Volatile acids, determination

Pilone, G.J. (1967). Effect of lactic acid on volatile acid determination of wine. J. OenoL, 18, 149-156. 

Volatile Acid Determination. Part III. Toxicity of Propionic Acid, Tech. Paper No. 239, Florida Engineering and Industrial Experiment Station (1962) 16, 10. 

The importance of carbon dioxide in the volatile acid determination was emphasized by Marsh (1936). He recommended boiling the distillate for 1 minute and titrating hot. Removal of carbon dioxide is more difficult from sparkling wines. Pato and Salvador (1949) titrated the volatile acid distillate to a pH of 6.33 and then to 9. At a pH of 6.33, n (ml. 0.1 JV NaOH) = 0.79A -I- 0.5C, where A is the volatile acidity expressed as acetic acid and C represents the bicarbonate content. At a pH of... 

The distillate may contain volatile neutral compounds as well as volatile acids and phenols. Add a slight excess of 10-20 per cent, sodium hydroxide solution to this distillate and distil until the liquid passes over clear or has the density of pure water. The presence of a volatile, water-soluble neutral compound is detected by a periodic determination of the density (see Section XI,2) if the density is definitely less than unity, the presence of a neutral compound may be assumed. Keep this solution Si) for Step 4. 

The most common chromatogram in the distilled spirits industry is the fusel oil content. This consists of / -propyl alcohol, isobutyl alcohol, and isoamyl alcohol. Other common peaks are ethyl acetate, acetaldehyde, and methanol. The gc columns may be steel, copper, or glass packed column or capillary columns. Additional analyses include deterrninations of esters, total acids, fixed acids, volatile acids, soHds or extracts (used to determine... 

In the determination of formic acid in more complicated reaction-mixtures (for example, in the presence of buffers,22 69a in solutions containing non-volatile acids,49- 67 and in solutions containing ammonia234), it was necessary to distil the formic acid from the reaction solution (after destruction of the excess periodate with ethylene glycol or arsenite) before it could be titrated. 

Analysing volatile acids in aqueous systems, resulting mainly from the presence of water, have been reported [19]. The volatile acids high polarity as well as their tendency to associate and to be adsorbed firmly on the column require esterification prior to gas chromatographic determination. The presence of water interferes in esterification so that complex drying techniques and isolation of the acids by extraction, liquid solid chromatography, distillation, and even ion exchangers had to be used [20-23],... 

NH - Acid gases - Water Systems. The same type of treatment could be applied to other volatile acids or base like NHj - SO2 -CO2 and SH2 but limitations in the determination of constants can... 

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

Benzoe Sumatra resinoid is a dark brown viscous liquid with a warm, powdery, sweet-balsamic odor. Its main volatile, odor-determining components are derivatives of benzoic and cinnamic acids and vanillin [284, 284a],... 

A wide range of volatile compounds from Indian mango were identified by pioneer group research [20,21]. Esters, lactones, monoterpenes, sesquiterpenes, and furanones were among the volatiles. It has been suggested that the ratio of palmitic to palmitoleic acids determines the flavour quality of the ripe fruit, a ratio of less than 1 resulting in strong aroma and flavour [44]. 

The amount of ammonia volatilized was determined from the amount of standard sulfuric acid consumed in the traps. Ethylenediamine was determined by the salicylaldehyde method (14). The sample for cobalt(II) determination was made slightly acidic with hydrochloric acid immediately upon removal of the sample from the reaction flask, in order to prevent further oxidation of the cobalt (18). The carbon was removed by filtration, and the cobalt (II) concentration was determined spectrophotometrically as the cobalt-ammonium thiocyanate complex, (NH4)2Co(NCS)4 (28). 

It is probable that GLC determination of acetic acid, as distinguished from other volatile acids (propionic, lactic, etc.), will be used more often. A specific enzymatic procedure for acetate (35) reveals that only about two-thirds of the volatile acidity is acetic acid. However, the volatile acidity of commercial wines in modem wineries is usually well below the legal limits. 

Sorbic Acid and Sorbates. In addition to the correction of the volatile acidity for sorbic acid already mentioned, both sorbic acid and sorbates must be determined directly. The colorimetric procedure of Jaulmes et al. (10) is appropriate oxidation of sorbic acid to malonic dialdehyde and a red color developed by reaction with 2-thiobarbituric acid (4). 

Acetic acid content is used as a criterion for aerobic bacterial spoilage in wines. We can easily analyze two wines and determine that one has a lower volatile acidity than the other. But by every available standard of product quality judgment, the wine with the higher level of acetic acid may be the superior product. It is no accident that Subpart ZZ, Part 240, Title 26 of the Code of Federal Regulations allows the direct addition of acetic acid to correct natural deficiencies in grape wine. As sanitation practices have improved, the so-called natural acetic acid content diminished, and this has been correlated with lower consumer acceptance in certain cases (2). 

Volatile Acid Number. The volatile acid number or the Reichert-Meissl number denotes the number of c.c. of N/10-alkali required to neutralise the volatile acids, soluble in water, obtained from 5 grams of butter fat, previously melted and filtered. It is determined exactly as described in flit- chapter headed Tatty Substances (Vol. I, p. 377). 

Cacao Butter.—Use is made of Polenske s method, according to which the number of c.c. of N/io-alkali required to neutralise the insoluble volatile acids is determined (Polenske number, Insoluble volatile acid number, New butter number). This number may be determined directly or indirectly. 

The filtrate serves, as usual, for the determination of the soluble acids, whilst the insoluble volatile acids collected on the filter (if these are liquid the presence of cacao butter is highly probable) are washed three times with 15 c.c. of distilled water, which is previously used each time to wash the tube of the condenser and the flask. These three washings are usually sufficient to remove all the soluble volatile acids if the last 10 c.c. of wash water are not neutralised by a drop of N/10-alkali, a fourth washing is carried out. 

Acidity.—If volatile acids are not present, this determination is made on the solution obtained as in 2 (above), a known volume being titrated with N/10-alkali in presence of phenolphthalein and the result expressed in c.c. of N-alkali per 100 grams of substance. 

In presence of appreciable amounts of volatile adds, a separate weighed portion of the substance is mixed with cold water to a definite volume and an ab quot part of the liquid decanted or, if necessary, filtered through glass wool, and titrated as above (total acidity). The fixed acidity is determined by evaporating almost to dryness on a water-bath a known volume of the solution obtained as in 2 (above), the residue being taken up in water and titrated as before volatile acidity = total acidity minus fixed aridity. 

The acidity of beer is due partly to various organic acids (especially lactic), partly to acid phosphates and, particularly in badly kept beers, partly to volatile acids (acetic). In some cases, the volatile acidity is determined separately from the fixed acidity. 

Volatile Acidity.—This is determined by distilling the wine in a current of steam and estimating the acidity of the distillate as follows ... 

Fixed Acidity.—This is determined by difference. The volatile acidity is multiplied by 1-25 to refer it to tartaric add, the number thus obtained being subtracted from the total acidity calculated as in (1) the remainder represents the fixed acidity in grams of tartaric acid per litre. 

To apply this rule, the alcoholic strength (by volume) and the fixed acidity of the wine are determined. The latter, expressed as sulphuric acid, is increased by 07 (this corresponding with the maximum value of the volatile acidity in ordinary normal wines), and the value thus obtained divided by the alcoholic strength the quotient is the ratio sought. 

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