can also provide a quantitative estimation of the element content. Atomic adsorption spectrometry is the complement of atomic emission spectrometry, in that the absorption of light specific to a particular element is measured, as opposed to the light emitted. In principle, the amount of light absorbed is proportional to the amount of the element that is present which, in turn, is proportional to the amount of the element that is continuously fed into the flame or furnace.   The Flame Atomic Absorption Spectrometer   A diagram of a flame atomic absorption spectrometer is shown in figure 22. The light source used in an atomic adsorption spectrometer is usually a cold cathode lamp that is designed to produce (almost exclusively) light of that wavelength that would be naturally emitted by the element of interest. Lamps are available for the majority of the elements of general analytical interest. It follows, that the light generated will contain specifically those

a combined system. The older types of spectrometer were a little cumbersome, and, relatively, not very sensitive, but with the advent of simple and inexpensive ways of producing inert gas plasma the situation has changed radically. The atomic spectrometer is now very sensitive and, in conjunction with the gas chromatograph, has been used successfully for a number of years as a combination system for specific element detection.   The Atomic Emission Spectrometer   The atomic emission spectrometer is an extremely versatile device, with a very high sensitivity and excellent selectivity. The model described here was originally designed and manufactured by the Hewlett-Packard Corporation. Basically, atomic emission is achieved by means of a helium plasma, and the light emitted is analyzed by a diode array spectrometer. A diagram showing the basic principles of the helium plasma atomic emission spectrometer is shown in figure 21. The plasma is microwave induced into a helium

or both) the ions can be separated from one another on the basis of their individual masses. By means of a suitable scanning procedure, each individual ion mass is then sensed and its mass identified. The advantages of this type of analytical approach and its value combined with a GC instrument are very obvious.   There are three basic types of mass spectrometer, the sector mass spectrometer, the quadrapole mass spectrometer (which includes the mass analyzer) and the time-of-flight mass spectrometer. All three types of mass spectrometer have been used (and, indeed, are still used) in combined configurations with gas chromatographs. It follows, that the basic principles of all three types of mass spectroscopic systems will need to be described. It should be noted, however, that the quadrapole mass spectrometer in one of its various forms is by far the most popular mass spectrometer to be used in a combined system, but the function of the sector instrument is the simplest to

nbsp;   The ICP Mass Spectrometer Ion Source   The inductively coupled plasma (ICP) ion source evolved directly from the ICP atomic emission spectrometer and is now probably more commonly employed in LC/MS than GC/MS. Nevertheless, it is sometimes employed in GC/MS, usually in the examination of organometallic materials and in metal speciation analyses.   Figure 58. The ICP Mass Spectrometer Ion Source

the individual mass of charged ions) and to nuclear magnetic spectroscopy (which measures the precession frequency of asymmetric spinning atomic nuclei when situated in a magnetic field). The only common factor that remains between the different spectroscopy's is that, in their traditional manner of presentation, the different types of spectra bear some slight resemblance to each other.   The three major spectroscopic techniques that are associated with GC are infra red spectroscopy, atomic spectroscopy and mass spectroscopy, the first two, as already stated, involves the absorption of electromagnetic waves whereas the last the measurement of ion masses. There are rare examples of the use of the UV spectrometer and the fluorescence spectrometer in conjunction with a GC but, for the reasons discussed below, these combinations have very limited advantages., nevertheless, they will be discussed.   Electromagnetic radiation consists of a sinusoidal electric field in phase

nbsp; The ICP ion source is almost identical to the volatalizing unit of the ICP atomic emission spectrometer. A diagram of the ICP ion source is shown in figure 58. The argon plasma is an electrodeless discharge, usually initiated by a Tesla coil spark, but maintained by rf energy, that is inductively coupled to the inside of the torch by an external coil, wrapped round the torch stem. The plasma is at atmospheric pressure and is maintained at an average temperature of about 8000 K.   Physically, the ICP torch takes the form of three concentric fused silica tubes.