Surface sampling concentration and reaction probe
A method of analyzing a chemical composition of a specimen is described. The method can include providing a probe comprising an outer capillary tube and an inner capillary tube disposed co-axially within the outer capillary tube, where the inner and outer capillary tubes define a solvent capillary and a sampling capillary in fluid communication with one another at a distal end of the probe; contacting a target site on a surface of a specimen with a solvent in fluid communication with the probe; maintaining a plug volume proximate a solvent-specimen interface, wherein the plug volume is in fluid communication with the probe; draining plug sampling fluid from the plug volume through the sampling capillary; and analyzing a chemical composition of the plug sampling fluid with an analytical instrument. A system for performing the method is also described.
1. A method of analyzing a chemical composition of a specimen, comprising:
providing a probe comprising an outer capillary tube having an inner diameter H and an inner capillary tube disposed co-axially within said outer capillary tube, said inner and outer capillary tubes defining a solvent capillary and a sampling capillary in fluidic communication with one another at a distal end of the probe and h is a distance between a tip of said outer capillary tube and a tip of said inner capillary tube;
contacting a target site on a surface of a specimen with a solvent in fluid communication with said probe, said solvent forming a continuous liquid microjunction across the surface of the specimen spanning at least the inner diameter H of the outer capillary tube;
maintaining a plug volume proximate a solvent-specimen interface and within the liquid microjunction, the plug volume having a height less than h, wherein said plug volume is in fluid communication with said probe and wherein, during said maintaining step, a capillary ratio (h/H) exceeds 1.0;
draining plug sampling fluid from said plug volume through said sampling capillary; and
analyzing a chemical composition of said plug sampling fluid with an analytical instrument.
2. The method according to claim 1 , wherein said draining comprises modifying a sampling characteristic of said probe.
3. The method according to claim 2 , wherein said sampling characteristic is selected from the group consisting of (i) decreasing a distance between a tip of said outer capillary and a tip of said inner capillary, (ii) increasing said sampling capillary flow rate relative to said solvent capillary flow rate, and (iii) breaking a liquid junction between said specimen and said solvent in fluid communication with said probe.
4. The method according to claim 1 , wherein said specimen comprises a plurality of target sites, and said method further comprises:
repeating said contacting, maintaining, draining and analyzing steps for each of said plurality of target sites.
5. The method according to claim 4 , further comprising:
plotting a property of a chemical component for each of said plurality of target sites.
6. The method according to claim 1 , wherein said solvent comprises a reactant selected to react with a target analyte.
7. The method according to claim 1 , wherein said maintaining step lasts for at least 5 seconds.
8. The method according to claim 1 , further comprising, translating said probe from said target site to a second target site while said solvent remained in fluidic communication with said probe and with said surface of said specimen.
9. The method according to claim 8 , wherein said solvent in fluid communication remains in contact with each of said target site and said second target site for at least 5 seconds.
10. The method of claim 1 , wherein the capillary ratio is at least 1.5.
11. The method of claim 1 , wherein the capillary ratio is at least 1.75.
12. The method of claim 1 , wherein the capillary ratio is at least 2.0.
13. The method of claim 1 , wherein the capillary ratio is from 1.0 to 2.0.