Sampling probe with internal sampling for use in mass spectrometry systems and methods
MS-based methods and systems are provided herein in which a desorption solvent desorbs one or more analyte species from an SPME device within a sampling interface that is fluidly coupled to an ion source for subsequent mass spectrometric analysis. In accordance with various aspects of the applicants teachings, the sampling interface includes an internal sampling conduit that provides increased interaction between the desorption solvent and the sampling substrate, thereby improving mass transfer (e.g., increased extraction or desorption speed).
1. A system for analyzing a chemical composition of a specimen, comprising:
a substrate sampling probe comprising:
an inner tube extending from a proximal end to a distal end, said inner tube defining a sampling conduit extending from a distal inlet to a proximal outlet configured to fluidly couple to an ion source probe for discharging desorption solvent in an ionization chamber in fluid communication with a sampling orifice of a mass spectrometer;
an outer tube extending from a proximal end to a distal end and disposed about said inner tube, said outer tube defining a desorption solvent conduit extending from an proximal inlet configured to be in fluid communication with a desorption solvent source to a distal outlet,
wherein the distal end of the inner tube is disposed relative to the distal end of the outer tube so as to define a fluid chamber extending distally from the distal end of the inner tube to a liquid/air interface, wherein the fluid chamber is in fluid communication with the distal outlet of the desorption solvent conduit and the distal inlet of the sampling conduit,
wherein the sampling conduit comprises a sampling volume within the distal end of the inner tube adjacent to the fluid chamber, the sampling volume exhibiting a cross sectional area greater than a cross sectional area of a proximal portion of the sampling conduit, the sampling volume being configured to receive a coated surface of a sample substrate having one or more analyte species adsorbed thereto such that the coated surface is in contact with the desorption solvent within the sampling volume as the desorption solvent flows from the inlet of the desorption solvent conduit through the fluid chamber to the outlet of the sampling conduit.
2. The system of claim 1 , wherein a maximum fluid velocity through the sampling volume is lower than a maximum fluid velocity through the proximal portion of the sampling conduit when the coated surface of the sample substrate is not disposed within the sampling volume.
3. The system of claim 1 , wherein the distal end of the inner tube is recessed relative to the distal end of the outer tube such that the fluid chamber comprises a volume between the distal end of the inner tube and the distal end of the outer tube.
4. The system of claim 1 , wherein the sample substrate comprises a SPME substrate.
5. The system of claim 1 , wherein the sampling volume is sized such that the entire coated surface of the sample substrate may be disposed within the sampling volume.
6. The system of claim 1 , wherein the sampling volume exhibits a circular cross-sectional shape.
7. The system of claim 1 , wherein the sampling volume exhibits a rectangular cross-sectional shape.
8. The system of claim 1 , wherein a distal portion of the inner tube comprising the sampling volume is configured to be replaced with a second distal portion exhibiting a second sampling volume that is different in at least one of shape and cross-sectional area from the sampling volume.
9. The system of claim 1 , further comprising:
at least one desorption solvent source fluidly coupled to the inlet of the desorption solvent conduit; and
a pump mechanism for delivering the desorption solvent from the at least one desorption solvent source to the inlet of the desorption solvent conduit.
10. The system of claim 1 , further comprising an ion source probe, an ionization chamber, and a mass spectrometer system, wherein the ion source probe is in fluid communication with the outlet of the sampling conduit and comprises a terminal 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.
11. The system of claim 1 , further comprising a specimen holder configured to support the sample substrate; and
an actuation mechanism coupled to the specimen holder and configured to insert the sample substrate into the distal end of the outer tube such that the coated surface of said sample substrate is in contact with the desorption solvent within the sampling volume.
12. A method for performing chemical analysis, comprising:
inserting at least a portion of a sample substrate into an open end of a substrate sampling probe, said sample substrate having a surface coated with an extraction phase to which one or more analyte species are adsorbed, said substrate sampling probe comprising:
an inner tube extending from a proximal end to a distal end, said inner tube defining a sampling conduit extending from a distal inlet to a proximal outlet;
an outer tube extending from a proximal end to a distal end and disposed about said inner tube, said outer tube defining a desorption solvent conduit extending from a proximal inlet configured to be in fluid communication with a desorption solvent source,
wherein the distal end of the inner tube is disposed relative to the distal end of the outer tube so as to define a fluid chamber extending distally from the distal end of the inner tube to a liquid/air interface, wherein the fluid chamber is in fluid communication with the distal outlet of the desorption solvent conduit and the distal inlet of the sampling conduit, and
wherein the sampling conduit comprises a sampling volume within the distal end of the inner tube adjacent to the fluid chamber, the sampling volume exhibiting a cross sectional area greater than a cross sectional area of a proximal portion of the sampling conduit;
flowing said desorption solvent from the inlet of the desorption solvent conduit, through the fluid chamber, and to the outlet of the sampling conduit such that at least a portion of said one or more analyte species is desorbed from the coated surface and is delivered to ion source probe within said desorption solvent;
discharging said desorption solvent containing said portion 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.
13. The method of claim 12 , wherein inserting at least the portion of the sample substrate comprises disposing the coated surface into the sampling volume within the inner tube.
14. The method of claim 12 , further comprising inserting the sample substrate into a sample so as to adsorb said one or more analyte species contained within the sample to the coated surface.
15. The method of claim 12 , wherein performing mass spectrometric analysis comprises further comprising performing MRM3 quantitation.
16. The method of claim 12 , further comprising transmitting said one or more ionized analyte species through a differential mobility spectrometer prior to performing mass spectrometric analysis.
17. The method of claim 12 , further comprising replacing a distal portion of the inner tube with a second distal portion comprising a second sampling volume that is different in at least one of shape and cross-sectional area.
18. The method of claim 12 , wherein flowing said desorption solvent comprises providing an elution gradient to the sampling volume while the sample substrate is disposed within the sampling volume.
19. The method of claim 12 , wherein flowing said desorption solvent comprises adjusting the composition of the desorption solvent to which the sample substrate is exposed when disposed within the sampling volume.
20. The method of claim 12 , wherein a desorption solvent conduit volumetric flow rate is greater than a sampling volume volumetric flow rate such that at least a portion of said desorption solvent overflows from the distal end of the outer conduit when the sample substrate is inserted into the open end of a substrate sampling probe.