Abstract
The authors applied the Fujiwara reaction, which is employed for the determination of chloroform and other polyhalogen compounds, to the determination of micro amount of dichloromonofluoromethane (Freon-21) dissolved in fresh water.
When the squeous solution of Freon was heated with some appropriate amounts of pyridine and sodium hydroxide at 40°C for 15 minutes, the mixture indicated reddish color with the sbsorption maximum at 525mμ. This absorption had been used by some other authors in the past for the colorimetric determination of polyhalogen compounds. However, the above color was not very stable and gradually disappeared when it was heated successively. Then, the authors obtained an absorption at 366mμ which was more stable and sensitive than that at 525mμ. Thus, the determination of Freon was carried out as follows by estimating the absorbance at 366Mμ
20ml of aqueous solution containing more than 2μg of Freon was gently mixed with 9 ml of pyridine and 1 ml of 5 N sodium hydroxide, and the reaction mixture was heated at 50°C for 50 minutes. After it was cooled, the absorption at 366mμ was measured. This method was applicable to the determination of 0.1mg/l-7.0mg/l of Freon within the relative standard deviation of 1.0%. Also, its interference with dissolved metals were examined, and magnesium, calcium and copper were found to decrease their recoveries to some extent (Table 2).
