8O 6O o 40 .ID 20 o G ~ 3 C -- 2 1 0 0 (b) o o o o o o o 0 0 0 0 0 0 (a) S S R 3 o o o o o A 10 30 50 70 90 Temperature/°C FIG. 4. Temperature dependencies of the integrated band intensities of the second (a) and first (b) overtones of the OH stretching mode for the monomeric form of Z-9-octadecen-l-ol. (~) Data from the raw spectra (after density correction); (A) data from the difference spectra. Fig. 4b. The intensities in both Fig. 4a and 4b increase with increasing temperature in the same way. In the present study results based on both the second and first overtone seem to be reliable. Both the second and first overtones of the OH stretching mode of the monomeric form can probably be used to monitor the spectral changes. However, the use of the second over- tone might be more convenient because one can deter- mine accurate integrated intensity in an easier way. CONCLUSION The present paper demonstrates that the second over- tone of the OH stretching mode of the monomeric form of Z-9-0ctadecen-l-ol in pure liquid is very useful for probing the temperature-dependent change in the in- tegrated intensities, which is related to the dissociation of hydrogen-bonded alcohols. More thorough NIR stud- ies of the structure and thermodynamic properties of alcohols are now in progress in our group and will be reported soon. 1. M. Iwahashi, N. Hachiya, Y. Hayashi, H. Matsuzawa, M. Suzuki, Y. Fujimoto, and Y. Ozaki, J. Phys. Chem. 97, 3129 (1993). 2. M. Iwahashi, Y. Hayashi, N. Hachiya, H. Matsuzawa, and H. Ko- bayashi, J. Chem. Soc. Faraday Trans. 89, 707 (1993). 3. M. A. Czarnecki, Y. Liu, Y. Ozaki, M. Suzuki, and M. Iwahashi, Appl. Spectrosc. 47, 2162 (1993). 4. B. G. Osborne and T. Fearn, in Near In[rared Spectroscopy in Food Analysis (John Wiley & Sons, New York, 1986), p. 21. 5. Near-Infrared Technology in the Agricultural and Food Industries, P. Williams and K. Norris, Eds. (American Association of Cereal Chemists, St. Paul, Minnesota, 1990), p. 17. 6. A. S. Banana, and P. R. Griffiths, J. Near Infrared Spectrosc. l, 13 (1993). 7. V. Zanker, Z. Phys. Chem. 200, 250 (1952). Comment on a "Simple and Efficient Method to Eliminate Spike Noise from Spectra Recorded on Charge-Coupled Device Detectors" WIELAND HILL Institut fEr Spektrochemie und angewandte Spek- troskopie (ISAS), P.O. Box 101352, 44013 Dortmund, Germany Index Headings: Computer applications; Raman spectroscopy. INTRODUCTION Recently, Takeuchi et al. proposed a simple, so-called "robust summation" method for the efficient elimination of spike noise from charge-coupled device (CCD) data. 1 In their paper, robust summation was shown to be ad- vantageous in comparison to median filters, which had been occasionally employed to remove spikes from data recorded with CCD detectors. 2 In our opinion, missing-point fitting is the most ad- vanced method for spike removal. 3-5 Even the algorithm by Phillips and Harris 3 is superior to the use of median filters and robust summation with regard to several fea- tures. DISCUSSION Missing-point correction of spikes is based on a com- parison of measured values with estimates calculated from a number of neighboring data points within the same spectrum or within successively recorded spectra. The point in question, as well as identified neighboring spikes, is deleted for the calculation of these estimates. By this algorithm, accurate estimates are obtained and can be used for efficient spike correction. Robust summation is based on a comparison with a single neighboring value measured on the time axis. In comparison to missing-point fitting, this principle has the disadvantages described below. The standard deviation of the measured neighboring values is generally larger than that of missing-point es- timates. This factor leads to less reliable spike identifi- cation. Consequently, a higher proportion of unspiked data points need to be "corrected." Generally, it is unknown whether the consecutively recorded spectra contain exactly the same spectral in- formation. The proposed scaling, using the total intensity of each spectrum, 1 compensates for intensity fluctuations due to laser instabilities or changing adjustments. Other disturbances, such as changing stray room light, changing fluorescence background due to a degradation of fluo- rescent impurities, or imperfect beam pointing onto an inhomogeneous sample, may further seriously influence the results of the spike correction by this method. Fur- Received 19 March 1993; revision received 18 June 1993. Volume 47, Number 12, 1993 0~3-7028/93/4712-217152.00/0 APPLIED SPECTROSCOPY 2171 © 1993 Society for Applied Spectroscopy