Near infrared analytical instrument
Near infrared spectrometer can be divided into five types: fixed wavelength filter, grating chromatic dispersion, fast Fu Liye transform, acousto-optic tunable filter and array detector.The filter type is mainly used as a special analytical instrument, such as a grain moisture meter. Because of the limited number of filters, it is difficult to analyze samples of complex systems. Grating scanning has high signal-to-noise ratio and resolution. Because the moving parts in the instrument (such as the grating axis) may have wear problems in the continuous high intensity operation, thus affecting the reliability of the spectral acquisition, it is not suitable for on-line analysis. The Fu Liye transform near infrared spectrometer has high resolution and scanning speed, and the weakness of this kind of instrument is that there are moving parts in the interferometer and the strict working environment is needed. Acousto optic tunable filter adopts birefringent crystal to adjust the scanning wavelength by changing the RF frequency. The whole instrument system has no moving parts, and the scanning speed is fast. But the resolution of these instruments is relatively low and the price is higher.
With the array detection device production technology is mature, with a fixed optical path, grating, array detector composed of NIR instrument, with the characteristics of stable performance, fast scanning speed, high resolution, high signal-to-noise ratio and good price performance ratio is people pay more and more attention. The array detector is matched with a fixed optical path, used a charge coupled device (CCD) and diode array (PDA) of two types, including CCD spectrometer for short wavelength near-infrared region, PDA detector is used in near-infrared region. In the selection or use of near infrared spectrometer, it is an important question for analysts to consider which indexes of instruments meet the requirements of analysis. When evaluating a near infrared spectrometer, it is necessary to understand the main performance parameters of the instrument.
For any particular near infrared spectrometer, it has an effective spectral range, and the spectral range is mainly determined by the optical path design of the instrument, the type of detector and the light source. The wavelength range of near infrared spectrometer is usually divided into two sections, the short wave near infrared spectrum region of 700 ~ 1100nm and the near infrared spectrum region of 1100 ~ 2500nm.In the calibration process, the number of standard samples, directly affect the accuracy of analysis results, the quantity is too little to reflect the measured sample groups normal distribution, in order to improve the calibration results, the calibration curve has a wide range of applications, the variation range of relatively large sample according to the principle of screening specific. A plurality of calibration, in order to improve the accuracy of calibration and test results. Generally speaking, one kind of pure samples as the sample containing the chemical properties of stability, the amount of information is relatively small, so the calibration is relatively easy, such as corn, wheat, soybeans and other pure samples; mixed sample information is complex, in this spectral region will cause different groups overlapping peaks, information analysis, calibration difficulties, such as various in animal husbandry, feed feed, concentrated feed etc..Long wave near infrared spectrum region.
