Gas Sensing Detectors

Tab. S Examples of some bioanalytically useful potentiometric enzyme-based biosensors that can be prepared for monitoring important biomolecules using appropriate immobilized enzymes and ISE or gas sensing detectors...

Gas-sensing detectors. These devices sense the production of combustion gases by a fire. Gas-sensing detectors act more rapidly than... 

Conventional ion-selective electrodes have been used as detectors for immunoassays. Antibody binding measurements can be made with hapten-selective electrodes such as the trimethylphenylammonium ion electrode Enzyme immunoassays in which the enzyme label catalyzes the production of a product that is detected by an ion-selective or gas-sensing electrode take advantage of the amplification effect of enzyme catalysis in order to reach lower detection limits. Systems for hepatitis B surface antigen and estradiol use horseradish peroxidase as the enzyme label and... 

These measure the potential difference between the transducing electrode and a reference electrode under conditions of zero current. Three types of potentiometric detectors are commonly employed ion-selective electrodes (ISE), gas-sensing electrodes and field effect transistors (FET). 

Bowman, M. C., Beroza, M. Gas chromatographic detector for simultaneous sensing of phosphorus and sulfur containing compounds by flame photometric. Anal. Chem. 40, 1448 (1968). 

One particular advantage with gas leak detectors is the constant distance from the leak to the thermal conductivity sensing device. This constant distance makes the time lag consistent wherever you are sniffing with the probe. When relying on installed thermocouples (on the vacuum system), a leak located right near the thermocouple will provide an immediate and full-strength response, whereas a leak some distance from the thermocouple will have a more subtle effect and will require some time before this effect is observed. 

Further developments have increased the potential of proportional counting by placing a grid of anode wires between two large plates, 1.5 mm above and below, serving as cathodes. Ions formed in the gas-filled volume drift toward the nearest anode wire where they undergo multiplication each event is automatically localized. Thus, two-dimensional localization may be accomplished by these position-sensing detectors. 

Figure 1. Schematic of static (A) and continuous flow (B) gas sensing system using solvent/polymeric ion-selective membrane electrodes as detectors.

Remote gas-sensing systems can also be grouped according to the type of equipment used at the remote end. For example, double-ended systems, such as DOAS, have a remote source, while TDLAS is often operated with a remote reflector or detector. The principal example of a single-ended system is DIAL, which depends on atmospheric backscatter and therefore has a single apparatus that includes both the transmitter and the receiver. 

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