Organic acids volumetric methods

The preferred method of determining water in glycerol is by the Kad Fischer volumetric method (18). Water can also be determined by a special quantitative distillation in which the distilled water is absorbed by anhydrous magnesium perchlorate (19). Other tests such as ash, alkalinity or acidity, sodium chloride, and total organic residue are included in AOCS methods (13,16,18). 

Many methods have been used to determine organic acids in foods, including volumetric, electrochemical, enzymatic, and chromatographic (paper, thin-layer, gas-liquid, or HPLC) methods. However, most of these are not able to assay organic acids comprehensively for example, the enzymatic methods are specific kits for individual organic acids (i.e., they only detect one of the acids present). Therefore, to analyze the sample comprehensively using enzymatic methods would be extremely time consuming and costly, as the analysis would have to be run separately for each acid and would require several kits. 

Of the methods listed above, HPLC is the best for analyzing all organic acids in a sample, as it is able to quantitatively identify several different acids in one run. HPLC provides a method that is fast, sensitive, and reliable, which is an advantage over spectrophotometric and volumetric methods. HPLC methods are also very reproducible the retention times of the compounds are fairly constant. However, there will be differences in retention times between columns and there will invariably be... 

Preparation of the sample for analysis of organic acids in wine is analogous to the method reported for preparation of the must sample by using SPE C18 cartridge (paragraph 1.2.2) but, instead of collecting the eluate of a lmL diluted sample in a 20-mL volumetric flask, a 10-mL volumetric flask is used (the final sample is diluted 10-fold). To improve... 

The overall reaction is characterized by product analyses and coulombic efficiency determinations. Carbon dioxide, which is the primary product in most organic reactions at noble-metal anodes, can be removed from acidic solutions in the anode compartment of the electrolytic cell by passing an inert gas through the cell, and then reacting quantitatively, e.g., with Ba(OH)2 or Ascarite. Carbon dioxide is not as easily determined in alkaline electrolyte, which must be analyzed, e.g., by volumetric methods or chromatography. Nonvolatile products from the oxidation are determined by analysis of the electrolyte, e.g., by gas chromatography, preferably with a flame ionization detector, or mass spectroscopy. Organic products can be extracted from the electrolyte... 

Since practically all nitrates are soluble, no gravimetric method is suitable with the exception of precipitation with an organic basernitron. The usual volumetric method is to reduce nitrate to ammonia, which is distilled into a known excess of standard acid, back titrating the excess with standard alkali (compare Sec. 14.6.1). 

The importance of the determination of sulphuric acid and sulphates lies very largely in the fact that sulphur in various forms of combination, and also free sulphur, is frequently determined quantitatively by primary conversion into sulphuric acid or sulphate, followed by actual estimation in the latter form. For example, a convenient volumetric process applicable to the Carius method for determining sulphur in organic compounds is to neutralise the solution of sulphuric acid after removal of the excess of nitric acid by evaporation, and then add silver nitrate, by which the sulphate is converted into silver sulphate. This is separated from the excess of silver nitrate by means of its insolubility in alcohol, and is then estimated by dissolving in dilute nitric acid and titrating the silver with standard thiocyanate solution.3... 

Nitrates and nitrites in water are frequently estimated together, e.g. by reduction to ammonia,1 which can be determined m the manner described below alternative processes are based on the reduction of these salts to nitric oxide which may be measured volumetrically, and on reduction of the nitrate to nitrite when the total nitrite may be estimated eolonmetncaUy by the addition of sulphanihc acid and a-naphthylamine.3 For the estimation of nitrites and mtrates separately, organic colorimetric methods are usually applied.4... 

Kuhn-Roth method for C-methyl determination. Oxidation of organic compounds with chromic and sulfuric acids in such a manner that the C-methyl groups are converted to acetic acid which can be assayed volumetrically. The method has been modified and extended (1) to saturated fatty acids and alcohols containing up to about 20 carbon atoms, and (2) to aliphatic long-chain compounds of very high molecular weight. 

Probably the simplest of all decomposition systems involves the heating of the sample in a silica or porcelain crucible in a muffle furnace in the presence of air at 400-800°C. After decomposition, the residue is dissolved in acid and transferred to a volumetric flask prior to analysis. This allows organic matter to be destroyed. However, the method may also lead to the loss of volatile elements, e.g. Hg, Pb, Cd, Ca, As, Sb, Cr and Cu. Thus, while compounds can be added to retard the loss of volatiles, its use is limited. Due to the disadvantages of this method, namely ... 

The Food and Agriculture Organization of the United Nations has recommended methods for the determination of mercury in pesticides. The method selected depends on the other constituents of the formulation and in the presence of copper the method of Brookes and Solomon (see p. 419) is most suitable. In the presence of most other constituents the selected method is one in which the sample is refluxed with concentrated sulphuric acid and potassium nitrate before determining the mercury volumetrically with thiocyanate. When large amounts of calcium carbonate or highly chlorinated compounds e,g, benzene hexachloride) are present, the mercury is isolated as a sulphide before conversion to the ionic form with strong acid. 

Many standard procedures are available for studying adsorption by volumetric or titrimetric methods. Adsorption of fatty acid [17] has frequently been determined by titration with aqueous alkali, even if the fatty acid was previously dissolved in organic solvent. Extraction of fatty acid from the solvent caused no problems, especially if warm ethyl alcohol is added [13], but the validity of the method needs to be checked by titration of a known sample each time. 

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