UV-vis region of the electromagnetic spectrum

The determination of an analyte s concentration based on its absorption of ultraviolet or visible radiation is one of the most frequently encountered quantitative analytical methods. One reason for its popularity is that many organic and inorganic compounds have strong absorption bands in the UV/Vis region of the electromagnetic spectrum. In addition, analytes that do not absorb UV/Vis radiation, or that absorb such radiation only weakly, frequently can be chemically coupled to a species that does. For example, nonabsorbing solutions of Pb + can be reacted with dithizone to form the red Pb-dithizonate complex. An additional advantage to UV/Vis absorption is that in most cases it is relatively easy to adjust experimental and instrumental conditions so that Beer s law is obeyed. 

The use of ultraviolet (UV) spectroscopy for on-line analysis is a relatively recent development. Previously, on-line analysis in the UV-visible (UV-vis) region of the electromagnetic spectrum was limited to visible light applications such as color measurement, or chemical concentration measurements made with filter photometers. Three advances of the past two decades have propelled UV spectroscopy into the realm of on-line measurement and opened up a variety of new applications for both on-line UV and visible spectroscopy. These advances are high-quality UV-grade optical fiber, sensitive and affordable array detectors, and chemometrics. 

NIR (near infra red) spectroscopy — Besides optical absorption in the UV-Vis region of the electromagnetic spectrum, absorption in the near infrared region can be employed to study electrochemical processes. This part of the electromagnetic spec-... 

Fundamentals. Species involved in electrochemical reactions that show optical absorption caused by electronic transitions in the UV-Vis region of the electromagnetic spectrum can be studied in situ with a variety of spectroelectrochemical techniques. The choice of a suitable technique depends on the type of species to be investigated and upon the exact location of the species (e.g. directly adsorbed on the metallic electrode surface, incorporated in a film attached to the electrode surface, dissolved in the electrolyte solution). Basically, two families of spectroelectrochemical techniques have been established so far (see Fig. 5.1) ... 

All references in allied photochemical standards, to the intensity of the incident radiation, use radiometric instruments and the more accurate terms "watts/m " or "microwatts/cm " for both the UV and VIS regions of the electromagnetic spectrum. Using the same term for both regions of the spectrum facilitates the comparison of... 

A number of important pollutant gases and vapors have signatures in the UV region of the electromagnetic spectrum. Among these are NO , SO CO, O3, benzene, toluene, and the xylenes. UV-vis spectroscopy of a host of environmentally relevant gases and vapors is reported by Bosch Ojeda and Sanchez Rojas." In this chapter, two cases are presented toluene (see Section 4.7) and ozone. 

The photochemically active region of the electromagnetic spectrum has been divided into five sub bands the vacuum-UV (VUV), UV-C, UV-B, UV-A and VIS (Fig. 3-8). The subdivision of the UV spectral domain is mainly due to phenomenological reasons (Fig. 3-9) that are related to physical, biological or medicinal effects. The UV-B region is usually defined between X of 280 nm and 315 nm (van-... 

On the other hand, medium-pressure (MP) Hg lamps can be operated with much higher electrical input power up to 30 kW, but with a reduced UV radiant power efficiency of 30 to 40%. Their dimensions are more compact than the dimensions of the LP Hg lamps, but their polychromatic emission ranges from the UV (UV-C - 15-23%, UV-B - 6-7 %, UV-A - 8%) over the VIS (-15%) to the IR (-47-55%) region of the electromagnetic spectrum (e.g. McClean, 2001). Lam-brecht (1999) reported the power balance of electromagnetic radiation of an industrially used high-pressure mercury lamp with a power density of 200 W cm as follows 13.2% UV-C, 7.15% UV-B, 7.15% UV-A, 21% VIS, and 14% IR... 

Absorption of NIR radiation corresponds to certain vibrations of the molecule and is due to overtones and combinations of parent absorption bands in the mid-infrared (IR) region. Generally, these absorptions are weaker than the parent absorptions in the IR but the decrease in intensities is not the same for all molecnles. It can be seen as a complementary techniqne to conventional IR, exploiting a different region of the electromagnetic spectrum. For example, water has less absorption in the NIR compared with mid IR, so NIR spectra of aqneons samples are often sharper. A NIR absorption spectrum is usually a plot of absorbance versns wavelength and has more fine structure than a UV or UV-Vis spectrum. NIR absorbance also follows the Beer-Lambert Law, so can be used as a quantitative techniqne. 

Here, cis a constant and vand X are inversely proportional. We are concerned with only the ultraviolet (10-380 nm) and visible (380-780 nm) regions of the electromagnetic spectrum when considering UV/Vis and diode array detectors. 

In UV/Vis and diode array detectors, the analytes elute from the column in the flow of the mobile phase where it enters a flow cell inside the HPLC instrument. The flow cell is held in the path of a beam of UV/Vis radiation and the detector detects analytes that absorb in this region of the electromagnetic spectrum. 

A UV-Vis spectrophotometer (Fig. 13.8) measures the amount of light absorbed by a sample at each wavelength of the UV and visible regions of the electromagnetic spectrum. 

No other material shows as much versatility as an electrode as does electrically conducting, CVD diamond. The material can be used in electroanalysis to provide low detection limits for analytes with superb precision and stability for high current density electrolysis (1-10 A/cm ) in aggressive solution environments without any morphological or micro-structural degradation and as an optically transparent electrode (OTE) for spectroelectrochemical measurements in the ultraviolet-visible (UV-Vis) and infrared (IR) regions of the electromagnetic spectrum. 

Several factors influence the optical transparency of CVD diamond in different regions of the electromagnetic spectrum [176,177]. These include (1) reflectance losses in the UV/Vis due to a high refractive index... 

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