Page 2 - Combined_12_OCR
P. 2

Nitrite-EthyI Cellosolve (Ranta) Method




              REFERENCES
                  1.  Zapp, J. A.: Hazards of Isocyanates in Polyurethane Foam Plastic Production. A.M.A.
              Arch. Ind. Health 15: 324 (1957).
                   to  Marcali, K.: Microdetermination of Toluenediisocyanate in Atmosphere. Anal. Chem. 29: 552
              (1957).
                  3.  Grim, K. E. and A. L. Linch: Revision - Recent Isocyanate-in-Air Analysis Studies. Pre-
              sented at the Amer. Ind. Hyg. Assoc. 24th Annual Meeting, Cincinnati, Ohio, May, 1963.
                  4.  Union Industrial Equipment Corp., Port Chester, New York.

              METHOD OF COLLECTION
                  Air is drawn at 2.8 liters per minute for 10 minutes (1 cu ft sample) through 10 ml of a solu­
              tion of boric acid and sodium nitrite dissolved in ethyl cellosolve contained in an all-glass standard
              midget impinger.

              PRINCIPLE
                  Both the absorbed TDI and TDI urea in the presence of nitrite in ethyl cellosolve produce a yel­
              low color of unknown composition. Boric acid is added to intensify the color. The absorbance may
              be determined either spectrophotometrically at 450 mg, or colors compared visually with liquid col­
              or standards.

             INTERFERENCES
                  Freshly distilled ethyl cellosolve must be used in preparing the absorber solution, and the rea­
              gent should be discarded as soon as any yellow color develops (less than one week). Acetic acid,
             dichlorobenzene, and dimethylformamide hinder color formation.

             SENSITIVITY
                  The method is applicable to the range 0.01 to 0.4 ppm in a 28 liter air sample. TDI urea can
             be determined by analyzing a sample taken simultaneously by the Marcali method and subtracting
             from the Ranta result for total TDI and TDI urea. At 0.01 ppm in the presence of 0.25 ppm TDI,
             the precision is + 30% of the amount of TDI urea present.

             SPECIAL REAGENTS AND EQUIPMENT
                              neter, or
                              standards4
             COMMITTEE COMMENT
                 Since the physiological response information can be obtained only in the presence of water vapor,
             the intrinsic activity of TDI urea is unknown, and the ratio of TDI to TDI urea is variable; reliable
             air surveys should include both factors.
   1   2