Patent Publication Number: US-2022221442-A1

Title: Sample dispenser including an internal standard and methods of use thereof

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. nonprovisional application Ser. No. 16/935,683, filed Jul. 23, 2020, which is a continuation of U.S. nonprovisional application Ser. No. 15/357,048, filed Nov. 21, 2016, which is a continuation of U.S. nonprovisional application Ser. No. 13/784,094, filed Mar. 4, 2013, which is a continuation-in-part of U.S. nonprovisional application Ser. No. 13/265,110, filed Jan. 31, 2012, which is a 35 U.S.C. § 371 national phase application of PCT/US2010/032881, filed Apr. 29, 2010, which claims the benefit of and priority to each of U.S. provisional patent application Ser. No. 61/174,215, filed Apr. 30, 2009, U.S. provisional patent application Ser. No. 61/246,707 filed Sep. 29, 2009, and U.S. provisional patent application Ser. No. 61/308,332, filed Feb. 26, 2010. The present application also claims the benefit of and priority to U.S. provisional application Ser. No. 61/608,944, filed Mar. 9, 2012. The content of each of application is incorporated by reference herein in its entirety. 
    
    
     GOVERNMENT SUPPORT 
     This invention was made with government support under RR031246 and GM103454 awarded by National Institutes of Health. The government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to a sample dispenser including an internal standard and methods of use thereof. 
     BACKGROUND 
     Quantitative analysis of complex mixtures using mass spectrometry is one of the most important territories in analytical chemistry. Each phase of the quantitative analysis procedure should be carefully optimized and precisely calibrated. Representative methods for quantitative analysis includes high-performance liquid chromatography-mass spectrometry (HPLC-MS) and gas chromatography-mass spectrometry (GC-MS). Both have been developed for decades and are already widely used for drug metabolism, biomarker discovery, protein/lipid study, environmental monitoring, food safety and forensic applications. A general procedure using a modern MS analysis system typically starts from sample preparation. Sample preparation typically involves analytes being concentrated, purified and extracted into pure solution, then chromatographically separated and analyzed using mass spectrometry in a successive manner. Either external standards or internal standards should be used for calibration. LC/GC-MS is a powerful method for quantitative analysis for complex mixtures, but is still labor intensive and time consuming, the operators also must be highly trained to use the instrument and to design and troubleshoot methods. 
     Elimination of sample preparation benefits MS analysis in quantitation, which has become a reality by using ambient ionization methods. Ambient analysis involves the interrogation of samples in their native environment to reduce the time required for analysis and to simplify the operations. One drawback is that analysis of untreated complex samples can lead to ion suppression, in which the detection of the analyte of interest is compromised due to the presence of other interfering chemicals. The sensitivity and reproducibility of the method can suffer due to these matrix effects. As in traditional quantitative MS analysis, the introduction of internal standards allows the best quantitative performance for ambient analysis. A problem with methods for introducing internal standards to samples is accurate reproducibility when dealing with small volumes. In such circumstance, using an air displacement pipette to transport sub-microliter liquid may result in a 12% error in pipetting accuracy, which is even worse for blood. Spiking internal standard into samples in a vial using pipetting and vortex mixing is not suitable either when dealing with microliter samples. 
     SUMMARY 
     The invention generally provides fluid dispensing devices and methods for quantitative analysis of trace compounds in small volumes of complex mixtures (˜1 μL). Dispensing devices of the invention generally have a fluid chamber in which at least a portion of an inner wall of the chamber is coated with internal standard on its inner surface. Fluid containing the analytes that is taken into the chamber mixes with the internal standard so that dispensed fluid includes the internal standard. The internal standard automatically mixes into the sample during this process and the volumes of the internal standard solution and sample are both regulated by the volume of the chamber. The precision in quantitation is not sensitive to the variations in volume of the chamber. Devices of the invention significantly improved quantitation accuracy for analysis of 1 μL samples using various analysis techniques, such as ambient ionization methods. 
     In certain aspects, the invention provides a fluid dispenser that includes a fluid chamber. A portion of an inner wall of the chamber includes an internal standard. The chamber is configured such that fluid introduced to the chamber must interact with the portion of the chamber wall that includes the internal standard prior to flowing through an outlet of the chamber. The dispenser also includes a member coupled to the chamber such that it can control movement of fluid within the chamber. Generally, the chamber outlet is also an inlet for the fluid, but devices of the invention are not limited to such a configuration. 
     The fluid chamber may be any chamber capable of holding a liquid. In certain embodiments, the chamber is an elongate tube, such as a capillary tube. Typically, the internal standard coats a portion of an inner wall of the tube. In certain embodiments, the internal standard coats an entirety of the inner walls of the tube. 
     The member is typically a device that controls movement through application of pneumatic pressure. Any exemplary member is a compressible hollow bulb, such as the bulb of a pipette. 
     Another aspect of the invention provides a method for dispensing fluid. The method generally involves providing a fluid dispenser including a fluid chamber, in which a portion of an inner wall of the chamber includes an internal standard, the chamber being configured such that fluid introduced to the chamber must interact with the portion of the chamber wall that includes the internal standard prior to flowing through an outlet of the chamber; and a member coupled to the chamber such that it can control movement of fluid within the chamber. A fluid sample is loaded into the dispenser. Once loaded, the sample is given time (e.g., a few seconds to a few minutes, to a few days) sufficient for the sample to interact with the internal standard such that internal standard is introduced into the sample. The sample now containing internal standard is dispensed through the outlet. The member may facilitate loading the sample into the dispenser, or dispensing the sample through the outlet. Although, in some embodiments, capillary action alone is enough to load the sample into the dispenser and to accomplish a majority of the dispensing. Accordingly, the member does not need to be solely responsible for the loading and the dispensing. 
     Dispensers of the invention may be used with any liquid to which an internal standard needs to be introduced. In certain embodiments, the internal standard is a body fluid, such as blood, urine, or serum. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a drawing of a sample solution being fed to a piece of paper for electrospray ionization.  FIG. 1B  is a drawing of a sample solution pre-spotted onto the paper and a droplet of solvent being subsequently supplied to the paper for electrospray ionization. 
         FIG. 2A  is a MS spectrum of heroin (concentration: 1 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 2B  is a MS/MS spectrum of heroin (concentration: 1 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). 
         FIG. 3A  is a MS spectrum of caffeine (concentration: 10 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 3B  is a MS/MS spectrum of caffeine (concentration: 10 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). 
         FIG. 4A  is a MS spectrum of benzoylecgonine (concentration: 10 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 4B  is a MS/MS spectrum of benzoylecgonine (concentration: 10 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). 
         FIG. 5A  is a MS spectrum of serine (concentration: 1 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 5B  is a MS/MS spectrum of serine (concentration: 100 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). 
         FIG. 6A  is a MS spectrum of peptide bradykinin2-9 (concentration: 10 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 6B  is a 
       MS/MS spectrum of bradykinin2-9 (concentration: 1 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). 
         FIG. 7A  is a MS/MS spectrum showing that heroin can be detected from whole blood sample by a “spot” method.  FIG. 7B  shows the MS/MS spectrum of the blood spot without heroin. 
         FIG. 8A  MS/MS spectrum shows heroin can be detected from raw urine sample by a “spot” method.  FIG. 8B  shows the MS/MS spectrum of the urine spot without heroin. 
         FIG. 9A  is a MS spectrum showing the caffeine detected from a cola drink without sample preparation.  FIG. 9B  is a MS spectrum showing caffeine detected from coffee powder. A paper slice was used to collect the coffee powder from a coffee bag by swabbing the surface. 
         FIGS. 10A and 10B  show MS spectra of urine analysis without sample preparation.  FIG. 10A  is a MS spectrum showing that caffeine was detected in urine from a person who consumed coffee.  FIG. 10B  is a MS spectrum showing that caffeine was not detected in urine from a person who had not consumed any coffee. 
         FIGS. 11A and 11B  are MS spectra showing the difference between peptide analysis (10 ppm of bradykinin 2-9) on ( FIG. 11A ) paper triangle and ( FIG. 11B ) PVDF membrane using the same parameters (˜2 kV, Solvent: MeOH:H 2 O=1:1). 
         FIGS. 12A-D  show direct MS spectra of plant tissues using sliced tissues of four kinds of plants. ( FIG. 12A ) Onion, ( FIG. 12B ) Spring onion, and two different leaves ( FIG. 12C ) and ( FIG. 12D ). 
         FIGS. 13A and 13B  show MS/MS spectra of Vitamin C.  FIG. 13A  direct analysis of onion without sample preparation.  FIG. 13B  using standard solution. 
         FIG. 14A  panel A is a picture showing dried blood spot analysis on paper; 0.4 μL of whole blood is applied directly to a triangular section of chromatography paper (typically height 10 mm, base 5 mm). A copper clip holds the paper section in front of the inlet of an LTQ mass spectrometer (Thermo Fisher Scientific, San Jose, Calif.) and a DC voltage (4.5 kV) is applied to the paper wetted with 10 μL methanol/water (1:1 v/v).  FIG. 14B  shows the molecular structure of imatinib (GLEEVEC) and paper spray tandem mass spectrum of 0.4 μL whole blood containing 4 μg/mL imatinib. Imatinib is identified and quantified (inset) by the MS/MS transition m/z 494→m/z 394 (inset).  FIG. 14C  shows a quantitative analysis of whole blood spiked with imatinib (62.5-4 μg/mL) and its isotopomers imatinib-d8 (1 μg/mL). Inset plot shows low concentration range. 
         FIG. 15  is a paper spray mass spectrum of angiotensin I solution. The inset shows an expanded view over the mass range 630-700. 
         FIG. 16  is a mass spectrum showing direct analysis of hormones in animal tissue by probes of the invention. 
         FIGS. 17A and 17B  are mass spectra showing direct analysis of human prostate tumor tissue and normal tissue. 
         FIG. 18  is a mass spectrum of whole blood spiked with 10 μg/mL atenolol. The data was obtained by combining systems and methods of the invention with a handheld mass spectrometer. 
         FIGS. 19A-19F  show mass spectra of cocaine sprayed from six different types of paper (Whatman filter paper with different pore sizes: ( FIG. 19A ) 3 μm, ( FIG. 19B ) 4-7 μm, ( FIG. 19C ) 8 μm, and ( FIG. 19D ) 11 μm, ( FIG. 19E ) glass fiber paper and ( FIG. 19F ) chromatography paper). The spray voltage was 4.5 kV. 
         FIG. 20A  shows a schematic setup for characterizing the spatial distribution of paper spray.  FIG. 20B  is a 2D contour plot showing the relative intensity of m/z 304 when the probe is moved in the x-y plane with respect to the inlet of the mass spectrometer.  FIG. 20C  is a graph showing signal duration of m/z 304 when loading cocaine solution on paper with different concentrations or volumes, or sealed by Teflon membrane. 
         FIGS. 21A-D  are a set of MS spectra of pure chemical solutions and their corresponding MS/MS spectra. Spectra were obtained for ( FIG. 21A ) serine, ( FIG. 21B ) methadone, ( FIG. 21C ) roxithromycin, and ( FIG. 21D ) bradykinin 2-9. 
         FIGS. 22A-G  are a set of mass spectra showing analysis of chemicals from complex mixtures and direct analysis from surfaces without sample preparation.  FIGS. 22A and 22B  are mass spectra of COCA-COLA (cola drink), which was directly analyzed on paper in both of ( FIG. 22A ) positive and ( FIG. 22B ) negative mode.  FIG. 22C -is a mass spectrum of caffeine.  FIG. 22D  is a mass spectrum of potassium benzoate.  FIG. 22E  is a mass spectrum of acesulfame potassium.  FIG. 22F  is a mass spectrum of caffeine detected from urine.  FIG. 22G  is a mass spectrum of heroin detected directly from a desktop surface after swabbing of the surface by probes of then invention. 
         FIG. 23A  shows images of a probe of the invention used for blood analysis. In this embodiment, the porous material is paper. The panel on the left is prior to spotting with whole blood. The panel in the middle is after spotting with whole blood and allowing the spot to dry. The panel on the right is after methanol was added to the paper and allowed to travel through the paper. The panel on the right shows that the methanol interacts with the blood spot, causing analytes to travel to the tip of the paper for ionization and analysis.  FIG. 23B  is a mass spectrum of Atenolol from whole blood.  FIG. 23C  is a mass spectrum of heroin from whole blood. 
         FIG. 24  shows analysis of two dyes, methylene blue (m/z 284) and methyl violet (m/z 358.5), separated by TLC. Dye mixture solution (0.1 μl of a 1 mg/mL solution) was applied onto the chromatography paper (4 cm×0.5 cm) and dried before TLC and paper spray MS analysis. 
         FIGS. 25A-E  show different shapes, thicknesses, and angles for probes of the invention.  FIG. 25A  shows sharpness.  FIG. 25B  shows angle of the tip.  FIG. 25C  shows thickness of the paper.  FIG. 25D  shows a device with multiple spray tips.  FIG. 25E  shows a DBS card with micro spray tips fabricated with sharp needles. 
         FIGS. 26A and 26B  are a set of mass spectra of imatinib from human serum using direct spray from a C4 zip-tip of conical shape. Human serum samples (1.5 μL each) containing imatinib were passed through the porous C4 extraction material three times and then 3 μL methanol was added onto the zip-tip with 4 kV positive DC voltage applied to produce the spray.  FIG. 26A  shows a MS spectrum for 5 μg/mL.  FIG. 26B  shows a MS/MS spectrum for 5 ng/mL. 
         FIG. 27A  is a picture showing different tip angles for probes of the invention. From left to right, the angles are 30, 45, 90, 112, 126 degree, respectively.  FIG. 27B  is a graph showing the effect of angle on MS signal intensity. All MS signals were normalized to the MS signal using the 90 degree tip. 
         FIG. 28A  is a picture of a high-throughput probe device of the invention.  FIG. 28B  shows spray from a single tip of the device into an inlet of a mass spectrometer.  FIG. 28C  is a set of mass spectra showing MS signal intensity in high-throughput mode. 
         FIG. 29A  is a schematic depicting a protocol for direct analysis of animal tissue using probes of the invention.  FIGS. 29B-29D  are mass spectra showing different chemicals detected in the tissue. 
         FIG. 30A  shows a mass spectral analysis of a dried serum spot on plain paper.  FIG. 30B  shows a mass spectrum analysis of a dried serum sport on paper preloaded with betaine aldehyde (BA) chloride.  FIG. 30C  shows a MS/MS analysis of reaction product [M+BA] +  (m/z 488.6). 
         FIGS. 31A and 31B  show MS/MS spectra recorded with modified ( FIG. 31A ) and unmodified ( FIG. 31B ) paper substrates. 
         FIG. 32  is a mass spectrum showing that ions can be generated using a negative ion source potential but positively charged ions are mass-analyzed. 
         FIG. 33A  is a schematic showing the design of a sample cartridge with volume control and overflowing vials. A soluble plug with internal standard chemical is used to block the bottom of the volume control vial.  FIG. 33B  shows a step-by-step process of applying blood samples onto the cartridge to prepare a dried blood spot on paper from a controlled volume of blood. 
         FIGS. 34A and 34B  show mass spectra of agrochemicals that are present on a lemon peel purchased from a grocery store and swabbed with paper. 
         FIG. 35  shows a design of a substrate for paper spray with multiple corners. The angle of the corner to be used for spray is smaller than that of other corners. 
         FIGS. 36A and 36B  show a spray tip fabricated on a piece of chromatography paper using SU-8 2010 photoresist.  FIG. 36C  shows a MS spectrum of methanol/water solution containing a mixture of asparagines. 
         FIG. 37A  shows a sampling glass capillary (0.4 mm I.D., about 8 mm long) that was prepared by filling it with an internal standard solution through capillary action and drying in air to form an internal standard coating on its inner surface.  FIG. 37B  is a schematic showing a glass capillary placed in the lower opening of a 1000 μL pipette tip.  FIG. 37C  is a schematic showing using sampling capillary to transfer finger-stick blood and to deposit it onto paper substrate to make a dried blood spot. 
         FIG. 38A  is a photograph showing sampling capillaries with different sampling volumes (from left to right, 1, 2, 4, 8 μL).  FIG. 38B  is a photograph showing blood samples collected in the sampling capillaries. The length of each capillary is noted. 
         FIG. 39A  shows Imatinib measurements in blood (1000, 200, 50 and 200 ng/mL for each set) using sampling capillaries of varied lengths. Capillaries are coated with imatinib-d8 (100 ng/mL) as internal standard. Dashed lines are theoretical concentrations. The RSDs of measured concentration of imatinib with each set of capillaries are noted (n=5).  FIG. 39B  shows the ratio of MS/MS ion current for imatinib (m/z 494→m/z 394, 200 ng/mL) to that for imatinib-D8 (m/z 502→m/z 394, 100 ng/mL) measured from DBS prepared with sampling capillaries (top) and pipetting pre-mixed samples (bottom). 
         FIG. 40A  shows array of blood spots prepared on chromatography paper using sampling capillaries. Paper triangles were cut out along the dash lines and used for paper spray ionization. RSD of the area of the blood spots: 7.7%, n=8.  FIG. 40B  shows analysis of imatinib in blood with sampling capillaries and paper spray ionization. Bovine blood (1 μL) was applied directly to chromatography paper with the capillary dispenser coated with 0.1 ng imatinib-d8 as internal standard. DC voltage (4.2 kV) was applied to the paper wetted with 35 μL spray solvent (acetonitrile/water, 90:10, v:v). Inset shows the low-concentration range. Error bars represent the standard deviation for at least three replicates. 
         FIG. 41A  shows quantitative analysis of complex mixtures with different ambient ionization methods. Dried sample spots prepared on non-porous materials. a) Analysis of atrazine in river water (10-500 ng/mL) using LTP, dried sample spot on PTFE.  FIG. 41B  shows analysis of cocaine in urine (33-1000 ng/mL) using DESI, dried sample spot prepared on a glass slide. 
         FIG. 42A  is a photograph showing that liquid samples with low viscosity (methanol solution, urine, serum) could be dispensed on paper using capillary action only. Array of samples prepared with blue dye in methanol solution were prepared with the dispensers.  FIG. 42B  is a photograph showing that blood was transferred on chromatography paper to form array of dried blood spots of different sizes.  FIG. 42C  is a graph showing area of sample spot (Pixel count obtained from ( FIG. 42B )) vs. capillary volume. 
     
    
    
     DETAILED DESCRIPTION 
     A new method of generating ions from fluids and solids for mass spectrometry analysis is described. Porous materials, such as paper (e.g. filter paper or chromatographic paper) or other similar materials are used to hold and transfer liquids and solids, and ions are generated directly from the edges of the material when a high electric voltage is applied to the material ( FIG. 1 ). The porous material is kept discrete (i.e., separate or disconnected) from a flow of solvent, such as a continuous flow of solvent. Instead, sample is either spotted onto the porous material or swabbed onto it from a surface including the sample. The spotted or swabbed sample is then connected to a high voltage source to produce ions of the sample which are subsequently mass analyzed. The sample is transported through the porous material without the need of a separate solvent flow. Pneumatic assistance is not required to transport the analyte; rather, a voltage is simply applied to the porous material that is held in front of a mass spectrometer. 
     In certain embodiments, the porous material is any cellulose-based material. In other embodiments, the porous material is a non-metallic porous material, such as cotton, linen wool, synthetic textiles, or plant tissue. In still other embodiments, the porous material is paper. Advantages of paper include: cost (paper is inexpensive); it is fully commercialized and its physical and chemical properties can be adjusted; it can filter particulates (cells and dusts) from liquid samples; it is easily shaped (e.g., easy to cut, tear, or fold); liquids flow in it under capillary action (e.g., without external pumping and/or a power supply); and it is disposable. 
     In certain embodiments, the porous material is integrated with a solid tip having a macroscopic angle that is optimized for spray. In these embodiments, the porous material is used for filtration, pre-concentration, and wicking of the solvent containing the analytes for spray at the solid type. 
     In particular embodiments, the porous material is filter paper. Exemplary filter papers include cellulose filter paper, ashless filter paper, nitrocellulose paper, glass microfiber filter paper, and polyethylene paper. Filter paper having any pore size may be used. Exemplary pore sizes include Grade 1 (11 μm), Grade 2 (8 μm), Grade 595 (4-7 μm), and Grade 6 (3 μm), Pore size will not only influence the transport of liquid inside the spray materials, but could also affect the formation of the Taylor cone at the tip. The optimum pore size will generate a stable Taylor cone and reduce liquid evaporation. The pore size of the filter paper is also an important parameter in filtration, i.e., the paper acts as an online pretreatment device. Commercially available ultra filtration membranes of regenerated cellulose, with pore sizes in the low nm range, are designed to retain particles as small as 1000 Da. Ultra filtration membranes can be commercially obtained with molecular weight cutoffs ranging from 1000 Da to 100,000 Da. 
     Probes of the invention work well for the generation of micron scale droplets simply based on using the high electric field generated at an edge of the porous material. In particular embodiments, the porous material is shaped to have a macroscopically sharp point, such as a point of a triangle, for ion generation. Probes of the invention may have different tip widths. In certain embodiments, the probe tip width is at least about 5 μm or wider, at least about 10 μm or wider, at least about 50 μm or wider, at least about 150 μm or wider, at least about 250 μm or wider, at least about 350 μm or wider, at least about 400μ or wider, at least about 450 μm or wider, etc. In particular embodiments, the tip width is at least 350 μm or wider. In other embodiments, the probe tip width is about 400 μm. In other embodiments, probes of the invention have a three dimensional shape, such as a conical shape. 
     As mentioned above, no pneumatic assistance is required to transport the droplets. Ambient ionization of analytes is realized on the basis of these charged droplets, offering a simple and convenient approach for mass analysis of solution-phase samples. 
     Sample solution is directly applied on the porous material held in front of an inlet of a mass spectrometer without any pretreatment. Then the ambient ionization is performed by applying a high potential on the wetted porous material. In certain embodiments, the porous material is paper, which is a type of porous material that contains numerical pores and microchannels for liquid transport. The pores and microchannels also allow the paper to act as a filter device, which is beneficial for analyzing physically dirty or contaminated samples. 
     In other embodiments, the porous material is treated to produce microchannels in the porous material or to enhance the properties of the material for use as a probe of the invention. For example, paper may undergo a patterned silanization process to produce microchannels or structures on the paper. Such processes involve, for example, exposing the surface of the paper to tridecafluoro-1,1,2,2-tetrahydrooctyl-1-trichlorosilane to result in silanization of the paper. In other embodiments, a soft lithography process is used to produce microchannels in the porous material or to enhance the properties of the material for use as a probe of the invention. In other embodiments, hydrophobic trapping regions are created in the paper to pre-concentrate less hydrophilic compounds. 
     Hydrophobic regions may be patterned onto paper by using photolithography, printing methods or plasma treatment to define hydrophilic channels with lateral features of 200˜1000 μm. See Martinez et al. ( Angew. Chem. Int. Ed.  2007, 46, 1318-1320); Martinez et al. ( Proc. Natl Acad. Sci. USA  2008, 105, 19606-19611); Abe et al. ( Anal. Chem.  2008, 80, 6928-6934); Bruzewicz et al. ( Anal. Chem.  2008, 80, 3387-3392); Martinez et al. ( Lab Chip  2008, 8, 2146-2150); and Li et al. ( Anal. Chem.  2008, 80, 9131-9134), the content of each of which is incorporated by reference herein in its entirety. Liquid samples loaded onto such a paper-based device can travel along the hydrophilic channels driven by capillary action. 
     Another application of the modified surface is to separate or concentrate compounds according to their different affinities with the surface and with the solution. Some compounds are preferably absorbed on the surface while other chemicals in the matrix prefer to stay within the aqueous phase. Through washing, sample matrix can be removed while compounds of interest remain on the surface. The compounds of interest can be removed from the surface at a later point in time by other high-affinity solvents. Repeating the process helps desalt and also concentrate the original sample. 
     Methods and systems of the invention use a porous material, e.g., paper, to hold and transport analytes for mass spectral analysis. Analytes in samples are pre-concentrated, enriched and purified in the porous material in an integrated fashion for generation of ions with application of a high voltage to the porous material. In certain embodiments, a discrete amount of transport solution (e.g., a droplet or a few droplets) is applied to assist movement of the analytes through the porous material. In certain embodiments, the analyte is already in a solution that is applied to the porous material. In such embodiments, no additional solvent need be added to the porous material. In other embodiments, the analyte is in a powdered sample that can be easily collected by swabbing a surface. Systems and methods of the invention allow for analysis of plant or animal tissues, or tissues in living organisms. 
     Methods and systems of the invention can be used for analysis of a wide variety of small molecules, including epinephrine, serine, atrazine, methadone, roxithromycin, cocaine and angiotensin I. All display high quality mass and MS/MS product ion spectra (see Examples below) from a variety of porous surfaces. Methods and systems of the invention allow for use of small volumes of solution, typically a few μL, with analyte concentrations on the order of 0.1 to 10 μg/mL (total amount analyte 50 pg to 5 ng) and give signals that last from one to several minutes. 
     Methods and systems of the invention can be used also for analysis of a wide variety of biomolecules, including proteins and peptides. Methods of the invention can also be used to analyze oligonucleotides from gels. After electrophoretic separation of oligonucleotides in the gel, the band or bands of interest are blotted with porous material using methods known in the art. The blotting results in transfer of at least some of the oligonucleotides in the band in the gel to the porous material. The porous material is then connected to a high voltage source and the oligonucleotides are ionized and sprayed into a mass spectrometer for mass spectral analysis. 
     Methods and systems of the invention can be used for analysis of complex mixtures, such as whole blood or urine. The typical procedure for the analysis of pharmaceuticals or other compounds in blood is a multistep process designed to remove as many interferences as possible prior to analysis. First, the blood cells are separated from the liquid portion of blood via centrifugation at approximately 1000×g for 15 minutes (Mustard, J. F.; Kinlough-Rathbone, R. L.; Packham, M. A.  Methods in Enzymology;  Academic Press, 1989). Next, the internal standard is spiked into the resulting plasma and a liquid-liquid or solid-phase extraction is performed with the purpose of removing as many matrix chemicals as possible while recovering nearly all of the analyte (Buhrman, D. L.; Price, P. I.; Rudewicz, P. J.  Journal of the American Society for Mass Spectrometry  1996, 7, 1099-1105). The extracted phase is typically dried by evaporating the solvent and then resuspended in the a solvent used as the high performance liquid chromatography (HPLC) mobile phase (Matuszewski, B. K.; Constanzer, M. L.; Chavez-Eng, C. M., Ithaca, N.Y., Jul. 23-25 1997; 882-889). Finally, the sample is separated in the course of an HPLC run for approximately 5-10 minutes, and the eluent is analyzed by electrospray ionization-tandem mass spectrometry (Hopfgartner, G.; Bourgogne, E.  Mass Spectrometry Reviews  2003, 22, 195-214). 
     Methods and systems of the invention avoid the above sample work-up steps. Methods and systems of the invention analyze a dried blood spots in a similar fashion, with a slight modification to the extraction procedure. First, a specialized device is used to punch out identically sized discs from each dried blood spot. The material on these discs is then extracted in an organic solvent containing the internal standard (Chace, D. H.; Kalas, T. A.; Naylor, E. W.  Clinical Chemistry  2003, 49, 1797-1817). The extracted sample is dried on the paper substrate, and the analysis proceeds as described herein. 
     Examples below show that methods and systems of the invention can directly detect individual components of complex mixtures, such as caffeine in urine, 50 pg of cocaine on a human finger, 100 pg of heroin on a desktop surface, and hormones and phospholipids in intact adrenal tissue, without the need for sample preparation prior to analysis (See Examples below). Methods and systems of the invention allow for simple imaging experiments to be performed by examining, in rapid succession, needle biopsy tissue sections transferred directly to paper. 
     Analytes from a solution are applied to the porous material for examination and the solvent component of the solution can serve as the electrospray solvent. In certain embodiments, analytes (e.g., solid or solution) are pre-spotted onto the porous material, e.g., paper, and a solvent is applied to the material to dissolve and transport the analyte into a spray for mass spectral analysis. 
     In certain embodiments, a solvent is applied to the porous material to assist in separation/extraction and ionization. Any solvents may be used that are compatible with mass spectrometry analysis. In particular embodiments, favorable solvents will be those that are also used for electrospray ionization. Exemplary solvents include combinations of water, methanol, acetonitrile, and THF. The organic content (proportion of methanol, acetonitrile, etc. to water), the pH, and volatile salt (e.g. ammonium acetate) may be varied depending on the sample to be analyzed. For example, basic molecules like the drug imatinib are extracted and ionized more efficiently at a lower pH. Molecules without an ionizable group but with a number of carbonyl groups, like sirolimus, ionize better with an ammonium salt in the solvent due to adduct formation. 
     In certain embodiments, a multi-dimensional approach is undertaken. For example, the sample is separated along one dimension, followed by ionization in another dimension. In these embodiments, separation and ionization can be individually optimized, and different solvents can be used for each phase. 
     In other embodiments, transporting the analytes on the paper is accomplished by a solvent in combination with an electric field. When a high electric potential is applied, the direction of the movement of the analytes on paper is found to be related to the polarity of their charged forms in solution. Pre-concentration of the analyte before the spray can also be achieved on paper by placing an electrode at a point on the wetted paper. By placing a ground electrode near the paper tip, a strong electric field is produced through the wetted porous material when a DC voltage is applied, and charged analytes are driven forward under this electric field. Particular analytes may also be concentrated at certain parts of the paper before the spray is initiated. 
     In certain embodiments, chemicals are applied to the porous material to modify the chemical properties of the porous material. For example, chemicals can be applied that allow differential retention of sample components with different chemical properties. Additionally, chemicals can be applied that minimize salt and matrix effects. In other embodiments, acidic or basic compounds are added to the porous material to adjust the pH of the sample upon spotting. Adjusting the pH may be particularly useful for improved analysis of biological fluids, such as blood. Additionally, chemicals can be applied that allow for on-line chemical derivatization of selected analytes, for example to convert a non-polar compound to a salt for efficient electrospray ionization. 
     In certain embodiments, the chemical applied to modify the porous material is an internal standard. The internal standard can be incorporated into the material and released at known rates during solvent flow in order to provide an internal standard for quantitative analysis. In other embodiments, the porous material is modified with a chemical that allows for pre-separation and pre-concentration of analytes of interest prior to mass spectrum analysis. 
     The spray droplets can be visualized under strong illumination in the positive ion mode and are comparable in size to the droplets emitted from a nano-electrospray ion sources (nESI). In the negative ion mode, electrons are emitted and can be captured using vapor phase electron capture agents like benzoquinone. Without being limited by any particular theory or mechanism of action, it is believed that the high electric field at a tip of the porous material, not the fields in the individual fluid channels, is responsible for ionization. 
     The methodology described here has desirable features for clinical applications, including neotal screening, therapeutic drug monitoring and tissue biopsy analysis. The procedures are simple and rapid. The porous material serves a secondary role as a filter, e.g., retaining blood cells during analysis of whole blood. Significantly, samples can be stored on the porous material and then analyzed directly from the stored porous material at a later date without the need transfer from the porous material before analysis. Systems of the invention allow for laboratory experiments to be performed in an open laboratory environment. 
     In other embodiments, the sample can be transferred using the capillary dispensers to substrates made from non-porous materials, such as PTFE or glass. 
     Incorporation by Reference 
     References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made throughout this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes. 
     Equivalents 
     Various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including references to the scientific and patent literature cited herein. The subject matter herein contains important information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and equivalents thereof. 
     EXAMPLES 
     The following examples are intended to further illustrate certain embodiments of the invention, and are not to be construed to limit the scope of the invention. Examples herein show that mass spectrometry probes of the invention can ionize chemical and biological samples, allowing for subsequent mass analysis and detection. An exemplary probe was constructed as a paper triangle, which was used to generate micron scale droplets by applying a high potential on the paper. The analytes were ionized from these electrically charged droplets and transported into a conventional mass spectrometer. 
     Examples below show that a wide range of samples could be directly analyzed in the ambient environment by probes of the invention in both of pure state and complex mixtures. The results showed that paper-based spray has the following benefits: it operated without sheath gas, i.e. , few accessories were required for in situ analysis; biological samples (dried blood, urine) could be stored on the precut filter papers for months before analysis; filter paper minimized matrix effects seen with electrospray or nano electrospray in many samples (blood cells, salt and proteins) and enhanced the MS signal of chemicals in complex samples; 
     powdered samples were easily collected by swabbing surfaces using paper pieces and then directly analyzed; the paper could be pretreated to contain internal standards that were released at known rates during solvent flow in quantitative analysis; and the paper could be pretreated to contain matrix suppression or absorption sites or to perform ion exchange or to allow on-line chemical derivatization of selected analytes. 
     Detection of most analytes was achieved as low as ppb levels (when examined as solutions) or in the low ng to pg range (when solids were examined) and the detection time was less than one minute. Certain Examples below provide a protocol for analyzing a dried blood spot, which can also be used for in situ analysis of whole blood samples. The dried blood spot method is also demonstrated to be compatible with the storage and transport of blood sample for blood screening and other clinical tests. 
     Devices of the invention integrated the capabilities of sampling, pre-separation, pre-concentration and ionization. Methods and systems of the invention simplify the problem of sample introduction in mass analyzers. 
     Example 1: Construction of an MS Probe 
     Filter paper was cut into triangular pieces with dimensions of 10 mm long and 5 mm wide and used as a sprayer ( FIG. 1 ). A copper clip was attached to the paper, and the paper was oriented to face an inlet of a mass spectrometer ( FIG. 1 ). The copper clip was mounted on a 3D moving stage to accurately adjust its position. A high voltage was applied to the copper clip and controlled by a mass spectrometer to generate analyte ions for mass detection. 
     Samples were directly applied to the paper surface that served as a sample purification and pre-concentration device. Filter paper allowed liquid samples to move through the hydrophilic network driven by capillary action and electric effects and to transport them to the tip of the paper. Separation could take place during this transport process. Sample solution was sprayed from the tip and resulted in ionization and MS detection when a high voltage (˜4.5 kV) was applied to the paper surface. 
     All experiments were carried out with a Finnigan LTQ mass spectrometer (Thermo Electron, San Jose, Calif.). The typical temperature of the capillary inlet was set at 150° C. while 30° C. for heroin detection. The lens voltage was set at 65 V for sample analysis and 240 V for survival yield experiment. Tandem mass spectra were collected using collision-induced dissociation (CID) to identify analytes in tested samples, especially for complex mixtures and blood samples. 
     Example 2: Spray Generation 
     Spray was produced by applying a high potential on the wetted paper triangle. One paper triangle was placed in front of the inlet of LTQ with its sharp tip facing to the inlet, separated by 3 mm or more. Typically, 10 uL sample solution was applied to wet the paper triangle. The solution can wet or saturate the paper or form a thin layer of liquid film on the surface of the paper. A high potential (3-5 kV) was applied between the paper triangle and mass inlet to generate an electric field, which induced a charge accumulation on the liquid at the tip of paper triangle. The increasing coulombic force breaks the liquid to form charged droplets and then the solvent evaporated during the flight of droplets from the paper tip to the mass analyzer. Paper spray required no sheath gas, heating or any other assistance to remove the solvent. 
     When liquid accumulated on the paper triangle, a Taylor cone was observed at the tip when examined with a microscope. The droplets formed were clearly visible under strong illumination. The Taylor cone and visible spray disappeared after a short time of evaporation and spray. However, the mass signal lasted for a much longer period (several minutes). This revealed that the paper triangle could work in two modes for mass analysis. In a first mode, the liquid was transported inside the paper at a rate faster than the liquid could be consumed as spray at the paper tip, resulting in a large cone being formed at the paper tip and droplets being generated. In a second mode, the liquid transport inside the paper was not able to move at a rate fast enough to keep up with the spray consumption, and droplets were not visible. However, it was observed that ionization of analytes did take place. The first mode provided ESI like mass spectra and the second mode provided spectra with some of the features APCI spectra. In the latter case, the paper triangle played a role analogous to a conductive needle to generate a high electric field to ionize the molecules in the atmosphere. It was observed that the mass signal in the first mode was stronger than the mass signal in the second mode by approximately two orders of magnitude under the conditions and for the samples tested. 
     Example 3: Probe Considerations 
     Probe Materials 
     A number of porous materials were tested to generate charged droplets for mass spectrometry. The materials were shaped into triangles having sharp tips and sample solution was then applied to the constructed probes. Data herein show that any hydrophilic and porous substrate could be used successfully, including cotton swab, textile, plant tissues as well as different papers. The porous network or microchannels of these materials offered enough space to hold liquid and the hydrophilic environment made it possible for liquid transport by capillary action. Hydrophobic and porous substrates could also be used successfully with properly selected hydrophobic solvents. 
     For further investigation, six kinds of commercialized papers were selected and qualitatively tested to evaluate their capabilities in analyte detection. Filter papers and chromatography paper were made from cellulose, while glass microfiber filter paper was made from glass microfiber.  FIG. 19  shows the mass spectra of cocaine detection on those papers. The spectrum of glass fiber paper ( FIG. 19E ) was unique because the intensity of background was two orders of magnitude lower than other papers and the cocaine peak (m/z, 304) could not be identified. 
     It was hypothesized that the glass fiber paper was working on mode II and prohibiting efficient droplet generation, due to the relative large thickness (˜2 mm). This hypothesis was proved by using a thin layer peeled from glass fiber paper for cocaine detection. In that case, the intensity of the background increased and a cocaine peak was observed. All filter papers worked well for cocaine detection, ( FIGS. 19A-19D ). Chromatography paper showed the cleanest spectrum and relative high intensity of cocaine ( FIG. 19F ). 
     Probe Shape and Tip Angle 
     Many different probe shapes were investigated with respect to generating droplets. A preferred shape of the porous material included at least one tip. It was observed that the tip allowed ready formation of a Taylor cone. A probe shape of a triangle was used most often. As shown in  FIGS. 25A-25C , the sharpness of the tip, the angle of the tip ( FIGS. 27A-25B ), and the thickness of the paper substrate could effect the spray characteristics. The device of a tube shape with multiple tips ( FIG. 25 -D) is expected to act as a multiple-tip sprayer, which should have improved spray efficiency. An array of micro sprayers can also be fabricated on a DBS card using sharp needles to puncture the surface ( FIG. 25E ). 
     Example 4: Configuration of Probe with Inlet of a Mass Spectrometer 
     A paper triangle was mounted on a 2D moving stage to determine how the mass signal was affected by the relative positions of the paper triangle and the mass spectrometer inlet. The paper triangle was moved 8 cm in the y-direction in a continuous manner and 3 cm in the x-direction with a 2 mm increment for each step ( FIG. 20A ). Cocaine solution (1 ug/mL, methanol/water, 1:1 v/v) was continuously fed onto the paper surface. The mass spectrum was continuously recorded during the entire scan. A contour plot of the peak intensity of protonated cocaine (m/z, 304) was created from the normalized data extracted from the mass spectrum ( FIG. 20B ). The contour plot shows that it was not necessary for the paper triangle to be placed directly in-line with the inlet of the mass spectrometer to generate droplets. 
     Spray duration was also tested ( FIG. 20C ). Paper triangles (size 10 mm, 5 mm) were prepared. First, 10 uL solutions were applied on the paper triangles with different concentration of 0.1, 1 and 10 ug/mL. The spray time for each paper was just slightly varied by the difference of concentration. After that, 1 ug/mL cocaine solutions were applied on the paper triangles with different volumes of 5 uL, 10 uL and 15 uL. The spray times showed a linear response followed by the increasing sample volumes. 
     In another test, the paper was sealed with a PTFE membrane to prevent evaporation of solution, which prolonged the spray time by about three times. These results indicate that paper spray offers long enough time of spray for data acquisition even using 5 uL solution, and the intensity of signal is stable during the entire spray period. 
     Example 5: Separation and Detection 
     Probes of the invention include a porous material, such as paper, that can function to both separate chemicals in biological fluids before in situ ionization by mass spectrometry. In this Example, the porous material for the probe was chromatography paper. As shown in  FIG. 24 , a mixture of two dyes was applied to the paper as a single spot. The dyes were first separated on the paper by TLC (thin layer chromatograph) and the separated dyes were examined using MS analysis by methods of the invention with the paper pieces cut from the paper media ( FIG. 24 ). Data show the separate dyes were detected by MS analysis ( FIG. 24 ). 
     The chromatography paper thus allowed for sample collection, analyte separation and analyte ionization. This represents a significant simplification of coupling chromatography with MS analysis. Chromatography paper is a good material for probes of the invention because such material has the advantage that solvent movement is driven by capillary action and there is no need for a syringe pump. Another advantage is that clogging, a serious problem for conventional nanoelectrospray sources, is unlikely due to its multi-porous characteristics. Therefore, chromatography paper, a multi-porous material, can be used as a microporous electrospray ionization source. 
     Example 6: Pure Compounds: Organic Drugs, Amino Acids, and Peptides 
     As already described, probes and methods of the invention offer a simple and convenient ionization method for mass spectrometry. Paper triangles were spotted with different compounds and connected to a high voltage source to produce ions. All experiments were carried out with a Finnigan LTQ mass spectrometer (Thermo Electron, San Jose, Calif.). Data herein show that a variety of chemicals could be ionized in solution phase, including amino acid, therapeutic drugs, illegal drugs and peptides. 
       FIG. 2A  shows an MS spectrum of heroin (concentration: 1 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 2B  shows MS/MS spectrum of heroin (concentration: 1 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). 
       FIG. 3A  shows MS spectrum of caffeine (concentration: 10 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 3B  shows MS/MS spectrum of caffeine (concentration: 10 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). Peak 167 also exists in the blank spectrum with solvent and without caffeine. 
       FIG. 4A  shows MS spectrum of benzoylecgonine (concentration: 10 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 4B  shows MS/MS spectrum of benzoylecgonine (concentration: 10 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). 
       FIG. 5A  shows MS spectrum of serine (concentration: 1 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 5B  shows MS/MS spectrum of serine (concentration: 100 ppb, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). Peak 74 and 83 also exist in the blank spectrum with solvent and without serine.  FIG. 21A  shows MS spectrum of serine (m/z, 106) using probes of the invention.  FIG. 21A  also shows MS/MS spectrum of serine (m/z, 106). 
       FIG. 21B  shows MS spectrum of methadone (m/z, 310) using probes of the invention.  FIG. 21B  also shows MS/MS spectrum of methadone (m/z, 310).  FIG. 21C  shows MS spectrum of roxithromycin (m/z, 837) using probes of the invention.  FIG. 21B  also shows 
     MS/MS spectrum of roxithromycin (m/z, 837). 
       FIG. 6A  shows MS spectrum of peptide bradykinin2-9 (concentration: 10 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)) using probes of the invention.  FIG. 6B  shows MS/MS spectrum of bradykinin2-9 (concentration: 1 ppm, volume: 10 μl, solvent: MeOH/H 2 O/HOAc (50:49:1, v/v/v)). The hump in the spectrum is assumed to be caused by polymers, such as polyethylene glycol (PEG), which are frequently added to materials in industry.  FIG. 21 d    shows MS spectrum of bradykinin 2-9 (m/z, 453) using probes of the invention.  FIG. 21D  also shows MS/MS spectrum of bradykinin 2-9 (m/z, 453).  FIG. 21D  further shows adduct ions [M+H] (m/z, 904), [M+2H] 2+  (m/z, 453), [M+H+Na] 2+  (m/z, 464) and [M+2Na] 2+  (m/z, 475). The m/z 453 peak was double charged adduct ion confirmed by the MS/MS spectrum. 
       FIG. 11  is an MS spectra showing the difference between peptide analysis (10 ppm of bradykinin 2-9) on ( FIG. 11A ) paper slice and ( FIG. 11B ) PVDF membrane using the same parameters (˜2 kV, Solvent: MeOH:H 2 O=1:1). 
     Data herein show that probes of the invention work well over the mass/charge range from 50 to over 1000 for detection of pure compounds. Data further shows that detection was achieved down to as low as 1 ng/mL for most chemicals, including illegal drugs, such as heroin, cocaine and methadone. 
     Example 7: Complex Mixtures 
     Complex mixtures such as urine, blood, and cola drink were examined using methods, devices, and systems of the invention. All experiments were carried out with a Finnigan LTQ mass spectrometer (Thermo Electron, San Jose, Calif.). 
       FIG. 7A  shows an MS/MS spectrum that shows that heroin was detected from whole blood sample by a “spot” method. 0.4 μl of whole blood sample containing 200 ppb heroin was applied on the center of the triangle paper to form a 1 mm 2  blood spot. After the spot was dry, 10 μl of solvent (MeOH/H 2 O/HOAc (50:49:1, v/v/v)) was applied to the rear end of the triangle paper. Due to the capillary effect, the solvent moved forward and dissolved the chemicals in the blood spot. Finally, electrospray occurred when the solvent reached the tip of the paper. To demonstrate the effectiveness of the “blood spot” method mentioned above, the whole blood was added on the paper for electrospray directly. MS/MS spectrum showed that heroin was not detected from 10 μl of whole blood sample, even when the concentration was as high as 20 ppm ( FIG. 7B ). 
       FIG. 8A  shows an MS/MS spectrum that shows that heroin can be detected from raw urine sample by a “spot” method. 0.4 μl of raw urine sample containing 100 ppb heroin was applied on the center of the triangle paper to form a 1 mm 2  urine spot. After the spot was dry, 10 μl of solvent (MeOH/H 2 O/HOAc (50:49:1, v/v/v)) was applied to the rear end of the triangle paper. Due to the capillary effect, the solvent moved forward and dissolved the chemicals in the blood spot. Finally, electrospray occurred when the solvent reached the tip of the paper. To demonstrate the effectiveness of the “spot” method mentioned above, the raw urine was added on the paper for electrospray directly. MS/MS spectrum showed heroin was not detected from 10 μl of raw urine sample when concentration was 100 ppb ( FIG. 8B ). 
       FIG. 9A  is an MS spectrum showing that caffeine was detected from a cola drink without sample preparation.  FIG. 9B  is an MS spectrum showing that caffeine was detected from coffee powder. A paper triangle was used to collect the coffee powder from a coffee bag by swabbing the surface. 
       FIGS. 22A and 22B  show the spectra of COCA-COLA (cola drink), analyzed in positive mode and negative mode, respectively. The peak of protonated caffeine, m/z 195, identified in MS/MS spectrum, was dominated in the mass spectrum in positive mode due to the high concentration of caffeine (100 ug/mL) in this drink ( FIG. 22C ). Two high concentrated compounds, potassium benzoate and acesulfame potassium were identified in the MS/MS spectrum in negative mode ( FIGS. 22D-22E ). 
       FIG. 22F  shows spectra of caffeine in urine from a person who had drunk COCA-COLA (cola drink) two hours before the urine collection. Urine typically contains urea in very high concentration, which is also easily ionized. Therefore, protonated urea [m/z, 61] and urea dimmer [m/z, 121] dominated the MS spectrum. However, the protonated caffeine was identified in the MS/MS spectrum, which showed good signal to noise ratio in the urine sample. 
       FIGS. 10A and 10B  show MS spectra of urine taken for analysis without sample preparation.  FIG. 10A  is a mass spectra of caffeine that was detected in urine from a person who had consumed coffee.  FIG. 10B  is a mass spectra showing that caffeine was not detected in urine from a person who had not consumed any coffee. 
       FIG. 22G  shows the MS spectrum of heroin (m/z, 370) collected as a swabbed sample. A 5 uL solution containing 50 ng heroin was spotted on a 1 cm 2  area of a desktop. The paper triangle was wetted and used to swab the surface of the desktop. The paper triangle was then connected to the high voltage source for mass detection. This data shows that probes of the invention can have dual roles of ionization source as well as a sampling device for mass detection. Trace sample on solid surface could be simply collected by swabbing the surface using probes of the invention. Dust and other interferences were also collected on the paper triangle, but the heroin could be directly detected from this complex matrix. 
     Example 8: Plant Tissue Direct Analysis by ESI without Extraction 
       FIGS. 12A-D  show] direct MS spectra of plant tissues using sliced tissues of four kinds of plants. ( FIG. 12A ) Onion, ( FIG. 12B ) Spring onion, and two different leaves ( FIG. 12C ) and ( FIG. 12D ). 
       FIGS. 13A and 13B  show an MS/MS spectra of Vitamin C analysis ( FIG. 13A ) direct analysis of onion without sample preparation, ( FIG. 13B ) using standard solution. 
     Example 9: Whole Blood and Other Biofluids 
     Body fluids, such as plasma, lymph, tears, saliva, and urine, are complex mixtures containing molecules with a wide range of molecular weights, polarities, chemical properties, and concentrations. Monitoring particular chemical components of body fluids is important in a number of different areas, including clinical diagnosis, drug development, forensic toxicology, drugs of abuse detection, and therapeutic drug monitoring. Tests of blood, including the derived fluids plasma and serum, as well as on urine are particularly important in clinical monitoring. 
     A wide variety of chemicals from blood are routinely monitored in a clinical setting. Common examples include a basic metabolic panel measuring electrolytes like sodium and potassium along with urea, glucose, and creatine and a lipid panel for identifying individuals at risk for cardiovascular disease that includes measurements of total cholesterol, high density lipoprotein (HDL), low density lipoprotein (LDL), and triglycerides. Most laboratory tests for chemicals in blood are actually carried out on serum, which is the liquid component of blood separated from blood cells using centrifugation. This step is necessary because many medical diagnostic tests rely on colorimetric assays and therefore require optically clear fluids. After centrifugation, detection of the molecule of interest is carried in a number of ways, most commonly by an immunoassay, such as an enzyme-linked immunosorbent assay (ELISA) or radioimmunoassay (RIA), or an enzyme assay in which the oxidation of the molecule of interest by a selective enzyme is coupled to a reaction with a color change, such as the tests for cholesterol (oxidation by cholesterol oxidase) or glucose (oxidation by glucose oxidase). 
     There is considerable interest in the pharmaceutical sciences in the storage and transportation of samples of whole blood as dried blood spots on paper (N. Spooner et al.  Anal Chem.,  2009, 81, 1557). Most tests for chemicals found in blood are carried out on a liquid sample, typically serum or plasma isolated from the liquid whole blood. The required storage, transportation, and handling of liquid blood or blood components present some challenges. While blood in liquid form is essential for some tests, others can be performed on blood or other body fluids that have been spotted onto a surface (typically paper) and allowed to dry. 
     Probes and methods of the invention can analyze whole blood without the need for any sample preparation. The sample was prepared as follows. 0.4 uL blood was directly applied on the center of paper triangle and left to dry for about 1 min. to form a dried blood spot ( FIG. 23A ). 10 uL methanol/water (1:1, v/v) was applied near the rear end of the paper triangle. Driven by capillary action, the solution traveled across the paper wetting it throughout its depth. As the solution interacted with the dried blood spot, the analytes from the blood entered the solution and were transported to the tip of the probe for ionization ( FIG. 23A ). The process of blood sample analysis was accomplished in about 2 min. 
     Different drugs were spiked into whole blood and the blood was applied to probes of the invention as described above. Detection of different drugs is described below. 
     Imatinib (GLEEVEC), a 2-phenylaminopyrimidine derivative, approved by the FDA for treatment of chronic myelogenous leukemia, is efficacious over a rather narrow range of concentrations. Whole human blood, spiked with imatinib at concentrations including the therapeutic range, was deposited on a small paper triangle for analysis ( FIG. 14A ). The tandem mass spectrum (MS/MS,  FIG. 14B ) of protonated imatinib, m/z 494, showed a single characteristic fragment ion. Quantitation of imatinib in whole blood was achieved using this signal and that for a known concentration of imatinib-d8 added as internal standard. The relative response was linear across a wide range of concentrations, including the entire therapeutic range ( FIG. 14C ). 
     Atenolol, a β-blocker drug used in cardiovascular diseases, was tested using the dried blood spot method to evaluate paper spray for whole blood analysis. Atenolol was directly spiked into whole blood at desired concentrations and the blood sample was used as described above for paper spray. The protonated atenolol of 400 pg (1 ug/mL atenolol in 0.4 uL whole blood) in dried blood spot was shown in mass spectra, and the MS/MS spectra indicated that even 20 pg of atenolol (50 ug/mL atenolol in 0.4 uL whole blood) could be identified in the dried blood spot ( FIG. 23B ). 
       FIG. 23C  is a mass spectra of heroin in whole blood. Data herein show that 200 pg heroin in dried blood spot could be detected using tandem mass. 
     It was also observed that the paper medium served a secondary role as a filter, retaining blood cells. Significantly, samples were analyzed directly on the storage medium rather than requiring transfer from the paper before analysis. All experiments were done in the open lab environment. Two additional features indicated that the methodology had the potential to contribute to increasing the use of mass spectrometry in primary care facilities: blood samples for analysis were drawn by means of a pinprick rather than a canula; and the experiment was readily performed using a handheld mass spectrometer ( FIG. 18  and Example 10 below). 
     Example 10: Handheld Mass Spectrometer 
     Systems and methods of the invention were compatible with a handheld mass spectrometer. Paper spray was performed using a handheld mass spectrometer (Mini 10, custom made at Purdue University). Analysis of whole blood spiked with 10 μg/mL atenolol. Methanol/water (1:1; 10 μL) was applied to the paper after the blood (0.4 uL) had dried (˜1 min) to generate spray for mass detection ( FIG. 18 ). The inset shows that atenolol could readily be identified in whole blood using tandem mass spectrum even when the atenolol amount is as low as 4 ng. 
     Example 11: Angiotensin I 
       FIG. 15  is a paper spray mass spectrum of angiotensin I solution (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu (SEQ ID NO: 1), 10 μL, 8 μg/mL in methanol/water, 1:1, v/v) on chromatography paper (spray voltage, 4.5 kV). The inset shows an expanded view over the mass range 630-700. The protonated ([M+2H] 2+ ) and sodium-adduct ions ([M+H+Na] 2+ , [M+2Na] 2+ ) are the major ionic species. 
     Example 12: Agrochemicals on Fruit 
     Sample collection by paper wiping followed by analysis using probes of the invention was used for fast analysis of agrochemicals on fruit. Chromatography paper (3×3 cm) wetted with methanol was used to wipe a 10 cm 2  area on the peel of a lemon purchased from a grocery store. After the methanol had dried, a triangle was cut from the center of the paper and used for paper spray by applying 10 μL methanol/water solution. The spectra recorded ( FIG. 34A-34B ) show that a fungicide originally on the lemon peel, thiabendazole (m/z 202 for protonated molecular ion and m/z 224 for sodium adduct ion), had been collected onto the paper and could be identified easily with MS and confirmed using MS/MS analysis. Another fungicide imazalil (m/z 297) was also observed to be present. 
     Example 13: Tumor Sample 
     Systems and methods of the invention were used to analyze human prostate tumor tissue and normal tissue. Tumor and adjacent normal tissue sections were 15 μm thick and fixed onto a glass slide for an imaging study using desorption electrospray ionization (DESI). A metal needle was used to remove a 1 mm 2 ×15 μm volume of tissue from the glass slide from the tumor region and then from the normal region and place them onto the surface of the paper triangle for paper spray analysis. 
     A droplet of methanol/water (1:1 v:v; 10 μl) was added to the paper as solvent and then 4.5 kV positive DC voltage applied to produce the spray. Phospholipids such as phosphatidylcholine (PC) and sphingomyelin (SM) were identified in the spectrum ( FIG. 17A-17B ). The peak of [PC(34:1)+K] +  at m/z 798 was significantly higher in tumor tissue and peaks [SM(34:1)+Na] +  at m/z 725, [SM(36:0)+Na] +  at m/z 756, and [SM(36:4)+Na] +  at m/z 804 were significantly lower compared with normal tissue. 
     Example 14: Therapeutic Drug Monitoring 
     The administration of a drug depends on managing the appropriate dosing guidelines for achievement of a safe and effective outcome. This guideline is established during clinical trials where the pharmacokinetics (PK) and pharmacodynamics (PD) of the drug are studied. Clinical trials use PK-PD studies to establish a standard dose, which may be fixed or adjusted according formulas using variables like body mass, body surface area, etc. However, the drug exposure, i.e. the amount of drug circulating over time, is influenced by a number of factors that vary from patient to patient. For example, an individuals&#39; metabolic rate, the type and level of plasma proteins, and pre-existing conditions such as renal and/or hepatic impairment all play a role in affecting the exposure of the drug in vivo. Further, administration of a drug in combination with other medications may also affect exposure. As a result, it is often difficult to predict and prescribe an optimum regimen of drug administration. 
     Over- or underexposure to a drug can lead to toxic effects or decreased efficacy, respectively. To address these concerns, therapeutic drug monitoring (TDM) can be employed. TDM is the measurement of active drug levels in the body followed by adjustment of drug dosing or schedules to increase efficacy and/or decrease toxicity. TDM is indicated when the variability in the pharmacokinetics of a drug is large relative to the therapeutic window, and there is an established relationship between drug exposure and efficacy and/or toxicity. Another requirement for TDM is that a sufficiently precise and accurate assay for the active ingredient must be available. Immunoassays and liquid chromatography mass spectrometry (LC-MS) are commonly used methods for TDM. In comparison with immunoassay, LC-MS has advantages which include wide applicability, high sensitivity, good quantitation, high specificity and high throughput. Probes of the invention may be coupled with standard mass spectrometers for providing point-of-care therapeutic drug monitoring. 
     The drug Imatinib (GLEEVEC in USA and GLIVEC in Europe/Australia, for the treatment of chronic myelogenous leu-kemia) in a dried blood spot was analyzed using paper spray and a lab-scale LTQ mass spectrometer. Quantitation of Imatinib in whole blood was achieved using the MS/MS spectra with a known concentration of Imatinib-d8 being used as the internal standard ( FIG. 14C ). The relative response was linear across a wide range of concentrations, including the entire therapeutic range ( FIG. 14C ). 
     Example 15: High-Throughput Detection 
     Multiple-tip devices were fabricated and applied for high throughput analysis ( FIG. 28A ). The multiple-tip device was a set of paper triangles all connected to a single copper strip ( FIG. 28A ). An electrode was connected to the copper strip. Multiple samples were put on a single paper substrate and analyzed in series using the multiple-tip probe ( FIG. 28B - FIG. 28C ). Each tip was pre-loaded with 0.2 uL methanol/water containing 100 ppm sample (cocaine or caffeine) and dried. Then the whole multiple-tip device was moved on a moving stage from left to right with constant velocity and 7 uL methanol/water was applied from the back part for each tip during movement. 
     To prevent the contaminant during spray, blanks were inserted between two sample tips.  FIG. 28C  shows the signal intensity for the whole scanning. From total intensity, six tips gave six individual high signal peaks. For cocaine, peaks only appeared when tip 2 and tip 6 were scanned. For caffeine, the highest peak came from tip 4, which was consistent with the sample loading sequence. 
     Example 16: Tissue Analysis 
     Direct analysis of chemicals in animal tissue using probes of the invention was performed as shown in  FIG. 29A . A small sections of tissue were removed and placed on a paper triangle. Methanol/water (1:1 v:v; 10 μl) was added to the paper as solvent and then 4.5 kV positive DC voltage was applied to produce the spray for MS analysis. Protonated hormone ions were observed for porcine adrenal gland tissue (1 mm 3 ,  FIG. 29B ).  FIG. 16  is a mass spectrum showing direct analysis of hormones in animal tissue by paper spray. A small piece of pig adrenal gland tissue (1 mm×1 mm×1 mm) was placed onto the paper surface, MeOH/water (1:1 v:v; 10 μl) was added and a voltage applied to the paper to produce a spray. The hormones epinephrine and norepinephrine were identified in the spectrum; at high mass the spectrum was dominated by phospolipid signals. 
     Lipid profiles were obtained for human prostate tissues (1mm 2 ×15 μm,  FIGS. 29C and 29D ) removed from the tumor and adjacent normal regions. Phospholipids such as phosphatidylcholine (PC) and sphingomyelin (SM) were identified in the spectra. The peak of 
     [PC(34:1)+K] +  at m/z 798 was significantly more intense in tumor tissue ( FIG. 29C ) and peaks [SM(34:1)+Na] +  at m/z 725, [SM(36:0)+Na] +  at m/z 756, and [SM(36:4)+Na] +  at m/z 804 were significantly lower compared with normal tissue ( FIG. 29D ). 
     Example 17: On-Line Derivatization 
     For analysis of target analytes which have relatively low ionization efficiencies and relatively low concentrations in mixtures, derivatization is often necessary to provide adequate sensitivity. On-line derivatization can be implemented by adding reagents into the spray solution, such as methanol/water solutions containing reagents appropriate for targeted analytes. If the reagents to be used are stable on paper, they can also be added onto the porous materal when the probes are fabricated. 
     As a demonstration, 5 μL methanol containing 500 ng betaine aldehyde chloride was added onto a paper triangle and allowed to dry to fabricate a sample substrate preloaded with a derivatization reagent for the analysis of cholesterol in serum. On-line charge labeling with betaine aldehyde (BA) through its reaction with hydroxyl groups has been demonstrated previously to be very effective for the identification of cholesterol in tissue (Wu et al.,  Anal Chem.  2009, 81:7618-7624). When the paper triangle was used for analysis, 2 μL human serum was spotted onto the paper to form a dried spot and then analyzed by using paper spray ionization. A 10 μL ACN/CHCl 3  (1:1 v:v) solution, instead of methanol/water, was used for paper spray to avoid reaction between the betaine aldehyde and methanol. 
     The comparison between analysis using a blank and a reagent-preloaded paper triangle is shown in  FIGS. 30A and 30B . Without the derivatization reagent, cholesterol-related peaks, such as protonated ion [Chol+H] +  (m/z 387), water loss [Chol+H−H 2 O] +  (m/z 369), and sodium adduction [Chol+Na] +  (m/z 409), were not observed ( FIG. 30A ). With the derivatization reagent, the ion [Chol+BA] +  was observed at m/z 488.6 ( FIG. 30B ). MS/MS analysis was performed for this ion and a characteristic fragment ion m/z 369 was observed ( FIG. 30C ). 
     Example 18: Peptide Pre-Concentration Using Modified Paper Spray Substrate 
     Pre-concentration of chemicals on the paper surface using photoresist treatment. Chromatography paper was rendered hydrophobic by treatment with SU-8 photoresist as described previously (Martinez et al.,  Angew Chem Int. Ed.,  2007, 46:1318-1320). Then 5 μl bradykinin 2-9 solution (100 ppm in pure H 2 O) was applied on the paper surface. When the solution was dry, the paper was put into water and washed for 10 s. After washing, the paper triangle was held in front of the MS inlet, 10 μl pure MeOH was applied as solvent and the voltage was set at 4.5 kV for paper spray. The same experiment was done with untreated paper substrate for comparison. 
       FIG. 31A  shows the tandem MS spectrum of bradykinin 2-9 from paper with photoresist treatment. The intensity of the most intense fragment ion 404 is 5.66E3.  FIG. 31B  shows the tandem MS spectrum of bradykinin 2-9 from normal chromatography paper without photoresist treatment. The intensity of the most intense fragment ion 404 is only 1.41E1. These data show that the binding affinity between photoresist-treated chromatography paper and peptide is much higher than that between normal chromatography paper and peptide, thus more peptide can be kept on the paper surface after washing by water. When pure methanol is applied, these retained peptides will be desorbed and detected by MS. This method can be used to pre-concentrate hydrophobic chemicals on the paper surface, and other hydrophilic materials (e.g. salts) can also be removed from the paper surface. 
     Example 19: Inverted Polarities 
     The polarity of the voltage applied to the probe need not match that used in the mass analyzer. In particular, it is possible to operate the probes of the invention with a negative potential but to record the mass spectrum of the resulting positively changed ions. In negative ion mode, a large current of electrons (or solvated electrons) is produced in paper spray. These electrons, if of suitable energy, can be captured by molecules with appropriate electron affinities to generate radical anions. 
     Alternatively, these electrons might be responsible for electron ionization of the analyte to generate the radical cation or alternatively ESI might involve a solvent molecule which might then undergo charge exchange with the analyte to again generate the radical cation. If this process occurs with sufficient energy, characteristic fragment ions might be produced provided the radical cation is not collisionally deactivated before fragmentation can occur. 
     An experiment was done on a benchtop LTP using toluene vapor, with a probe of the invention conducted at −4.5kV with methanol:water as solvent applied to the paper. The spectrum shown in  FIG. 32  was recorded. One notes that ion/molecule reactions to give the protonated molecule, m/z 93 occur as expected at atmospheric pressure. One also notes however, the presence of the radical cation, m/z 92 and its characteristic fragments at m/z 91 and 65. 
     An interesting note is that the “EI” fragment ions were most easily produced when the source of toluene vapor was placed close to the MS inlet; i.e., in the cathodic region of the discharge between the paper tip and MS inlet. This suggests that direct electron ionization by energetic electrons in the “fall” region might be at least partly responsible for this behavior. 
     Example 20: Cartridge for Blood Analysis 
       FIG. 33A  shows an exemplary case for spotting blood onto porous material that will be used for mass spectral analysis. The cartridge can have a vial with a volume at the center and vials for overflows. A plug, such as a soluble membrane containing a set amount of internal standard chemical, is used to block the bottom of the vial for volume control. A drop of blood is placed in the vial ( FIG. 33B ). The volume of the blood in the vial is controlled by flowing the extra blood into the overflow vials ( FIG. 33B ). The blood in the vial is subsequently dissolved in the membrane at the bottom, mixing the internal standard chemical into the blood ( FIG. 33B ). Upon dissolution of the plug, blood flows to the paper substrate, and eventually forms a dried blood spot having a controlled amount of sample and internal standard ( FIG. 33B ). 
     Example 21: Sample Dispenser Including an Internal Standard 
     This example provides a device for transfer of complex mixture using, e.g., glass capillaries coated with internal standard. A sampling glass capillary was prepared by filling it with an internal standard solution through capillary action and drying in air to form an internal standard coating on its inner surface. The capillary was used to take a liquid sample containing the analyte, also through capillary action, and to transfer it to a sample substrate for ambient analysis. During this process the internal standard was automatically mixed into the sample. Since the volumes of the internal standard solution and sample are both regulated by the capillary volume, accurate control of the capillary length of volume is not necessary to retain quantitative accuracy, which is good for mass production of the capillaries. The performance of using sampling capillary for quantitative analysis of different chemicals in complex mixtures, including blood, river water and urine was characterized. Significant improvements in quantitation accuracy were obtained for analysis of 1 μL samples using various ambient ionization methods, including paper spray ionization, low temperature plasma (LTP) and desorption electrospray ionization (DESI). 
     Materials 
     Glass capillaries (ID. 0.4 mm; length, 75 mm) were purchased from Drummond Scientific Co. (Broomall, Pa.). Pipette tips (1000 μL) were purchased from Eppendorf (Hauppauge, N.Y.). Whatman Grade 1 chromatography paper was purchased from GE Healthcare UK Limited (Buckinghamshire, England). Imatinib was purchased from Santa Cruz 
     Biotechnology (Santa Cruz, Calif.), imatinib-d8 was purchased from EJY Tech (Rockville, Md.). Atrazine, atrazine-d5, cocaine, and cocaine-d3 were purchased from Sigma-Aldrich (Milwaukee, Wis.). Bovine blood (sodium citrate) was purchased from Innovative Research (Novi, Mich.). River water was collected from Wabash River (West Lafayette, Ind.). Urine was collected from a group member. 
     Blood samples were examined with paper spray ionization by using a TSQ Quantum Access Max (Thermo Scientific, San Jose, Calif.) in the selected reaction monitoring (SRM) mode. River water and urine samples were examined with LTP and DESI, respectively, by using an Exactive Orbitrap (Thermo Scientific, San Jose, Calif.) in full scan mode. For paper spray mass spectrometry, the chromatography paper was cut into triangle (5 mm in base and 10 mm in height). The paper triangle was held by clip and placed in front of the MS inlet with a 5 mm distance. Spray solvent (35 μL acetonitrile:water, 90:10, v:v) was applied on the blood spot to extract chemicals for MS detection. For LTP measurement, the river water was deposited on glass slide and allowed to dry. Experiment conditions for LTP includes Helium gas flow 0.5 L/min, 10 mm distance between sample and LTP probe, 5 mm distance between sample and MS inlet. For DESI measurement, the urine was 10×diluted with methanol and deposited on PTFE sheet and allowed to dry. Experiment conditions for DESI includes 150 psi nitrogen gas, 4.5 kV spray voltage, methanol/water (50:50, v:v) flow rate 3 μL/min, 5 mm distance between sample and DESI probe, 1 mm distance between sample and MS inlet. 
     Results 
     A sampling capillary was prepared for taking about 1 μL liquid sample while mixing internal standard from the walls of the capillary into the sample at an accurate concentration without requiring the use of normal in-lab procedures. The sampling capillary was fabricated by cutting glass capillaries (0.4 mm I.D., 75 mm long) into ˜8 mm long sections then a coating procedure was developed to immobilize the internal standard onto the inside wall of the capillary sections. As shown in  FIG. 37A , one end of the capillary was touched to a bulk internal standard solution (e.g., methanol solution) and the capillary was filled by capillary action so that the total volume of the solution matched the capillary volume. The capillary was then held in a vertical position in air at 60° C. for 5 min (Table 1 below provides a characterization of drying time) while the solvent was dried. The chosen temperature was close to the boiling point of methanol (65° C.) while low enough to avoid the decomposition of the internal standard. A 1000 μL plastic pipette tip was used as a holder for easy handling of the sampling capillary ( FIG. 37B ). The pipette tip also helped to apply a pneumatic pressure to push the viscous samples out of the capillary by using an air displacement pipette or a plastic bulb ( FIGS. 37A and 37B ). When used for taking liquid samples as shown in  FIG. 37C , the sampling capillary already coated with internal standard is filled with sample solution again through capillary action and in a volume that matches the internal volume of the capillary. As this is done the internal standard dissolves from the walls and mixes into the liquid sample. The concentration of the internal standard introduced into the sample is well controlled since the volumes of the internal standard solution and sample are both regulated by the capillary volume. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Drying time for coating the capillary using methanol solution 
               
               
                 containing internal standard; oven temperature, 60° C. 
               
               
                 For methanol 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Volume (μL) 
                 1 
                 2 
                 4 
                 8 
               
               
                   
                 Drying time (s) 
                 106 ± 3 
                 211 ± 3 
                 310 ± 8 
                 796 ++ 58 
               
               
                   
                   
               
            
           
         
       
     
     An important aspect of dispensers of the invention is that an accurate capillary length is not required. Rather, the volumes of internal standard solution and liquid sample are both fixed by the capillary volume, regardless of any variation in the actual volume. This is a self-regulating feature of devices of the invention. Besides that, the organic solvent used for dissolution of internal standard is completely removed during the drying process, minimizing matrix effects due to solvent. 
       FIGS. 39A and 39B  show the analysis of imatinib in blood at different concentrations using capillaries coated with imatinib-d8 as internal standard. Capillaries of different lengths (6-12 mm, corresponding to 0.75-1.5 μL in volume) were used for this test. The variations in capillary length for the first three sets are around 25% (RSD, n=5), while the variations of measured concentration of imatinib obtained with these capillaries are only ˜5% (RSD, n=5). This value is comparable to that obtained with the fourth set (RSD of measured concentration, 3.7%, n=5), in which the lengths were much more tightly controlled (RSD 2.4% in capillary length, n=17). 
     For evaluation, the sampling capillary was used for quantitative analysis of imanitib in blood with paper spray mass spectrometry. Paper spray mass spectrometry is described herein and is an ambient ionization method that is a fast and convenient means of quantitative analysis of therapeutic drugs in blood. Good sensitivity and dynamic range as well as high reproducibility have been obtained for quantitation of a set of oncology drugs in blood. It is preferred to use a streamlined protocol for paper spray MS for point-of-care (POC) analysis. 
     While good quantitative analysis has been achieved by mixing the internal standards into the blood before a small amount of sample (several microliters) is loaded onto the paper substrate for paper spray MS, this sample preparation procedure requires the skill set typical of an analytical chemist and a relatively large amount of blood (hundreds of microliters). Embodiments herein show pre-printing the internal standards onto the paper substrate. This only requires the operator to load blood of a fixed volume onto the paper. The internal standard already on the paper and the analyte in the applied blood sample mix and allow quantitative measurements. Adequate accuracy in quantitation with RSD values smaller than 15% has been achieved using this method. Although adequate limits of quantitation (LOQs) have been obtained with blood of volumes less than 1 μL, 15 μL blood is typically loaded onto the paper substrate to avoid significant variations in blood volume during pipetting. 
     Using devices described herein, the blood sample was placed on a glass slides and sampled from there to simulate finger-stick blood sampling. The blood in the capillary was transferred onto a paper substrate by allowing the end of the capillary to touch the paper. A dried blood spot (DBS) array was easily be generated on paper as shown in  FIG. 40A . Paper triangles cut out along the dashed lines were used for paper spray MS to analyze the chemicals in blood. Quantitative analysis of imatinib in blood with the concentration varying from 10 ng/mL to 4 μg/mL was successfully performed with RSD of 3-5% (RSD, n≥3) for the entire range of concentrations ( FIG. 40B ). 
     Using of devices of the invention to introduce internal standard to a sample was compared to traditional methods of premixing internal standard into blood. A comparison was made between the dried blood spots prepared by pipetting 1 μL blood containing imatinib at 200 ng/mL with imatinib-d8 premixed at 100 ng/mL and those prepared by direct sampling using the coated capillaries (imatinib at 200 ng/mL in blood, imatinib-d8 at 100 ng/mL in standard solution for coating). The MS/MS ion current of imatinib (m/z 494 to m/z 394) and imatinib-d8 (m/z 502 to m/z 394) were measured with paper spray MS and the ratio of these two signals was plotted as a function of paper spray time in  FIG. 40B . Comparable stability in ratio was observed for both methods. 
     The recovery of coated internal standard was also investigated. To evaluate the recovery of internal standard eluted during the sampling process, sampling capillary coated with 0.1 ng imatinib-d8 were eluted with blood spiked with 120 ng/ml imatinib. The elution was performed exactly the same as blood test with paper spray ionization as described previously. The tested recovery of imatinib-d8 is 99.6±6.7% (n=5), indicating most of the internal standard was spiked into the blood during the sampling process. 
     Devices and methods of the invention can be used with any analytical technique, for example, chromatography techniques, such as high performance liquid chromatography (HPLC), mass spectrometry techniques, and other analytical techniques. 
     In particular embodiments, devices and methods of the invention are used for preparation of a sample for analysis by mass spectrometry. Any mass spectrometry technique known in the art may be used with methods of the invention. Exemplary mass spectrometry techniques that utilize ionization sources at atmospheric pressure for mass spectrometry include electrospray ionization (ESI; Fenn et al., Science, 246:64-71, 1989; and Yamashita et al., J. Phys. Chem., 88:4451-4459, 1984); atmospheric pressure ionization (APCI; Carroll et al., Anal. Chem. 47:2369-2373, 1975); and atmospheric pressure matrix assisted laser desorption ionization (AP-MALDI; Laiko et al. Anal. Chem., 72:652-657, 2000; and Tanaka et al. Rapid 
     Commun. Mass Spectrom., 2:151-153, 1988). The content of each of these references in incorporated by reference herein its entirety. 
     Exemplary mass spectrometry techniques that utilize direct ambient ionization/sampling methods including desorption electrospray ionization (DESI; Takats et al., Science, 306:471-473, 2004 and U.S. Pat. No. 7,335,897); direct analysis in real time (DART; Cody et al., Anal. Chem., 77:2297-2302, 2005); Atmospheric Pressure Dielectric Barrier Discharge Ionization (DBDI; Kogelschatz, Plasma Chemistry and Plasma Processing, 23:1-46, 2003, and PCT international publication number WO 2009/102766), Low Temperature Plasma (PCT/US2009/033760), and electrospray-assisted laser desoption/ionization (ELDI; Shiea et al., J. Rapid Communications in Mass Spectrometry, 19:3701-3704, 2005). The content of each of these references in incorporated by reference herein its entirety. In certain embodiments, the mass spectrometry technique is a paper spray based technique as described herein. 
     For example, devices of the invention were used for quantitative analysis of river water samples with low temperature plasma (LTP) and urine samples with desorption electrospray ionization, respectively. For LTP analysis, river water samples containing atrazine at 10-500 ng/mL were deposited on a glass slide, allowed to dry and analyzed with a LTP probe ( FIG. 41A ). For DESI analysis, diluted urine samples containing cocaine at 33-1000 ng/mL were deposited on a PTFE sheet, allowed to dry and analyzed with DESI ( FIG. 41B ). Sample amounts of about 1 μL were used for all tests and RSDs better than 5% were achieved for all quantitation measurements (Table 2). 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Using sampling capillaries for quantitative analysis of atrazine in 
               
               
                 river water with LTP and cocaine in urine with DESI, respectively. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Relative 
               
               
                   
                 Analyte 
                 Mean 
                   
                 standard 
               
               
                   
                 Con. 
                 analyte/IS 
                 Standard 
                 deviation 
               
               
                 Samples 
                 (ng/mL) 
                 (n = 5) 
                 deviation 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Atrazine 
                 500 
                 4.79 
                 0.23 
                 4.8 
               
               
                 1 μL 
                 100 
                 0.91 
                 0.025 
                 2.7 
               
               
                 river water 
               
               
                 (IS: 100 ng/mL 
                 40 
                 0.37 
                 0.012 
                 3.2 
               
               
                 atrazine-d5) 
               
               
                 LTP 
                 10 
                 0.08 
                 0.006 
                 7.5 
               
               
                 Cocaine 
                 1000 
                 9.59 
                 0.23 
                 2.4 
               
               
                 1 μL urine 
                 180 
                 1.76 
                 0.034 
                 1.9 
               
               
                 (IS: 100 ng/mL 
                 80 
                 0.84 
                 0.016 
                 1.9 
               
               
                 cocaine-d3) 
               
               
                 DESI 
                 30 
                 0.31 
                 0.010 
                 3.2 
               
               
                   
               
            
           
         
       
     
     By varying the length of the capillary, a series of glass capillaries was fabricated with sampling volumes varying from 1 μL to 8 μL ( FIGS. 38A-38C ). Most liquids are able to be collected and dispensed with these capillaries, including aqueous solutions, organic solvents, and biofluids ( FIGS. 42A-42C ). Characterization of the sampling process for methanol, urine, blood and serum was performed ( FIGS. 42A-42C ). For urine, methanol and serum, sampling times are around 1 s for an 8 μL capillary but shorter for smaller capillary (Table 3 below). For blood, the sampling time varies from ˜15 s for an 8 μL capillary to less than 0.5 s for a 1 μL capillary, which is fast enough for taking finger-stick blood for POC analysis. Dispensing times for different liquids have also been measured. For urine, methanol and serum, liquids can be simply dispensed onto paper by capillary action due to the porous nature of paper. The dispensing time is about an order of magnetite longer than the loading time for each liquid (Table 3 below). When dispensing blood, the micropores on paper could be blocked by blood cells. Using a bulb on the dispenser holder to put some pressure through the capillary can help to complete the blood transfer within one or two seconds. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Sample collection time and dispensing time for different liquids using capillary action. 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Urine 
                 Methanol 
                 Blood 
                 Serum 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Viscosity 
                 0.8 
                 0.59 
                 ~10 
                 ~10 
                 3-4 
                 3-4 
                 1.4-1.8 
               
               
                 (mPa · s, 
                   
                   
                   
                   
                 (37° C.) 
                 (37° C.) 
               
               
                 20° C.) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Surface 
                 ~66 
                 22.6 
                 ~61 
                 ~61 
                 ~58 
                 ~58 
                 ~59 
                 ~59 
                 ~53 
                 ~53 
               
               
                 tension 
                   
                   
                   
                   
                 (37° C.) 
                 (37° C.) 
                   
                   
                 (37° C.) 
                 (37° C.) 
               
               
                 (mN/m, 
               
               
                 20° C.) 
               
               
                 Volume 
                 8 
                 8 
                 8 
                 4 
                 2 
                 1  
                 8 
                 4 
                 2  
                 1  
               
               
                 (μL) 
               
               
                 Loading 
                  1.0 ± 0.1 
                 1.2 ± 0.1 
                 15.4 ± 0.8 
                 3.8 ± 0.3 
                 1.2 ± 0.1 
                 &lt;0.5 
                 1.0 ± 0.1 
                 &lt;0.5 
                 &lt;0.5 
                 &lt;0.5 
               
               
                 time 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Dispensing 
                 13.8 ± 0.6 
                 6.4 ± 0.3 
                 N/A 
                 11.2 ± 0.7  
                 4.9 ± 0.7 
                 2.7 ± 0.1 
                 1.2 ± 0.1 
               
               
                 time (s) 
               
               
                   
               
               
                   a  A smearing action or pressurizing is required to dispense blood. 
               
            
           
         
       
     
     In conclusion, a method using internal standard coated capillary has been developed for quantitative measurement of compounds in liquid samples. Accurate quantitation can be achieved with a sample volume at 1 μL and traditional laboratory procedures of sample preparation are not required. This method bridges the crude samples and the ionization sources in a simple fashion and with user-friendly procedures. This method also addresses two fundamental issues related to chemical analysis in quantitation: 1) how to collect sample in an easy, fast and accurate manner; 2) how to quantitatively spike internal standards into the collected samples. The capillaries loaded with internal standards are stable at 4° C. for at least days. As such, it is suitable for point-of-care applications. High throughput processes for analysis can also be developed using this method for preclinical study, where quantitative measurement must be performed with limited amounts of biofluidic samples from small animals.