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.