Chemical sensors ammonia

Figure 5.6 — Flow-through chemical sensor for the determination of ammonia. For details, see text. (Adapted from [9] with permission of the American Chemical Society).

The catalytic detection of ammonium ions has not been extensively investigated in contrast with the large variety of potentiometric and amperometric chemical sensors and optical sensors described in the literature [236], Similarly, the detection of ammonia in air has merited diflierent approaches in the field of chemical sensors. Screen-printed electrodes modified with Meldola s Blue and covered with a polycarbonate membrane constitute the basis of the catalytic detection of NHj. The measurement is based on the electrocatalytic reduction of NADH upon addition of glutamate dehydrogenase to a stirred solution containing NADH, 2-oxoglutarate and ammonium ions. The rate of current decrease (nA s ), measured at 50 mV, correlates to the concentration of ammonium ions in the sample. Recoveries of ammonium ions in spiked pond and tap waters at the level of 0.1 ppm are close to 100%, which demonstrates the feasibility of this assay for the detection of ammonium ions in waters [237],... 

Combined electrodes have been developed to measure dissolved gases such as carbon dioxide (CO2), ammonia (NH3) and sulfur dioxide (SO2). These chemical sensors contain an internal solution that is isolated from the sample solution by an hydrophobic membrane which is permeable to dissolved gas molecules... 

Composites of PANI-NFs, synthesized using a rapid mixing method, with amines have recently been presented as novel materials for phosgene detection [472]. Chemiresistor sensors with nanofibrous PANI films as a sensitive layer, prepared by chemical oxidative polymerization of aniline on Si substrates, which were surface-modified by amino-silane self-assembled monolayers, showed sensitivity to very low concentration (0.5 ppm) of ammonia gas [297]. Ultrafast sensor responses to ammonia gas of the dispersed PANI-CSA nanorods [303] and patterned PANI nanobowl monolayers containing Au nanoparticles [473] have recently been demonstrated. The gas response of the PANI-NTs to a series of chemical vapors such as ammonia, hydrazine, and triethylamine was studied [319,323]. The results indicated that the PANI-NTs show superior performance as chemical sensors. Electrospun isolated PANI-CSA nanofiber sensors of various aliphatic alcohol vapors have been proven to be comparable to or faster than those prepared from PANI-NF mats [474]. An electrochemical method for the detection of ultratrace amount of 2,4,6-trinitrotoluene with synthetic copolypeptide-doped PANI-NFs has recently been reported [475]. PANI-NFs, prepared through the in situ oxidative polymerization method, were used for the detection of aromatic organic compounds [476]. 

Fluorophore- and Chromophore-Based Biosensors Chromophore and fluorophore molecules show a change in absorbance or fluorescence at a particular wavelength due to a change in oxidation state of the molecule. Thus, a chemical sensor can be constructed for the usual chemical parameters, such as pH, oxygen, and ammonia, which then can be coupled to enzyme reactions. 

In this paper, we present an overview of our work on polyaniline nanofiber chemical sensors. SpeciHcally, we show how polyaniline nanofibers outperform conventional polyaniline as chemical sensors upon exposure to hydrochloric acid (HCl), ammonia (NH3), hydrazine (N2H4), and hydrogen sulfide (H2S). We will also give examples of how the sensor response can be enhanced by using polyaniline nanofiber composite films. 

Wolfbeis OS (1991) Fiber optic chemical sensors and biosensors, vol 1. CRC Press, Boca Raton, FL Wolfbeis OS (ed) (1992) Fiber optic chemical sensors and biosensors, vol 2. CRC Press, Boca Raton, FL Wolfbeis OS (2005) Materials for fluorescence-based optical chemical sensors. J Mater Chem 15 2657-2669 Wolfbeis OS, Posch HE (1986) Fiber-optic fluorescing sensor for ammonia. Anal Chim Acta 185 321-327 Wolfbeis OS, Weis LJ, Leiner MJP, Ziegler WE (1988) Fiber-optic fluorosensor for oxygen and carbon dioxide. Anal Chem 60 2028-2030... 

Symons EA (1992) Catalytic gas sensors. In Sberveglieri G (ed) Gas sensors. Kluwer, Dordrecht, pp 169-185 Talazac L, Brunet J, Battut V, Blanc JP, Pauly A, Germain JP, Pellier S, Soulier C (2001) Air quality evaluation by monolithic InP-based resistive sensors. Sens Actuators B 76 258-264 Taylor RF (1996) Chemical and biological sensors markets and commercialization. In Taylor RF, Schultz JS (eds) Handbook of chemical sensors and biosensors. lOP Publishing, Bristol Taylor RF, Schultz JS (eds) (1996) Handbook of chemical sensors and biosensors. lOP Publishing, Bristol Timmer B, Olthuis W, van den Berg A (2005) Ammonia sensors and their apphcations—a review. Sens Actuators B 107 666-677... 

Janata J, Josowicz M (2003) Conducting polymers in electronic chemical sensors. Nat Mater 2 19-24 Jesenius H, Thaysen J, Rasmussen AA, Veje LH, Hansen O, Boisen A (2000) A microcantilever-based alcohol vapor sensor-application and response model. Appl Phys Lett 76 2615-2617 Jiang L, Jun H-K, Hoh Y-S, Lim J-O, Lee D-D, Huh J-S (2005) Sensing characteristics of polypyrrole-poly(vinyl alcohol) methanol sensors prepared by in situ vapor state polymerization. Sens Actuators B 105 132-137 Jin Z, Su YX, Duan YX (2001) Development of a polyanUine-based optical ammonia sensor. Sens Actuators B 72 75-79... 

Room temperature chemical sensors for alcohol, acetone, water vapor and ammonia detection were developed [1,2] by using beta alumina and xerogel of antimonic acid hydrate. The sensitivity and selectivity depend on ion-exchange and preparative methods. Ammonia-exchanged samples of beta alumina were sensitive to water and ammonia vapor. Potentiometric and amperometric sensors are made by using ion conducting material as the substrate, an Au electrode as the reference and Pd (or Ag, Ni, Pt) as the sensitive electrode. 

A use of carbon nanotubes as chemical sensors for nitrogen dioxide and ammonia was discovered recently by Kong and co-workers [107]. When exposed to these gases, the electrical resistance of single-walled carbon nanotubes changes dramatically and very quickly. Unfortunately, recovery is slow and requires heat at the present state of development. 

Figure 8 Typical fingerprint mass spectra for a peppermint oil obtained using an Agilent MS chemical sensor in three different modes (a) electron impact ionization, (b) positive chemical ionization with methane reagent gas, and (c) positive chemical ionization with ammonia reagent gas.

Dar GN, Umar A, Zaidi SA, Baskoutas S, Hwang SW, Abaker M, Al-Hajry A, Al-Sayaii SA (2012) Ultra-high sensitive ammonia chemical sensor based on ZnO nanopencils. Talanta 89 155-161... 

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