Infrared IR spectrometry

Photomultiplier tubes or photodiodes (light sensors) are used as detectors in UV-VIS spectrophotometers, while thermcouples (heat sensors) are used as detectors for infrared (IR) spectrometry. This is the reason UV-VIS instruments are called spectrophotometers while IR instrument are called spectrometers. 

Freon-extractable material is reported as total organic material from which polar components may be removed by treatment with silica gel, and the material remaining, as determined by infrared (IR) spectrometry, is defined as total recoverable petroleum hydrocarbons (TRPHs, or total petroleum hydrocarbons-IR). A number of modifications of these methods exist, but one particular method (EPA 418.1 see also EPA 8000 and 8100) has been one of the most widely used for the determination of total petroleum hydrocarbons in soils. Many states use or permit the use of this method (EPA 418.1) for identification of petroleum products and during remediation of sites. This method is subject to limitations, such as interlaboratory variations and inherent inaccuracies. In addition, methods that use Preon-113 as the extraction solvent are being phased out and the method is being replaced by a more recent method (EPA 1664) in which n-hexane is used as the solvent and the n-hexane extractable material (HEM) is treated with silica gel to yield the total petroleum hydrocarbons. 

Molecular spectroscopic techniques have been widely used in pharmaceutical analysis for both qualitative (identification of chemical species) and quantitative purposes (determination of concentration of species in pharmaceutical preparations). In many cases, they constitute effective alternatives to chromatographic techniques as they provide results of comparable quality in a more simple and expeditious manner. The differential sensitivity and selectivity of spectroscopic techniques have so far dictated their specihc uses. While UV-vis spectroscopy has typically been used for quantitative analysis by virtue of its high sensitivity, infrared (IR) spectrometry has been employed mainly for the identihcation of chemical compounds on account of its high selectivity. The development and consolidation of spectroscopic techniques have been strongly influenced by additional factors such as the ease of sample preparation and the reproducibility of measurements, which have often dictated their use in quality control analyses of both raw materials and finished products. 

Total petroleum hydrocarbons (TPH) and the various petroleum and coal-tar fractions in aqueous and nonaqueous samples can be determined by methods based on infrared (IR) spectrometry and gas chromatography (GC) techniques as summarized below. 

Raman scattering spectrometry has some advantages over an infrared (IR) spectrometry in the sensitivity, the space resolution, and the applicability to aqueous solution. It can attain high sensitivity, when it is performed under the resonance Raman condition, or under the surface enhanced condition, where silver or gold nanoparticle is used as a source of plasmon. These techniques have been applied successfully for the measurement of extremely small amount of molecules adsorbed at the liquid-liquid interfacial region. 

Infrared (IR) spectrometry is less sensitive than MS, and it therefore requires cells with a long optical path length, but IR. spectrometry has also proven quite useful as an identification method in... 

We have included what we feel are the six currently most popular analytical techniques ultraviolet (UV) spectrophotometry, infrared (IR) spectrometry, proton nuclear magnetic resonance (NMR) spectrometry, mass spectrometry (MS), gas chromatography (GC), and high pressure liquid chromatography (HPLC). As we felt that the quality of data presented was of paramount importance in a reference source, we generated all of our data in our laboratory under uniform, reproducible conditions using state-of-the-art technology and verified chemical standards. 

An important issue in forensic science is the criteria required for a positive identification of a single organic compound. An opinion held by some forensic scientists is that such identification cannot be based on chromatographic methods only, even when several such methods are applied. It is argued that other methods, such as infrared (IR) spectrometry, nuclear magnetic resonance (NMR) spectrometry, or mass spectrometry (MS), should be included. 

---