Microchemical Journal 77 (2004) 47–51 0026-265X/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.microc.2003.12.002 Spectrophotometric determination of formaldehyde with chromotropic acid in phosphoric acid medium assisted by microwave oven Andrea C. Gigante, Mara A. Gotardo, Joao O. Tognolli, Leonardo Pezza, Helena R. Pezza* ´ ˜ Instituto de Quımica – UNESP, P.O.Box 355, CEP 14801-970, Araraquara, SP, Brazil ´ Received 28 October 2003; received in revised form 1 December 2003; accepted 3 December 2003 Abstract In the present study, a spectrophotometric method for the determination of formaldehyde by using chromotropic acid was devised, in which the use of potentially hazardous and corrosive concentrated sulfuric acid was eliminated and advantageously replaced by a mixture of H PO and H O . The reaction between formaldehyde and chromotropic acid (CA) in a concentrated 3 4 2 2 phosphoric acid medium was accelerate by irradiating the mixture with microwave energy for 35 s (1100 W), producing a violet– red compound (l s570 nm). Beer’s Law is obeyed in a concentration range of 0.8–4.8 mg l of formaldehyde with a good y1 max correlation coefficient (rs0.9968). The proposed method was applied in the analysis of formaldehyde in commercial disinfectants. Recoveries were within 98.0–100.4%, with standard deviations ranging from 0.03 to 0.13%.  2003 Elsevier B.V. All rights reserved. Keywords: Formaldehyde; Chromotropic acid; Spectrophotometry; Microwave oven 1. Introduction The uses of formaldehyde cover a wide range of fields. In the food chemistry, it is used as a food additive and it is also employed as chemical intermediate in the industrial synthesis of a large number of organic com- pounds. Moreover, formaldehyde is commonly used in the production of plastics and it can be added to some pharmaceutical products as a preservative. Formalde- hyde kills viruses, bacteria, fungi and parasites and has found wide use as a disinfectant with a broad efficiency. Otherwise, it is considered one of the most significant industrial hazard and air pollutants w1x. The toxicity of formaldehyde to man and animals has been reported w2–4x. The International Agency for Research on Cancer has concluded that formaldehyde is a potential carcino- gen for animals and that there is a limited evidence for the carcinogenicity of formaldehyde in human beings w1x. An efficient disinfectant should contain an adequate formaldehyde level. In order to assure the efficient use of disinfectants containing formaldehyde with regard to *Corresponding author. Fax: q55-16-222-7932. E-mail address: hrpezza@iq.unesp.br (H.R. Pezza). its toxicity and antiseptic activity, suitable analytical techniques are required. The most widely used methods for the determination of formaldehyde are based on spectrophotometry w5–8x and the chromotropic acid (CA) method has been recommended by NIOSH w9,10x in its P&CAM 125, 235 and 3500 reference methods. In the NIOSH method formaldehyde is detected by warming it with chromotropic acid, in the presence of concentrated sulfuric acid, yielding a soluble violet–red colour w6,11x. The spectrophotometric measurements are highly selective and other aldehydes do not interfere according to the literature w11x. The major drawback presented by the NIOSH method has been the use of concentrated H SO , which is potentially hazardous and 2 4 corrosive, and the heating of the resulting solution for approximately 1 h in a steam bath (100 8C), making your utilization little attractive in routine analysis. In previous study w12x, modifications to the NIOSH procedure were described based on investigations con- cerning of the oxidation step of the reaction between formaldehyde and CA, in which the use of concentrated H SO was eliminated and replaced by a mixture of 2 4 HCl and H O . However, the aforementioned method 2 2 even so requires a long heating time of the reaction mixture under strongly acidic conditions.