Infrared sample preparation

Work in a logical, tidy manner and minimize risks by thinking ahead. Alway clear up spillages, especially around balances, infrared sample preparation areas, etc., for the next worker. 

Infrared Sample Preparation Liquid Samples Solid Samples... 

Electronic Absorption and Emission Spectroscopy Visible Spectroscopy Ultraviolet Spectroscopy Luminescence Spectroscopy Electron Spectroscopy Atomic Identification and Analysis Infrared and Raman Spectroscopy Infrared Spectroscopy Infrared Sample Preparation Internal Reflection Spectroscopy (IRS, ATR) Reflection Absorption (RAIR or IRRAS)... 

Infrared Sample Preparation. Details of sample preparation for obtaining infrared spectra are discussed for films, capillary layers, demountable cells, fixed thickness cells, pressed halide pellets, and oil mulls in the above references by Potts and Smith and in ASTM methods (27). Other more specialized techniques are described briefly below. 

The pale brown, paramagnetic compounds are moderately air-sensitive and should be stored under a dinitrogen atmosphere. In air, solid samples can be kept without apparent decomposition, but solutions rapidly decompose. All the dicarbonyl complexes are soluble in chlorinated solvents and tetrahydro-furan but only sparingly soluble in acetonitrile, alcohols, diethyl ether, and hydrocarbons. Solution infrared samples prepared in air show an additional peak at 1980 cm due to the formation of Tp WOX(CO) during sample preparation. 

A disk using spectroscopic-grade polyethylene powder (commercially available), instead of the KBr powder used for mid-infrared sample preparations, may be formed with some solid samples. Whether such a disk is firmly and usefully formed depends on the affinity between the sample and the polyethylene powders. 

In some cases, the infrared sample preparation techniques that may be required for the examination of a particular sample may destroy or modify the characteristics of interest. For Raman, very little, if any, sample preparation may be required. 

Reflectance sampling is the second major family of infrared sample preparation methods. In reflection techniques the light is reflected from the surface of the sample, as shown in Figure 4.34. 

There is a unique chapter on how to correctly use spectral processing to tackle the thorny problem of mixture analysis. Half the battle in obtaining a good infrared spectrum is proper sample preparation learn to win that battle by reading the Preparing Samples Properly chapter covering in detail the most important development in infrared sample preparation in decades diamond ATRs. The final chapters examine single analyte quantitative analysis and how infrared microscopy is used to catch criminals and solve industrial problems. 

D.H. Anderson and T.E. Wilson, "Novel Approach to Micro Infrared Sample Preparation". Anal. Chem., 47, 2482-2483 (1975), IR-21. 

When the spectral characteristics of the source itself are of primary interest, dispersive or ftir spectrometers are readily adapted to emission spectroscopy. Commercial instmments usually have a port that can accept an input beam without disturbing the usual source optics. Infrared emission spectroscopy at ambient or only moderately elevated temperatures has the advantage that no sample preparation is necessary. It is particularly appHcable to opaque and highly scattering samples, anodized and painted surfaces, polymer films, and atmospheric species (135). The interferometric... 

Mark, H. "Use of Mahalanobis Distances to Evaluate Sample Preparation Methods for Near-Infrared Reflectance Analysis", Anal. Chem. 1987 (59) 790-795. 

Carbon Dioxide Adsorption on Dried Polymer. Other unexpected interactions of these hydrolytic polymers have been noted previously during the measurement of infrared spectra of dried Pu(IV) polymers (like those used for diffraction studies). Vibrational bands first attributed to nitrate ion were observed in samples exposed to room air however, these bands were not present in samples prepared under nitrogen atmospheres (see Fig. 4) (6). Chemical analyses established enough carbon in the exposed samples to confirm the assignment of the extraneous bands to the carbonate functional group... 

FIGURE 26 Fourier transform infrared spectroscopy of polymer samples prepared at either 130, 145, or 160°C with or without cyclo-benzaprine hydrochloride (CBP). Polymer prepared from 3,9-bis-(ethylidene-2,4,8,10-tetraoxaspiro[5,5)undecane) and a 25 75 mole ratio of trans-cyclohexane dimethanol and 1,6-hexanediol and contained 3 wt% phthalic anhydride and 7.5 wt% cyclobenzaprine hydrochloride (CBP). 

Fig. 2 Infrared spectra taken after metal deposition and exposure to increasing amounts of CO at a constant temperature a 0.02 ML Rh, 60 K b 0.013 ML Pd, 60 K c 0.2ML V, 90 K. CO bands present on nominally clean surfaces are due to CO adsorption from the background during sample preparation...

Standard practices for GC-IR analysis have been described (ASTM E 1642-94). Griffiths [200] has discussed GC-FTIR designs. Sample preparation methods for hyphenated infrared techniques, in particular GC-FTIR, have been reported [201]. The technique has been reviewed repeatedly [167,183,201-204] a monograph [205] has appeared. 

Several additional instrumental techniques have also been developed for bacterial characterization. Capillary electrophoresis of bacteria, which requires little sample preparation,42 is possible because most bacteria act as colloidal particles in suspension and can be separated by their electrical charge. Capillary electrophoresis provides information that may be useful for identification. Flow cytometry also can be used to identify and separate individual cells in a mixture.11,42 Infrared spectroscopy has been used to characterize bacteria caught on transparent filters.113 Fourier-transform infrared (FTIR) spectroscopy, with linear discriminant analysis and artificial neural networks, has been adapted for identifying foodbome bacteria25,113 and pathogenic bacteria in the blood.5... 

Infrared spectroscopy/microscopy certainly is the primary method of choice when organic substances have to be identified. Sample preparation usually is simple for identification purposes, but will be an issue for imaging experiments, and spatial resolution may then well be only in the range of a few micrometers, depending on the used experimental approach (transmission, ATR). 

NIR (near-infrared) imaging has also been well introduced into polymer characterization, mainly because no laborious sample preparation is necessary. Spatial resolution approaches the range of mid-infrared imaging. 

A comprehensive review of compositional and failure analysis of polymers, which includes many further examples of analysis of contaminants, inclusions, chemical attack, degradation, etc., was published in 2000 [2], It includes details on methodologies, sampling, and sample preparation, and microscopy, infrared spectroscopy, and thermal analysis techniques. 

Near-infrared spectroscopy is quickly becoming a preferred technique for the quantitative identification of an active component within a formulated tablet. In addition, the same spectroscopic measurement can be used to determine water content since the combination band of water displays a fairly large absorption band in the near-IR. In one such study [41] the concentration of ceftazidime pentahydrate and water content in physical mixtures has been determined. Due to the ease of sample preparation, near-IR spectra were collected on 20 samples, and subsequent calibration curves were constructed for active ingredient and water content. An interesting aspect of this study was the determination that the calibration samples must be representative of the production process. When calibration curves were constructed from laboratory samples only, significant prediction errors were noted. When, however, calibration curves were constructed from laboratory and production samples, realistic prediction values were determined ( 5%). 

Modern spectroscopy plays an important role in pharmaceutical analysis. Historically, spectroscopic techniques such as infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS) were used primarily for characterization of drug substances and structure elucidation of synthetic impurities and degradation products. Because of the limitation in specificity (spectral and chemical interference) and sensitivity, spectroscopy alone has assumed a much less important role than chromatographic techniques in quantitative analytical applications. However, spectroscopy offers the significant advantages of simple sample preparation and expeditious operation. 

The pharmaceutical industry comprises the largest segment, roughly 15 to 20%, of the infrared (IR) market. Modern mid-infrared instrumentation consists almost exclusively of Fourier transform (FT) instruments. Because of its ability to identify molecular species, FT-IR is routinely used as an identification assay for raw materials, intermediates, drug substances, and excipients. However, the traditional IR sample preparation techniques such as alkali halide disks, mulls, and thin films, are time-consuming and not always adequate for quantitative analysis. 

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