In the Laboratory
An Inexpensive Demountable IR Cell Fitted with Glass Windows Keiichi Ohno, Hiroatsu Matsuura, and Haruhiko Tanaka Hiroshima University, Kagamiyama, Higashi-Hiroshima 739, Japan Low-cost Fourier-transform and grating IR spectrophotometers equipped with personal computers are now extensively used for chemical analyses in most undergraduate laboratory courses. IR spectroscopy is one of the most powerful tools for an investigation of hydrogen bonding. IR measurements of dilute solutions of hydroxyl group–containing compounds enable one to distinguish between free OH, intramolecular H-bonded OH, and intermolecular H-bonded OH. Since commercial IR solution cells are rather expensive and difficult to maintain, we propose here an inexpensive demountable IR cell fitted with glass windows for studying hydrogen bonding in solutions. The proposed cell, illustrated in Figure 1, consists of several components. The cover glass is commercially available, inexpensive, and insoluble in water. The Teflon spacers with any desired thickness are easily made of a Teflon rod (diameter 3 cm). The demountable IR cell fitted with glass windows described here has no problem with deterioration of the windows; most common IR solution cells made with sodium chloride windows are subject to deterioration from the inside by the introduction of water and other substances. An IR spectrum of a cover glass, as shown in Figure 2(d), indicates that the low-wavenumber limit of the IR cell with glass windows is about 1600 cm{1 . The interference fringes1 due to the cover glass are removed by subtracting the solvent spectrum from the solution spectrum. As a typical example of the hydrogen-bonding systems most frequently studied, the IR spectra of ethanol in tetrachloro-
Figure 1. Demountable IR cell fitted with glass windows. A and A′, commercially available stainless steel liquid cell holders; B and B′, rubber O-rings; C and C′, 24 × 24-mm cover glass windows; D, a Teflon spacer with two 1-mm diameter inlet holes or a lead spacer. The cell is assembled from left to right.
methane2 with different concentrations are shown in Figures 2(a)–(c), which clearly show an effect of the concentration on the O–H stretching bands. This cell with glass windows is also useful for measurements of IR spectra of water-containing solutions. Notes 1. Smith, D.C.; Miller, E. C. J. Opt. Soc. Am. 1944, 34, 130– 134; the thickness of a cover glass, d, is evaluated from the relationship, d = m / [2 n (ν1 – ν2)], where n is the refractive index of the cover glass and m is the number of maxima (or minima) of the interference fringes between the wavenumbers ν1 and ν2. 2. CAUTION: Tetrachloromethane is toxic, causes liver damage, and is a suspected carcinogen. Use only when adequate ventilation is possible. To avoid contact with tetrachloromethane, wear plastic gloves and use a Pasteur pipet in a test tube attached to a 1-pt bottle for dispensing purposes. A possible alternative to tetrachloromethane is hexafluoro-1,2,3,4-tetrachlorobutane, which can be used safely and has lately been made commercially available from Horiba Ltd., Kyoto.
Figure 2. IR spectra of ethanol, measured with the demountable cell with glass windows: (a) neat liquid, (b) 0.1 mol dm{3 in tetrachloromethane (spacer 3 mm), and (c) 0.01 mol dm{3 in tetrachloromethane (spacer 3 mm); (d) IR spectrum of a cover glass (0.16 mm thickness). The scale of absorbance is applicable to the cover glass (d).
Vol. 74 No. 8 August 1997 • Journal of Chemical Education
961
