UV-VIS Instrumentation

UV/VIS absorption spectroscopy, pioneered by Beckman (1941), is one of the oldest and most widely used instrumental techniques, despite being regarded by some analysts as obsolete. Recently there has been a renaissance in UV spectroscopy with many new techniques, instruments and data processing methods [8]. Modem highest specification UV/VIS absorption and fluores-cence/phosphorescence spectrometer instruments extend their wavelength region from the far UV (175 nm) into the NIR region (1100 nm). Small footprint UV/VIS spectrometers (200-1100 nm) are now available. Paul [9] has traced the history of UV/VIS instrumental developments. 

Tossing a mental coin, the decision was to analyze the case of noise proportional to the square root of the signal. This, as you will recall, is Poisson-distributed noise, characteristic of the noise encountered when the limiting noise source is the shot noise that occurs when individual photons are detected and represent the ultimate sensitivity of the measurement. This is a situation that is fairly commonly encountered, since it occurs, as mentioned previously, in UV-Vis instrumentation as well as in X-ray and gamma-ray measurements. This noise source may also enter into readings made in mass spectrometers, if the detection method includes counting individual ions. We have, in... 

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. 

Note The actual wavelength maxima may vary slightly depending on the matrix/solution containing the calibration component. Therefore, a calibration solution should always be cross-checked with a calibrated stand-alone UV-Vis instrument. 

The emergence of sensitive and affordable array detectors in 1980s and 1990s has also improved measurement capability in the UV-vis. Commercially available UV-vis instrumentation with photodiode-array (PDA) detectors appeared in the mid-1980s. This made it possible to produce a UV-vis spectrophotometer... 

With the explosion of organic synthesis, infrared spectrometers became common in almost every laboratory for identification of pure materials and structure elucidation. With the appearance of commercial ultraviolet/visible (UV/vis) instruments in the 1950s to complement the mid-range IRs, little was done with near-infrared. 

Early NIR work was performed using either a UV-Vis instrument with extension units for low wavenumbers or IR spectrometers with accessories for high wave-numbers. With these instruments, the quality of the collected spectrum was low. However, in modern times, good quality dispersive- and FT-NIR spectrometers exist that provide high quality spectra. 

The intense interest in recent years in determining DNA, ribonucleic acid (RNA), proteins, and the like in limited amounts of biological samples, as well as the drive in chemical laboratories to reduce sample and reagent volumes, thereby reducing waste, and the need for speed in many laboratories has led to the development of a variety of microvolume UV/VIS instruments, many of... 

This section provides correlation charts and operational information for the design and interpretation of ultraviolet-visible spectrophotometric (UV-Vis) measurements. While UV-Vis is perhaps not as information-rich as infrared or nuclear magnetic resonance, it nonetheless has value in structure determination and sample identification. Moreover, it is extremely valuable in quantitative work. Typical UV-Vis instruments cover not only the UV and visible spectrum, but the near-infrared as well. Although there is overlap among the ranges, the approximate breakdown is ... 

The workhorse infrared instrument used for routine characterization of materials in the undergraduate organic laboratory is the optical-null double-beam grating spectrometer (Fig. 8.3a). For a discussion of double-beam spectrometers, see the UV-vis instrumentation discussion (p. 604). Although many... 

Why can t an atomic absorption instrument be designed like a simple UV/VIS instrument, where a lamp is the source and a monochromator isolates the wavelength of interest, such as 589.3 for sodium ... 

Naphthalene (N) dissolved in CTA films was excited by filtered light not absorbed by the polymer (v < 33,000 cm , k > 300 nm). In this spectrum region, optical density of the samples was below 0.1 that provided for uniform light absorption in the sample thickness. The phototransformation was searched for by changes in UV absorption spectra which were measured by a Specord UV-VIS instrument. 

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