Solutions, formaldehyde precautions

If sampling is not followed immediately by analysis, the sample must be treated with a preservative, but not such as to falsify the analytical results use is made of 10% potassium dichromate solution, formaldehyde, hydrogen peroxide, alcoholic solution of phenol, mercuric chloride (about 5% solution), etc., a few drops being added. The last of these preserves milk very well for several days without altering its composition or disturbing the determinations, but its poisonous character necessitates precautions. 

Urea-formaldehyde resins are generally prepared by condensation in aqueous basic medium. Depending on the intended application, a 50-100% excess of formaldehyde is used. All bases are suitable as catalysts provided they are partially soluble in water. The most commonly used catalysts are the alkali hydroxides. The pH value of the alkaline solution should not exceed 8-9, on account of the possible Cannizzaro reaction of formaldehyde. Since the alkalinity of the solution drops in the course of the reaction, it is necessary either to use a buffer solution or to keep the pH constant by repeated additions of aqueous alkali hydroxide. Under these conditions the reaction time is about 10-20 min at 50-60 C. The course of the condensation can be monitored by titration of the unused formaldehyde with sodium hydrogen sulfite or hydroxylamine hydrochloride. These determinations must, however, be carried out quickly and at as low temperature as possible (10-15 °C), otherwise elimination of formaldehyde from the hydroxymethyl compounds already formed can falsify the analysis. The isolation of the soluble condensation products is not possible without special precautions, on account of the facile back-reaction it can be done by pumping off the water in vacuum below 60 °C imder weakly alkaline conditions, or better by careful freeze-drying. However, the further condensation to crosslinked products is nearly always performed with the original aqueous solution. 

Notes Formalin is an aqueous solution of formaldehyde, 37% by weight or 40% by volume. Caution Poisonous vapors attack mucous membrane of the eyes, nose, throat, causing intense irritation. Use in a well-ventilated area and exercise all handling precautions. Unless your mixing area has an effective fume hood, it is highly recommended that you mix formaldehyde outdoors, and even then an appropriately rated fume mask should be used. These masks are available from chemical supply houses. 

Flammable chemicals should be stored in appropriate containers and facilities. Smaller amounts may be stored in laboratories in appropriate cabinets. A 10% neutral buffered formalin solution, commonly known as formaldehyde, is potentially carcinogenic. In 1987, precautions for laboratory workers were put in place as the Formaldehyde Standard CFR 1919.1048. Xylene is potentially hazardous and should be handled appropriately, see OSHA, 29 CFR 1910.1450. An excellent website is available for on fine location of Material... 

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