Near Infrared Spectroscopy (NIR)
Near Infrared Spectroscopy (NIR)

Near infrared spectroscopy (NIR) is a fast and efficient modern analytical technique that combines the latest research from a variety of disciplines, including computer science, spectroscopy and chemometrics. With its unique advantages in many The field has been increasingly widely used.
Near-infrared light is an electromagnetic wave between visible light (VIS) and mid-infrared light (MIR). The wavelength range of the near infrared spectroscopy defined by ASTM is 780 to 2526 nm (12820 to 3959 cm-1) Divided into near infrared shortwave (780 ~ 1100nm) and near infrared longwave (1100 ~ 2526nm) two regions.
Near infrared spectroscopy is mainly due to the non-resonant vibrational molecular vibration molecular vibration generated from the ground state to high energy transitions, the main recorded hydrogen-containing groups X-H (X = C, N, O) Frequency absorption. The NIR absorption wavelength and intensity of different groups (such as methyl, methylene, benzene ring, etc.) or the same group in different chemical environments are significantly different. NIR spectroscopy has abundant structure and compositional information and is very suitable for use The composition and properties of hydrocarbon organic substances are measured.
However, in the NIR region, the absorption intensity is weak, the sensitivity is relatively low, the absorption band is wide and the overlap is serious. Therefore, it is very difficult to rely on the traditional method of establishing working curve for quantitative analysis. The development of chemometrics has laid a mathematical foundation for the solution of this problem.
Principle introduction
Near infrared spectroscopy is based on the near infrared absorption spectrum of the material used for quantitative analysis. This technique is generally not used in the sample pretreatment, nor the use of internal standard method.
The working principle is that if the samples have the same composition, their spectra are the same, and vice versa. If we establish the correspondence between the spectra and the parameters to be measured (called the analytical model), we can get the required mass parameters quickly by measuring the spectrum of the sample and the above correspondence.
The near-infrared spectrum of a sample contains information about the composition and structure of the sample, and the nature parameters (such as relative density, distillation range and flash point of the oil) are also related to its composition and structure. Therefore, there must be an intrinsic relationship between the near-infrared spectrum of a sample and its properties. The use of chemometrics, a mathematical method to correlate the two, establishes a quantitative or qualitative relationship between the two, ie, a model of correction. After establishing the model, as long as the near-infrared spectrum of unknown sample is measured, the model library is automatically searched by software and the correct model is selected. Based on the calibration model and the near-infrared spectrum of the sample, the properties of the sample can be predicted.
Near-infrared spectroscopy consists of: near-infrared spectroscopy, chemometrics software and various calibration models. Near infrared spectroscopy instrument to provide near infrared spectroscopy of the sample, as the analytical information carrier. Chemometrics software is a software tool for correlating spectra and properties. The model is a quantitative or qualitative working curve that has been established to reflect the correspondence between the spectrum and the nature of the sample.
Instrument technical characteristics
1, near infrared spectroscopy superiority of technology
(1) fast analysis
The measurement of the spectrum can be completed within 1 ~ 2min. The chemical composition or properties of the sample can be quickly determined through the calibration model established.
(2) high efficiency analysis
Through a spectrum of measurements and multiple calibration models that have been established, multiple components and properties of a sample can be determined simultaneously.
(3) non-destructive analysis techniques
In the near infrared spectroscopy, the sample is not damaged during the measurement process, and the sample will not be affected from the appearance to the interior. In view of this, the technology is being applied more and more in the fields of in vivo analysis and clinical medicine.
(4) Analysis of low cost, non-polluting
In the sample analysis process does not consume the sample itself, do not use any chemical reagents, analysis of the degree of majors lower, and does not cause any environmental pollution, are "green analysis" technology.
(5) Samples generally do not need pretreatment, easy to operate
Due to the strong penetrating ability and scattering effect of near-infrared light, transmission and diffuse reflectance spectrometry can be selected according to the intensity of the sample state and the light-transmitting ability. Through the corresponding sample-loading device can be directly measured liquid, solid, semi-solid and gelatinous samples of different states.
(6) good test reproducibility
Due to the stability of the spectrometric measurements, the test results are less subject to human factors and near-infrared spectroscopy generally shows better reproducibility than the standard or reference methods.
(7) to facilitate online analysis
Due to the good transmission characteristics of near infrared spectroscopy in optical fiber, the optical fiber can make the instrument away from the sampling site, it is suitable for the production process and sample analysis in harsh and hazardous environments, online analysis and remote monitoring

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