Metrohm Information: Special NIRS Edition
42Pages

SPECIAL NIRS EDITION Near-infrared spectroscopic solutions by Metrohm NIRSystems Theory of NIR spectroscopy NIR instruments and software for lab and process Applications for NIRS and fields of use

Dear Readers, The fogs of winter are receding, and from my window I can see the silhouette of Mt. Säntis beginning to emerge. This mountain has a very distinctive outline and everyone in eastern Switzerland immediately recognizes its contour. When a sample is exposed to light of a defined wavelength range, a portion of this light will be absorbed. If the remaining spectrum resembles an alpine mountain chain, the chances are very good that it is an NIR spectrum (NIR = near-infrared). Light in the NIR wavelength range triggers vibration in molecules with a changeable (asymmetric molecule) or...

petrochemical, and pharmaceutical industries as well as for training and environmental analysis. Through this alliance, FOSS can focus more strongly on the food and agricultural products markets. In addition to the names Metrohm, Metrohm Applikon, and Metrohm Autolab, in the future you will also see the name «Metrohm NIRSystems – designed by FOSS.» We are your expert partner when it comes to solutions for all your analytical challenges, whether in industry processes or in the laboratory. I hope you enjoy this special edition of Metrohm Information with its many interesting details about the...

Second Overtone Region Second Overtone Region Third Overtone Region Third Overtone Region ArOH RNH2 ArOH ArCH RNHR’ ArCH CH First Overtone Region RNH2 ArOH RNH2 ArOH RNH2 ArOH CONH2 RNH2 ArCH RNHR’ ArCH ArCH Combination Band Region Combination Band Region First Overtone Region Introduction • History and importance of NIR spectroscopy Theory – a first approach • Interaction of light and physical matter • Harmonic and anharmonic oscillator • Implications for NIRS • NIRS, MIR, and Raman • Data pretreatment and data reduction techniques Instruments and Vision® software • Laboratory and atline...

Some of the participants of the NIRS training held in Herisau in March 2013 Many instruments for near-infrared spectroscopy (NIR spectroscopy or NIRS) are added to Metrohm’s product portfolio. For the customer, this offers even more options to choose from and find the perfect solution for their analytical tasks in the lab and in the process. To be able to offer the finest solutions for NIR spectroscopy, Metrohm entered into a strategic alliance with the Danish manufacturer FOSS. While Metrohm will become the sole global distributor of FOSS NIR instruments for the chemical, petrochemical,...

06 Theory – a first approach Names as «overtone vibrational spectroscopy» and «anharmonic vibrational spectroscopy» illustrate that the understanding of the NIRS theory is by far not easy. Although it is beyond the scope of this special NIRS edition to provide an overview of the theoretical background of vibrational spectroscopy, it cannot do without delving into some basic principles that facilitate spectra interpretation. Interaction of light and physical matter Spectroscopy uses light – electromagnetic radiation – to analyze materials by describing the energy transfer between light and...

Harmonic oscillator - the ideal case These molecular vibrations can be described using the classical physics model of the harmonic diatomic oscillator as the simplest vibrating system. Two vibrating masses connected with a spring with a given force constant lead to changes in the internuclear distance. Combing Hook's law with Newton's force law, the vibrational frequency corresponds to: ■ - bond frequency of absorption . 1, band 1 Ik ■ (Eq. 2) - force constant of the bond 2tt u M ft — reduced mass of the bonded According to Hook's law, the potential energy V of the harmonic...

Second Overtone Region Third Overtone Region First Overtone Region ArOH RNH2 ArOH ArCH RNHR’ ArCH Combination Band Region Wavelength [nm] Figure 1: Major analytical bands and relative peak positions for prominent near-infrared absorptions. Most chemical and biological products exhibit unique absorptions that can be used for qualitative and quantitative analysis. NIR spectral region From the aforesaid, it is obvious that the most prominent absorption bands occurring in the NIR region are related to the overtone and combination bands (Figure 1, Table 1) of the fundamental molecular vibrations...

Table 2: Some characteristics of NIR, MIR, and Raman spectroscopies Raman homonuclear bonds such as C–C, C=C, S–S polar bonds such as C=O, C–O, C–F H-containing bonds such as C–H, O–H, N–H, S–H scattered radiation absorbed radiation (basic vibration) absorbed radiation (overtones and combination) well-resolved, assignable to specific chemical groups well-resolved, assignable to specific chemical groups series of overlapping bands Signal intensity change of dipole moment μ change of dipole moment μ low, requires calibration and chemometrics broad fluorescence baseline Water, physical...

Figure 2: Moisture determination in ethanol: (a) NIR spectra of ethanol samples containing different water amounts; (b) corresponding second-derivative spectra; (c) enlarged section of second-derivative spectra between 1828 and 1972 nm (first overtone O-H vibration of water). Data pretreatment Sample-to-sample variations in the overall path length that the photons have to travel before they reach the detector originate from nonhomogeneous distribution of particles in a sample, particle size differences, sample density variations, sample morphology differences (shape and roughness of sample...

Second-derivative intensity Second-derivative intensity A popular regression model used by the Vision® software of Metrohm NIRSystems is multiple linear regression (MLR) that is applied on second-derivative spectra on a calibration set of samples. To overcome the multicollinearity problem and to obtain a strong and robust predictive model, the number of wavelengths used for the analysis is cut down considerably. Normally, using MLR implies considering only two to ten carefully selected wavelengths. They belong to a representative part of the recorded spectra, that is not at all or at least...