Wavelength Calibration of a Dispersive Near-Infrared Spectrometer Using Trichloromethane as a Calibration Standard

Abstract

Since differences in wavelength calibration between instruments are arguably a primary source of error encountered in the transfer of calibration models from one instrument to another in near-infrared (NIR) spectroscopy, a readily available, convenient, inexpensive secondary wavelength calibration standard for the NIR spectral region is needed. This paper describes the advantages of trichloromethane as a wavelength standard for the calibration of dispersive NIR spectrometers used in the transmission mode. The spectrum of trichloromethane, taken with a Fourier transform NIR spectrometer whose wavenumber scale was calibrated with the ro-vibrational lines of ethyne as determined by the National Institute of Standards and Technology (NIST), is presented. The wavelengths of four strong, sharp, well-resolved bands of trichloromethane were determined with the calibrated Fourier transform NIR spectrometer and were found to be 1152.13 ± 0.01 nm (3v1), 1410.21 ± 0.01 nm (2v1 + v4), 1691.9 ± 0.7 nm (2v1), and 1861.22 ± 0.01 nm (v1 + 2v4). These bands were then used to calibrate the wavelength scale of a commercial 0.25 m monochromator equipped with a 300 line mm−1 grating. The calibration revealed that, while the wavelength scale of the monochromator was linear, there was a systematic error of about + 12 nm in the NIR region.

Design and Evaluation of a Near-Infrared Dispersive Spectrometer That Uses a He-Ne Laser for Automatic Internal Wavelength Calibration

“…The wavenumber scale of the FT-NIR spectrometer was calibrated as described previously. 3 Table I shows the wavelength reproducibility obtained from ve spectra with four trichloromethane bands when laser wavelength calibration is employed. Use of laser wavelength calibration improves the wavelength reproducibility of the spectrometer and reduces the uncertainty in the m easured wavelength values to less than 1 nm (average value 0.73 nm).…”

“…In previous work on the use of trichloromethane as an NIR wavelength standard, a calibrated FT-NIR spectrometer was used to determine the wavelength of four bands in the trichlorom ethane NIR spectrum. 3 In this study, the wavelengths of these same bands were re-measured with a calibrated FT-NIR spectrometer and compared with those obtained with the laser-corrected spectrometer. Table III summarizes the wavelength values obtained to date for the four trichloromethane bands that have been proposed as wavelength standards for NIR spectroscopy.…”

“…Recently, Busch and co-workers have proposed the use of trichloromethane as a substance with sharp, isolated absorption bands that are suitable for wavelength calibration of spectrometers in the NIR region. 3 This paper describes an instrumental approach that automatically calibrates the wavelength scale of a dispersive NIR spectrom eter w ith out th e need for ex ternal w aveleng th calibration materials. Figure 1 shows the general features of the NIR spectrometer used in this study.…”

NIR Spectrum Analysis of Natural Gas Based on Hollow-Core Photonic Bandgap Fiber

“…The 2ν 3 overtone band of CH 4 molecule has absorption lines in the 1620-1800-nm region, and the other alkane gases have overlapped absorption spectra in the 1650-1780-nm region. Traditional analysis normally adopts the linear model based on statistical probability theory and evolutionary theory, and these multi-components and varied concentrations greatly affect the results of the analysis [12,13].…”

Determination of the Stray Light Levels in a Dispersive Near-Infrared Spectrometer with Trichloromethane

“…In a previous study, trichloromethane was proposed as a wavelength standard for calibrating NIR spectrometers used in the transmission mode over the wavelength range from 1100 to 1900 nm. 6 The wavelengths of four strong, isolated absorption bands were determined with a calibrated Fourier transform NIR (FT-NIR ) spectrometer and found to be 1152, 1410, 1692, and 1861 nm. In this study, the use of trichloromethane for the evaluation of the photometric perform ance of an NIR spectrometer is proposed.…”