Page 48 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology en001d42 April 28, 2001 15:9

772 Atomic Spectrometry

(HEN) is ideally suited for applications requiring efficient
nebulization at low solution-flow rates. In general, while
the ultrasonic nebulizer is more expensive than HEN and
cross-flow systems, it does provide for a better analytical
detection limit.

2. Instrumentation for Multi-Element Analysis

One of the primary advantages of an ICP is that it provides
good sensitivity for the determination of a wide range of
elements without significant chemical interferences. With
the use of any multichannel detection system, one can
detect the emission coming from many elements simulta-
neously. The spectrometers shown in Fig. 3 are capable

FIGURE 6 Schematic representation of an inductively coupled
plasma torch during operation.

into the center of the plasma where excitation is more effi-
cient. As shown in Fig. 6, the plasma may be divided into
observation zones where atomic or ionic species are more
abundant.
The sample is introduced into the plasma commonly
through a nebulizer. The function of the nebulizer is to
convert the sample solution into a fine aerosol spray. The
nebulizers are often coupled to a spray chamber where
large droplets are preferentially removed from the aerosol
stream. Discrimination against larger droplets facilitates
more stable plasmas and a better measurement precision.
The most frequently used nebulizers are depicted in Fig. 7.
Cross-flow nebulizers are robust aerosol generators suit- FIGURE 7 Three popular nebulizers used for introduction of so-
able for most applications. The high-efficiency nebulizer lutions into an atom cell.