Carboxylic acid volatile

Various methods have been described for the extraction of the C1-C5 acids from physiological fluids, the most simple of which is direct solvent extraction using ether (Jellum etal., 1971 Lambert and Moss, 1972 Eldjarn etal., 1974), ethyl acetate (Gibbs et al., 1973 Mamer and Gibbs, 1973) or chloroform/methanol for plasma (Kuksis et al., 1976 Kuksis, 1977 Section 2.2.1). Solvent extraction with ether and solvents other than chloroform/methanol ( lipid extract) is non-quantitative because of the unfavourable partition coefficients for the organic acids between water and even the most suitable solvents (Henkel, 1971). In addition, volatilization losses occur on removal of the solvent before analysis (Lambert and Moss, 1972). However, this extraction procedure has advantages when analysis of 

Alternative procedures for the determination of short-chain carboxylic acids involve the direct injection of the acidified physiological fluid into the gas chromatograph (Van den Berg and Hommes, 1974) or the release of the free acids from their salts by mixing urine with Dowex 50 (H ) followed by injection of the supernatant into the chromatograph (Chalmers, 1974 Chalmers etal., 1974a). The latter method enables the simultaneous determination of neutral volatile components, for example, acetone, butanone, methanol and ethanol, and the determination of a variety of volatile acids, alcohols, aldehydes and ketones by this procedure. 

Most methods for the estimation of the C1-C5 carboxylic acids involve the separation of the free acids by gas-liquid chromatography or gas-solid 

In all of these methods, the use of glass analytical gas-chromatographic columns is recommended to avoid adsorption losses. Silanized surfaces have been considered incompatible (Ottenstein and Bartley, 1971). Most work reported has used flame ionization detection as the most suitable and sensitive gas-chromatographic detector these detectors produced virtually no response to water, but suffer from the disadvantage that their response to formic acid is very limited. Thermal conductivity detection can be used for the latter acid, although the sensitivity of the analysis is greatly reduced. 

Ackman, R.G., Bannerman, M. A. and Vandenheuvel, F.A. (1960), Decomposition of short-chain dicarboxylic acid esters during separation on polyester gas chromatography media. Anal. Chem., 32,1209. 

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Spanel P and Smith D 1998 SIFT studies of the reactions of FijO", NO and Ot with a series of volatile carboxylic acids and esters Int. J. Mass Spectrom. Ion Proc. 172 137-47... 

Aliphatic carboxylic acids upto nine carbon atoms are colourless liquids at room temperature with unpleasant odours. The higher acids are wax like solids and are practically odourless due to their low volatility. Carboxylic acids are higher boiling liquids than aldehydes, ketones and even alcohols of comparable moleeular masses. This is due to more extensive association of carboxylic acid molecules through intermolecular hydrogen bonding. The hydrogen bonds are not broken completely even in the vapour phase. In fact, most carboxylic acids exist as dimer in the vapour phase or in the aprotie solvents. 

Canale, A., Valente, M.E. and Ciotti, A. (1984) Determination of volatile carboxylic acids (C i-Cj.) and lactic acid in aqueous extracts of silage by high performance liquid chromatography. Journal of the Science of Food and Agriculture 35, 1178-1182. 

ESSA extractable, semivolatile, strong acids extracted at pH 1 (less volatile carboxylic acids, strong phenols, etc.). 

VOS A volatile, strong acids isolated on anion-exchange resin (volatile carboxylic acids, generally [Pg.92]

A standard official method has been issued for the determination of Ci to C6 volatile carboxylic acids and lactic acid in silage juice [5,6]. 

It is noteworthy that in practice even the reverse of the above may occur. Often it is necessary to analyse compounds that are too volatile. Significant losses during the preliminary treatment of the sample (e.g., extraction, removal of the solvent), due to this volatility, may introduce errors into the quantitative evaluation. Analysis of volatile carboxylic acids in biological samples is an example. Conversion of these compounds into less volatile derivatives is therefore advantageous from the viewpoint of both GC proper and preliminary isolation of the compounds and sample treatment. 

Barth T. (1987) Quantitative determination of volatile carboxylic acids in formation waters by isotachophoresis. Anal. Chem. 59, 2232-2237. 

Phosphorus trichloride (PC13), b.p. 74.5°, is used particularly for preparation of volatile carboxylic acid chlorides (reaction b). Usually about 1.1 moles of the carboxylic acid is allowed to react with 0.5 mole of PC13 at room temperature or with slight warming until evolution of HC1 ceases and then the acid chloride is distilled off see, for instance, the preparation of acetyl chloride from glacial acetic acid and PCl3.33b The carboxylic acid chloride can also be taken up in a solvent (benzene, light petroleum, or CS2) at the end of the reaction and used directly for further reactions ... 

Reaction (a) is used for preparation of volatile carboxylic acids from 1 mole of the corresponding acid and 1.5-2 moles of benzoyl chloride.1111,1112... 

Chromosorb 102 Porapak Q Light and permanent gases, volatile carboxylic acids, alcohols, glycols, ketones, hydrocarbons, esters, nitriles and nitroalkanes. Not recommended for amines, anilines. Nitrated by nitrogen oxide gases. 

Uses of Formic Acid, Formamide, and DMF. Traditional markets for formic acid developed as a result of some of the unusual properties of this inexpensive, volatile carboxylic acid. It is nearly as acidic as sulfuric acid but may react either as an acid or an aldehyde because the carboxyl group is bound to a hydrogen rather than an alkyl group. It decomposes readily by dehydration, dehydrogenation, or through a bimolecular reaction (15]. 

Components tentatively identified in cow headspace volatiles on the basis of mass spectral data included aldehydes (to and benzaldehyde), ketones (to C ),volatile carboxylic acids, phenols, sulfides and hydrocarbons. ... 

Both MTBSTFA [295-299] and TBDMCS/imidazole/ DMF [300] reagents have been used for silylation in this field. The best method of preparing TBDMS derivatives is to use MTBSTFA, in view of its ease of reaction and convenience, since there is no need for sample purification prior to GC or GC-MS analysis. The method of derivatization set out below is equally well applied to volatile and non-volatile carboxylic acids. 

The above procedure overcomes many of the problems associated with the analysis of volatile carboxylic acids by performing derivatizations on the TEA salts and... 

Propionic acid bacteria have been successfully used to obtain a number of practically valuable substances, products of synthetic and/or catabolic reactions. These products are volatile carboxylic acids (propionic and acetic), porphobilinogen, porphyrins, vitamin B12, aspartic and malic acids, nucleotides and their derivatives. In general, these products can be produced both by free and by immobilized cells. The first process, in which immobilized cells of P. shermanii were used, was a multi-step synthesis of propionic acid (Vorobjeva, 1978). 

Based on these principles, oil or fat samples are heated imder constant air flow at a temperature between 100 °C and 140 °C. These variables cause the dissociation of volatile carboxylic acids, especially formic and acetic acids produced during the oxidation process, which undergo solubilization and consequently increase water conductivity. The response to this conductivity increase is expressed as an oxidation curve that exhibits the induction time, followed by a subsequent shift toward higher oxidation. The interpretation of this curve refers to the number of hours required until the end of the induction time [19]. 

Monseur, X., Walravens, J., Dourte, P., Termonia, M. (1981). Determination of volatile carboxylic acids in animal wastes by (GC)2 of their benzyl esters. Journal of High Resolution Chromatography A, 49-53. 

Barteau MA, Bowker M, Madix RJ (1981) Formation and decomposition of acetate intermediates on the Ag(llO) surface. J Catal 67 118-128 Barth T (1987) Quantitative determination of volatile carboxylic acids in formation waters by isotachophoresis. Anal Chem 59 2232-2237 Bell JLS (1991) Acetate decomposition in hydrothermal solutions. PhD Thesis, The Pennsylvania State University, University Park, 228 pp Bell JLS, Palmer DA, Barnes HL, Drummond SE (1993) Thermal decomposition of acetate. Part III. Catalysis by mineral surfaces. Geochim Cosmochim Acta (in press) Benziger JB, Madix RJ (1979) The decomposition of formic acid on Ni(lOO). Surface Sci 79 394-412... 

Organic acids in water. Roberts et al. also compared how three fibers (Carboxen/PDMS, Carbowax/DVB, and Polyacrylate) extracted volatile carboxylic acids from aqueous solutions. Figure 6 shows that Carbowax/PDMS provided the best overall sensitivity for these compounds. However, Carboxen/ PDMS was more sensitive for the smaller acids (i.e., acetic and propionic). 

Figure 6 Comparison of different fibers for the analysis of volatile carboxylic acids. Conditions aqueous solution (0.2 mL) in 2 mL vial, 30°C, pH 2, saturated with NaCl, and 60 minutes headspace extraction. Concentrations of acids acetic, 11 ppm propionic, 0.7 ppm isobutyric, 0.7 ppm butyric, 0.8 ppm isovaleric, 0.6 ppm valeric, 0.7 ppm.

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