Double beam near-infrared spectrometer for compensation of background water absorption and instrumental drift in intensity

Abstract

A double beam near-infrared spectrometer is developed to compensate the water absorption and instrumental drift in intensity. The spectrometer may be used for both single and double beam measurements, and the two operation modes are compared. The results show that the double beam technique eliminates instrumental drift in the single beam measurement and therefore the stability of the system increases by more than 20%. The compensation of the double beam system on water absorption is verified by the measurement of fat content in milk. The results show that the spectrum data based on double beam mode get better calibration model and lower prediction error than traditional single beam mode. CLC numbers: TH744.1; TN219; O433.1 Document code: A Article ID: 1673-1905(2007)03-0211-04 DOI Near-infrared (NIR) spectroscopy is a rapid, reagent-less, and non-destructive analytical technique, which is being increasingly employed in chemistry, pharmaceutics industry and food engineering. Recently, the efforts have turned to biomedical applications, such as detection in the level of glucose in blood [1][2][3] , determination of blood parameter [4][5] , concentration monitoring hemoglobin, oxyhemoglobin and deoxyhemoglobin in human tissue [6][7] . With its unique superiority, NIR spectroscopy is an attractive alternative to traditional chemical assays and is lowly developing into a viable technology.The key of NIR spectroscopy technique used for quantification is that it can detect and predict concentrations with acceptable repeatability and precision. To achieve this goal, NIR spectral instrumental drift and intrinsic strong background absorption have to be overcome. Most conventional NIR spectrometers are single beam (SB) modes and require periodic measurements of reference (background) spectra to remove the variations caused by changing background absorption and instrument conditions. This approach is only if the reference is constant and the intensity of instruments does not drift during the measurements of the reference and the sample. Under some conditions, however, the temporal difference of the two measurements may be effective on the test results because the instrumental drift in intensity may be comparable to the signals from the components of interest.Therefore we have developed a double beam (DB) spectrometer for constituent concentration measurements. For NIR spectra of aqueous based biological samples, water is always a critical matrix component. We firstly concentrate on the compensation of background water absorption. The purpose is to improve measurement accuracy by using the double beam technique.A major problem in the design of DB system is the choice of reference, which is based on the composition and absorbance characteristics of the analyte. Water is a strong absorber in NIR spectral region, the spectrum of aqueous stuff usually shows similar characters to the one of water, and the intensity of transmitted light through water is in the same range as for aqueous stuff. Therefore, if the reference is measured...

Calibration of the spectral sensitivity of instruments for the near infrared region

“…In the near IR region, the problem can be solved by using appropriate solvents such as tetrachloromethane, and absorption by water in the air can be taken into account in the calibration curve. In the mid-IR and far IR regions, when absorption by gases in the air becomes substantial, it is desirable to use a dual-beam measurement scheme [10] or spectrometers with a short beam path.…”