On-Line Linear Sweep Voltammetry−Electrospray Mass Spectrometry

150

192

Desorption electrospray ionization-mass spectrometry (DESI-MS) was evaluated for the direct analysis of liquid samples. Several interesting results were found. First, in contrast to the previous DESI analysis of dried solid samples that was limited to proteins with MW Յ 25 kDa (Anal. Chem. 2007, 79, 3514), bovine serum albumin (BSA, 66 kDa) was successfully ionized from solutions by DESI with observation of corresponding multiply charged ions. Second, direct DESI analysis of protein tryptic digest solutions without chromatographic separation, sample clean-up, and the sample drying step was demonstrated, providing reasonably good sequence coverage of 52% to 97%. Third, direct analysis of biofluids such as an undiluted urine sample without sample pretreatment is possible, emphasizing the high tolerance of DESI with salt. These results suggest that a charged droplet pick-up mechanism is responsible for desorption and ionization of liquid samples by DESI. Also, unlike in electrospray ionization (ESI), inhibition of electrochemical reduction in the negative ion mode was observed for liquid sample DESI. In addition, reactive DESI can be performed with ion/ion reactions of Zn(II) complexes for the selective binding of phosphoserine in the presence of serine. DESI experiment can also be carried out directly to liquid samples flowing out of a pumped syringe needle tip, allowing rapid analysis. Furthermore, on-line coupling of electrochemical cell with DESI-MS was demonstrated, in which perylene radical cations generated in the cell were successfully transferred to the gas-phase for MS detection by DESI. This study extended the scope of DESI-MS applications, which could have potentials in bioanalytical and forensic analysis. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] have been introduced as rapid tools to provide efficient desorption, ionization, and further mass spectrometric characterization of target compounds. As a representative ambient ionization method, desorption electrospray ionization (DESI) has become very successful in the fast analysis of a variety of different analytes including pharmaceuticals [17][18][19], metabolites [20,21], drugs of abuse [22,23], explosives [24 -26], chemical warfare agents [27], and even intact tissues [28,29] as well as thin-layer chromatography plate [30]. In the DESI experiments, ionization occurs via the interaction of charged microdroplets generated in a pneumatically assisted electrospray of an appropriate solvent with samples placed on surfaces. Typically, solid samples on the surface are desorbed and ionized during DESI-MS analysis, and liquid samples typically undergo drying on surface in air before ionization. One practical reason for this is that liquid samples could be blown away from the surface immediately (i.e., splashing of liquids) by the high-velocity nebulizing gas employed for the generation of charged microdroplets. As a consequence, the resulting ion signal, if any, will not last long. Recently, two novel sample introduction methods have been reported ...

Section: Coupled On-line With Electrochemical Cellmentioning

confidence: 99%

Direct analysis of liquid samples by desorption electrospray ionization-mass spectrometry (DESI-MS)

Miao

Chen

2009

150

192

“…Efficient analyte electrolysis can be utilized, for example, to enhance analyte ionization and detection [6 -9], to create in abundance and study ions not normally produced by an ES ion source or by other ionization sources (e.g., multiply-charged cations formed by electron loss) [10,11] or to study the products of electrode reactions and their homogenous reaction products [12]. A major advantage of using the inherent CCE process for these applications is simplicity, versus, for example, a discrete controlled-potential electrochemical (CPE) cell added upstream in the system, or a controlled potential emitter cell [13][14][15]. Only the ES emitter electrode is needed and no additional control devices are required.…”

mentioning

confidence: 99%

Efficient analyte oxidation in an electrospray ion source using a porous flow-through electrode emitter

Berkel

Kertész

Ford

et al. 2004

This article describes the components, operation, and use of a porous flow-through electrode emitter in an electrospray ion source. This emitter electrode geometry provided enhanced mass transport to the electrode surface to exploit the inherent electrochemistry of the electrospray process for efficient analyte oxidation at flow rates up to 800 L/min. An upstream current loop in the electrospray source circuit, formed by a grounded contact to solution upstream of the emitter electrode, was utilized to increase the magnitude of the total current at the emitter electrode to overcome current limits to efficient oxidation. The resistance in this upstream current loop was altered to control the current and "dial-in" the extent of analyte oxidation, and thus, the abundance and nature of the oxidized analyte ions observed in the mass spectrum. The oxidation of reserpine to form a variety of products by multiple electron transfer reactions and oxidation of the ferroceneboronate derivative of pinacol to form the ES active radical cation were used to study and to illustrate the performance of this new emitter electrode design. Flow injection, continuous infusion, and on-line HPLC experiments were performed. (J Am Soc Mass Spectrom 2004, 15, 1755-1766

“…It was proposed and experimentally proven that the ES device operates as a controlled-current electrolytic cell [5,6]. Counting ES approaches among them, there have been many successful reports of the combination of on-line electrochemistry and mass spectrometry to analyze electrochemical products, including the utilization of electrochemical transformations to ionize neutral products, thereby rendering them amenable to mass spectral analyses [7][8][9][10][11][12][13][14].…”

mentioning

confidence: 99%

Negative ion mode evolution of potential buildup and mapping of potential gradients within the electrospray emitter

Pozniak

Cole

2004

Self Cite

Differential electrospray emitter potential (DEEP) maps, displaying variations in potential in the electrospray (ES) capillary and in the Taylor cone, have been generated in the negative ion mode of ES operation. In all examples, measured potential was found to be the highest at the points furthest into the Taylor cone, and values descended to zero at distances beyond approximately 15 mm within the ES capillary. In agreement with results obtained previously in the positive ion mode, negative mode data show a strong influence of electrolyte concentration on measured potentials. Weakly conductive solutions exhibited the highest values, and the steepest gradients, at points furthest into the Taylor cone. However, these same low conductivity solutions did not yield nonzero measured potentials to as deep a distance into the ES capillary as was possible from their higher conductivity counterparts. Addition of a readily reducible compound lowered measured potentials at all points near the ES capillary exit, in accordance with the description of the ES device as a controlled-current electrolytic cell. The development of potential inside the ES capillary upon the onset of ES was also studied, and initial results are presented. Potential waves are observed that can require 15 min or longer, to stabilize. The slow drift to steady potentials is evidence of upstream movement of electrochemically-produced species and follow-up reaction products; low conductivity solutions require longer intervals to reach a steady state. Potentials measured along the central ES axis reflect those at the ES capillary surface, although equipotential lines can be considered to be more compressed at the latter surface. (J Am Soc Mass Spectrom 2004, 15, 1737-1747