The use of an electrochemically based probe for in situ determination of heavy metals in groundwater is described. The in situ probe, consisting of a microlithographically fabricated iridium ultramicroelectrode array sensor (UMEA), a custom-built miniaturized potentiostat and microcontroller, is connected to a laptop computer for control and data acquisition. The utility of this probe for rapid on-site screening of heavy metals was shown by conducting a proof-ofconcept field demonstration at a metals contaminated landfill site located at Hanscom Air Force Base in Bedford, MA. Using the electroanalytical technique of square wave anodic stripping voltammetry (SWASV), the sensor was used to measure both the labile and total pH <2 forms of copper, lead, cadmium, and zinc at the parts-per-billion level. The on-site and in situ measurements were compared to laboratory-based electroanalytical measurements and to contract laboratory U.S. EPA Method 200.7 ICP analysis. The results indicate that in situ electroanalytical measurements of labile metal species are feasible, providing a rough estimation of metals concentrations and trends in their behavior. The in situ and on-site results agree to within an order of magnitude with the laboratory determinations. This study demonstrates that such electroanalytical-based devices may be of value for an initial, rapid, low-cost, screening of heavy metal contaminated sites.

The analytical performance of several mercury-coated iridium ultramicroelectrode arrays (IrUMEAs) was studied using square wave anodic stripping voltammetry (SWASV) for determination of cadmium in a pH 4.5 acetate buffer. The microlithographically fabricated IrUMEAs consisted of either 20 or 25 individual disk shaped UMEs, each 10 mm in diameter. The insulating layer utilized in the fabrication process was either silicon dioxide (5000 Å ) or silicon nitride (1500 Å or 2500 Å ). Calibration plots demonstrated good linearity for cadmium from 0-100 ppb. Standard deviations, detection limits, and correlation coefficients were calculated to determine the stability and reproducibility of the IrUMEAs. Repetitive cycles of depositing and stripping Hg at the IrUMEA surface resulted in increased distortion and loss of the SWASV signal. Atomic force microscopy revealed a subtle transformation in the IrUMEA surfaces.

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A new technique (Flash Titration™) for the determination of total acidity and total alkalinity was applied to food and beverage analysis. Requiring no liquid titrants, Flash Titration is a technique made possible through microfabrication of electrochemical components on a silicon chip. Acidic or basic titrant was generated electrochemically at a noble-metal electrode that intimately surrounded an ion-selective, field-effect transistor pH sensor. As acid or base was generated through electrolysis, sample alkalinity or acidity, respectively, was neutralized in the immediate vicinity of the electrode. Through diffusion, a zone comprising a gradient of partially to totally neutralized sample expanded from the generating electrode into the volume element sensed by the nearby pH sensor. An analysis of the pH signal versus time revealed an end point inflection at an elapsed time related to the total alkalinity or acidity of the sample. End point times were typically a few seconds. In this paper, Flash Titration was applied to the analysis of a variety of samples, including juices, soft drinks, wines, and food products. The differences between the results obtained by the Flash Titration method and a commonly used conventional volumetric method were less than 2% in most food products tested. Analysis costs were reduced both through time saving and reduction or elimination of hazardous liquid titrant disposal, by the use of the Flash Titration method.