Solomon Zaromb

Theoretical basis for identification and measurement of air contaminants using an array of sensors having partly overlapping selectivities

Abstract The objective of this paper is to provide a theoretical basis for the selection and effective use of an array of chemical sensors for a particular application. The array is to be used in conjunction with a microprocessor in a small portable device capable of detecting, identifying and quantifying any of a large number N of hazardous compounds, either singly or in mixtures of up to A such compounds. A compact array of S different sensors is used, each of which can operate in M differently selective modes so as to yield P=MS parameters, or data channels. The minimum number of parameters required to identify the compounds solely on the basis of the presence or absence of significant signals in the various channels is determined by the inequality For example, P ⩾ 18 or P ⩾ 22 for N = 100 and A = 3 or 4, respectively. A computational approach is proposed to first eliminate all candidate compounds whose known response patterns do not overlap the channels exhibiting the strongest signals. The remaining candidate compounds are then quantified by solving simultaneous linear equations. A determinant, which is used to solve the simultaneous equations, provides a measure of the selectivity and/or non-redundancy of the set of channels exhibiting the strongest signals. This determinant is also inversely proportional to the experimental error or to the required accuracy of the measurements. By computing the values of this determinant for various mixtures, the selectivities and/or non-redundancies of alternative sets of P parameters with respect to a given set of N hazardous compounds can be evaluated and compared.

Monitoring of electrochemically inactive compounds by amperometric gas sensors

Abstract Electrochemical sensors have many useful applications in air and toxic gas monitoring, but they are extremely limited in the gaseous species that they can detect. To extend the applicability of amperometric gas-sensing instruments to electrochemically inactive compounds, gas samples were exposed to a heated platinum or gold filament before being introduced into the sample chambers of several different amperometric sensors. The sensors were of the three-electrode type, having platinum-black reference and counter electrodes and sensing electrodes made of platinum black, powdered gold or vapor-deposited platinum or gold on porous tetrafluoroethylene membranes. All three electrodes were in contact with a 25 – 30 wy.% sulfuric acid solution. The responses of four different sensors to various compounds at 20°C were measured at sensing electrode potentials ranging from 0.9 V to 1.4 V versus RHE (reversible hydrogen electrode in the same electrolyte), with and without a heated platinum filament at the sample inlet. Of 10 compounds tested, only two elicited significant responses without the filament. With the filament heated to about 700 °C, each of the tested compounds elicited a significant response under certain conditions. Moreover, the particular sensors and electrode potentials corresponding to the strongest responses were different for each compound. Qualitatively similar, but quantitatively more pronounced, responses were obtained with the same filament heated to 800 °C or 1050 ± 50 °C, or with a gold filament heated to 950 ± 50 °C. The responses were proportional to concentration in the 0 – 50 ppm range, and usually proportional in the 0 – 200 ppm range.

A room-temperature electrochemical sensor and instrument for monitoring methane

Abstract Electrochemical sensors at room temperature that quantitatively detect methane in air have been developed. Methane is directly oxidized using a highly anodic working-electrode potential and a non-aqueous electrolyte. Stable and durable sensors have been fabricated that incorporate sintered glass wicks and glass fibre filters as electrolyte reservoirs. The monitoring instrument has two potentiostats that regulate two sensors, one of which is used to compensate for background current variations. The instrument requires less than 250 mW to power all components. The response of the monitor is proportional to methane concentration over a wide range, from the minimum detectable concentration (0.6% methane in air) to 100% methane. It is also substantially independent of fluctuations in relative humidity and flow rate. The response time is less than one minute to 90% of signal at a flow rate of 100 cm3/min. The monitor exhibits a net sensitivity of 0.5 – 1 μA/% CH4. It also exhibits low sensitivity to parts-per-million levels of CO or NO2, but yields measurable responses to 0.3% H2, 49 ppm NO and 50% C2H6.

Detection of airborne cocaine and heroin by high-throughput liquid-absorption preconcentration and liquid chromatography—electrochemical detection

A high-throughput liquid-absorption preconcentrator (HTLAP) for rapid and/or ultrasensitive detection and analysis of trace contaminants samples air at a rate of 600-700 l/min and collects analytes from vapors or aerosols at an efficiency of 40-60% into a small volume of liquid absorbent dripping at a rate of 0.1-2 ml/min. These features combine to reduce the lower detection limit (LDL) of available analytical instrumentation by a factor of > 1000 and/or to permit faster sampling and far more rapid on-site air monitoring than were previously practicable. LDLs of ca. 1:10(13) (v/v) of alkaloids have been achieved with LC and electrochemical detection. The HTLAP is directly adaptable to most liquid-phase analyzers. The small rate of liquid collection is also compatible with available interfaces to mass spectrometers. Moreover, the HTLAP permits detection and quantitation of polar or highly reactive compounds that cannot be readily analyzed by conventional preconcentration and GC.

Electrolytic Separation and Recovery in Caustic of Steel and Zinc from Galvanized Steel Scrap

Abstract Experiments were conducted to examine the technical and economic feasibility of a single-step process for electrochemically separating and recovering in hot caustic the components of galvanized steel. Electrochemical separation is practical because: 1. maximum anodic zinc dissolution currents yield commercially acceptable throughputs and are 1000 times greater than those for steel, 2. steel is not seriously corroded by caustic under conditions proposed and 3. the process is robust in the presence of expected aluminum, lead, cadmium and iron impurities. Stripping experiments in 5 M NaOH at 90°C indicate that a G-90 grade (275 g Zn/m2) of galvanized steel can be stripped in about five minutes at a current density of 200 mA/cm2 in a cell with parallel electrodes separated 15 to 59 mm. Tests with scrap at densities of 30 and 150 lbs/ft2 were successful at estimated current densities of about 20 mA/cm2. Residual zinc levels on the steel are less than 0.1 wt%. A technical and economic analysis of alter...

Simple permeation absorber for sampling and preconcentrating hazardous air contaminants

A permeation absorber was developed and experimentally evaluated for sampling and preconcentrating vapors of a primary aromatic amine into a small volume (ca. 0.1 ml) of a liquid extractant that can be directly injected into a chromatograph or other analytical instrument. Starting with 1-l or 4-l samples containing dry or humidified air (0, 7% or 35% relative humidity) and 0.5-5 parts per million by volume of aniline, the measured collection efficiency (fraction of aniline recovered in the extractant) ranged between 60 and 100% when the samples were recirculated 3-6 times. For a single-pass non-recirculating mode, the collection efficiency is calculated to be 40-50%. The degree of preconcentration is directly proportional to the volume V of the sampled air. The collection method is simple and fast and should also be applicable to the sampling and preconcentration of other hazardous air contaminants.

Aluminum‐Consuming Fluidized‐Bed Anodes

This report summarizes and interprets the results of seven experimental runs with aluminum-chip fluidized-bed anodes performed as part of an aluminum-air battery development program at the Alcoa Technical Center. These experiments tested the feasibility of developing electrochemical power sources fueled by particulate aluminum

Cryogenic sampling for aniline vapor with subsequent liquid chromatography-electrochemical detection analysis

Abstract A cryogenic sampler for aniline vapors was evaluated by collecting samples of 10 ppm aniline in air and directly analyzing the collected aniline by liquid chromatography with electrochemical detection. The cryogenic sampler achieved nearly 100% collection and recovery efficiency, with a detection limit of ≈ 4 parts-per-billion (109) aniline in air for a sample collected at 10 cm3/min for 40 s in a 200-μl stainless-steel loop at — 10°C. About 5 min was necessary to dissolve the trapped aniline into 200 μl of a mobile phase desorbing solution at 20°C.