Evaluation of a dual-beam near-infrared spectrometer based on acousto-optic tunable filters

A dual-beam near-infrared (NIR) spectrometer was constructed and evaluated, The instrument was designed to work with the two monochromatic beams produced by each one of the two acoustooptic tunable filters (AOTFs) evaluated, capable of scanning the wavelength range 800-1600 or 1500-2400 nm. Two temperature-controlled, cooled InAs detectors were employed for comparison of the two monochromatic beams produced by the AOTF. Data were obtained in a controlled ambient temperature, (25 +/- 1) degreesC, and were compared for their intensity and wavelength coincidence for each of the 300 values of radio frequency (85-160 and 56-92 MHz) applied to the AOTF. The results show that the two beams present good concordance as a function of the wavelength (mean Delta lambda < 0.30 inn for both AOTFs investigated, The normalized intensities of the two beams were quite different, and their ratio values (0.9 to 1.2) depend on the wavelength. inversion of intensities was observed in the present case and can be attributed to the unmatched position of the two detectors and to the difference in responsivity. On the other hand, the use of the two beams revealed that it can provide a robust way to correct for light-source intensity fluctuation as high as 10%. The mean standard deviation for long-term operation and for a zero absorbance baseline was reduced three times when the dual-beam instrument was employed. The instrument has also been evaluated for determination of water in fuel ethanol, The results for water content demonstrate the good analytical performance of the spectrometer with a relative error of 0.07 and 0.03% (w/w) for water determination in the ranges 0.20-10.0 and 0.20-3.00%, respectively.55445445

Determination Of Ethanol And Methyl Tert-butyl Ether (mtbe) In Gasoline By Nir-aotf-based Spectroscopy And Multiple Linear Regression With Variables Selected By Genetic Algorithm

This paper describes a near infrared spectroscopic method developed for determination of ethanol and methyl tert-butyl ether (MTBE) as additives in gasoline. The methodology employs data collected from a near infrared spectrophotometer whose monochromator is an Acousto-Optic Tunable Filter (AOTF) operating in the 1500-2400 nm range. Genetic Algorithm variable selection was used in the multiple linear regression (MLR) modelling. Seven wavelengths were selected by the algorithm and the results obtained by MLR revealed that the method produces improved results, when compared with the PLS regression method, as confirmed by the lower RMSEP obtained for ethanol and MTBE determination. Besides the improvement achieved in the analytical results, the variable selection allows a reduction in the time necessary for data acquisition. This fact has special importance when AOTFs are being used as the monochromator element. The AOTF's capability of random access to the selected wavelengths can be employed to access the necessary information very rapidly, enabling the methodology to be used for in-line monitoring of fuel additives.61-4333339Lambert, D., Descales, B., Bages, S., Llinas, J.R., Loublier, M., Maury, J.P., Martens, A., (1995) Analusis, 23, pp. M10Rohrback, B.G., (1991) Trends Anal. Chem., 10, p. 269Descales, B., Cermelli, I., Llinas, J.R., Margail, G., Martens, A., (1993) Analusis, 21, pp. M25Prufer, H., Mamma, D., (1995) Analusis, 23, pp. M14Workman Jr., J.J., Mobley, P.R., Kowalski, B.R., Bro, R., (1996) Appl. Spectrosc. Reviews, 31, p. 73Cooper, J.B., Wise, K.L., Welch, W.T., Bledsoe, R.R., Sumner, M.B., (1996) Appl. Spectrosc., 50, p. 917Choquette, S.J., Chesler, S.N., Duewer, D.L., Wang, S., O'Haver, T.C., (1996) Anal. Chem., 68, p. 3525Huhne, M., Eschenauer, U., Siesler, H.W., (1995) Appl. Spectrosc., 49, p. 177Baptista, M.S., Tran, C.D., Gao, G.H., (1996) Anal. Chem., 68, p. 971Turner II, J.F., Treado, P.J., (1996) Appl. Spectrosc., 50, p. 277Poppi, R.J., Pasquini, C., (1993) Chemometrics Intell. Lab. Syst., 19, p. 243Fodor, G.E., Kohl, K.B., Mason, R.L., (1996) Anal. Chem., 68, p. 23Pan, S., Chung, H., Arnold, M.A., Small, G.W., (1996) Anal. Chem., 68, p. 1124Draper, N., Smith, H., (1981) Applied Regression Analysis, , Wiley, New York, 2nd EdnHibbert, D.B., (1993) Chemometrics Intell. Lab. Syst, 19, p. 277Jouan-Rimbaud, D., Massart, D.L., Leardi, R., De Noord, O.E., (1995) Anal. Chem., 67, p. 4295Geladi, P., Kowalski, B.R., (1986) Anal. Chim. Acta, 185, p.