Wavelength sensitivity emission spectrometers

Induced Coupled Plasma Spectrometry (ICP). An even more sensitive instrument has been developed to detect and quantitate, simultaneously, all inorganic species contained with a sample matrix. One such system is the ICP-OES (optical emission spectrometer) (Figure 25.5). The ICP-OES takes an aliquot of sample that has been acid digested and mixes it with a gas (e.g., argon) forming a plasma (i.e., an ionized gas) that is channeled into a nebulizer. Energy is applied to excite the atoms that are converted by the optics of the instrument into individual wavelengths. The... 

Procedure Use an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES), or equivalent instrumentation with similar capabilities. Follow the instrument manufacturer s instructions for setting instrument parameters for assay of cadmium. Select appropriate background correction points for the cadmium analyte according to the recommendations of the instrument manufacturer. Select analytical wavelengths to yield adequate sensitivity and freedom from interference. 

Wavelength Sensitivity. The overall wavelength sensitivity of emission spectrometers plays a central role in determining the accuracy of the recorded data and the range of emission wavelengths that can effectively be studied by a particular apparatus. The upconversion method adds a source of wavelength dependent sensitivity that is both useful and problematic. 

The AED employs a microwave-induced He plasma to dissociate eluted analyte molecules to their component atoms and excite them to emit at characteristic wavelengths. This is very similar to the mechanism in the argon plasma inductively coupled plasma source (cf. Section 7.3.1). A spectrometer with a diode array detector (Figure 7.26b and c) isolates and measures the intensity of sensitive emission lines unique to each element. Depending on the relative sensitivity and proportion of atoms in the molecules, separate element response channels may display peaks in several element-selective chromatograms. These data may be combined with retention... 

Place cuvette into the sample holder of the fluorescence spectrometer, set the excitation wavelength and monitor the most sensitive emission wavelength for the labeled kinase while rapidly stirring the sample (see Note 29). 

AFS is based on the absorption of radiation of a certain frequency (the energy transition from the outermost electronic orbitals to a higher energy state) and the subsequent deactivation of the excited atoms with the release of radiation. The most useful type of fluorescence, resonance fluorescence, involves a fluorescence emission radiation of the same wavelength as that used for excitation. Because of the inherent sensitivity of the fluorescence emission process, AFS is one of the most sensitive atomic techniques. All the benefits of AFS are enhanced when this spectromet-ric technique is used in combination with vapor generation methods, especially for covalent-hydride-forming elements. 

A major breakthrough came in Australia when Alan Walsh1,2 realized that light sources were available for many elements which emitted atomic spectral lines at the same wavelengths as those at which absorption occurred. By selecting appropriate sources, the emission line widths could be even narrower than the absorption line widths (Figure 2). Thus the sensitivity problem was solved more or less at a stroke, and the modern flame atomic absorption spectrometer was bom. 

Relative state populations (NvJ or Nv) are derived from the observed spectrum in two stages. First, the spectrometer-detector unit must be calibrated with a standard blackbody source to allow for changes in sensitivity with wavelength. Then the corrected relative intensities are converted to the NvJ (or Nv) using values of the spontaneous emission coefficients. This procedure is quite simple when individual rotational lines can be resolved [101, 102]. Karl et al. have described a computational technique for analyzing the overlapped first overtone (Av = 1) spectra of CO [261] and NO [262] when the rotational distribution is known to be equilibrated, and Hancock and Smith [256] have extended this method. 

The nebulized sample is exitated in an argon-plasma at approximately 10000 Kelvin. A spectrometer with a polychromator system can determine several elements by measuring their specific emission wavelength with photomultipliers as sensitive detectors. The system requires one photomultiplier for each detectable element. The detection limits of this modem technique are usually between those of the Graphite-Furnace- and the Flame-AAS. The advantages of this system are the very high... 

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