Spectrophotometer definition

In spectrophotometric analysis a source of radiation is used that extends into the ultraviolet region of the spectrum. From this, definite wavelengths of radiation are chosen possessing a bandwidth of less than 1 nm. This process necessitates the use of a more complicated and consequently more expensive instrument. The instrument employed for this purpose is a spectrophotometer. 

Equipment used in GLP studies must be validated for appropriateness. Each piece of equipment must have SOPs for operation, calibration, and routine maintenance. All routine and nonroutine maintenance must be documented. What is the definition of a piece of equipment Any item that can have an impact on the results of an anal5dical procedure. In the typical non-GLP laboratory, records are kept on analytical equipment such as spectrophotometers or gas chromatography units. Under GLP, however, the definition expands to include items such as pipets, thermometers, incubators, refrigerators, and mixing devices, as long as it is possible that the use of the item can affect the outcome of the test. For the non-GLP lab, implementation of this standard will dramatically increase the number of equipment-related SOPs. 

There are some potential problems that should be taken into account when interpreting such spectra. A spectrophotometer measures transmission (and maybe also reflection) but not absorption. What is measured as absorption is a transmission measurement that is mathematically manipulated to convert it to absorption. Absorption is usually measured as absorbance. A, which by definition is given by... 

Analysis of Defined Fractions. Quantitative infrared analysis was used for those fractional groups that have definitive bands average absorptivities were estimated using model compounds (12, 16, 17). Table I lists the infrared bands and the apparent integrated absorption intensities (B) used. Quantitative IR spectra were measured in methylene chloride with 0.05 cm sodium chloride cells, using a Perkin-Elmer 521 infrared spectrophotometer. Peak area was measured by planimetry. Molecular weights were determined by vapor-pressure osmometry in benzene. 

The activity of die unknown sample is expressed relative to the standard, whidi has a well-defined activity, assigned by collaborative assay and based on kinetic analysis. The stability of the standard is guaranteed by die Centre for Standards. Sensitivity of substrate batches and spectrophotometer variation are not allowed form an absolute type of assay or unit definition. 

Infrared spectra of the impacted area of these materials were obtained on a Perkin-Elmer 521 grating infrared spectrophotometer. Comparison of these spectra with those obtained from unimpacted areas revealed definite changes in the structures of the poly (vinyl fluoride) and the polycarbonate materials, with indications of possible changes in the polyimide. Table I summarizes the changes noted for the poly (vinyl fluoride) and gives probable assignments. 

Diode-Array detection systems become more and more standard detectors in HPLC-analysis. Based on the principle of UVA/lS-spectrophotometers, DAD facilitates the simultaneous detection and registration of UV-chromatograms at different wavelength and the spectra of the single substances. This additional spectrum information is often required for the definite identification of the single substance peaks in UV/ VIS-chromatograms [15]. 

The principal element of the spectrophotometer is the monochromator which serves for dispersion of the radiation emitted by the source and isolation of a beam of monochromatic radiation of definite wavelength. The monochromator comprises a system of slits, a collimator, a light-dispersing element, and lenses or mirrors to focus the dispersed radiation. The dispersing system is the essential part of the monochromator. The degree of monochromatization is an important feature of the dispersing element. 

The sample solution is titrated, at a definite wavelength, in a titration vessel placed inside the spectrophotometer. For this reason the spectrophotometers commonly applied require some adaptations that enable one to place a suitable titration vessel, the tip of the burette, and a mixer inside it. In this technique, the parameter of primary importance is not the absolute value of the absorbance measured but its changes during the course of titration. To reduce the effect of dilution on the absorbance one is recommended to use concentrated titrant solutions and micrometric syringes. 

The dependence of the recorded signal upon the instrument parameters is a disadvantage of this technique. Reproducible results are obtained on using one — and the same — type of spectrophotometer and identical conditions of spectra recording, or by adaptation of a definite method to the available apparatus. 

As mentioned previously, the now routine integration of a pc means that the data collected from either a colorimeter or spectrophotometer can be transformed to XYZ, CIELAB, HunterLab or other colour system as specified by the user and provided by the software. The initial step from instmment response to XYZ requires the definition of standard observer functions. 

The reason why some clinical methods should be labelled automatic or not Is not completely clear. The generic definition does not establish the extent to which human effort need be replaced or the method concerned be facilitated for the latter to deserve to be categorized as automatic . A manual method is rarely considered automatic merely because It calls for a water-bath whose temperature Is adjusted by means of a feed-back mechanism. On the other hand, self-contained continuous-flow instruments including the sampler, peristaltic pump, dialyser, spectrophotometer with flow-cell and recorder are common although, according to IUPAC s definition, Improperly called automated . In fact, few of the elements of such Instruments, apart from the dialyser bath or the recorder servo, are regulated by a feed-back mechanism. 

The fundamental components of a Michelson interferometer are depicted schematically in Fig. 1. One possible misconception regarding the use of a Michelson interferometer at visible wavelengths is that it is difficult to obtain a sufficiently precise movement for the scanning mirror,, to provide useful resolution in the absorption spectrum (Fourier transformed inter-ferogram). This is definitely not the case. The actual reason that FT techniques are not commonplace in visible spectroscopy is that the usual visible spectrophotometer with a photomultiplier tube for a detector is source-noise-limited rather than detector-noise-limited so that FT methodology does not improve (and actually degrades) the quality of the measured spectrum. 

Pulse radiolysis has been used with great success in studies of the hydrated electron e (aq). If the pulse of electrons from a linear accelerator (5-15 MeV) is passed through an aqueous solution, several chemical species are produced. The spectral changes in solution can be followed spectrophotomet-rically, either at a definite time after the electron pulse with a spectroscopic flash and a spectrograph, or continously at a fixed wavelength with a steady light source and a photomultiplier. Instead of the electron beam of an accelerator, X-rays pulse can be applied for one or two microseconds. ... 

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