Near-Infrared, Mid-Infrared, And Raman Spectroscopy
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.C H A P T E R3Near-Infrared, Mid-Infrared,and Raman Spectroscopyc0003Ouissam Abbas, Pierre Dardenne, Vincent BaetenO U T L I N E3.1. Introduction623.2. Theory623.3. Instrumentation3.3.1. Near-Infrared Spectrometers3.3.2. Mid-Infrared Spectrometer3.3.3. Raman Spectrometers656566673.4. Sample Presentation3.4.1. Near-Infrared Accessories3.4.2. Mid-Infrared Accessories3.4.3. Raman Accessories686869693.5. New Generation of Spectrometers3.5.1. On-line Systems3.5.2. Mapping and Imaging Systems696970Chemical Analysis of Food: Techniques and ApplicationsDOI: 10.1016/B978-0-12-384862-8.00003-03.6. Advantages and Limitationsof Spectroscopic Techniques713.7. Chemometric Approach723.8. Applications in Food Analysis3.8.1. Geographic Origin3.8.2. Species Discrimination3.8.3. Detection of Adulteration3.8.4. Process Control3.8.5. Physico-Chemical Properties3.8.6. Food Quality737375777981843.9. Conclusion856110003-PICO-9780123848628Copyright Ó 2012 Elsevier Inc. All rights reserved.
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.623. NEAR-INFRARED, MID-INFRARED, AND RAMAN SPECTROSCOPYList of AbbreviationNIR Near InfraredMIR Mid-InfraredATR Attenuated Total ReflectanceFT Fourier TransformPCA Principal-Component AnalysisPLS Partial Least SquaresMPLS Modified Partial Least SquaresPLS-DA Partial Least Squares e DiscriminantAnalysisPLSR Partial Least Squares RegressionSVM Support Vector MachineLS-SVM Least Squares Support Vector MachineLDA Linear Discriminant AnalysisSEP Standard Errors of PredictionRMSEP Root Mean Standard Errors of PredictionSECV Standard Errors of Cross-Validations0010p0100advances and their applications (Wilson &Tapp, 1999; Cen & He, 2007). The spectroscopicapproach can be applied both in laboratorybasic research and in the factory as an on-linetool for monitoring food products, productionprocesses, and quality (Baeten et al., 2010).In this case, reference methods would beapplied if deviation from standard values wasobserved.In this review, we highlight the new advances p0110in infrared (NIR and MIR) and Raman spectroscopic methods which, combined with multivariate analyses, have broad food applications,mainly in relation to composition analysis,quality control authentication, and adulterationdetection (Trends in analytical chemistry, 1998;Da-Wen Sun; Vermeulen et al., 2010; Karoui &De Baerdemaeker, 2007).3.2. THEORY3.1. INTRODUCTIONConsumers are increasingly aware of foodsafety and quality issues. One response to thishas been the gradual substitution of tedious andtime-consuming reference chemical and classicalmethods by rapid and environment-friendlyanalytical techniques. Among the panoply ofanalytical tools used are vibrational spectroscopic techniques (near-infrared [NIR], midinfrared [MIR], and Raman), now attractinggrowing interest and based on the fact that foodproducts have a specific composition of characteristics that gives them an individual “fingerprint”. Vibrational spectroscopy techniques alsooffer rapid, nondestructive, and inexpensiveanalysis.p0105For many years, spectroscopic methods havebeen considered as tools for molecular structureand organic matter studies. The rapid development of spectroscopic instrumentation hasexpanded the application of these techniquesto many areas of food research and the foodindustry. There is a growing output of scientificpapers describing the new technologicals0015Spectroscopy can be defined as the study of p0115the interaction between electromagnetic radiation and matter. Electromagnetic radiation ischaracterized by its wavelength l (the lengthof one wave, cm), its frequency n (the numberof vibrations per unit time, Hz), and itswave number n (the number of waves per unitlength, cm 1).When photons of electromagnetic radiation p0120interact with a molecule, radiation can beabsorbed, transmitted, or scattered (Baranska,1987). Radiation is absorbed in the case of IRspectroscopy where the absorption of incidentradiation at a particular frequency in the IRregion is related to this specific vibrational excitation energy. Radiation is scattered in the caseof Raman spectroscopy. The incident radiationis at a frequency that might be in the visible,UV, or NIR region; it is scattered without anychange in the energy of the incident photon(Rayleigh scattering) or when there is a changein that energy (Raman scattering). Both IRabsorption and Raman scattering are mainlyI. CHEMICAL ANALYSIS OF FOOD10003-PICO-9780123848628
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.3.2. THEORYbased on vibrational transitions that occur inthe ground electronic state of the molecule(Li-Chan, 1996). The energy possessed bya molecule at any given moment is defined asthe combination of the contributing energycomponents: electronic, vibrational, rotational,and translational (Adapa et al., February,2009). Translational energy relates to thedisplacement of molecules in a space as a function of the normal thermal motions of matter.Rotational energy is observed as the tumblingmotion of a molecule, resulting from the absorption of energy in the microwave region. Vibrational energy corresponds to the absorption ofenergy by a molecule as the component atomsvibrate around the mean center of their chemicalbonds. Electronic energy is linked to the transitions of electrons while they are distributedthroughout the molecule, either localized withinspecific bonds or delocalized over structures.p0125In essence, the interaction of electromagneticradiation with a molecule might lead to anabsorption that then induces an electronic,vibrational, or rotational transition, dependingon the energy of this radiation. Energy E in eVfor a single photon is calculated using thefollowing equation:hclwhere h is the Planck constant (6.6256 10 34 Js)and c the velocity of light in vacuum (2.998 1010 cm/s).p0130Vibrational energy, like other molecular energies, is quantized. Molecules can occupy discreteenergy levels defined by whole numbers (0, 1, 2,etc.). Normally, molecules occupy the lowestenergy level 0. A transition from level 0 to 1 leadsto a fundamental transition in the molecule,whereas transitions from energy level 0 to 2 or3 are defined as first and second overtones. Overtone frequencies are in the NIR spectral region,whereas fundamentals are in the MIR spectralregion. This section outlines the theory behindeach technique, in order to better understandE ¼ hv ¼63the basic principles of the information providedby each of the studied methods: NIR, MIR, andRaman spectroscopy.Infrared spectroscopy is the absorptionmeasurement of different IR frequencies bya sample positioned in the path of an IR beam(i.e. NIR and MIR beams); when the frequencyof a specific vibration is equal to the frequencyof the IR radiation directed at the molecule,this molecule absorbs the radiation.Absorption spectroscopy is based on theBeereLambert law that says that, for a homogeneous and nonscattering liquid sample, theconcentration of an absorber is proportional tothe sample absorbance.This absorption information is presented inthe form of a spectrum with wave numbers inMIR spectroscopy or wavelengths in NIR spectroscopy on the x-axis and absorbance intensityor percentage transmittance on the y-axis (see,as an example, MIR and NIR spectra of linseedoil in Fig. 3.1).Mid-infrared spectroscopy allows structuralelucidation and compound identification; functional groups absorb photons at characteristicfrequencies of MIR radiation. The MIR regionis between 4000 and 400 cm 1. Absorption positions are presented according to wave numbers(y) (in cm 1). MIR spectra include mainly bandsthat come from stretching and bending fundamental vibrations. Stretching vibrations arethose where the distance between atomsdecreases or increases while atoms remain inthe same bond axis. In bending vibrations, thepositions of the atoms change with respect totheir original bond axis (Introduction to Infraredand Raman Spectroscopy, 1990; Yadav, 2005).They need less energy than stretching vibrationsdo, hence the lower frequencies for bendingvibrations. Absorption bands resulting fromthese vibrations provide information on thestructure of the sample analyzed. The spectraare divided in three regions rich in structuralinformation: the region above 3000 cm 1,including bands of hydroxyl or amino groups;I. CHEMICAL ANALYSIS OF FOOD10003-PICO-9780123848628p0135p0140p0145p0150
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.643. NEAR-INFRARED, MID-INFRARED, AND RAMAN SPECTROSCOPYthe region between 3000 and 1500 cm 1,including stretching vibrations of the acyl chainand carbonyl and alkene groups; and the regionbelow 1500 cm 1, characterized mainly bybending vibrations and some stretching vibrations of the acyl chain and functionalizedgroups, respectively. The region below1500 cm 1 is considered as a fingerprint of onecompound because of its specificity and thehigh number of bands occurring in this region,making it difficult to have two samples with anidentical spectral signature (Coates, 2000).Compounds with similar structures mightexhibit similar spectra profiles in the regionabove 1500 cm 1. It is important to note thatmultiple functional groups might absorbphotons at one frequency range, but that a functional group often has multiple characteristicabsorptions (Handbook of Instrumental Techniques for Analytical Chemistry). In order toevaluate the composition of a complex foodsample, spectral interpretations should not belimited to one or two bands e the wholeMIR spectrumFIGURE 3.1 MIR and NIR spectraabsorbanceof linseed oil.NIR spectrumWavenumber (cm-1)Log (1/R)f0010spectrum needs to be taken into consideration.For MIR and NIR techniques, the overlappingof many different overtone and combinationvibrations results in broad bands with low structural selectivity in NIR spectra compared withMIR spectra where fundamentals are moreresolved, allowing the structure of a sample tobe better elucidated (Karoui et al., 2003). Onthe other hand, the higher energy of NIR radiation and the implication of combination vibrations enable NIR spectroscopy to provide morecomplex structural information than MIR(Luykx & van Ruth, 2008).Near-infrared spectroscopy is widely used to p0155determine organic matter constituents. It isbased on the absorption of electromagnetic radiation by a sample at wavelengths in the800e2500 nm range. NIR absorption frequenciesare presented as wavelengths (l) expressed innm. NIR spectra are composed of broad bandsarising from overlapping absorption corresponding mainly to overtones and combinationsof vibrational mode CeH, NeH, and OeHWavelength (nm)I. CHEMICAL ANALYSIS OF FOOD10003-PICO-9780123848628
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.3.3. INSTRUMENTATIONchemical bonds (Osborne, 2000a,b). Overtones½AU1 correspond to energy transitions that are higherthan those for fundamentals. The frequenciesof first and second overtones correspond toabout two or three times that of the fundamentals. Combination bands result from transitionsinvolving two or more different vibrationalmodes of one functional group occurring simultaneously; the frequency of a combination bandis the sum or the multiples of the relevantfrequencies. The absorption intensity decreaseswhen the overtone level increases.p0160Raman spectroscopy provides chemical andstructural information. A sample is radiatedwith monochromatic UV, visible, or NIR beamgenerated by a laser. Raman scattering occursas a result of the interactions of the incidentphotons with the polarizability or shape of theelectron distribution in a molecule as it vibrates.The vibrational energy levels in the moleculesrise from the ground state to a short-lived,high-energy collision state, which returns toa lower energy state through the scattering ofa photon with a lower frequency than the laserbeam (Stokes Raman scattering). The differencebetween the frequency of the laser and that ofthe scattered photon is known as the Ramanshift. This shift corresponds to the frequencyof the fundamental MIR absorbance band ofthe bond. The spectra are presented as the intensity of the scattered light vs. the shift in thefrequency between the incident and the scattered light defined by wave numbers. The interpretation of Raman spectra bands is carried outin the same way as for MIR signals.p0165Spectroscopic methods give complementaryinformation about a molecule vibration. In theMIR and Raman techniques, vibration thatresults in changes in the dipole moment leadsto be MIR active, whereas vibration that resultsin a change in polarizability leads to be Ramanactive (Pistorius, 1995). Some vibrations can beboth MIR and Raman active. For example, theC]C bond is generally more intense in Ramanthan in IR spectra because the double bond65connects two identical parts of the moleculethat lead to high polarizability changes, whereasa C]O bond exhibits a high electric dipolemoment leading to a more intense band inMIR than in Raman spectra. Water bands arevery weak in Raman spectra, but they presenta high broad band in MIR spectra because ofthe weakness of OeH bond polarizability.Bonds such as CeH are visible in both MIRand Raman spectra. Major food compounds(fat, protein, and carbohydrates) present CeHbands in both Raman and MIR, but with variable intensities.3.3. INSTRUMENTATIONs0020Raman and IR spectroscopic techniques are p0170suitable for both at-line (e.g. in the lab) analysesand on-/in-line process control. Infrared instruments allow spectra to be collected by detectingchanges in the absorption or transmittanceintensity at different frequencies, whereasRaman instruments allow spectra to be recordedby detecting changes in the scattering intensityat different frequencies (Raman shift).3.3.1. Near-Infrared Spectrometerss0025Near-infrared spectrometers can be classified p0175on the basis of such features as radiation source,wavelength selectors, sampling accessories, anddetectors. There are two types of radiation sources:thermal and nonthermal. Thermal sources (Nernstfilament, quartzehalogen, or tungstenehalogenlamps) consist of a radiant filament that producesthermal radiation covering a narrow or a widerange of frequencies in the NIR spectral range(Osborne et al., 1993). Nonthermal sources(discharge lamps, light-emitting diodes, laserdiodes, or lasers) emit narrower bands of radiationthan those emitted by thermal sources. They areconsidered to be more efficient because most ofthe energy consumed is emitted and can be electronically adjusted (McClure, 2001).I. CHEMICAL ANALYSIS OF FOOD10003-PICO-9780123848628
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.66p01803. NEAR-INFRARED, MID-INFRARED, AND RAMAN SPECTROSCOPYWavelength selectors allow NIR instrumentsto be classified into two groups; those based ona discrete wavelength selection and those basedon a continuous spectrum. Discrete wavelengthinstruments using filters or light-emitting diodesirradiate at only few wavelengths selectedfor specific molecules for special applications.Continuous-spectrum instruments are moreflexible and can be used for a wide range of applications (McClure, 2001). They occur in severalconfigurations, such as grating monochromator,acousto-optical tunable filter, photodiode array,and Fourier transform (FT) interferometer technologies (Blanco & Villarroya, 2002):u0010 grating monochromators allow radiation tobe spread out according to wavelengths(McClure, 2001); corresponding instrumentsallow measurements to be made in bothtransmittance and reflectance mode, and aresuitable for a large number of applicationsand to solve analytical issues that need a widerange of wavelengths (Osborne, 2000a,b),u0015 acousto-optical tunable filters producediscrete wavelengths over a wide spectralrange (McClure, 2001); they are characterizedby their great stability and scanreproducibility, making the instrumentscontaining them suitable for use underdifficult measurement conditions, such asproduction plants,u0020 photodiode array systems allow allwavelengths to be measured simultaneously(McClure, 2001; Blanco & Villarroya, 2002;Osborne, 2000a,b); instruments equippedwith this system are suitable for analyzingmoving samples such as on-line applicationsor rotating sample holders,u0025 FT interferometer-based instruments aresystems in which the detector collectsinformation at several frequenciessimultaneously; it offers high wavelengthprecision, accurate scan speed, and a highsignal-to-noise ratio (SNR). More detailsabout this technology are given later (in theparagraph on FT-MIR spectroscopy).After this, light is directed to the sample. NIR p0205spectrometers can be equipped with a largevariety of sampling accessories that make itpossible to measure solid or liquid samples.There is more detail on this later (in the paragraph on the sample presentation of the differentspectroscopic techniques discussed in thischapter). Finally, light from the sample isoriented to single- or multichannel photon detectors (Osborne et al., 1993). The way singlechannel detectors function depends on the typeof semiconductor that they include; lead sulfidecovers the 1100e2500 nm spectral range, siliconthe 400e1100 nm range, and epitaxially grownindium gallium arsenide (InGaAs) the800e1700 nm range (Osborne et al., 1993; Blanco& Villarroya, 2002). Multichannel detectorsconsist of diode arrays where the detectionelements are arranged in rows or charge-coupleddevices (CCDs) in which the detection elementsare arranged in planes (Stchur et al., 2002).3.3.2. Mid-Infrared Spectrometers0030Infrared instruments can be classified into p0210two groups: dispersive and FT spectrometers(Handbook of Instrumental Techniques forAnalytical Chemistry).3.3.2.1. Dispersive Spectrometerss0035Dispersive spectrometers were the first IR p0215instruments. They were invented in the 1940s.They are composed of three basic parts: a radiationsource, a monochromator, and a detector. Thecommon radiation source is an inert solid heatedelectrically to 1000e1800 C, providing differentradiation energy profiles. The monochromator isa device that allows a broad spectrum of radiationto be dispersed and provides a continuous calibrated series of electromagnetic energy bandswith a defined wavelength range. Prisms orI. CHEMICAL ANALYSIS OF FOOD10003-PICO-9780123848628
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.3.3. INSTRUMENTATIONgratings are the dispersive components used inconjunction with variable-slit mechanisms,mirrors, and filters. There are two types of detectors: thermal detectors for measuring the heatingeffect produced by IR radiation and photon detectors based on the interaction between the IR radiation and the semiconductor material. Thermaldetectors provide a linear response over a widerange of frequencies, whereas photon detectorshave shorter response times and higher sensitivity. In dispersive IR spectrometers, radiationfrom a broad-band source passes through thesample and is dispersed by a monochromatorinto component frequencies; each componentfrequency is viewed sequentially. The beam isdirected onto the detector, producing an electricalsignal that is converted into a recorded spectralresponse.s0040 3.3.2.2. Fourier Transform Spectrometersp0220Fourier transform MIR spectrometers havereplaced dispersive spectrometers because oftheir higher speed and sensitivity; all frequenciesare examined simultaneously. FT-MIR spectrometers have significantly increased the capabilitiesand applications of MIR spectroscopy.p0225FT-MIR instruments have three components:a radiation source, an interferometer, anda detector. The source radiation is the same asthat used for dispersive instruments, but withthe advantage being water-cooled in order toobtain more power and stability. Light is thendirected onto an interferometer. The mostcommon one is a Michelson interferometer. Itconsists of a beam splitter and two mirrors ea moving mirror and a fixed mirror e that areperpendicular to each other. Radiation froma broad-band source is collimated and directedinto the interferometer, and then goes throughthe beam splitter, where the half of it is transmitted to the fixed mirror and the remaininghalf is reflected to the moving mirror. Thedivided beams are then reflected from the twomirrors and are recombined at the beam splitter.67With the changes in the position of the movingmirror in relation to the fixed one, an interference pattern is generated. The generated beampasses through the sample and focuses on thedetector. The record of the interference signalis known as an interferogram, which is a timedomain spectrum and records the detectorresponse changes in relation to the time of themirror scan. The interferogram is then converted by applying FT (a mathematical operation) to the final MIR spectrum, which is theusual frequency domain spectrum (intensityversus frequency). Two types of detectors aregenerally used: a deuterated-triglycine sulfate(DTGS) detector and a nitrogen-cooled mercurycadmium telluride (MCT) photon detector. Bothdetectors provide very fast responses and highsensitivity, with a better performance obtainedwith the MCT detector.FT-MIR spectrometers have several advan- p0230tages over dispersive spectrometers, includingfaster speed and higher sensitivity, as well asmaking it possible to observe all frequenciessimultaneously and to obtain a complete spectrum in a single scan. Other advantages includeincreased optical throughput, an internal laserreference that allows automatic calibration(without the need for an external one), greater reliability because of the simpler mechanical design,elimination of stray light and emission contributions, and a powerful computerized data system.3.3.3. Raman Spectrometerss0045Two kinds of Raman instruments are usually p0235used: dispersive spectrometer and an FT spectrometer. In addition, Raman spectrometerscan be classified according to the frequency ofthe exciting laser.In dispersive spectrometers, the scattered light is p0240collected through a filter and focused ontoa monochromator that allows the different energies of the Raman scattering to be separated. Theradiation is then directed to a CCD; frequenciesI. CHEMICAL ANALYSIS OF FOOD10003-PICO-9780123848628
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.683. NEAR-INFRARED, MID-INFRARED, AND RAMAN SPECTROSCOPYof the scattered light are separated and theRaman spectrum is collected. It should be notedthat with the use of CCDs, all scattering is accumulated during the exposure of the sample tothe exciting light, thus improving the intensityof recorded signals. The main disadvantage ofvisible dispersive spectrometers is the problemof fluorescence. The likelihood of this happeningis much higher in the VIS region than it is in NIRregion; large signals could interfere with theweak Raman scattering peaks.p0245Fourier transform spectrometers use an NIRlaser source, for instance, a neodymium-dopedyttrium aluminum garnet (Nd3þ:YAG) laseremitting at 1064 nm. At this wavelength, radiation energy is weak, completely or partly overcoming the fluorescence problem. But becauseabsorption in this region is not as efficient as itin the VIS one, high laser powers are used. Inaddition, the FT system provides more sensitivity, and detectors functioning at roomtemperature or cooled with nitrogen for moresensitivity are used. FT spectrometers have anadvantage over dispersive spectrometers interms of analyzing a sample in its bottle,because dispersion from nonideal surfaces isless important in FT systems and there is lessfluorescence from the bottles.s0050p02503.4. SAMPLE PRESENTATIONSampling is a very important issue in achievinggood qualitative and quantitative analyses. IRand Raman spectroscopy have the advantage oflittle or no need for sample preparation beforeconducting measurements. Depending on thecase, grinding, slicing, or cutting might be necessary. For some products, such as milk, homogenization is performed before analyses. However,parameters such as temperature and moisturehave to be controlled and kept constant beforeand during measurements.p0255Raman and IR spectroscopic methodsprovide a wide range of sample presentationdevices for conducting measurements inoptimum conditions. More details on each technique are presented here.3.4.1. Near-Infrared Accessoriess0055NIR spectrometers make it possible to p0260measure a great variety of food samples invarious forms, including liquids, powders, andall kinds of solid products (Fig. 3.2). Transparentliquids can be measured in transmittance modewhere the pathlength is constant; it meanswhere the thickness of the sample, quartzcuvette, or flow cell is constant. In these conditions, the absorption depends only on theconcentration of the absorbing component. Ifthe sample is opaque, such as milk (because ofthe presence of fat globule), measurement willbe conducted in a diffuse transmittance modebecause in this case part of light is scattered(Coventory, 1988; Osborne, 2000a,b). Some solidproducts, such as meat and cheese, are alsoanalyzed in this mode (Penner, 1994). However,solid and granular samples (Osborne, 2000a,b)are measured using the diffuse reflectance mode.The information collected is based on theabsorbed light and the scattered light that lacksany information on the chemical composition ofthe sample. Another mode combines reflectanceand transmittance, forming the transflectancemode that is suitable for analyzing turbid or clearliquids (Osborne, 2000a,b). The sample is placedbetween a quartz window and a diffuselyReflectancecell for solidTransmissioncell for liquidTransflectioncell for liquidFIGURE 3.2 Examples of sample presentation in near f0015infrared spectroscopy.I. CHEMICAL ANALYSIS OF FOOD10003-PICO-9780123848628
To protect the rights of the author(s) and publisher we inform you that this PDF is an uncorrected proof for internal business use only by the author(s), editor(s), reviewer(s),Elsevier and typesetter TNQ Books and Journals Pvt Ltd. It is not allowed to publish this proof online or in print. This proof copy is the copyright property of the publisherand is confidential until formal publication.3.5. NEW GENERATION OF SPECTROMETERSreflecting metal plate. The incident radiation istransmitted through the sample, reflected fromthe diffusely reflecting plate and then transmitted back through the sample.s0060 3.4.2. Mid-Infrared Accessoriesp0265FT-MIR spectrometers are used also for foodanalyses. Several sample presentation techniques are proposed for liquid analyses suchas transmission cells, thermostated flow cells,and polymer thin films such as IR-cards in polyethylene. For solids, halide pellets (KBr) areused. Recently, more flexible presentation techniques have been proposed as attenuated totalreflectance (ATR) accessories (Fahrenfort, 1961;Harrick, 1967). With these accessories, thesample is put in a close contact with a crystalwith a high refraction index, made mainly ofZnSe, Ge, ZnS, Si, or diamond. ATR is suitablefor both solid and liquid analyses. It is particularly useful for sampling the surface of flatmaterials that are too thick or too opaque forIR transmission (Fig. 3.3).s0065 3.4.3. Raman Accessoriesp0270Ram
scopic techniques (near-infrared [NIR], mid-infrared [MIR], and Raman), now attracting growing interest and based on the fact that food products have a specific composition of charac-teristics that gives them an individual "finger-print". Vibrational spectroscopy techniques also offer rapid, nondestructive, and inexpensive analysis.
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Low Mid High Launch Spin Low Mid High Launch Spin KBS Hi-Rev 2.0 Wedge Flex R S X Tip.355" .355" .355" Weight (g) 115 125 135 Torque N/A N/A N/A Launch Mid Mid Mid Program Stock Stock Stock KBS TOUR 105 Flex R S X Tip.355" .355" .355" Weight (g) 105 110 115 Torque 2.5 2.5 2.5 Launch Mid-High Mid-High Mid-High Spin Mid-High M
conventions for infrared spectroscopy and for practical reasons are divided wavelengths of radiation to the area close to (A - NIR - Near infrared) 750-900 nm, medium (B-MIR - Middle infrared) from 1.55 to 1.75 micron and far (C - FIR - Far Infrared), 10.4 to 12.5 micron according to field use. To measure the amount of incident light are used
1 Infrared spectroscopy Chapter content Theory Instrumentation Measurement techniques Mid-infrared (MIR) – Identification of organic compounds – Quantitative analysis – Applications in food analysis Near-infrared (NIR) – Properties of the technique – Applications in food analysis Infrared spectroscopy
IR-Spectroscopy & Physical Tables IR-Window Material Infrared Tables Near Infrared Table Sources Detectors Beamsplitters Conversion Table of Energy and Wavelength Units for Far and Mid Infrared Conversion Table of Ener
ecule. Mid-infrared is less popular in RMID than NIR due to the strong absorption coefficient in the mid-IR spectral range, which limits the path length into the samples and sometimes requires dilution of the samples using infrared transparent materials.3 In general, NIR and Raman are com-plementary in nature. Both techniques have found broad
The infrared and Raman spectra of 3,4,5-trimethoxybenzaldehyde (3,4,5-TMB) were reported by Gupta et al (1988). But only thirteen fundamental vibrations have been observed. In the present investigation laser Raman, infrared and Fourier's transform far infrared spectra of 3,4,5-TMB are recorded and forty four funda mentals are reported.
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