Instant Notes: Analytical Chemistry

analyzed, for example, a zinc source lamp to determine zinc. These are called

resonance linesources, and may be a hollow cathode lamp (HCL)or an elec-

trodeless discharge tube, both described below. Continuum source instruments

require very high-resolution monochromators.

In a similar way to the flame emission spectrometers described in Topic E4, a

flame may be used to volatilize the sample. Nonflame atomizers, particularly

the graphite furnace, are very useful especially when only small volumes of

sample are available.

Instrumentation The source is often a hollow cathode lamp (HCL) as shown in Figure 1(b). This
has a glass envelope with a quartz window and contains a gas such as argon,
which is excited by an electric discharge. The excited argon atoms bombard the
cathode, which is made of the element to be determined and the atoms of that
element are then excited in the discharge too. The excited atoms decay back to
their ground state, emitting the characteristic radiation. A turret with several
lamps allows multi-element determinations.

E7 – Atomic absorption and atomic fluorescence spectrometry 219

Octal base plug

Connecting pins

Supports Cathode Mica shields Glass envelope Graded seal

U.V. glass

window

Silica

window

Anode

(b)

Fig. 1. (a) Schematic of a flame atomic absorption spectrometer. (b) A typical hollow cathode lamp. Reproduced
from F.W. Fifield & D. Kealey, Principles and Practice of Analytical Chemistry, 5th edn, 2000, with permission from
Blackwell Science Ltd.

Resonance

line source

Flame

Monochromator

Detector

Amplifer

Spray

chamber

Fuel

Nebulizer

Oxidant

Sample

Printer

Recorder

Meter

(a)