BCIRA copper cast iron .pdf


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I
l

to the element being

I

analysed'
wavelengths sPecihc
Howevei unliki atomic absorption, the energy from the light
sourcc is not seen bY the detector.

Instruments adaptld for flamc atomic-fluoresceoce have

been available for ieveral years' but thc technique has not
achieved the popularity of atomic absorption. The reasons

for this are

as follows:

A large noise signal is emitted from the flame.
Interferences are causcd by scattering ofthe light from the
hollow-cathode lamP.

The detection limit is dependent on the intensity of the
external light source and, for useful lirnits of detection'

special clecirodeless discharge lamps are required. These are
expensive and require separate Power sources.
Interfcrences lound iu aromic absorption spectloscopy are

also prescnt,

Replacins the conventional flame with an argon
induitively-coupled plasma is said to solve many of these

Coupling-The a.c. coupling between the hollow-cathod!l

lamos and the detecror elEctronlcs tllters out mucn oI ultl
d,c. and low-frequcncy a c. background interference fron i
rhe Dlasma and nebulizer systems. This makes it possibkl
ro uie the lower-intensity hollow-cathode lamps rather rhu i
the more expensive electrodeless discharge lamps whilst stil'
obtaining a Ligh signal/background ratio for manY elemenu'l

Calibration-Litear calibration for up to

4-5

orders

0i;

masnitude is claimed, owing to the optically thin tail-flau'
of rle plasma which reduces molecular absorption and light'

scatte;ing effects found

in flame

atomic-absorPtior

I

spectrometry.

Specrrum-The spectrum produced is simple and
corresoonds mainly to the atomic-fluorescence resonanc!
transitlons. This overcomes the problem of interferencs
found in atomic cmission sPectrometry due to overlapping
emission

lines.

I

problems.a

De

The inductively coupled plasma atomicf luorescence spectrometer
The spectrometer manufactured by Baird Atomic

flame atomic-absorption spectrometry. However,

recrjon-Publishe d data indicate that, for non-refractor;l
I
elements, detcction limits are in general similar to rhose fol
forl

refractory elements, the detection limits are superior to thost,
Inc.

consists of up to twelve elcment modules surrounding an

argon inductivcly coupled plasrna rorch. Each module
(Fig. 3) consists ofa hollow-cathode lamp, a photomultiplier
tube, an optical-interference hlter which is situated in front
of the photomultiPlier, and lenses

by flame atomic-absorption spectrometry, bul
inferior to dctection limits obtained with plasma atomic i
obtained
emission

spectrometry.

i

Ad justability-The hollow-cathode lamp of each module is I
adjustable, so that it can be direcred at the positioo of tht '

plasma which gives optirnum performance' Howevet,l
compromise settings for plasma gas-flow rates and radio
frequency inductive-heating power must be established lol :
the elements which are to be analysed. This may provc
diflicult if the elements being analysed include refractoric i
and alkali metals.

A brief demonstration of the equipment has shown thalr
the technique may have considerable potential in both thr
ferrous and non-ferrous castings industries. The nail

artradion is that problems associated with interference from

Table

1

Typical results reported tor the analysis of
stainless steel by plasma atomic-fluorescence

spectrometry,
Fig

3

a! .lcmelt modulc of the
Baird Atomic lac. inductivcly coupled plasma
Schcmatic diagiam of

Elemen't

atooic-fl uorcsccncc Epactromctcr.

0.101
18.45
0.172
1 .64

Each module can be adiusted so that the radiation from
the hollow-cathode lamp is directed at the plasma tail-flame
by means ofa focusing lens. Some ofthe fluoresccnt radiation
fiom the atoms in the plasma passes through a narrow-band
optical filter, used to exclude unwanted radiation, onto a

Ni

photomultiplier tube.

o=

The hollow-cathode lamps of the modules are pulsed at
a modulation ftequency of500 Hz in such a way that at any
siven time onlv one hollow-cathode lamp is on, and one
itomic-fluorescince signal is being produced and detected

The detector electronics are

synchronized

wlth

12'26
2.38
0.509

N4o

Tablo

Measured composition
% by weight a o

r

0.002

12'19

r

0'10

0.510

i

0.04
0.02

0.111

t 0.20
0. 174 a 0.002
1.50 I 0.010

18.63

2.38 r

standard deviation

2

Typicsl rssults reported for the analysis ol
low-alloy st69l by plasma atomic-f luorescencg

spsctrometry.

the

modulation frequency of the hollow-cathode lamp' TtIe
instrument has a microprocessor which is used for two-point
calibrations and dala handling.

Standard composition
Elsmont
Co

spectroscoPy.

Ni

0.30

030
0.50
1

.04

u.59
0.068

Pulsing-The pattem ofpulsing ofthe hollow<athode lamps
allows very fast sequential multi-element determination with
thc instrument, for up to tvelve elements.

% by woight
0.095

The technique has the following six principle features
which combine many of the advantages of flame atomicabsorption spectroscopy and plasma atomic-emission

110

Standard composition
% by woight

0.39

o=

Measured composition
% by weight o

i

t
i

0.095 0 002
0.288 a 0.0G
0 m5
0.331
0.4a3 r 0.003
0.994 r 0'010
0.598 r 0 006
0.071 0 004

t

0.38 r 0

02

standard deviation

March

1984