Paper-Based Electrochemical Cell Coupled to Mass Spectrometry

Abstract

Abstract. On-line coupling of electrochemistry (EC) to mass spectrometry (MS) is a powerful approach for identifying intermediates and products of EC reactions in situ. In addition, EC transformations have been used to increase ionization efficiency and derivatize analytes prior to MS, improving sensitivity and chemical specificity. Recently, there has been significant interest in developing paper-based electroanalytical devices as they offer convenience, low cost, versatility, and simplicity. This report describes the development of tubular and planar paper-based electrochemical cells (P-EC) coupled to sonic spray ionization (SSI) mass spectrometry (P-EC/SSI-MS). The EC cells are composed of paper sandwiched between two mesh stainless steel electrodes. Analytes and reagents can be added directly to the paper substrate along with electrolyte, or delivered via the SSI microdroplet spray. The EC cells are decoupled from the SSI source, allowing independent control of electrical and chemical parameters. We utilized P-EC/SSI-MS to characterize various EC reactions such as oxidations of cysteine, dopamine, polycyclic aromatic hydrocarbons, and diphenyl sulfide. Our results show that P-EC/SSI-MS has the ability to increase ionization efficiency, to perform online EC transformations, and to capture intermediates of EC reactions with a response time on the order of hundreds of milliseconds. The short response time allowed detection of a deprotonated diphenyl sulfide intermediate, which experimentally confirms a previously proposed mechanism for EC oxidation of diphenyl sulfide to pseudodimer sulfonium ion. This report introduces paper-based EC/MS via development of two device configurations (tubular and planar electrodes), as well as discusses the capabilities, performance, and limitations of the technique.

Mass spectrometric snapshots for electrochemical reactions

“…15,16 The development of DESI and easy ambient sonic-spray ionization (EASI) reduced the sampling time in the order of milliseconds. 17 Recently, Liu et al 18 have established a paper based electrochemical cell which can be coupled directly to a mass spectrometer, and reaction products as well as intermediates can be detected. Brown et al 19–21 have built a water-wheel shaped electrochemical cell, and by using DESI for sampling and ionization, fleeting intermediates in electro-oxidation reactions can be detected.…”

Electrochemical Aspects of Mass Spectrometry: Atmospheric Pressure Ionization and Ambient Ionization for Bioanalysis

“…By sandwiching paper between two mesh stainless steel electrodes and then positioning the EC cell between and orthogonal to the mass spectrometer and SSI capillary, microdroplets impacting the EC cell could desorb analytes for MS detection. The potential difference (ΔV) between the two mesh electrodes led to oxidation of PAHs, which was not possible in control experiments where ΔV=0 . Furthermore, P‐EC/SSI‐MS was used to distinguish between two PAH isomers (benzo[α]pyrene and perylene, C 20 H 12 ; 252 Da) by observation of peak intensities of oxidation products after spraying different ratios of the isomers.…”

“…Furthermore, P‐EC/SSI‐MS was used to distinguish between two PAH isomers (benzo[α]pyrene and perylene, C 20 H 12 ; 252 Da) by observation of peak intensities of oxidation products after spraying different ratios of the isomers. The P‐EC/SSI‐MS technique demonstrated response times, or the time between electrochemical product formation and detection via MS, in the hundreds of milliseconds regime …”

“…The potential difference (DV) between the two mesh electrodes led to oxidation of PAHs, which was not possible in control experiments where DV = 0. [108] Furthermore, P-EC/SSI-MS was used to distinguish between two PAH isomers (benzo[a]pyrene and perylene, C 20 H 12 ; 252 Da) by observation of peak intensities of 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 oxidation products after spraying different ratios of the isomers. The P-EC/SSI-MS technique demonstrated response times, or the time between electrochemical product formation and detection via MS, in the hundreds of milliseconds regime.…”

Recent applications of paper‐based point‐of‐care devices for biomarker detection

“…da Silva and co‐workers have published a review on the technologies, applications, and advances of the PSI technique and the development of portable MS and the coupling of PSI and portable MS . Furthermore, paper‐based electrochemical cell coupled to MS was proposed for monitoring of EC reactions in situ, such as oxidations of cysteine, dopamine, polycyclic aromatic hydrocarbons, and diphenyl sulfide , paper‐based ESI‐MS was developed for monitoring of the amine‐aldehyde condensation reaction of butylamine and benzaldehyde and paper‐based enzyme‐free MS immunoassay was invented as a new platform for the detection of Plasmodium falciparum histidine‐rich protein 2 antigen, cancer antigen 125 (CA‐125) and carcinoembryonic antigen (CEA) . These new developments and high resolution MS miniaturized systems or portable MS would enable the coupling of MS to PADs, which can be beneficial for rapid, on‐site, and high‐throughput analyses.…”