Anodic Stripping Voltammetry Coupled On-Line with Inductively Coupled Plasma Mass Spectrometry:  Optimization of a Thin-Layer Flow Cell System for Analyte Signal Enhancement

Abstract

Parameters affecting analyte signal enhancement in anodic stripping voltammetry-inductively coupled plasma mass spectrometry (ASV-ICP-MS), using a thin-layer ASV cell and microconcentric nebulization (MCN), have been examined. Silver was used as a test analyte and was deposited at a glassy carbon working electrode. The MCN allowed use of solution flow rates that were beneficial to optimum electrolytic performance of the thin-layer cell. High analyte deposition efficiencies obtained with the thin-layer cell, combined with minimal sample consumption of the MCN, allowed substantial signal enhancement (>400 times higher than continuous nebulization level) to be obtained with 2-3 mL of sample and deposition times of less than 30 min. Signal enhancement was strongly influenced by the opposing effect of flow rate on the electrolytic deposition efficiency (deposition efficiency decreases with increasing flow rate) and on the quantity of analyte delivered to the cell (analyte mass throughput increases with increasing flow rate). Excellent linearity for stripping peak heights was demonstrated for a wide range of analyte deposition times and for peak heights and peak areas (r > 0.999) over a wide concentration range (25 ng/L-20 μg/L). Precision was good (RSD typically <3% for n = 3-6) except for a high Ag blank contributed to by corrosion of the counter electrode and by Ag diffusion from the reference electrode into the cell. Details of the flow manifold and ASV cells are discussed, along with relevant performance characteristics of the MCN.

Electrochemical sample pretreatment coupled on-line with electrospray mass spectrometry for enhanced elemental analysis

“…The utility of this on-line, electrochemically modulated, approach to elemental preconcentration and cleanup has been previously demonstrated by our group at Oak Ridge with ICP-MS [28][29][30] and by others with ICP-AES or ICP-MS. [31][32][33][34][35][36][37][38] In our work, using a thin-layer, flow-by electrode cell design, we have demonstrated rapid (`90 s) elimination of high levels of problematic matrices and simultaneous signal enhancements (in some cases greater than 2 orders of magnitude) with several different elements using deposition times of 2 to 15 min. Furthermore, a dynamic range of 10 4 has been shown as well as excellent quantification via standard additions.…”

“…The majority of these factors are the same as those we previously addressed in coupling this same thin-layer flow cell system on-line with ICP-MS. 29 In general, one must operate under conditions that optimize electrolytic performance of the cell (both deposition and stripping), minimize matrix washout times, minimize dispersion of the stripping peak as analyte is released from the cell, and maximize sample throughput.…”

“…In ICP-MS, a H 2 O/HNO 3 (99/1 v/v) electrolyte/solvent system worked well in terms of gas-phase ion generation and also provided sufficient conductivity for control of the electrochemical cell. 28,29,30 Moreover, metals were quite soluble in this solvent, and therefore, cell and transfer line washout was efficient and rapid. Gas-phase ion generation in ES-MS is much more susceptible to solvent and matrix than in ICP-MS. 22,23 The amount of acid and H 2 O must be minimized in the solvent system used with ES-MS for maximum generation of gas-phase metal ions (see below).…”

Nafion-coated bismuth film and nafion-coated mercury film electrodes for anodic stripping voltammetry combined on-line with ICP-mass spectrometry

“…The flow cell has been slightly modified from the design used by Van Berkel [5,9] and coworkers and that for our previous work [4,10] (Figure 1a). The Pt foil auxiliary electrode is replaced by a 3-mm-diameter gold disk electrode positioned next to the working electrode.…”

“…The error bars were calculated from at least three replicates. Hg), (2) the slower flow rate used for the DIN work (45 to 55 L/min [4] increases the analyte deposition efficiency [5], and (3) as aforementioned, the preconcentration efficiency of Cd 2ϩ at the Nafion-coated electrodes is relatively low (e.g., lower than Pb 2ϩ ).…”