Emission Spectrophotometers

In a simple flame (emission) photometer an interference filter (Section 17.7) can be used. In more sophisticated flame emission spectrophotometers which require better isolation of the emitted frequency, a prism or a grating monochromator is employed. 

Solutions and precipitates were analyzed on a Beckman Spectra-Span VI direct current plasma emission spectrophotometer (DCP), Precision for the Ca2 + analyses was 3% and for the Ba2 + 2% except for the most dilute samples In which It rose as high as 5%. Calcite mineralogy was determined on a Philips x-ray diffractometer calcite was the only phase recorded except In speed runs of under one hour In duration (not Included In this study) which produced vaterite. Details of analytic procedures are available In Pingitore and Eastman (30,31). 

M.J. Pelletier, New developments in analytical instruments Raman scattering emission spectrophotometers, in Process/Industrial Instruments and Controls Handbook, G.K. McMillan and D.M. Considine (Eds), McGraw-Hill, New York, 1999. 

The radioactivity can be measured by a beta counter. The metal at trace concentrations can be determined by an atomic absorption or emission spectrophotometer. 

All sodium compounds impart a golden yellow color to flame. Sodium can be identified spectroscopically by characteristic line spectra. Trace sodium may be measured quantitatively by flame atomic absorption or flame emission photometric method. The element may be measured at 589 nm using an air-acetylene flame. If using an ICP-atomic emission spectrophotometer, sodium may be measured at 589.00 or 589.59nm. Metallic sodium may be analyzed quantitatively by treating with ethanol and measuring the volume of hydrogen liberated. 

An atomic emission spectrophotometer (Fig. 6.2) is composed of the following components ... 

The value of the ratio Ne/N0 does not imply that all excited atoms return to their initial state as they emit a photon. As the temperature increases, the emission spectrum becomes more complex, particularly due to the emission of lines emanating from ionised atoms (see Fig. 14.3). It thus becomes necessary to have good quality optics in order to use this technique. The corresponding instruments are atomic emission spectrophotometers, which will be discussed in Chapter 15. 

Present atomic emission spectrophotometers allow multi-element analyses to be performed either simultaneously or sequentially. This ability is the result of progress made in optics, excitation sources, detectors and microcomputers. Atomic emission, which was initially used in the metallurgical industry, has now expanded into many areas and competes with atomic absorption. 

At a high enough temperature, any element can be characterised and quantified because it will begin to emit. Elemental analysis from atomic emission spectra is thus a versatile analytical method when high temperatures can be obtained by sparks, electrical arcs or inert-gas plasmas. The optical emission obtained from samples (solute plus matrix) is very complex. It contains spectral lines often accompanied by a continuum spectrum. Optical emission spectrophotometers contain three principal components the device responsible for bringing the sample to a sufficient temperature the optics including a mono- or polychromator that constitute the heart of these instruments and a microcomputer that controls the instrument. The most striking feature of these instruments is their optical bench, which differentiates them from flame emission spectrophotometers which are more limited in performance. Because of their price, these instruments constitute a major investment for any analytical laboratory. 

Flame photometric detection has been used for a relatively long time in conjunction with GC for determination of compounds containing phosphorus or sulphur. Based on this principle, it is possible to profit from the high temperatures of plasma emission analysis to obtain information on the elemental composition of eluting molecular compounds. For this purpose, an atomic emission spectrophotometer is placed at the outlet of a GC column (Fig. 15.8). 

Figure 15.8—Coupling of a gas chromatograph with an atomic emission spectrophotometer. Effluents from the capillary column are injected into the plasma and decomposed into their elements. Each chromatogram corresponds to the compound containing the element of interest. For a given retention time, indication as to the elements included in a compound can be obtained. The plasma in this example is generated by heating the carrier gas (He) with a microwave generator confined in a cavity at the exit of the column. A diode array detector system can be used for simultaneous detection of many elements (chromatograms courtesy of a Hewlett Packard document).

Pelletier, M.J. New Developments in Analytical Instruments Raman Scattering Emission Spectrophotometers. In McMillan, G.K. Considine, D.M. (eds) Process/Industrial Instruments and Controls Handbook 5th Edition McGraw-Hill New York, 1999 pp. 10.126-10.132. 

Thus, the conductivity of any aqueous sample may be precisely calculated, as we see in the above two examples, if we know the concentrations of the metal ions and the anions in the sample. The presence of such metal ions and the anions and their concentrations may be simultaneously measured by ICP atomic emission spectrophotometer and ion chromatograph, respectively. 

Apparatus Use a suitable Inductively Coupled Plasma Emission Spectrophotometer set to 226.502 nm for cadmium and to 371.029 for yttrium (internal standard) with an axial view mode. (This method was developed using a Perkin-Elmer Model 3300 DV equipped with a sapphire injector, low-flow GemCone nebulizer, cyclonic spray chamber, and yttrium internal standard.) Use acid-rinsed plastic volumetric flasks and other labware. 

FIGURE 12.3 Schematic layout of components of an emission spectrophotometer. 

Fig. 1 Comparison of major components of atomic absorption and (A) emission spectrophotometers (B). (Courtesy of Perkin-Elmer Instruments.)...

Most absorption and emission spectrophotometers are interfaced to a computer, allowing for digital recording of the spectra. If the spectra change in time, for example when a photoreaction is monitored intermittently by absorption spectroscopy, one obtains a series of spectra such as that shown in Figure 3.18, where the absorbance data are stored in a... 

The primary components of automobiles are steel or aluminum, so one of the fastest methods for analysis with the least amount of preparation of the sample is the emissions spectrometer. From Table 2.1, we can see that a carbon sulfur analyzer, such as a Leco, or atomic absorption spectrophotometer scanning electron microscopy (SEM) x-ray and GC-MS are also used for this type of analysis. However, an emissions spectrophotometer is most often used because of its lack of sample preparation. Again, it is not our attempt here to go into great detail on each method. Within an automotive analytical laboratory, however, speed is a priority so that a material is identified and classified rapidly. An emissions spectrophotometer is such an instrument. 

Figure 14.12 Coupling of a gas chromatograph with an atomic emission spectrophotometer. The effluent from the capUlaiy column is injected into a plasma, which effects the decomposition into the corresponding elements. Each chromatographic signal corresponds to a compound containing the element being studied. This is the principle of speciation analysis (chromatograms taken from a Hewlett-Packard document).

The samples were first run on the Jarrell-Ash instrument, with the three burner set and the same instrument was used as a flame emission spectrophotometer for the determination of sodium and potassium. A statistical summary of analytical precision for eight elements in the eight samples are shown in Table 1. Here the precision is expressed as the % standard deviation (coeflBcient of variation), which is defined as one hundred times the ratio of standard deviation to the mean concentration (9). It can be seen from this data that the last three elements, which are present in a quantity near the limit of detection, have large deviations. It is clear that these figures could be lowered if the analysis were run using higher concentrations. But our purpose was to evaluate the usefulness of the technique for routine determinations. 

Atomic-absorption and atomic-emission spectrophotometers both require an atomizer, a monochromator, and a detector. Atomic absorption requires, in addition, a radiation source. 

The nebulizer and burner system is probably the most important component of the atomic-absorption or emission spectrophotometer, because it is imperative that neutral (un-ionized) atoms of the test element be presented to the optical system. When the sample solution passes into the flame, it must be in the form of small droplets. The process of breaking down a solution into a fine spray is known as nebulization. Nebulization is generally carried out with the support or oxidant gas. 

The production laboratory at the Herculaneum smelter performs quality analytical work for all the processes. The laboratory equipment includes a spark emission spectrophotometer, inductively coupled plasma atomic emission spectrometer, wavelength dispersive X-ray fluorescence spectrometer, sulfur analysis equipment, and wet chemistry equipment. The laboratory conducts the analysis for all process materials, including sinter, blast furnace slag, lead bullion, all finished lead products, and environmental samples. 

The basic components of a flame emission spectrophotometer are shown in Figure 8.33. The individual components are discussed below. 

Atomic absorption and flame-emission spectrophotometer, 10 cm slit burner, equipped with an arsenic measurement unit or equivalent and an arsenic hollow-cathode lamp. A schematic diagram of the apparatus used for the arsenic measurement is shown in Figure 1.10. 

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