Near IR spectroscopy

The formal approach of 2D correlation analysis to time-dependent spectral intensity fluctuations has been extended to UV, Raman [1010], and near-IR spectroscopy [1011-1014] 2D fluorescence is upcoming. 

Beside mid-IR, near-IR spectroscopy has been used to quantitate polymorphs at the bulk and dosage product level. For SC-25469 [34], two polymorphic forms were discovered (a and /3), and the /3-form was selected for use in the solid dosage form. Since the /3-form can be transformed to the a-form under pressure by enantiotropy, quantitation of the /3-form in the solid dosage formulation was necessary. Standard mixtures of both forms in the formulation matrix were prepared, and spectra were measured in the near-IR via diffuse reflectance. Utilizing a standard, near-IR multiple linear regression, statistical approach, the a- and /3-forms could be predicted to within 1% of theoretical. This extension of the diffuse reflectance IR technique shows that quantitation of polymorphic forms at the bulk and/or dosage product level can be performed. 

The extent of homogeneous mixing of pharmaceutical components such as active drug and excipients has been studied by near-IR spectroscopy. In an application note from NIRSystems, Inc. [47], principal component analysis and spectral matching techniques were used to develop a near-IR technique/algorithm for determination of an optimal mixture based upon spectral comparison with a standard mixture. One advantage of this technique is the use of second-derivative spectroscopy techniques to remove any slight baseline differences due to particle size variations. 

The application of near-IR spectroscopy for real-time monitoring of glucose, lactic acid, acetic acid and biomass in liquid cultures of microorganisms of the genera Lactobacillus and Staphylococcus has been recently published [76]. The NIR spectrum acquired by the optical-fibre probe immersed in the culture is exploited using a partial least squares (PLS) calibration step, a classical method for IR techniques. 

The phenomenon of fluorescence has been synonymous with ultraviolet (UV) and visible spectroscopy rather than near-infrared (near-IR) spectroscopy from the beginning of the subject. This fact is evidenced in definitive texts which also provide useful background information for this volume (see, e.g., Refs. 1-6). Consequently, our understanding of the many molecular phenomena which can be studied with fluorescence techniques, e.g., excimer formation, energy transfer, diffusion, and rotation, is based on measurements made in the UV/visible. Historically, this emphasis was undoubtedly due to the spectral response of the eye and the availability of suitable sources and detectors for the UV/visible in contrast to the lack of equivalent instrumentation for the IR. Nevertheless, there are a few notable exceptions to the prevalence of UV/visible techniques in fluorescence such as the near-IR study of chlorophyll(7) and singlet oxygen,<8) which have been ongoing for some years. 

R.L. Green, G. Thurau, N.C. Pixley, A. Mateos, R.A. Reed and J.P. Higgins, In-line monitoring of moisture content in fluid bed dryers using near-IR spectroscopy with consideration of sampling effects on method accuracy. Anal. Chem., 77(40), 4515 522 (2005). 

C. van der Vlies, K.J. Kaffka and W. Plugge, Qualifying pharmaceutical substances by fingerprinting with near-IR spectroscopy and the polar qualification system, Pharm. Technol. Eur, 7, 46 9 (1995). 

Even in modern quality control laboratories you will find a number of traditional methods for the identification of single flavour compounds, for example the estimation of optical rotation, refractive index, density and melting point, since these methods are generally accepted, effective and less time-consuming. Especially for the purpose of fast identification checks of more complex systems, spectroscopic methods, above all infrared (IR) and near-IR spectroscopy, are gaining more and more importance. 

Chang SY, Wang NS. Monitoring polymerization reactions by near-IR spectroscopy. ACS Symposium Series 1995, 598, 147-165. 

There is substantial history regarding the application of conventional vibrational spectroscopy methods to study the intact surface of skin, the extracted stratum corneum and the ceramide-cholesterol-fatty acid mixtures that constitute the primary lipid components of the barrier. The complexity of the barrier and the multiple phases formed by the interactions of the barrier components have begun to reveal the role of each of these substances in barrier structure and stability. The use of bulk phase IR to monitor lipid phase behavior and protein secondary structures in the epidermis, as well as in stratum corneum models, is also well established 24-28 In addition, in vivo and ex vivo attenuated total reflectance (ATR) techniques have examined the outer layers of skin to probe hydration levels, drug delivery and percutaneous absorption at a macroscopic level.29-32 Both mid-IR and near-IR spectroscopy have been used to differentiate pathological skin samples.33,34 The above studies, and many others too numerous to mention, lend confidence to the fact that the extension to IR imaging will produce useful results. 

Espinoza, L.H., D. Lucas, D. Littlejohn, and S. Kyauk. 1999. Total organic carbon content in aqueous samples determined by near-IR spectroscopy. Appl. Spectrosc. 53 103-107. 

Visible and near-IR spectroscopy of nonbiogenic carbonates experimental materials, 95 experimental procedures, 95-95 Visible and near-IR spectroscopy of skeletal carbonates... 

Alam, M.K. and Callis, J.B., Elucidation of species in alcohol-water mixtures using near-IR spectroscopy and multivariate statistics, Anal. Chem., 66, 2293-2301, 1994. 

Whereas near-IR spectroscopy provides an incisive probe of the electronic and thermal state of the heme after flash photolysis, it tells us nothing about the state in which the ligand is created. Mid-IR spectroscopy, on the other... 

Osborne and Fern (1986) have presented detailed band assignments in the near-IR range, and Wetzel (1983) and William and Norris (1987) have summarized the salient points of near-IR spectroscopy. The latter authors emphasize applications for the agricultural and food industries. Birkett et al. (1989) have reported the successful kappa number determination of pulps using spectra in the near-IR range. 

Among the large variety of in situ experiments that have been described one can distinguish (1) those whose purpose is investigation of the electrochemical doping process itself cyclic voltammetry, quartz balance [17], mirage effect [18], and ellipsometry [19], and (2) those developed for studies of the properties of the CP UV-near-IR spectroscopy [20], IR [21], ESR [22], conductivity [23], impedence [24], and so on. 

Buckton G, Yoremochi E. Near IR spectroscopy to quantify the silica content and differences between silicified miicrocrystalline cellulose and physical mixtures of microcrystalline cellulose and silica. Int J Pharm 1998 169 183—194. 

Buckton G, Yoremochi E, Yoon NL, Moffat AC. Water sorption and near IR spectroscopy to study the differences between microcrystalline cellulose and silicified miicrocrystalline cellulose after wet granulation. Int J Pharm 1999 181 41 7. 

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