Estimation of Formaldehyde

For pure dilute solutions the following is recommended. 10 c.cs. of the formaldehyde solution which must, if necessary, be diluted so that it is not more than a 2% solution, is mixed with 25 c.cs. of N/IO iodine solution. 10% caustic soda solution, which is free from nitrite, is added, with shaking, drop by drop from a burette until a clear yellow liquid is obtained after standing for 10 minutes, an equal quantity of 10% hydrochloric acid, plus an extra 5 c.cs., are added to liberate the excess of iodine which is 

The excess of iodine added forms iodide and iodate, and is liberated on addition of hydrochloric acid. 

This method is very satisfactory for formaldehyde provided other aldehydes are absent. In a solution containing 1 gm. CHaO per litre, two 

For impure dilute solutions of formaldehyde, especially those containing other aldehydes, the cyanide method should be used. The iodine 

The details are as follows 10 c.cs. of — silver nitrate acidified with 

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The compound (III) can however lose ethanol by an internal Claisen ester condensation (p. 264) to give the cyclohexane derivative (IV), which, being the ester of a (3-keto acid, in turn readily undergoes hydrolysis and decarboxylation to give 5,5Hiimethyl cyclohexan-i,3Hiione (V) or Dimedone, a valuable reagent for the detection and estimation of formaldehyde. 

Estimation of Formaldehyde in Biological Mixtures. J. biol. Chem. 158,... 

Mean values for FVC and FEV] were significantly lower than reference values in a group of 38 workers exposed to formaldehyde and other solvents used in lacquer applications, but the difference was small (<5-10% change from reference values) (Alexandersson and Hedenstiema 1988). The workers in the lacquer-applying workplace were employed for an average of 7.8 years estimates of formaldehyde concentrations in workplace air ranged from 0.2 to 2.1 ppm with a TWA mean of 0.3 ppm. 

Eikmann T, Prajsnar D, Einbrodt HJ. 1987. Quantitative estimation of formaldehyd exposure in normal population collectives on the basis of the formic acid excretion in urine [Abstract]. Zentralbl Bakteriol Mikrobiol Hyg [B] 183 483-484. 

Nash T. (1953) The colorimetric estimation of formaldehyde by means of the Hantzsch reaction. Bio-chem. J., 55, 416-421. 

Many techniques have been devised for the estimation of formaldehyde those most generally applied are ... 

In the previous chapter, we ha ne reviewed those methods which are best suited for the detection and estimation of formaldehyde in compositions in which it is a minor constituent. Such methods require a maximum of selectivity and sensitivity. We shall now consider methods of quantitative analysis which are best adapted to the accurate determination of formaldehyde in commercial solutions, pol mers and other compositions in which formaldehyde is present in quantity and in which impurities such as ketones, higher aldehydes, etc., which mterfere with the determination of formaldehyde, are either completely- absent or present in minor amounts. These methods possess a good d ee of accuracy but do not require the extreme sensitivity demanded by the procedures previously discussed. 

Hydro3Eylainiiie Hydrochloride Method. Occasionalh- useful for the estimation of formaldehyde in the presence of alkali sensiti -e product and impurities, such, as cresol, phenol, and resinous materials, is the method of Brochet and Cambier - - - based on the liberation of hi drochloric acid when hydroxylamine hydrochloride reacts with formaldehyde to form formaldoxime ... 

Noth. The above method can be successfully applied only to dilute solutions of formaldehyde which are free in particular from other alfphatic aldehydes, since the latter, if present, would undergo a similar oxidation. Formaldehyde, if mixed with other aldehydes, should be estimated by quantitative addition of potassium cyanide for details, see advanced text-books of quantitative organic analysis. 

The second channel, producing CO, was first observed by Seakins and Leone [64], who estimated 40% branching to this channel. Later measurements by Lockenberg et al. [65] and Preses et al. [66] concluded the branching to CO is 18%. Note that decomposition of formaldehyde formed in reaction (26a) is not a possible source of CO due to the large barrier for formaldehyde decomposition. Marcy et al. [67] recently combined time-resolved Lourier spectroscopy experiments with direct dynamics classical trajectory calculations to examine the mechanism of the CO product channel. They observed two pathways for CO formation, neither of which involve crossing a TS. 

Estimated Free Energy Changes of Selected Biological Reactions Involved in the Anaerobic Degradation of Formaldehyde and Methanol... 

Triphenyl phosphite is added in an excess and the rest of it is estimated colorimetrically after the introduction of formaldehyde and HC1. The latter forms colored triphenyl phosphonyl chloride [Ph3PCH2 OH]+Cl. 

Table X illustrates the successful application of formaldehyde precipitation as a means of estimating the flavonoid and nonflavonoid contents in a mixture. The mixture consisted of catechin as the flavonoid and caffeic, vanillic, and syringic acids as the nonflavonoids. The catechin was 86% precipitated (lower than usual because of the low level), but the other substances were not significantly precipitated. The slight apparent loss of caffeic acid is attributable to experimental variation since in many other experiments the lack of reaction and precipitation or co-precipitation of caffeic acid or chlorgenic acid has been demonstrated. Allowing for the same slight solubility of the catechin-formalde-hyde product in the mixtures as in the single component solution, the analysis of the mixtures gave 95.7-107.6% of the calculated value. This indicates no significant co-precipitation or entrainment of the nonflavonoids as the flavonoid was removed. This result has been verified a number of times with different substances added to model solutions and wines (21, 22).

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