Detector flame photometer

Many sophisticated analytical techniques have been used to deal with these complex mixtures.5,45,46 A detailed description is not possible here, but it can be noted that GLC, often coupled with mass spectrometry (MS), is a major workhorse. Several other GLC detectors are available for use with sulfur compounds including flame photometer detector (FPD), sulfur chemiluminescence detector (SCD), and atomic emission detector (AED).47 Multidimensional GLC (MDGC) with SCD detection has been used48 as has HPLC.49 In some cases, sniffer ports are provided for the human nose on GLC equipment. 

In addition to the emission due to the test element, radiation is also emitted by the flame itself. This background emission, together with turbulence in the flame, results in fluctuations of the signal and prevents the use of very sensitive detectors. The problem may be appreciably reduced by the introduction into the sample of a constant amount of a reference element and the use of a dual-channel flame photometer, which is capable of recording both the test and reference readings simultaneously. The ratio of the intensity of emission of the test element to that of the reference element should be unaffected by flame fluctuations and a calibration line using this ratio for different concentrations of the test element is the basis of the quantitative method. Lithium salts are frequently used as the reference element in the analysis of biological samples. 

The photometers are installed in the upper part of the analytical console. Each analytical channel is fitted with a double-beam filter photometer. The wavelength range is 340—900 nm. Flow cells are available in lengths of 10, 30 and SO mm. Detectors such as a flame photometer, conductivity cell or pFI electrode can also be connected externally when required. 

If the response of the detector of a flame photometer is proportional to the concentration of the element heated to a state of excitation, by what factor is the signal multiplied when the temperature passes from 2 000 K to 2 500 K ... 

Other gas chromatography detectors electron capture halogens, conjugated C=0, —C=N, -N02 nitrogen-phosphorus highlights R N flame photometer individual selected elements, such as R S, Sn, Pb photoionization aromatics, unsaturated compounds... 

Flame photometry (see also p. 168) is almost exclusively used for the determination of alkali metals because of their low excitation potential (e.g. sodium 5.14eV and potassium 4.34 eV). This simplifies the instrumentation required and allows a cooler flame (air-propane, air-butane or air-natural gas) to be used in conjunction with a simpler spectrometer (interference filter). The use of an interference filter allows a large excess of light to be viewed by the detector. Thus, the expensive photomultiplier tube is not required and a cheaper detector can be used, e.g. a photodiode or photoemissive detector. The sample is introduced using a pneumatic nebulizer as described for FAAS (p. 172). Flame photometry is therefore a simple, robust and inexpensive technique for the determination of potassium (766.5 nm) or sodium (589.0nm) in clinical or environmental samples. The technique suffers from the same type of interferences as in FAAS. The operation of a flame photometer is described in Box 26.2. 

Fig. 3 Flame housing of IL 943 flame photometer a) sodium filter, 589 nm b) potassium filter, 776 run c) lithium filter, 670 nm d) cesium filter, 852 nm e) ignition detector f) burner assembly g) rubber gasket h) spark electrode i) ignition coil wire j) chimney. (Courtesy of Instrumentation Laboratory, Inc.)...

Cheskis, S., Atar, E., and Amirav, A. Pulsed-flame photometer—A novel gas-chromatography detector. Analytical Chemistry, 1993, 65, 539. 

Amirav, A. and Jing, H.W. Pulsed flame photometer detector for gas-chromatography. Analytical... 

A flame photometer is an instrument in which the intensity of the filtered radiation from the flame is measured with a photoelectric detector. The filter interposed between the flame and the detector, transmits only a strong line of the element. 

FES, which is used for measuring a small number of elements, is of much simpler design. For example, when sodium is analysed with a flame photometer whose flame attains 2000 °C, the sodium atoms are practically the only ones emitting radiation. To measure the emitted light, a simple optical filter put between the flame and the detector, in the absence of a monochromator, isolates a rather broad spectral band including the yellow radiation emitted by the element. 

The flame photometer consists essentially of an atomizer, a burner, some means of isolating the desired part of the spectrum, a photosensitive detector, sometimes an amplifier and, finally, a method of presenting the desired emission, whether by galvanometer, null meter, or chart recorder. 

GC is the most commonly used technique. It has, thanks to capillary columns, a very good resolution and enables, when coupled with other specific detectors such as the electron capture detector (BCD), nitrogen phosphorus detector (NPD), flame photometric detector (FPD), pulsed flame photometer (PFPD) and AED separation, identification, and quantification of OPPs containing halogenated groups, or phosphorus or sulfur atoms. 

In flame emission spectrometry, the sample solution is sprayed or aspirated into a flame as a fine mist or aerosol. The sample is vaporized in the flame, and atomized by a combination of heat and the action of a reducing gas. The atoms are excited into higher electronic states by the heat, and as they revert to the ground state they emit photons, which are measured by the detector. The layout of a flame photometer is shown in Figure 2. 

The first detector to be used for SFA was a photometer, and photometric determinations still form the vast majority of current methods. Other detectors in common use are UV spectrophotometers, used primarily for pharmaceutical compovmds and for bitterness in beer flame photometers, for potassium and sodium determination fluorimeters, used primarily for measuring low levels of determinants in the presence of interferences, such as the determination of histamine in blood, and vitamins in food extracts and ion-selective electrode and pH detectors. In principle, almost any detector with flow-through capability can be used with SFA systems, and determinations based on densitometry, thermometry, and luminescence have been published, among others. 

The desirable features of the flame photometer are sensitivity, stability, and relatively large linear dynamic range. FPDs also require very little maintenance, and are ready to use in a very short time. An FPD s response to phosphorous is a first-order relationship, while its response to sulfiir components is second order because sulfur is detected as Sj. Analysis by an FPD without a GC column is considered real-time detection. Unfortunately, without GC involvement, the detector cannot provide possible compound identification due to its generic nature. The addition of GC capability permits identification of sample components that contain targeted elements, and reduces the false alarm rate. 

The ideal flame photometer is one which comprises a monochromator with motorised wavelength control, and to which can be attached any type of source unit. The detectors should be capable of responding to emission from 2,000A to 8,000A, and these should feed into an amplifier of wide sensitivity range. The output can be either read on a meter or passed into a recorder. This opinion is not intended to decry the use of simple equipment, but indicates what is required for the estimation of a large number of elements in all kinds of samples. 

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