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Schmidt_ þ _Haensch, http://www.schmidt-haensch.com/en/products/prod/ laboratory-instruments/refractometer/atr-w-series/ (accessed June 21, 2010). 27. O. R. Bolduc, L. S. Live, and J.-F. Masson, Talanta 77, 1680 (2009). 28. R. C. Jorgenson and S. S. Yee, Sens. Actuators, B 12, 213 (1993). 29. L. S. Jung, C. T. Campbell, T. M. Chinowsky, M. N. Mar, and S. S. Yee, Langmuir 14, 5636 (1998). 30. Y.-C. Li, Y.-F. Chang, L.-C. Su, and C. Chou, Anal. Chem. 80, 5590 (2008). 31. J. Pollet, F. Delport, K. P. F. Janssen, K. Jans, G. Maes, H. Pfeiffer, M. Wevers, and J. Lammertyn, Biosens. Bioelectron. 25, 864 (2009). A New Method to Obtain Fourier Transform Infrared Spectra Free from Water Vapor Disturbance YUJING CHEN, HAI-SHUI WANG,* and JUNZO UMEMURA* School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China (Y.C., H.S.W.); and 35-2 Todo-Ikeyama, Uji, Kyoto-fu, 611- 0013, Japan (J.U.) Infrared absorption bands due to water vapor in the mid-infrared regions often obscure important spectral features of the sample. Here, we provide a novel method to collect a qualified infrared spectrum without any water vapor interference. The scanning procedure for a single-beam spectrum of the sample is divided into two stages under an atmosphere with fluctuating humidity. In the first stage, the sample spectrum is measured with approximately the same number of scans as the background. If the absorbance of water vapor in the spectrum is positive (or negative) at the end of the first stage, then the relative humidity in the sample compartment of the spectrometer is changed by a dry (or wet) air blow at the start of the second stage while the measurement of the sample spectrum continues. After the relative humidity changes to a lower (or higher) level than that of the previously collected background spectrum, water vapor peaks will become smaller and smaller with the increase in scanning number during the second stage. When the interfering water lines disappear from the spectrum, the acquisition of a sample spectrum is terminated. In this way, water vapor interference can finally be removed completely. Index Headings: Water vapor interference; Noise elimination; Fourier transform infrared spectroscopy; FT-IR spectroscopy. INTRODUCTION Fourier transform infrared (FT-IR) spectroscopy has tremen- dous applications in the fields of environmental, material, life, pharmaceutical, chemical, and physical sciences. 1–3 It is also a very sensitive analytical technique that can detect even very small amounts of sample. 4–6 For infrared operators, moisture is one of the most annoying components of the atmosphere. If the single-beam spectrum of the sample contains more or less water vapor than that of the background, water vapor bands will appear as spectral interference against sample absorption bands. The intensity of water vapor bands should always be much less than the intensity of the bands of interest. In some cases, even though the bands of atmospheric water vapor in the spectrum are weak, they may also mask many weak absorption features due to some important components of a sample. Until now, the following countermeasures have convention- ally been adopted in order to remove water vapor interference. (1) Removal of water vapor by vacuum-pumping the closed FT-IR spectrometer; (2) Removal of water vapor by purging the instrument with pure nitrogen or dry air; (3) Use of a shuttle system in which the sample is repeatedly moved in to and out of the IR beam in some short period, thus equilibrating the amount of water vapor between the single-beam sample spectrum and the background spec- trum during multiple accumulations; (4) Measuring the spectrum of water vapor in advance, and then subtracting from the IR spectrum of the sample to reduce spectral interference; 2,3 (5) Applying multivariate analysis for the standardization of spectrometers to the high-resolution spectral data base HITRAN of water vapor measured at different tempera- tures to automatically reduce spectral interference by computations; 7,8 (6) Applying the polarization modulation method to use the IR beam with periodically changing polarization direction, which is incident upon the metal or water surfaces on which molecules are adsorbed. In this case, reflection spectra are obtained by computing the ratio of the difference to sum values. Spectral interferences by water vapor and carbon dioxide gas can be removed during the computation. These six methods have been in use for decades, but they have various disadvantages from the point of view of their desired performance or cost performance. For example, the vacuum spectrometer in method (1) is costly and this option also limits the sampling capabilities (e.g., infrared micro- scopes). In method (2), nitrogen gas or dry air supply is costly and requires sufficient time to exchange the atmosphere using dry air or the nitrogen supply after sample replacement. The sample shuttle device in method (3) works well for thin-film/ pellet-based transmission measurements but is not ideal for other sampling methods, such as attenuated total reflection (ATR) and diffuse reflection. As for method (4), it is usually very difficult to remove water vapor interference perfectly using the spectral subtraction technique. Thus, Ulman suggested that spectral subtraction is not a good practice, at least in the field of ultra-thin films, and should be avoided. 4 In method (5), the measured intensity and band shift is analyzed by multivariable analysis to obtain a theoretical spectrum and then it is subtracted from the measured spectrum. However, the theoretical spectrum Received 25 January 2010; accepted 8 July 2010. * Authors to whom correspondence should be sent. E-mail: hswhsw2000@yahoo.com.cn (H.S.W.); umejun@leto.eonet.ne.jp (J.U.). 1186 Volume 64, Number 10, 2010