Formaldehyde polarography

In the polarography of aqueous formaldehyde solutions the only reducible species is the unhydrated aldehyde, and under suitable conditions the observed current is dependent on the rate of dissociation of methylene glycol. This was first shown by Vesely and Brdidka (1947) and by Bieber and Triimpler (1947a) later work (BrdiiSka, 1955) demonstrated catalysis by borate and hydroxide ions, but no extensive study has been made by this method. An exact mathematical solution of the diffusion problem is difficult to obtain a recent review has been given by Brdi5ka (1960). 

Simple aldehydes, such as formaldehyde or acrolein may be analyzed by derivatizing into a suitable derivative for GC-FID or -NPD determination (Methods 2502, 2501, NIOSH 1984). The derivatizing agents for these compounds are 2-(benzylamino)ethanol and 2-(hydroxymethyl)piperidine, respectively, coated on a support. Formaldehyde may also be determined using colorimetry and polarography (Methods 3500 and 3501, NIOSH 1984). See Part 3 of this book. 

Formaldehyde may be analyzed by several techniques involving GC, colorimetry, polarography, HPLC, and GC/MS. 

A method based on polarography of the product formed by alkaline hydrolysis followed by heating with formaldehyde at pH5 had a detection limit of 10 pg/ml for amoxicillin in plasma [184], Obviously any penicilloic acid in the sample will also respond in this method. 

Low-temperature treatment of Cr(VI) /silica by ethylene can also produce Cr(II) as was shown in 1968 by Baker and Carrick [239], who reported the valence of a catalyst containing 0.5 wt% chromium, initially hexavalent, after it reacted with ethylene at 135 °C. Afterward, the catalyst was treated with deoxygenated dilute HC1 to dissolve the chromium. The solution was then analyzed by polarography to determine the chromium oxidation state. The authors measured 85-96% conversion to Cr(II) within a few minutes of exposure to ethylene. Formaldehyde was released as the major (probably only) by-product. More recently, formaldehyde was again confirmed as the by-product of Cr(VI) reduction by ethylene [232],... 

Formaldehyde can be analyzed by several instrumental techniques, such as GC, colorimetry, polarography, and GC/MS. The GC method involves the passage of air through a solid sorbent tube containing 2-(benzylamino)ethanol on Chro-mosorb 102 or XAD-2. The derivative, 2-benzyloxazolidine, is desorbed with isooctane and injected into GC equipped with an FID (NIOSH 1984, Method 2502). Car-bowax 20M or a fused-silica capillary column is suitable. 2-Benzyloxazolidine peak is sometimes masked under the peaks, due to the derivatizing agent or its decomposition and/or polymeric products. The isooctane... 

Alternatively, air is passed through 1-pm PTFE membrane and 1% sodium bisulfite solution. The solution is treated with chromotropic and sulfuric acid mixture. The color development due to formaldehyde is measured by a visible spectrophotometer at 580-mn absorbance (NIOSH 1984, Method 3500). In polarography analysis, a Girard-T reagent is used. Formaldehyde forms a derivative that is analyzed by sampled direct current DC polarography (NIOSH 1984, Method 3501). Auel et al. (1987) reported a similar electrochemical analysis of industrial air using an iridium electrode backed by a gas-permeable fluorocarbon-based membrane. 

The initial stage of the melamine/formaldehyde reaction has been studied by Nastke et al. [223], who succeeded in providing evidence not only of hydroxymethy-lation, but also of the formation of methylene and methylene ether bridges using polarography. The functionality of melamine is six, with a negative substitution effect of about 40% [224, 225]. 

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