Acetaldehyde measurement

AA Analyzer, Automatic acetaldehyde measuring system, TopWave International, Inc. 

With this equipment many small molecules are detectable (Table 1). Some of them are particularly important in fruit analysis. Water vapour detection allows one to monitor respiration processes ethanol and especially acetaldehyde measurements permit one to follow the onset of fermentation (Bijnen 1995) ethane is taken as an indicator of cell membrane damage. It should be noted that periodic release of methane by cockroaches is investigated in detail with this setup (Bijnen 1995). 

Acetaldehyde Measurement duct Once/ continuous Gas chromatogrs hy Enviromnental Protection Agency Armoimcement No. 9... 

Detailed analyses of the above experiments suggest that the apparent steps in k E) may not arise from quantized transition state energy levels [110.111]. Transition state models used to interpret the ketene and acetaldehyde dissociation experiments are not consistent with the results of high-level ab initio calculations [110.111]. The steps observed for NO2 dissociation may originate from the opening of electronically excited dissociation chaimels [107.108]. It is also of interest that RRKM-like steps in k E) are not found from detailed quantum dynamical calculations of unimolecular dissociation [91.101.102.112]. More studies are needed of unimolecular reactions near tln-eshold to detennine whether tiiere are actual quantized transition states and steps in k E) and, if not, what is the origin of the apparent steps in the above measurements of k E). 

FIGURE 21.2 Experimental apparatus used to measure the standard reduction potential of the indicated redox couples (a) the acetaldehyde/ethanol couple, (b) the fumarate/succi-nate couple, (c) the Fe /Fe" couple. 

Figure 21.2a shows a sample/reference half-cell pair for measurement of the standard reduction potential of the acetaldehyde/ethanol couple. Because electrons flow toward the reference half-cell and away from the sample half-cell, the standard reduction potential is negative, specifically —0.197 V. In contrast, the fumarate/succinate couple and the Fe /Fe couple both cause electrons to flow from the reference half-cell to the sample half-cell that is, reduction occurs spontaneously in each system, and the reduction potentials of both are thus positive. The standard reduction potential for the Fe /Fe half-cell is much larger than that for the fumarate/ succinate half-cell, with values of + 0.771 V and +0.031 V, respectively. For each half-cell, a half-cell reaction describes the reaction taking place. For the fumarate/succinate half-cell coupled to a H Hg reference half-cell, the reaction occurring is indeed a reduction of fumarate. 

Another and more accurate microwave method makes use of frequency measurements.1 11 16 28 31 Acetaldehyde is an example of the class of molecules to which this method has been applied. Here there are three equivalent potential minima because of the... 

The computation result yield acetaldehyde concentration as function of time. The value of kinetics parameters, ki, ka, k3 were adjusted to minimize the sum of square of error between the predicted and measured concentration using Hooke Jeeve method [3]. 

Induced oxidation of alcohols by hydrogen peroxide was studied by Kolthoff and Medalia . According to their measurements the value of F-, increases with the increase in the concentration of ethanol, while it decreases with increase in the acid concentration (see Table 16). In acetic acid medium the value of F[ is considerably lower. Chloride ions effectively suppress the induced oxidation of alcohols. The main product of the oxidation of ethanol is acetaldehyde which can be further oxidized to acetic acid. The data on the induced oxidation of alcohol (H2A) can be interpreted by reactions (53), (98), (99) and (57). 

Figure 3. Arrhenius plots for the formation of formaldehyde or acetaldehyde from methanol or ethanol, normalized by the number of vanadiums (open symbols) and by the amount of oxygen uptake measured at 625 K (filled symbols). Lines on the right panel are calculated from the data reported by Oyama and Somorjai [11].

Figure 52.3. Adsorbed acetaldehyde (CHsCHOad), adsorbed acetate (CHsCOO ad), and adsorbed formate (HCOO ad) IR relative intensities during the first 20 min of photocatalytic oxidation for the Pt/Ti02 and Ti02 catalysts. IR intensities were obtained by measuring the peak height of bands corresponding to intermediate species directly from the difference spectra presented in Fignre 52.2.

A method for the determination of formaldehyde in the presence of acetaldehyde was developed by Nicolet and Shinn.88,100 103 After the excess periodate had been destroyed, these workers swept the acetaldehyde (from the neutral reaction mixture) into a sodium bisulfite solution by means of a stream of carbon dioxide. The acetaldehyde was measured by conventional, bisulfite methods, and the residual formaldehyde was precipitated with Dimedon. This procedure was applied to protein hydroly-zates and to terminal deoxy structures of carbohydrates.88,280 ... 

Fig. 56. Dependence of Mwof the microgels on the polymer yield in the anionic polymerization of EDMA in toluene by n-BuLi [254] (see Figure 53 caption for the reaction conditions). Reduced viscosity vs concentration of microgels a) Composition (mol %) N,N -methyl-enebisacrylamide (55%), methacrylamide (33%), methacrylic acid (2%), methacrylamido acetaldehyd-dimethylacetal (10%),measured at 20 °C in water, b) Composition (mol %) 1,4-DVB (35%), propenic acid amide-2-methyl-N-(4-methyl-2-butyl-l,3-dioxolane prepared by emulsion copolymerization and measured in dimethylformamide.

The rate of the second order decomposition of acetaldehyde was measured over a temperature range. Find the activation energy and the frequency factor. 

Acetaldehyde vapor was passed through a plug flow reactor at atmospheric pressure and 600 C. The fraction remaining, f - na/na0 was measured as a function of Vr/na0 measured in seconds. 

We have recently performed a variety of these and related SPAIRS-voltammetric measurements on platinum and palladium <5c. 12b ), and have concluded that the adsorbed CO formed in most cases acts predominantly as a poison for organic electrooxidation. Interestingly, the potential at which the CO undergoes electrooxidation, and hence where the electrocatalysis commences, can be strongly dependent on the structure of the solution species involved. Thus for acetaldehyde, for example, this process occurs at about 0.3 V lower overpotentials than for benzaldehyde under comparable conditions (5c). 

Measurements of Raman spectra should in principle distinguish between hydrated and unhydrated species in solution, but rather concentrated solutions must be used, and little work has yet been done. The measurements of Matsushima (1963) on aqueous acetaldehyde are in qualitative accord with other methods. 

The reactions are accompanied by a considerable volume change, and a dilatometric method was employed by Bell and Higginson (1949), who added acetaldehyde-water mixtures (containing about equal quantities of MeCHO and MeCH(OH)2) to an excess of acetone, and thus measured kj, in presence of a large number of acid catalysts. The direct hydration of acetaldehyde in aqueous buffer solutions is inconveniently fast at room temperatures, but ( (j + A ) was measured dilatometrically at 0°C by Bell and Darwent (1950), who established the existence of general acid-base catalysis. 

New or improved methods are needed to measure local uptake experimentally. Such data can be used to verify the detailed dosage distribution predicted by the models. For example the retrograde catheter and tracheal cannula system used by Com et al. appears promising for transfer-coefficient measurements within segments of the tracheobronchial tree. A similar method was used by Battista and (3oyer to measure the absorption of acetaldehyde vapor in the dog lung. 

Kinetic and thermodynamic parameters have been measured for the chlorination of simple aliphatic and aryl alkyl ketones in strong acid media by chloramine-B (sodium A-chlorobenzenesulfonamide). Catalysis of the monochlorination of acetaldehyde in anhydrous carbon tetrachloride by trichloroacetic acid, and by hydrogen chloride, are reported. IR and UV spectroscopy have been used to probe the reaction of acetaldehyde with trichloroacetic acid in carbon tetrachloride. " Two cyclic 1 1 intermediates have been identified, and are found to be in equilibrium. 

Schauer et al. (2001) measured organic compound emission rates for volatile organic compounds, gas-phase semi-volatile organic compounds, and particle phase organic compounds from the residential (fireplace) combustion of pine, oak, and eucalyptus. The gas-phase emission rates of acetaldehyde were 1,704 mg/kg of pine burned, 823 mg/kg of oak burned, and 1,021 mg/kg of eucalyptus burned. 

Several nonhalogenated aldehydes were measured in the U.S. ICR effort, including formaldehyde, acetaldehyde, glyoxal, and methyl glyoxal [63]. These aldehydes are DBFs produced primarily by ozone, although both chlorine and chlorine dioxide... 

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