Formic acid sensor

J. Yeom, G. Z. Mozsgai, B. R. Flachsbart, et al. Microfabrication and characterization of a silicon-based millimeter scale, PEM fuel cell operating with hydrogen, methanol, or formic acid. Sensors Actuators B 107 (2005) 882-891. 

Formic Acid Sensor. Formic acid is found in culture media. Therefore, on-line determination of formic acid is required. 

Total oxygen demand (TOD) tells us how much 02 is required for complete combustion of pollutants in a waste stream. A volume of N2 containing a known quantity of 02 is mixed with the sample and complete combustion is carried out. The remaining 02 is measured by a potentiometric sensor (Box 17-1). Different species in the waste stream consume different amounts of O,. For example, urea consumes five times as much 02 as formic acid does. Species such as NH3 and H2S also contribute to TOD. 

The sensor did not respond to volatile compounds such as methyl alcohol, formic acid, acetic acid, propionic acid, and other nutrients for microorganisms such as carbohydrates, amino acids, and ions. The selectivity of the microbial sensor for ethyl alcohol was satisfactory. 

The calibration graphs obtained showed linear relationships between the current decrease and the concentration of acetic acid up to 72 mg l-. The minimum concentration for determination was 5 mg of acetic acid 1". The current difference was reproducible within 6 % for an acetic acid sample contaning 54 mg l 1. The standard deviation was 1.6 mg 1 in 20 experiments. The sensor did not respond to volatile compounds such as formic acid and methanol or to nonvolatile nutrients such as glucose and phosphate ions. 

A diagram of the microbial sensor is illustrated in Figure 2. When the sensor was inserted into a sample solution containing formic acid, formic acid permeated through the porous Teflon membrane. Hydrogen, produced from formic acid by butyricum, penetrated through the Teflon membrane, and was oxidized on the platinum anode. As a result, the current increased until it reached a steady state. The steady state current depended on the concentration of formic acid. The steady state current was obtained within 20 min. 

The sensor did not respond to nonvolatile and other volatile compounds. The microbial sensor was applied to the determination of formic acid in the cultivation medium of Aeromonas formicans. 

The formic acid concentration was measured by the gas chromatography and by the microbial sensor. Good agreement was obtained between both methods the regression coefficient was 0.98 for 10 experiments. 

Figure 2. Schematic diagram of the microbial sensor for formic acid. 1. Pt anode 2. Teflon membrane 3. Immobilized C. butyricum ...

The coordinative and/or dissociative adsorption of various probe molecules has been used to characterize the surface properties of Ti02) which finds applications as a catalyst, photocatalyst, and sensor. Among the molecules used as probes, we mention CO (37, 38, 563-576), C02 (563, 565, 577), NO (578,579), water (580,581), pyridine (582,583), ammonia (584,585), alcohols (586, 587), ethers (including perfluoroethers) (588), ozone (589), nitrogen oxide (590), dioxygen (591), formic acid (592-594), benzene (584), benzoic acid (595), and chromyl chloride (596). 

Matusnaga, T. Karube, I. Suzuki, S., A specific microbial sensor for formic acid, Appl. Microbiol. Biotechnol. 1980, 10, 235-245... 

The regeneration agent was either 2mg/mL pepsin in 50mM phosphate solution adjusted to pH 2 or 500mM formic acid (BZE-DADOO-modified sensors), respectively (see Note 3). The suggested measuring cycle consisted of the following steps (20,21) ... 

For regeneration, 500mM formic acid solution was used to dissociate the BZE-DADOO-cholinesterase complex. The sensor was used for more than 40 regeneration steps. Figure 3 shows the binding records for various concentrations of butyryl-cholinesterase. The binding of the enzyme to the immobilized BZE-DADOO could be detected at protein concentration down to 5 pg/mL. For the experiments with DFP, a certain BChE concentration was chosen (25 pg/mL) and incubated with different concentrations of DFP for 30 min. The results are shown in Fig. 4. The organophosphate could be detected at concentrations down to 0.1 nM. 

A major focus of more recent studies on adsorption at metal electrodes has been the investigation of the mechanism of electro-oxidation of organic fuels (methanol, formic acid, formaldehyde, etc. [55, 56]) and the electro-reduction of carbon dioxide. The former type of reaction is important in the context of the development of fuel cells a major problem has been the poisoning of the anode by carbon fragments and mechanistic insights are urgently needed. In the latter case, the development of C02 sensors has a high priority. 

Lauerhaas JM, Credo GM, Heinrich JL, Sailor MJ (1992) Reversible luminescence quenching of porous silicon by solvents. J Am Chem Soc 114(5) 1911-1912 Lazzerini GM, Strambini LM, Barillaro G (2013) Addressing reliability and degradation of chemitransistor sensors by electrical tuning of the sensitivity. Sci Rep 3 1161 Lee EJ, Ha JS, Sailor MJ (1995) Photoderivatization of the surface of luminescent porous silicon with formic acid. J Am Chem Soc 117 8295-8296 Letant SE, Sailor MJ (2000) Detection of HF gas with a porous silicon interferometer. Adv Mater 12(5) 355-359... 

Daniele, S., Bragato, C. and Battistel, D. (2012) Bismuth-coated mesoporous platinum micro-electrodes as sensors for formic acid detection. Electroanalysis, 24, 759-766. 

Tin dioxide, an n-type semiconductor with a wide bandgap (3.6 eV at 300 K), has been widely studied as a sensor, a (photo)electrode material and in oxidation reactions for depollution. The performance of tin(iv) oxide is closely linked to structural features, such as nanosized crystallites, surface-to-volume ratio and surface electronic properties. The incentive for carbon-dioxide transformation into value-added products led to examination of the electroreduction of carbon dioxide at different cathodes. It has been recognised that the faradic yield and selectivity to carbon monoxide, methane, methanol, and formic acid rely upon the nature of the cathode and pH. ° Tin(iv) oxide, as cathode, was found to be selective in formate formation at pH = 10.2 with a faradic yield of 67%, whereas copper is selective for methane and ethene, and gold and silver for carbon monoxide. Nano-tin(iv) oxide has been shown to be active and selective in the carboigrlation of methanol to dimethyl carbonate at 150 °C and 20 MPa pressure. The catalyst was recyclable and its activity and selectivity compare with that of soluble organotins (see Section 21.5). 

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