Spectrophotometry in chemistry is a quantitative measure of the reflection or transmission of material properties as a function of wavelength. It is more specialized than the term electromagnetic spectroscopy which is general in that spectrophotometry deals with near-ultraviolet, visible light, and near-infrared, but doesn’t cover the techniques of time-resolved spectroscopic . Spectrophotometer is used in Spectrophotometry. A spectrophotometer is a photometer that measures the intensity as a function of the wavelength of the light source.
Important features of spectrophotometers are linear range of absorption or reflectance measurement spectral and bandwidth. A spectrophotometer is used commonly for the transmittance measurement or solutions reflectance, opaque solids or transparent, such as gases, or polished glass. However they can be designed to measure the diffusivity of any of the listed light ranges that which cover around 200nm – 2500nm using different calibrations and controls. Calibrations are needed on the machine, within these ranges of light, using standards which vary in type depending on the wavelength of the photometric determination.
An example for spectrophotometry experiment is used is the determination of the solution equilibrium constant. A specific chemical reaction in a solution may occur in a reverse and forward direction where products break down into reactants and reactants form products. At some point, this chemical reaction will reach a point of balance called an equilibrium point. In order to determine the respective concentrations of products and reactants at this point, the light transmittance of the solution can be tested using spectrophotometry.
The amount of light that passes through the solution the concentration of certain chemicals is indicative that do not allow light to pass through. The use of spectrophotometers spans various scientific fields, such as materials science, physics, biochemistry, molecular biology , and chemistry. They are widely used in many industries including semiconductors, laser and optical manufacturing, printing and forensic examination, and as well in laboratories for the chemical substances study. Ultimately, a spectrophotometer is able to determine, depending on the control or calibration, what substances are present in a target and exactly how much through calculations of observed wavelengths.
IR Spectroscopy Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic techniques, it can be used to identify and study chemicals. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer. The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum.
The higher-energy near-IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite overtone or harmonic vibrations. The mid-infrared, approximately 4000–400 cm−1 (2.5–25 μm) may be used to study the fundamental vibrations and associated rotational-vibrational structure. The far-infrared, approximately 400–10 cm−1 (25–1000 μm), lying adjacent to the microwave region, has low energy and may be used for rotational spectroscopy. The names and classifications of these sub regions are conventions, and are only loosely based on the relative molecular or electromagnetic properties.
Types There are two basic types of infrared spectrometers. Fourier transform infrared (FTIR) spectrometers are single-beam instruments that use an interferometer to spread a sample with infrared light and measure the intensity of the infrared light not absorbed by the sample. The application of a Fourier transform converts the resulting time domain digital signal into a frequency domain digital signal. Dispersive infrared spectrometers use visible lasers, a grating, and charged coupled devices (CCDs) to collect data. The laser acts as a light source and irradiates the sample. Most of the radiation scatters elastically at the same energy as the incoming laser radiation. A small amount, approximately one photon in a million (0.00001%), scatters from the sample at a wavelength shifted slightly from the original wavelength. Techniques
* Fourier transforms infrared spectroscopy “FTIR” redirects here. FTIR may also refer to frustrated total internal reflection. Fourier transform infrared spectroscopy (FTIR) is a technique which is used to obtain an infrared spectrum of absorption, emission, photoconductivity or Raman scattering of a solid, liquid or gas. An FTIR spectrometer simultaneously collects spectral data in a wide spectral range. This confers a significant advantage over a dispersive spectrometer which measures intensity over a narrow range of wavelengths at a time. FTIR has made dispersive infrared spectrometers all but obsolete (except sometimes in the near infrared), opening up new applications of infrared spectroscopy. The term Fourier transform infrared spectroscopy originates from the fact that a Fourier transform (a mathematical process) is required to convert the raw data into the actual spectrum. * Near IR spectroscopy
Near-infrared spectroscopy (NIRS) is a spectroscopic method that uses the near-infrared region of the electromagnetic spectrum (from about 800 nm to 2500 nm). Typical applications include pharmaceutical, medical diagnostics (including blood sugar and pulse oximetry), food and agrochemical quality control, and combustion research, as well as research in functional neuroimaging, sports medicine & science, elite sports training, ergonomics, rehabilitation, neonatal research, brain computer interface, urology (bladder contraction) and neurology (neurovascular coupling). Theory:
Near-infraredspectroscopy is based on molecular overtone and combination vibrations. Such transitions are forbidden by the selection rules of quantum mechanics. As a result, the molar absorptivity in the near IR region is typically quite small. One advantage is that NIR can typically penetrate much farther into a sample than mid infrared radiation. Near-infrared spectroscopy is, therefore, not a particularly sensitive technique, but it can be very useful in probing bulk material with little or no sample preparation.
The molecular overtone and combination bands seen in the near IR are typically very broad, leading to complex spectra; it can be difficult to assign specific features to specific chemical components. Multivariate (multiple variables) calibration techniques (e.g., principal components analysis, partial least squares, or artificial neural networks) are often employed to extract the desired chemical information. Careful development of a set of calibration samples and application of multivariate calibration techniques is essential for near-infrared analytical methods. Applications:
The primary application of NIRS to the human body uses the fact that the transmission and absorption of NIR light in human body tissues contains information about hemoglobin concentration changes. When a specific area of the brain is activated, the localized blood volume in that area changes quickly. Optical imaging can measure the location and activity of specific regions of the brain by continuously monitoring blood hemoglobin levels through the determination of optical absorption coefficients. Typical applications of NIR spectroscopy include the analysis of foodstuffs, pharmaceuticals, combustion products and a major branch of astronomical spectroscopy.
University/College: University of California
Type of paper: Thesis/Dissertation Chapter
Date: 4 November 2016
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