Fabrication of porous polymer monoliths in polymeric microfluidic chips as an electrospray emitter for direct coupling to mass spectrometry

Coupling of polymeric microfluidic devices to mass spectrometry is reported using porous polymer monoliths (PPM) as nanoelectrospray emitters. Lauryl acrylate-co-ethylene dimethacrylate porous polymer monolith was photopatterned for 5 mm at the end of the channel of microfluidic devices fabricated from three different polymeric substrate materials, including the following: poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and cyclic olefin copolymer (COC). Spraying directly from the end of the chip removes any dead volume associated with inserted emitters or transfer lines, and the presence of multiple pathways in the PPM prevents the clogging of the channels, which is a common problem in conventional nanospray emitters. Spraying from a microfluidic channel having a PPM emitter produced a substantial increase in TIC stability and increased sensitivity by as much as 70x compared to spraying from an open end chip with no PPM. The performance of PPM emitter in COC, PMMA, and PDMS chips was compared in terms of stability and reproducibility of the electrospray. COC chips showed the highest reproducibility in terms of chip-to-chip performance, which can be attributed to the ease and reproducibility of the PPM formation due to the favorable optical and chemical properties of COC. We have further tested the performance of the COC chips by constant infusion of poly(propylene glycol) solution at organic content ranging from 10 to 90% methanol and at flow rates ranging from 50 to 1000 nL/min, showing optimum spraying conditions (RSD < 5%) at 50-70% organic content and at flow rates from 100 to 500 nL/min. The PPM sprayer was also used for protein preconcentration and desalting prior to mass spectrometric detection, and results were comparable with a chip spraying from an electrospray tip.     

Chemically etched open tubular and monolithic emitters for nanoelectrospray ionization mass spectrometry

We have developed a new procedure for fabricating fused-silica emitters for electrospray ionization-mass spectrometry (ESI-MS) in which the end of a bare fused-silica capillary is immersed into aqueous hydrofluoric acid, and water is pumped through the capillary to prevent etching of the interior. Surface tension causes the etchant to climb the capillary exterior, and the etch rate in the resulting meniscus decreases as a function of distance from the bulk solution. Etching continues until the silica touching the hydrofluoric acid reservoir is completely removed, essentially stopping the etch process. The resulting emitters have no internal taper, making them much less prone to clogging compared to, e.g., pulled emitters. The high aspect ratios and extremely thin walls at the orifice facilitate very low flow rate operation; stable ESI-MS signals were obtained for model analytes from 5-microm-diameter emitters at a flow rate of 5 nL/min with a high degree of interemitter reproducibility. In extensive evaluation, the etched emitters were found to enable approximately four times as many LC-MS analyses of proteomic samples before failing compared with conventional pulled emitters. The fabrication procedure was also employed to taper the ends of polymer monolith-containing silica capillaries for use as ESI emitters. In contrast to previous work, the monolithic material protrudes beyond the fused-silica capillaries, improving the monolith-assisted electrospray process.     

Elastomeric microchip electrospray emitter for stable cone-jet mode operation in the nanoflow regime

Despite widespread interest in combining laboratory-on-a-chip technologies with mass spectrometry (MS)-based analyses, the coupling of microfluidics to electrospray ionization (ESI)-MS remains challenging. We report a robust, integrated poly(dimethylsiloxane) microchip interface for ESI-MS using simple and widely accessible microfabrication procedures. The interface uses an auxiliary channel to provide electrical contact for the stable cone-jet electrospray without sample loss or dilution. The electric field at the channel terminus is enhanced by two vertical cuts that cause the interface to taper to a line rather than to a point, and the formation of a small Taylor cone at the channel exit ensures subnanoliter postcolumn dead volumes. Cone-jet mode electrospray was demonstrated for up to 90% aqueous solutions and for extended durations. Comparable ESI-MS sensitivities were achieved using both microchip and conventional fused silica capillary emitters, but stable cone-jet mode electrosprays could be established over a far broader range of flow rates (from 50-1000 nL/min) and applied potentials using the microchip emitters. This attribute of the microchip emitter should simplify electrospray optimization and make the stable electrospray more resistant to external perturbations.     

Microsphere entrapped emitters for sample preconcentration and electrospray ionization mass spectrometry

In this study a nano-electrospray emitter is constructed by precisely positioning entrapped octadecylsilane (ODS) particles within a photoinitiated polymer at the exit aperture of a capillary. Following poly-merization, the microsphere/polymer hybrid material is able to withstand pressures greater than 4000 psi for 1 cm length of material. Smaller microspheres (3 microm) patterned at the exit aperture of a capillary generated the most sensitive/stable electrospray from 100 to 1000 nL/min and moderately stable signal under 100 nL/min. Constant infusion of a standard PPG solution from a batch of eleven emitters resulted in a relatively small variance in total ion current (TIC) counts (8%). The entrapped microsphere emitter design yields an emitter that minimizes clogging and eliminates dead volume between the chromatographic bed and the electrospray emitter. The entrapped ODS microspheres can also be used for sample preparation prior to mass spectrometry (MS) analysis. We show the solid-phase extraction and preconcentration of 20-700 fmol of a peptide (leucine enkephalin) prior to MS analysis on an emitter with 1 cm of entrapped microspheres.     

MicroSPE-nanoLC-ESI-MS/MS using 10-microm-i.d. silica-based monolithic columns for proteomics

Silica-based monolithic capillary columns (25 cm x 10 microm i.d.) with integrated nanoESI emitters have been developed to provide high-quality and robust microSPE-nanoLC-ESI-MS analyses. The integrated nanoESI emitter adds no dead volume to the LC separation, allowing stable electrospray operation at flow rates of approximately 10 nL/min. In an initial application with a linear ion trap MS, we identified 5510 unique peptides that covered 1443 distinct Shewanella oneidensis proteins from a 300-ng tryptic digest sample in a single 4-h LC-MS/MS analysis. The use of an integrated monolithic ESI emitter provided enhanced resistance to clogging and provided good run-to-run reproducibility.     

A design for low-flow sheathless electrospray emitters

An extremely simple design has been developed for producing durable sheathless electrospray emitters that give highly stable electrospray for unlimited lifetimes. The emitters can be fashioned from any style fused-silica capillary and are ideally suited for generating "all-in-one" microcolumn-emitter systems thus eliminating unwanted void volumes. The emitters give stable electrospray at low (30 nL/min) as well as high (1 mL/min) flow rates without the aid of nebulizing gas. Fabrication of these emitters (aka the "fairy dust" technique) does not involve the use of a metallized coating but rather the adherance of 2-μm gold particles to the capillary tip resulting in a robust approach to the problem of making an electrical contact with the electrospray solvent.     

A conductive polymeric material used for nanospray needle and low-flow sheathless electrospray ionization applications.

A conductive polypropylene/graphite mixture is used for the production of polymeric nanospray needle emitters and as a coating on fused-silica capillaries that are used for sheathless electrospray ionization (ESI). The described production of these polymeric nanospray needle emitters and sheathless ESI contacts is exceptionally easy and at a very low cost. The described polymeric nanospray emitters have shown excellent features regarding their chemical inertness and spray performance. The long-term stability of the nanospray needles exceeds 24 h of continuous use. Furthermore, the resistance to electrical discharges, which is one of the factors that often limits the lifetime of metal coated tips, has proven to be outstanding. A voltage of up to 5 kV could be applied without loss of spray performance. The use of polypropylene emitters offers a number of desirable features, as compared to silica based emitters. Among these features are mechanical flexibility and simplified regeneration of the nanospray needle. Continuous nanospray of peptides and proteins in conjunction with orthogonal time-of-flight mass spectrometry are shown with signal relative standard deviations of 5%. In addition, the polypropylene/graphite mixture has also been applied as the conductive contact for sheathless ESI in fast capillary electrophoresis separations.     

High-efficiency nanoscale liquid chromatography coupled on-line with mass spectrometry using nanoelectrospray ionization for proteomics

We describe high-efficiency (peak capacities of approximately 10(3)) nanoscale (using column inner diameters down to 15 microm) liquid chromatography (nanoLC)/low flow rate electrospray (nanoESI) mass spectrometry (MS) for the sensitive analysis of complex global cellular protein enzymatic digests (i.e., proteomics). Using a liquid slurry packing method with carefully selected packing solvents, 87-cm-length capillaries having inner diameters of 14.9-74.5 microm were successfully packed with 3-microm C18-bonded porous (300-A pores) silica particles at a pressure of 18,000 psi. With a mobile-phase delivery pressure of 10,000 psi, these packed capillaries provided mobile-phase flow rates as low as approximately 20 nL/min at LC linear velocities of approximately 0.2 cm/s, which is near optimal for separation efficiency. To maintain chromatographic efficiency, unions with internal channel diameters as small as 10 microm were specially produced for connecting packed capillaries to replaceable nanoESI emitters having orifice diameters of 2-10 microm (depending on the packed capillary dimensions). Coupled on-line with a hybrid-quadrupole time-of-flight MS through the nanoESI interface, the nanoLC separations provided peak capacities of approximately 10(3) for proteome proteolytic polypeptide mixtures when a positive feedback switching valve was used for quantitatively introducing samples. Over a relatively large range of sample loadings (e.g., 5-100 ng, and 50-500 ng of cellular proteolytic peptides for 14.9- and 29.7-microm-i.d. packed capillaries, respectively), the nanoLC/nanoESI MS response for low-abundance components of the complex mixtures was found to increase linearly with sample loading. The nanoLC/nanoESI-MS sensitivity also increased linearly with decreasing flow rate (or approximately inversely proportional to the square of the capillary inner diameter) in the flow range of 20-400 nL/min. Thus, except at the lower loadings, decreasing the separation capillary inner diameter has an effect equivalent to increasing sample loading, which is important for sample-limited proteomic applications. No significant effects on recovery of eluting polypeptides were observed using porous C18 particles with surface pores of 300-A versus nonporous particles. Tandem MS analyses were also demonstrated using the high-efficiency nanoLC separations. Chromatographic elution time, MS response intensity, and mass measurement accuracy was examined between runs with a single column (with a single nanoESI emitter), between different columns (same and different inner diameters with different nanoESI emitters), and for different samples (various concentrations of cellular proteolytic peptides) and demonstrated robust and reproducible sensitive analyses for complex proteomic samples.     

Subattomole-Sensitivity Microchip Nanoelectrospray Source with Time-of-Flight Mass Spectrometry Detection

A microfabricated microfluidic device coupled with a nanospray tip for electrospray ionization of dilute solutions is described. The device has been interfaced with a time-of-flight mass spectrometer and evaluated for sensitive, high-speed detection of peptides and proteins. The electrospray voltage was applied through the microchip to the nanospray capillary that was attached at the end of a microfabricated channel. Fluid delivery rates were 20-30 nL min(-)(1) through the hybridized structure without any pressure assistance. On-line microchip electrophoresis has been demonstrated and the effect of the capillary-chip junction on band broadening examined. Full mass spectra are acquired within 10-20 ms at 50-100 spectra s(-)(1) storage rates. Detection of subattomole levels of sample from a 100 nM solution is demonstrated for infusion experiments.     

Ultra-low flow electrospray ionization-mass spectrometry for improved ionization efficiency in phosphoproteomics

The potential benefits of ultra-low flow electrospray ionization (ESI) for the analysis of phosphopeptides in proteomics was investigated. First, the relative flow dependent ionization efficiency of nonphosphorylated vs multiplyphosphorylated peptides was characterized by infusion of a five synthetic peptide mix with zero to four phophorylation sites at flow rates ranging from 4.5 to 500 nL/min. Most importantly, similar to what was found earlier by Schmidt et al., it has been verified that at flow rates below 20 nL/min the relative peak intensities for the various peptides show a trend toward an equimolar response, which would be highly beneficial in phosphoproteomic analysis. As the technology to achieve liquid chromatography separation at flow rates below 20 nL/min is not readily available, a sheathless capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) strategy based on the use of a neutrally coated separation capillary was used to develop an analytical strategy at flow rates as low as 6.6 nL/min. An in-line preconcentration technique, namely, transient isotachophoresis (t-ITP), to achieve efficient separation while using larger volume injections (37% of capillary thus 250 nL) was incorporated to achieve even greater sample concentration sensitivities. The developed t-ITP-ESI-MS strategy was then used in a direct comparison with nano-LC-MS for the detection of phosphopeptides. The comparison showed significantly improved phosphopeptide sensitivity in equal sample load and equal sample concentration conditions for CE-MS while providing complementary data to LC-MS, demonstrating the potential of ultra-low flow ESI for the analysis of phosphopeptides in liquid based separation techniques.     

Array of chemically etched fused-silica emitters for improving the sensitivity and quantitation of electrospray ionization mass spectrometry

An array of emitters has been developed for increasing the sensitivity of electrospray ionization mass spectrometry (ESI-MS). The linear array consists of 19 chemically etched fused-silica capillaries arranged with 500 microm (center-to-center) spacing. The multiemitter device has a low dead volume to facilitate coupling to capillary liquid chromatography (LC) separations. The high aspect ratio of the emitters enables operation at flow rates as low as 20 nL/min/emitter, effectively extending the benefits of nanoelectrospray to higher flow rate analyses. To accommodate the larger ion current produced by the emitter array, a multicapillary inlet to the mass spectrometer was also constructed. The inlet, which matched the dimensions of the emitter array, preserved ion transmission efficiency. Standard reserpine solutions of varying concentration were electrosprayed at 1 microL/min using the multiemitter/multi-inlet combination, and the results were compared to those from a standard, single-emitter configuration. A 9-fold sensitivity enhancement was observed for the multiemitter relative to the single emitter. A bovine serum albumin tryptic digest was also analyzed, and a sensitivity increase ranging from 2.4- to 12.3-fold for the detected tryptic peptides resulted; the varying response was attributed to reduced ion suppression under the nanoESI conditions afforded by the emitter array. An equimolar mixture of leucine enkephalin and maltopentaose was studied to verify that ion suppression is indeed reduced for the multiplexed ESI (multi-ESI) array relative to a single emitter over a range of flow rates.     

Simplifying CE-MS operation. 2. Interfacing low-flow separation techniques to mass spectrometry using a porous tip

A robust, reproducible, and single-step interface design between low flow rate separation techniques, such as sheathless capillary electrophoresis (CE) and nanoliquid chromatography (nLC), and mass spectrometry (MS) using electrospray ionization (ESI), is introduced. In this design, the electrical connection to the capillary outlet was achieved through a porous tip at the capillary outlet. The porous section was created by removing 1-1.5 in. of the polyimide coating of the capillary and etching this section by 49% solution of HF until it is porous. The electrical connection to the capillary outlet is achieved simply by inserting the capillary outlet containing the porous tip into the existing ESI needle (metal sheath) and filling the needle with the background electrolyte. Redox reactions of water at the ESI needle and transport of these small ions through the porous tip into the capillary provides the electrical connection for the ESI and for the CE outlet electrode. The etching process reduces the wall thickness of the etched section, including the tip of the capillary, to 5-10 microm, which for a 20-30 microm i.d. capillary results in stable electrospray at approximately 1.5 kV. The design is suitable for interfacing a wide range of capillary sizes with a wide range of flow rates to MS via ESI, but it is especially useful for interfacing narrow (<30 microm i.d.) capillaries and low flow rates (<100 nL/min). The advantages of the porous tip design include the following: (1) its fabrication is reproducible, can be automated, and does not require any mechanical tools. (2) The etching process reduces the tip outer diameter and makes the capillary porous in one step. (3) The interface can be used for both nLC-MS and CE-MS. (4) If blocked or damaged, a small section of the tip can be etched off without any loss of performance. (5) The interface design leaves the capillary inner wall intact and, therefore, does not add any dead volume to the CE-MS or nLC-MS interface. (6) Bubble formation due to redox reactions of water at the high-voltage electrode is outside of the separation capillary and does not affect separation or MS performances. The performance of this interface is demonstrated by the analyses of amino acids, peptide, and protein mixtures.     

Analytical characterization of the electrospray ion source in the nanoflow regime

A detailed characterization of a conventional low-flow electrospray ionization (ESI) source for mass spectrometry (MS) using solution compositions typical of reversed-phase liquid chromatography is reported. Contrary to conventional wisdom, the pulsating regime consistently provided better ESI-MS performance than the cone-jet regime for the interface and experimental conditions studied. This observation is supported by additional measurements showing that a conventional heated capillary interface affords more efficient sampling and transmission for the charged aerosol generated by a pulsating electrospray. The pulsating electrospray provided relatively constant MS signal intensities over a wide range of voltages, while the signal decreased slightly with increasing voltage for the cone-jet electrospray. The MS signal also decreased with increasing emitter-interface distance for both pulsating and cone-jet electrosprays due to the expansion of the charged aerosol plume. At flow rates below 100 nL/min, the MS signal increased with increasing flow rate due to increased number of gas-phase ions produced. At flow rates greater than 100 nL/min, the signal reached a plateau due to decreasing ionization efficiency at larger flow rates. These results suggest approaches for improving MS interface performance for low-flow (nano- to micro-) electrosprays.     

A colloidal graphite-coated emitter for sheathless capillary electrophoresis/nanoelectrospray ionization mass spectrometry

A colloidal graphite-coated emitter is introduced for sheathless capillary electrophoresis/nanoelectrospray ionization time-of-flight mass spectrometry (CE/ESI-TOFMS). The conductive coating can be produced by brushing the capillary tip to construct a fine layer of 2-propanol-based colloidal graphite. The fabrication involves a single step and requires less than 2 min. Full cure properties develop in approximately 2 h at room temperature and then the tip is ready for use. The coated capillary tip is applied as a sheathless electrospray emitter. The emitter has proven to bear stable electrospray and excellent performance for 50 microm i.d. x 360 microm o.d. and 20 microm i.d. x 360 microm o.d. capillaries within the flow rate of 80-500 nL/min; continuous electrospray can last for over 200 h in positive mode. Baseline separation and structure elucidation of two clinically interesting basic drugs, risperidone and 9-hydroxyrisperidone, are achieved by coupling pressure-assisted CE to ESI-TOFMS using the described sheathless electrospray emitter with a bare fused-silica capillary at pH 6.7. It is found that the signal intensity of m/z in sheathless CE/ESI-TOFMS at pH 6.7 is approximately 50 times higher than that at pH 9.0 for the two analytes, although the electroosmotic flow (EOF) at pH 9.0 provides sufficient flow rate (approximately 150 nL/min) to maintain electrospray.     

High capacity capillary electrophoresis-electrospray ionization mass spectrometry: coupling a porous sheathless interface with transient-isotachophoresis

A sheathless interface making use of a porous tip has been used for coupling capillary electrophoresis and electrospray ionization mass spectrometry. First, effective flow rates using the interface have been characterized. It was found that the interface is capable of generating a stable spray with flow rates ranging from below 10 nL/min to >340 nL/min, enabling its use in either the mass or concentration-sensitive region of the electrospray process. Subsequently, by analyzing peptide mixtures of increasing complexity, we have demonstrated that this platform provides exquisite sensitivity enabling the detection of very low amounts of materials with very high resolving power. Transient isotachophoresis (t-ITP) can also be integrated with this setup to increase the mass loading of the system while maintaining peak efficiency and resolution. Concentration limits of detection in the subnanomolar or nanomolar range can be achieved with or without t-ITP, respectively. The application of a vacuum at the inlet of the separation capillary further allowed the peak capacity of the system to be improved while also enhancing its efficiency. As a final step in this study, it was demonstrated that the intrinsic properties of the interface allows the use of coated noncharged surfaces so that very high peak capacities can be achieved.     

Electrospray ionization with a pointed carbon fiber emitter

A new type of electrospray ionization emitter employing a pointed carbon fiber has been developed for interfacing nanoliquid sampling techniques to mass spectrometry. The pointed carbon fiber protruding from an orifice with a surrounding hydrophobic surface confines a small Taylor cone at the tip, which generates a stable electrospray at the tip point. The small Taylor cone improves the electrospray efficiency thereby enhancing the detection limit. This emitter is rugged and able to generate stable electrospray over a wide range of flow rate, ESI voltage, and surface tension variation. Using a solution of angiotensin I, the carbon fiber emitter in 75-microm-i.d. fused-silica tubing was shown to give ion current comparable to that from a commercial 8 microm orifice nanospray emitter. Use of the emitter for ESI-MS/MS analysis of peptides was examined by infusing a mixture of cytochrome c and myoglobin tryptic digest peptides. Protein identification was demonstrated at the level of less than 1 fmol of the peptide consumed. The use of the carbon fiber emitter for interfacing monolithic capillary HPLC to MS was also demonstrated.     

Mapping of potential gradients within the electrospray emitter

A novel electrochemical probe has been designed, built, and used to characterize the distribution in solution potential within the metal capillary and Taylor cone of the electrospray (ES) device. The measurement system consists of three electrodes-a counter electrode held at highly negative potential that serves as the cathode, and two anodes consisting of a disk-shaped, mobile, internal (working) electrode, and the internal surface of the surrounding ES capillary (auxiliary electrode, held at ground potential). One-dimensional differential electrospray emitter potential (DEEP) maps detailing solution potential gradients within the electrospray emitter and in the region of the Taylor cone are constructed by measuring the potential at the working electrode vs the ES capillary, as a function of working electrode position along the emitter axis. Results show that the measured potential difference increases as the internal probe travels toward the ES capillary exit, with values rising sharply as the base of the Taylor cone is penetrated. Higher conductivity solutions exhibit potentials of higher magnitude at longer distances away from the counter electrode, but these same solutions show lower potentials near the ES capillary exit. Removal of easily oxidizable species from the solution causes the measured potential difference to have nonzero values at distances further within the capillary, and the values measured at all points are raised. Results are consistent with the characterization of the electrospray system as a controlled-current electrolytic flow cell. Elucidation of the electrochemical details of the electrospray process can lead to mass spectrometric signal enhancement of certain species present in the spraying liquid and also allow the detection of molecules that are usually not observable due to their low ionization efficiencies.     

Reproducibility in fabrication and analytical performance of polyaniline-coated nanoelectrospray emitters

Nanoelectrospray ionization mass spectrometry is an ideal technique for analysis of biomolecules when sample quantities are limited. With the use of this technique, 1-2 microL of sample can be electrosprayed for long time periods (hours) because of the low flow rate (nanoliters per minute) attainable. However, the long-term durability of such emitters has been an impediment to the routine use of nanoelectrospray. The development of longer-lasting nanoelectrospray emitters has often resulted in increasingly complex and tedious fabrication processes. Furthermore, an easily produced, reproducible, and durable nanoelectrospray emitter is the ultimately desired goal. Here, the reproducibility of the inner diameters and geometry for nanoelectrospray emitter glass substrates is assessed using scanning electron microscopy (SEM). The results indicate that provided that glass pulling parameters remain constant, reproducible inner diameters can be produced from glass capillary tubing within the same batch; however, there are interbatch differences. In addition, SEM revealed reproducible taper geometry could also be obtained. Borosilicate and fused-silica nanoelectrospray emitters produced by these protocols were then coated with polyaniline, and their analytical figures of merit were determined using a triple quadrupole mass analyzer. Over a 1-h run, polyaniline-coated emitters showed fairly stable signal with coefficients of variation ranging from 8.92 to 27.6%. Single-scan detection limits below 1 amol were achieved for polyaniline-coated fused-silica emitters for flow rates averaging <10 nL/min. Linear mass spectrometric response with solution concentration was observed for the polyaniline-coated emitters over the range 10 nM-10 microM, with coefficients of variation ranging from 1.44 to 7.26%. This indicates that when nanelectrospray emitter inner diameters are made reproducibly, it is possible to achieve linear quantitative response for nanoelectrospray.     

Generation of multiple electrosprays using microfabricated emitter arrays for improved mass spectrometric sensitivity

Arrays of microelectrospray emitters were fabricated on polycarbonate substrates using a laser etching technique. Stable multielectrosprays were successfully generated in the liquid flow rate range relevant to mass spectrometric applications. Comparison of electrosprays generated from the microfabricated emitter array and conventional fused-silica capillaries showed similar spray characteristics and reliability. Higher total electrospray ion currents were observed as the number of electrosprays increased at a given total liquid flow rate. Consistent with the theoretical prediction, the total spray current at a constant total liquid flow rate was shown experimentally to be approximately proportional to the square root of the number of electrosprays. It is further projected that when total flow rate is optimized the maximum achievable total current will be proportional to the number of emitters. Evaluation of the multielectrospray device using a triple quadrupole mass spectrometer showed a factor of 2-3 sensitivity enhancement for the spray numbers ranging from two to nine compared to a conventional single electrospray ionization source under the same operating conditions.     

Study of electrochemical reactions using nanospray desorption electrospray ionization mass spectrometry

The combination of electrochemistry (EC) and mass spectrometry (MS) is a powerful analytical tool for studying mechanisms of redox reactions, identification of products and intermediates, and online derivatization/recognition of analytes. This work reports a new coupling interface for EC/MS by employing nanospray desorption electrospray ionization, a recently developed ambient ionization method. We demonstrate online coupling of nanospray desorption electrospray ionization MS with a traditional electrochemical flow cell, in which the electrolyzed solution emanating from the cell is ionized by nanospray desorption electrospray ionization for MS analysis. Furthermore, we show first coupling of nanospray desorption electrospray ionization MS with an interdigitated array (IDA) electrode enabling chemical analysis of electrolyzed samples directly from electrode surfaces. Because of its inherent sensitivity, nanospray desorption electrospray ionization enables chemical analysis of small volumes and concentrations of sample solution. Specifically, good-quality signal of dopamine and its oxidized form, dopamine o-quinone, was obtained using 10 μL of 1 μM solution of dopamine on the IDA. Oxidation of dopamine, reduction of benzodiazepines, and electrochemical derivatization of thiol groups were used to demonstrate the performance of the technique. Our results show the potential of nanospray desorption electrospray ionization as a novel interface for electrochemical mass spectrometry research.