Microdetermination of Water in Hydrocarbon Solvents Using Ultraviolet Spectrophotometry, by Reaction with N-Benzylideneaniline Ignazio Renato Bellobono Istituto di chimica jisica dell' Uniaersita, Milan, Italy
A GREAT VARIETY of methods has been applied t o the microdetermination of water in organic solvents (I). Among the procedures, which are particularly well suited for accurate determinations of low concentrations of water, the gaschromatographic direct method ( 2 ) and the Karl Fischer reagent method (3-6) have been the subject of some recent investigations. Despite the many improvements, the described determinations typically show a lower detection limit of 1-2 ppm, with a n uncertainty of 1 0 . 2 ppm for the controlled potential method employing the Karl Fischer reagent (6). Recently (7) it has been observed that even a small content, as low as 0.05 ppm of water (nearly 4-4.5 X 10-6M), in a spectrograde hydrocarbon solvent may cause hydrolysis of a Schiff base-e.g., N-benzylideneaniline-by ultraviolet irradiation. In the present report, a method is described, which takes advantage of this reaction, for the determination of trace amounts of water in these solvents. EXPERIMENTAL
Apparatus. All absorbance measurements were made with a Beckman DK-2A recording spectrophotometer, a t room temperature in matched silica cells (sample path length 1 cm). Irradiation was effected directly in the spectrophotometric cells either by the hydrogen lamp of a Beckman D U spectrophotometer a t 262 nm (slit 0.2 mm) for 3 hours, or by a Hanau 500 W mercury arc-lamp for 1 hour. The amount of energy absorbed by the cell was measured under the same conditions by a uranyl oxalate actinometer solution, 0.01M with respect to uranyl oxalate and 0.04M with respect to oxalic acid (8): it resulted in 3900 and 5800 J, respectively. Reagents. N-benzylideneaniline was prepared by known methods, (the reagent grade chemical was also suitable (7) repeatedly crystallized from n-hexane (mp 52" C), and dried under vacuum (0.05 mm Hg) at room temperature over K O H (1) I. M. Kolthoff, P. J. Elving, and E. B. Sandell, "Treatise on Analytical Chemistry" Part 11, Vol. 1, 82-97, Interscience,
New York, 1961. (2) R. Aubeau, L. Champeix, and J. Reiss, J . Chromatog. 16, 7 (1964). (3) R. F. Swensen and D. A. Keyworth, ANAL.CHEM.,35, 863 (1963). (4) M. A. Rotheram, U. S. At. Energy Comm. NAA-SR-9734 (1964). (5) R . Veneroni and R. Friesen, AEC Accession No. 7270, Rept. No. EUR-2159e (1964). (6) M. R. Linbeck and H. Freund, ANAL.CHEM.,37, 863 (1963). (7) G. Favini and I. R. Bellobono, Guzz. Chim. Zrul., 96, 1423 (1966). (8) G. S. Forbes and L. J. Heidt, J. Am. Chem. SOC.,56, 2363 ( 1934). 1298
ANALYTICAL CHEMISTRY
and anhydrous Mg(Cl04)~. Benzaldehyde (reagent grade) was washed with 5 % aqueous Na2C03, dried over anhydrous Na2S04, and finally rectified in a nitrogen stream (bp 79" 80" C a t 25 mm Hg). Aniline (reagent grade) was redistilled over powdered Zn (bp 104"-105" C at 25 mm Hg). Anhydrous n-hexane (water content
