Stray-radiation

Unabsorbed radiation, stray light. All light must be absorbable to the same extent. 

Because all the rules that apply to absorbance detection apply equally well to CD, it is convenient to think of CD as a modified form of absorption spectrophotometry. Spectra are temperature- and pH-dependent non-linear correlations of signal versus concentration are commonplace and are produced for the same reasons, such as chemical equilibria, polychromatic radiation, stray light, etc. Fluorescence emission CD (FDCD) spectroscopy is observed whenever an analyte meets all... 

At a constant cell path length, Beer s law shows that the absorbance of radiation through a medium is proportional to the concentration of the solute. Beer s law is strictly valid only for monochromatic radiation. Stray light (i.e., scattered radiation), which reaches the detector without having passed through the desired beam path, molecular interactions such as hydrogen bonding, which varies with the sample concentration, and other instrumental factors such as slit width, all affect molar absorptivity and result in some deviations from Beer s law. For an accurate analysis of the concentration of an unknown sample, it is usually necessary to first create a calibration curve from standard... 

Stray radiation is the second contribution to instrumental deviations from Beer s law. Stray radiation arises from imperfections within the wavelength selector... 

For small concentrations of analyte, Pstray is significantly smaller than Pq and Py, and the absorbance is unaffected by the stray radiation. At higher concentrations of analyte, however, Pstray is no longer significantly smaller than Py and the absorbance is smaller than expected. The result is a negative deviation from Beer s law. 

The emission spectrum from a hollow cathode lamp includes, besides emission lines for the analyte, additional emission lines for impurities present in the metallic cathode and the filler gas. These additional lines serve as a potential source of stray radiation that may lead to an instrumental deviation from Beer s law. Normally the monochromator s slit width is set as wide as possible, improving the throughput of radiation, while being narrow enough to eliminate this source of stray radiation. 

Accuracy When spectral and chemical interferences are insignificant, atomic emission is capable of producing quantitative results with accuracies of 1-5%. Accuracy in flame emission frequently is limited by chemical interferences. Because the higher temperature of a plasma source gives rise to more emission lines, accuracy when using plasma emission often is limited by stray radiation from overlapping emission lines. 

A second instrumental limitation to Beer s law is stray radiation. The following data were obtained using a cell with a pathlength of 1.00 cm, when stray light is insignificant... 

Beyond the simple resistance of a material of construction to dissolution in a given chemical, many other properties enter into consideration when makiug an appropriate or optimum MOC selection for a given environmental exposure. These factors include the influence of velocity, impurities or contaminants, pH, stress, crevices, bimetallic couples, levels of nuclear, UV, or IB radiation, microorganisms, temperature heat flux, stray currents, properties associatea with original production of the material and its subsequent fabrication as an item of equipment, as well as other physical ana mechanical properties of the MOC, the Proverbial Siebert Changes in the Phase of the Moon, and so forth. 

Electrical sources static electricity, electrical current, lightning, stray currents (radiofrequency electromagnetic radiation, overhead high voltage transmission lines, galvanic and cathodic protection stray currents)... 

Stray light is the term given to unwanted radiation that is not removed by the monochromating system of a photometric instrument and is transmitted with the selected wavelengths. 

Imperfections in monochromators result in the presence of a small proportion of unwanted wavelengths in the incident radiation. Such stray light results in a deviation from a Beer-Lambert relationship (Figure 2.14) and the effect is that absorbance measurements are lower than they should be. 

It is possible to assess the proportion of stray light by measuring the amount of radiation transmitted by samples that are optically opaque at the wavelength to be assessed but that transmit radiation of other wavelengths. The instrument is set to zero and 100% transmittance in the normal way and the opaque substance introduced into the sample compartment. The amount of light transmitted by the sample, measured in percentage transmittance, is... 

Instruments with double monochromator configurations, or equivalent multi-pass configurations, can greatly reduce stray light (which is any radiation of wavelength other than that of the columnated light beam). Absorbance in the presence of stray light can be expressed as ... 

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