A flow-onto thin-layer electrochemical cell, incorporating Pt-based Hg microelectrodes, is used for fast-scan anodic stripping voltammetry (FS-ASV) at microbore flow rates. The slow flow rates are uniformly altered and controlled utilizing a gas displacement pump. Flow injection is carried out with a low-dead-volume six-port valve. In such a microflow system, the high precision that is observable in quiescent solutions is maintained. The detection limits (e.g., 0.17 nM for Cd2+ with a 2-min preconcentration, or 0.19 pg of Cd2+ at 4.9 μL/min) are remarkably lower than those previously reported in other flow systems utilizing Hg microelectrodes. Compared to ASV in quiescent solutions and in other flow systems, this setup has an excellent sample throughput and low sample consumption. For example, at moderately fast scan rates (e.g., 15 V/s), one analysis of a sample containing Pb2+ or Cd2+ at submicromolar levels takes about 10 s, with only 0.82 μL of sample consumed. Experimental conditions that govern the sensitivity, sample consumption, and throughput are discussed (i.e., scan rate, flow rate, Hg film thickness, and preconcentration time). Finally, potential use of this device for automatic analyses is demonstrated.

The redox reactions that take place in the metal capillary of an electrospray ion source to maintain charge balance alter the composition of the initial solution entering the capillary. Data presented here demonstrate that under certain ES conditions, solution pH may be decreased significantly (by at least 4 pH units) as a result of the electrolytic oxidation of water in positive ion mode electrospray-mass spectrometry (ES-MS). Furthermore, it is shown that this pH change can have an affect on the appearance of the ES mass spectrum of an of analyte. An ES ion source in which the pH of an indicator solution exiting the capillary is monitored optically, before the spraying process, is used to demonstrate that electrolytic reactions in positive ion mode ES can decrease the pH of the initial solution. ES-MS studies using bovine heart cytochrome c are used to illustrate the influence of the electrolytically-induced pH change on the gas-phase ion signals for the multiply protonated protein. The magnitude of electrolytically-induced changes in solution pH will be most significant in non-buffered solutions near neutral pH when using metal spray capillaries or metal contacts to solution comprised of difficult to oxidize material (e.g. platinum or gold). Any pH changes will increase in magnitude as the flow rate decreases and/or ES current increases (all other ES parameters constant). Therefore, the potential impact of these redox reactions in ES-MS, if any, will probably be most important in the very low flow rate ES-MS systems (≤ 1.0 μL min−1).