyte species to the coated surface portion. Additionally or alternatively, the method can also comprise rotating the elongate member about its longitudinal axis when the coated surface portion is disposed within the distal fluid chamber, for example, to increase the efficiency of analyte desorption within the desorption solvent.
In accordance with various exemplary aspects of the present teachings, a system and method for analyzing a chemical composition of a specimen is described, comprising: a substrate sampling probe comprising: an outer capillary tube extending from a proximal end to a distal end; and an inner capillary tube extending from a proximal end to a distal end and disposed within said outer capillary tube, wherein said distal end of the inner capillary tube is recessed relative to the distal end of the outer capillary tube so as to define a distal fluid chamber between the distal end of the inner capillary tube and the distal end of the outer capillary tube, wherein said inner and outer capillary tubes define a desorption solvent conduit and a sampling conduit in fluid communication with one another via said distal fluid chamber, said desorption solvent conduit extending from an inlet end configured to fluidly couple to a desorption solvent source to an outlet end in fluid communication with said distal fluid chamber, and said sampling conduit extending from an inlet end in fluid communication with said distal fluid chamber to an outlet end configured to fluidly couple to an ion source probe for discharging desorption solvent received at the inlet end of the sampling conduit into an ionization chamber in fluid communication with a sampling orifice of a mass spectrometer; and a substrate comprising an elongate member extending from a first end to a second end spaced apart from the first end by an outer surface, wherein the second end is sized and configured to be inserted within the distal fluid chamber, wherein the elongate member has a bore at least partially extending therethrough from the second end and defining an inner surface that is configured to at least partially surround the distal end of the inner capillary tube when the second end is inserted within the distal fluid chamber, and wherein at least a portion of said outer surface, said inner surface, and said second end of the elongate member comprises a surface coated with an extraction phase configured to adsorb one or more analyte species thereto, a first and second solvent source fluidly connected to the desorption solvent conduit; and a controller configured to control individual flow rates of first and second solvents from the first and second solvent sources, respectively, to the desorption solvent conduit.
In accordance with various exemplary aspects of the present teachings, a system and method for performing chemical analysis is described (utilizing devices described herein by way of example), the method comprising: inserting the second end of the elongate member into the distal fluid chamber of the substrate sampling probe such that at least a portion of the inner capillary tube is disposed within the bore of the elongate member; flowing a first composition of desorption solvent comprising the first and second solvents into said desorption solvent conduit such that at least a first portion of said one or more analyte species is desorbed from the coated surface portion and delivered to the ion source probe within said desorption solvent via the sampling conduit; flowing a second composition of desorption solvent comprising the first and second solvents into said desorption solvent conduit, the second composition differing from the first composition, such that at least a second portion of said one or more analyte species is desorbed from the coated surface portion and delivered to the ion source probe within said desorption solvent via the sampling conduit; discharging said first and second compositions of desorption solvents containing said first and second portions of the one or more analyte species from said ion source probe so as to ionize said one or more analyte species; and performing mass spectrometric analysis on said one or more ionized analyte species.
In accordance with various exemplary aspects of the present teachings a system for analyzing a chemical composition of a specimen is provided, comprising: a substrate sampling probe comprising: an outer capillary tube extending from a proximal end to a distal end; and an inner capillary tube extending from a proximal end to a distal end and disposed within said outer capillary tube, wherein said distal end of the inner capillary tube is recessed relative to the distal end of the outer capillary tube so as to define a distal fluid chamber between the distal end of the inner capillary tube and the distal end of the outer capillary tube, wherein said inner and outer capillary tubes define a desorption solvent conduit and a sampling conduit in fluid communication with one another via said distal fluid chamber, said desorption solvent conduit extending from an inlet end configured to fluidly couple to a desorption solvent source through a pump to an outlet end in fluid communication with said distal fluid chamber, and said sampling conduit extending from an inlet end in fluid communication with said distal fluid chamber to an outlet end configured to fluidly couple to an ion source probe for discharging desorption solvent received at the inlet end of the sampling conduit into an ionization chamber in fluid communication with a sampling orifice of a mass spectrometer; a pair of electrodes positioned around the distal fluid chamber at a height that defines a desired liquid height, a controller operably connected to the pair of electrodes and the pump, the controller configured such that when a liquid height within the distal fluid chamber is reached, the controller receives a signal from the pair of electrodes that a circuit has been completed and the controller controls the pump so as the maintain the liquid height at the desired liquid height; and a substrate comprising an elongate member extending from a first end to a second end spaced apart from the first end by an outer surface, wherein the second end is sized and configured to be inserted within the distal fluid chamber, wherein the elongate member has a bore at least partially extending therethrough from the second end and defining an inner surface that is configured to at least partially surround the distal end of the inner capillary tube when the second end is inserted within the distal fluid chamber, and wherein at least a portion of said outer surface, said inner surface, and said second end of the elongate member comprises a surface coated with an extraction phase configured to adsorb one or more analyte species thereto.
These and other features of the applicant's teachings are set forth herein.
The skilled person in the art will understand that the drawings, described below, are for illustration purposes only. The drawings are not intended to limit the scope of the applicant's teachings in any way.
It will be appreciated that for clarity, the following discussion will explicate various aspects of embodiments of the applicant's teachings, while omitting certain specific details wherever convenient or appropriate to do so. For example, discussion of like or analogous features in alternative embodiments may be somewhat abbreviated. Well-known ideas or concepts may also for brevity not be discussed in any great detail. The skilled person will recognize that some embodiments of the applicant's teachings may not require certain of the specifically described details in every implementation, which are set forth herein only to provide a thorough understanding of the embodiments. Similarly it will be apparent that the described embodiments may be susceptible to alteration or variation according to common general knowledge without departing from the scope of the disclosure. The following detailed description of embodiments is not to be regarded as limiting the scope of the applicant's teachings in any manner.
In accordance with various aspects of the applicant's teachings, MS-based analytical systems and methods are provided herein in which a desorption solvent utilized in a sampling interface to desorb one or more analyte species from a substrate is fluidly coupled to an ion source for ionizing the one or more analyte species desorbed into the desorption solvent for subsequent mass spectrometric analysis (e.g., without a liquid chromatography (LC) column between the sampling interface and the ion source). Whereas current methods for ionizing liquid samples derived from SPME devices often utilize complex sample preparation steps in which the extracted analytes are first desorbed from the substrate and subsequently subject to additional sample processing steps (e.g., concentration/purification via LC) that may not be amenable to automation prior to ionization/mass spectrometric analysis, systems and methods in accordance with various aspects of the present teachings provide a simplified workflow in which the substrates having one or more analytes adsorbed thereon can be coupled directly to the ion source of an MS system. In various aspects, the systems and methods described herein can eliminate the need for one or more time-consuming sample preparation steps while enabling fast coupling of substrates to the MS system (and fast desorption therefrom), with minimal alterations to the front-end of known systems, while nonetheless maintaining sensitivity, simplicity, selectivity, speed, and throughput. Moreover, in various aspects, the present teachings can enable a fully- or partially-automated workflow, thereby further increasing throughput while potentially eliminating sources of human error in the analysis of extracted samples. As discussed in detail below, devices, methods, and systems in accordance with various aspects of the present teachings provide substrates and/or sampling interfaces optimized relative to one another so as to increase the sensitivity of the extraction-based workflow.
In various aspects, the substrate can occupy at least 20 percent of the fluid volume in the substrate-receiving port (i.e., less than 80% of the volume of the substrate-receiving port is occupied by desorption solvent), while maximizing the coated surface area of the substrate that can be disposed in contact with a flowing desorption solvent in the vicinity of a sampling conduit inlet. The portion of the substrate inserted into the substrate sampling probe can have a variety of shapes so as to increase the surface area of the substrate and thereby increase the amount of sample that can be desorbed by the desorption solvent in the distal fluid chamber. In some aspects, for example, the extraction phase coating can be formed on the outer surface of the substrate as well as on a concave inner surface (e.g., a bore) of the substrate that can surround the distal end of the inner capillary tube when the substrate is inserted through the distal end of the outer capillary tube. In various aspects, the outer surface of the substrate or the concave inner surface can be a substantially continuously curved surface having surface features (e.g., a plurality of protrusions) configured to increase the surface area of the coated surface so as to maximize the analytes desorbed in the vicinity of the inlet end of the sampling conduit.
In the depicted embodiment, the ionization chamber 12 can be maintained at an atmospheric pressure, though in some embodiments, the ionization chamber 12 can be evacuated to a pressure lower than atmospheric pressure. The ionization chamber 12, within which analytes desorbed from the substrate 20 and contained in the desorption solvent that is discharged from the electrospray electrode 44 can be ionized, is separated from a gas curtain chamber 14 by a plate 14a having a curtain plate aperture 14b. As shown, a vacuum chamber 16, which houses the mass analyzer 60, is separated from the curtain chamber 14 by a plate 16a having a vacuum chamber sampling orifice 16b. The curtain chamber 14 and vacuum chamber 16 can be maintained at a selected pressure(s) (e.g., the same or different sub-atmospheric pressures, a pressure lower than the ionization chamber) by evacuation through one or more vacuum pump ports 18.
The ion source 40 can have a variety of configurations but is generally configured to generate ions from analyte(s) contained within a liquid (e.g., the desorption solvent) that is received from the substrate sampling probe 30. In the exemplary embodiment depicted in
With continued reference to
It will also be appreciated by a person skilled in the art and in light of the teachings herein that the mass analyzer 60 can have a variety of configurations. Generally, the mass analyzer 60 is configured to process (e.g., filter, sort, dissociate, detect, etc.) sample ions generated by the ion source 40. By way of non-limiting example, the mass analyzer 60 can be a triple quadrupole mass spectrometer, or any other mass analyzer known in the art and modified in accordance with the teachings herein. It will further be appreciated that any number of additional elements can be included in the mass spectrometer system including, for example, an ion mobility spectrometer (e.g., a differential mobility spectrometer) that is configured to separate ions based on their mobility through a drift gas rather than their mass-to-charge ratio. Additionally, it will be appreciated that the mass analyzer 60 can comprise a detector that can detect the ions which pass through the analyzer 60 and can, for example, supply a signal indicative of the number of ions per second that are detected.
With reference now to
As shown in
In accordance with various aspects of the present teachings, at least a portion of the substrate 220 can be inserted through the open end of the substrate sampling probe 230 such that the coated surface of the substrate upon which one or more analyte species are adsorbed are disposed in the desorption solvent (e.g., the desorption solvent within the distal fluid chamber 235). As shown in
It will be appreciated that substrate sampling probes in accordance with the present teachings can have a variety of configuration and sizes, with the depiction of substrate sampling probe 230 of
In addition to the exemplary substrates described below with reference to
Though any known device can be used or modified to be used in the system 10 of
With reference to
Moreover, as shown in phantom in
Likewise, the bore 323 need not be circular but can have a variety of shapes corresponding, for example, to the shape of the inner capillary tube 234, which as noted above can be circular, elliptical, superelliptical (i.e., shaped like a superellipse), or even polygonal (e.g., square). Moreover, with reference to
With reference now to
In addition, in addition to the substrates depicted herein, such as one or more of the substrates containing a bore and a plurality of protrusions as otherwise described herein, it will be appreciated that these substrates can be modified by removal of the bore to create substrates comprising a solid core such as those depicted in
In this manner, the exemplary substrates described herein can expose a relatively large coated surface area for adsorption of the analytes within a sample, as well as dispose the coated surface area relatively close to the inlet end upon insertion of the substrate 320 into the sampling probe. Moreover, it will be appreciated that upon insertion of the substrate 320 such that the bore 321 surrounds the exemplary inner capillary tube 234 of
With reference now to
In accordance with various aspects of the present teachings, the system 710 can additionally provide for the rotation of the substrate (e.g., about its central longitudinal axis) while the coated surface of the substrate 720 disposed within the sample in element 706 and/or desorption solvent of the sampling probe 730 to improve the efficiency between the substrate 720 and the surrounding solution. It will be appreciated that the protrusions on the inner and/or outer surfaces of the substrate 720 as otherwise discussed herein can create turbulent flow within the sample, which can significantly improve the kinetics for sample extraction/desorption. By way of non-limiting example, a person skilled in the art would appreciate that the sample holder 702 and/or actuation mechanism 704 can be configured to rotate the substrate. Alternatively, with reference to
With reference now to
Though the exemplary sampling probe 30 is depicted in
In accordance with various aspects of the present teachings, the exemplary substrates disclosed herein can be utilized in a substrate sampling probe to effect a separation. In particular, a substrate having more than one analyte adsorbed thereto can be inserted into the opening of a substrate sampling probe into which solvent is flowing. A gradient can then be created in the solvent, which varies the composition of solvent flowing into the distal fluid chamber over time in either a continuous or step-wise fashion. Because the analytes adsorbed to the substrate can have various affinities for the different solvent compositions, the analytes will be desorbed at different times depending on the composition of the solvent present in the distal fluid chamber. Accordingly, the analytes can be extracted in a selective manner and introduced downstream for further analysis (e.g., into a mass spectrometer). In such exemplary aspects, the method and apparatus can perform a separation similar to that performed in LC, but without the added apparatus or sample preparation required. Moreover, the solvent compositions introduced into the open port probe can be similar to those that would be utilized in liquid chromatography. Indeed, in some aspects, the separation performed by the substrate sampling probe can be performed using substrates other than those described herein. For example, substrates such as those for example disclosed in U.S. Pat. No. 6,759,126, which is incorporated by reference herein, can be introduced into a substrate sampling probe with the solvent composition introduced into the distal fluid chamber being varied over time so as to cause selective desorption from the coating material during the elution gradient.
In various aspects, the separation can be performed by using two pumps, one pump for the delivery of high aqueous solvent and the other pump for delivery of high organic solvent with a controller controlling the pump and the flow rate of each solvent, which can in some aspects be continuously adjusted. The two streams can then be mixed together before being introduced into the distal fluid chamber or the substrate sampling probe. Unlike in an HPLC gradient in which the total flow rate of the combined streams are kept constant, the total flow rate with high aqueous solvent ratio is lower than the total flow rate with high organic solvent ratio when used with the substrate sampling probe due to the aspiration and nebulizing flow rate being viscosity dependent. That is, the flow rate of solvent leaving the distal fluid chamber through the sampling conduit can vary depending on viscosity—a lower aspiration flow rate for high viscosity solutions such as aqueous solvents. It will be appreciated that the relationship between flow rate and the solvent composition can be pre-determined before an actual run and/or be subject to real-time control by a feedback control mechanism.
In certain aspects, the separation can be performed utilizing a step gradient, which utilizes a single solvent inlet. Two streams from two different pumps (e.g., aqueous and organic) can be merged together before being introduced into the desorption solvent conduit. In this exemplary setup, the solvent composition is not continuously adjusted, but changes between several certain ratios (e.g., pure aqueous, 30:70 water/organic, 50:50 water/organic, 70:30 water/organic, pure organic). This allows the use of thicker stationary phase coatings and allows for complete elution of a targeted analyte before switching to the next solvent composition.
Now referring to
In addition to the use of an actuation mechanism 904 for controlling the movement of individual substrates 922 relative to the sampling probe 930 as otherwise described herein, the system 910 depicted in
In addition, the use of an acoustic dispenser for liquid sampling into the probe 930 can additionally enable the use of different carrier fluids (other than the desorption solvent otherwise discussed herein). For example, by using a carrier fluid that is immiscible with the sample, the acoustic dispenser can eject small aqueous sample droplets (e.g., as small as 2.5 nL) into the distal fluid chamber of the “upside-down” probe 930 and maintain the droplets concentration over the length of the transport line (e.g., sampling conduit) to the ion source due to the immiscibility between the sample and the carrier fluid, thereby preventing significant dilution of the liquid sample plug and providing a significantly sharper peak being detected at the mass spectrometer. By way of example, the carrier fluid can be mineral oils, Fluorinert, or other suitable liquids that are immiscible with the liquid sample. For example, while dilutions of about 1000× would be typical when using a transfer line of approximately 50 cm, by keeping the injected volume at 2.5 nL and reducing the transport line to about 10 cm using an “upside-down” configuration, sub-attomole detection limits can be obtained in a very short time frame (e.g., a few seconds) for each sample. It has been demonstrated that the MS signal generated from plugs of sample droplets within immiscible oil provide a sharp contrast between the leading and trailing edge of the sample plug, as described for example in an article entitled “Label free screening of enzyme inhibitors at femtomole scale using segmented flow electrospray ionization mass spectrometry,” authored by Sun et al. and published in Analytical Chemistry 84(13), 5794-5800 (2012), which is incorporated by reference in its entirety.
The section headings used herein are for organizational purposes only and are not to be construed as limiting. While the applicant's teachings are described in conjunction with various embodiments, it is not intended that the applicant's teachings be limited to such embodiments. On the contrary, the applicant's teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.
This application claims the benefit of priority from U.S. Provisional Application Ser. No. 62/692,274, filed on Jun. 29, 2018, the entire contents of which is incorporated by reference herein.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2019/055505 | 6/28/2019 | WO | 00 |
Number | Date | Country | |
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62692274 | Jun 2018 | US |