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AECL-5311
ATOMIC ENERGY WSm L'ENERGIE ATOMIQUEOF CANADA LIMITED XjBBf DU CANADA UMITEE
AN AUTOMATED WAVELENGTH SELECTIOII
FOR FLAME SPECTROSCOPY
by
M. HURTEAU, J.P. MISLAN and R.W. ASHIEY
Chalk River Nuclear Laboratories
Ch~alk River, Ontario
January 1976
\\ AUTOMVI'I.n WAVFiLI-NfTIl Sf-.LF.(-rin\
Fi.VF SPI'f"T
M. Hurteau, .I.''. Mislan and '} .'<. \shlov
General Chemistry BranchAtomic Energy of Canada LimitedChalk River Nuclear Laboratories
Chalk River, Ontario, CanadaKO.J 1.T0
.Tanuarv 1976
-5311
Sélection automatique de longueurs d'ondes pour la spectroscopie â flamme
par
M. Hurteau, J.P. Mislan et R.W. Ashley
Résumé
On décr i t un simple système de programmation électromécanique
pouvant être employé avec un spectrophotomëtre a flamme. On i l l us t re
son application pour l 'analyse séquentielle automatisée à éléments
mult iples. La reproduct ib i l i té des réglages de longueur d'onde esto
à ±0.5 A. La précision et la sensib i l i té sont au moins aussi bonnes
que celles obtenues pour la détermination d'éléments simples.
L'Energie Atomique du Canada, LimitéeLaboratoires Nucléaires de Chalk River
Chalk River, OntarioKOJ 1J0
Janvier 1976
AECL-5311
AN AUTOMAT P. D WAVELENGTH SELECTION FOR
FLAME SPF.CTROSCOPY
''. Hurteau. I.P. Mislan and R.W. Ashley
Abstract
A simple electro-mechanical programming system is
described for use with a flame spectrophctometer. Its
application for automated sequential multi-element analysis
is illustrated. Reproducitility of wavelength settings areo
within .tO.5 A. Precision and sensitivities are at least
as good as those obtained for single element determinations. 1 •'
General Chemistry BranchAtomic Energy of Canada LimitedChalk River Nuclear LaboratoriesChalk River, Ontario, Canada
KOJ 1J0
January 1976
AECL-5311
A\ A U T O M A T E D KAVlil.HNCVTII Si.lJCl ION FOR
FI.AMC SIM.CTROSCOI'Y
^. M-.irtc-i'i, '.;\ "•-•. I/in a n d R . K . A s h l e y
INTRODUCTION
Two general approaches, which invilvv either < i'v.il t ar."<vtj ~
or ^euuential wrivel enet h seh-ctinn, can !-e u<eii for aut'^iat i c
mul t i - element ^latne snoc trope tr i c analv^is.
In the simultaneous-read ing instrument, individual photo-
multiplier detectors are positioned on the focal plane of the
instrument to monitor the intensity of a spectral line for
each elemei.i" of interest fi). These instruments are complex
and costly, and hence have enjoyed popularity only for
analyses where optical filters can be substituted for
diffraction gratings. Sullivan and Walsh (2) have shown that
simultaneous multi-element analysis can be achieved by using
special hollow cathodes as 'resonance' monochromators. This
arrangement permits monitoring of at least four elements.
Despite its apparent usefulness, this technique has not gained
wide acceptance.
Sequential wavelength selection can be simply achieved
by repetitive scanning of selected wavelength regions (3,8).
This approach has been reported by Dawson et al. (3). In-
terference filters mounted in a rotating wheel have been used
successfully for sequential wavelength selection in atomic
fluorescence spectroscopy (AFS) (4). This annroach is not generally
applicable to atomic absorption or atomic emission spectroscopy
because of high resolution requirements. Malmstadt and Cordos (5)
have reported the development of a programmable monochromator
which selects desired wavelengths via a computer actuated
stepping motor attached to the wavelength drive mechanism of
a commercial instrument. Results have been reported for multi-
element AFS.
We have developed a relatively simple and inexpensive
electro-mechanical programming module. Its usefulness for
sequential multi-element flame emission spectroscopy is described
in this report.
WAVELENGTH SELECTOR (shown in Fig. 1)
The wavelength selector is basically a 16.5 cm (6.5 in) diameter
hollow aluminum cylinder with a spiral groove (16 meters)
machined in the outer surface. It is rotated at 10 rpm by
a 28 rpm motor (Bodine Type N-1D) via a reduction gear. This
wavelength selector is interfaced to the monochromator of a
Techtron AA-5 spectrometer through a Techtron scanning attach-
ment (Model 70). Another gear train steps up rotation of this
scanner to 100 rpm. When continuous spectral line scanning is
desired the selector m e c h a n i s m can be quickly disengaged.
Adjustable a c t u a t o r s , shown in ':ig. 1, are positioned in
the groove of the wavelength selector at positions corresponding
to desired wavelengths. These actuators trip a tracking micro
switch, which moves along a threaded rod in synchronization with
the drum. This stops the motor and energizes a brake mechanism
which minimizes ger.r backlash.
Alignment of the wavelength selector for desired wavelengths
is done as follows:
d ) Disengage the wave l e n g t h selector from the scanning unit.
c
f 2 ̂ Set the monochromator 200 A below the Invest wavelcngt!.
des i red.
(3) With the motor disengaged, rotate the wavelength selector
to "start" posit:..' R -engage the wavelength selector
and scanning unit.
(4) Rotate the selector cylinder until the monochromator wave-
length indicator reads the lowest wavelength reauired in
the analysis.
(5) Install an actuator to trip the micro switch at this
point.
This procedure is repeated for all wavelengths required.
SYSTEM PROGRAMMING
All functions in the system are controlled automatically by
- 4 -
a Cramer multiple-pole program timer (Model 540} (Fig. 2).
The electrical circuits are shown in Figs. 3 and 4.
At the start of a cycle the Cramer programmer, via a
5-pole relay (Potter and Brumfield Model #KBP20AG), activates
the event marker pen indicating start of cycle, turns on the
recorder drive and opens the shutter. After 10 seconds, rotation
of the wavelength selector drum starts and the shutter closes
to record instrument background. Drum rotation continues
until the first pre-positioned actuator on the drum trips the
tracking switch. At this point a brake, controlled through
the tracking switch, locks the drum in position and the shutter
opens. Concurrently, an automatic sampler cycle is started
and solvent background and signal from the sample are recorded.
After about 1.5 minutes, the appropriate cam in the Cramer pro-
grammer overrides the tracking switch to allow the drum
rotation to continue. This operation is repeated for all the
spectral lines pre-selected. After the last emission line
signal has been recorded, the programmer actuates a relay to
return the wavelength selector drum to the starting position
and the equipment is ready for the next sample. Analysis time
is about 2 minutes per element.
A typical recorder trace is shown in Fig. 5.
RHSULTS
All flame emission measurements were made using a \2O
acetylene flame, slit width of 300 pm (band pass ',1.0 mn),
burner height of 8 mm, nebulization rate of -.5 ml/min, R-213
photomuJ tiplier.
Conditions chosen for emission measurements were a com-
promise of the optimum conditions determined for the individual
elements.
The system described has been tested for 1) wavelength
selection, 2) precision and 3) sensitivity.
[1) Wavelength Selection
With the wavelength selector directly coupled to the
Techtron scanning attachment,the wavelength range covered is
3000 A. This range can be increased by installation of a
suitable gear train between the selector and scanning attachment to
increase the rotation speed of the monochromator relative to the
selector. A two-fold increase (giving a wavelength range of
6000 A) is considered to be the maximum required.
The maximum resolution of the wavelength selector is
governed by the minimum spacing of the actuators which is attain-
able. In this system this was approximately 50 A.
The reproducibility of the wavelength selection was checked
by operating the instrument as described for 5 element selection
over 200 cycles. The selected wavelengths were recorded from
- 6 -
the d i g i t a l wavelength counter of the spec t rometer . The r e -
p r o d u c i b i l i t y observed was within ±0.S A.
(2) P rec i s ion
Standard solutions were prepav:d containing five elements
in the following concentrations: Cu = 30 yg/ml, Fe = 55 ug/ml
Ni = 100 ug/ml, Co = 100 ug/ml, Cr = 6 ug/ml.
These solutions were analyzed several times and the standard
deviation of results was found to be ±7%.
(31 Sensitivity
Sensitivities were compared with those reported by
Dvorak (6) for single element determinations using a nitrous
oxide-acetylene flame. This comparison is shown in Table 1.
TABLE 1
Comparison of Sensitivities(ppm/1% Transmission!
Dvorak CRNL
Copper
Cobalt
Nickel
Iron
Chromium
0.6
3.4
1.6
2 .5
0.4
2 .0
1.2
1.1
0 . 1
DISCUSSION
The system developed has proven to give satisfactory
reproducibility and sensitivity for standard solutions of five
elements in a monitoring mode. The system is versatile enough
to do sequential batch analyses or continuous on-line monitoring.
The instrument should not be limited to flame emission but could
be used for atomic absorption (using multi -element lamp) or
fluorescence measurements.
Since a peak signal is obtained for a pre-selected time,
the signal lends itself to averaging for better results. l\e
are developing a data processing system based on a programmable
calculator to take advantage of this feature.
REFERENCES
1. B.L. Vallee and M. Margoshes, Anal. Chem. 2_8, 175 (1956)
2. J.V. Sullivan and A. Walsh, Spec. Chim. Acta. 2J_, No. 4, "27 C19bS)
3. J.B. Dawson, D.J. Ellis and R. Milner, Spec. Chim. Acta.
23-B, 695 (1968)
4. D.G. Mitchell, Technicon International Congress, Nov. 24,
1970, New York
5. H.V. Malmstead and E. Cordos, American Laboratory,
Aug. 1972, p. 35
6. J. Dvorak, "Flame Photometry - Laboratory Practice",
Butterworth § Company (Canada) Ltd., Toronto
8 -
7. J.A. Dean and T.C. Rains, "Flame Emission and Atomic
Absorption Spectrometry", Vol. 1, p. 390 (1969). Marcel
^ekker Ltd., New York
8. D.L. Cook et al. Lab. Practice 21, No. 3, 171
3551-G
FIGURE I
ELECTRICAL PLUGS
\
TERMINAL STRIPS
WAVE LENGTH SELECTOR
WAVE LENGTHSCANNER
TRACKING SWITCH SHOWN INENERGIZEDDE.ENERGIZED
POSITIONSTRIPPER
.ROTATION
END VIEW ON DRUM
^^'^^^*m^mmmm^£sff^^m ^X s ir"1 / - ' ** vj FIGURE 2 KRAMER ELECTRO-MEGHAN ICAL PROGRAMMER
• r- ."...• t
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FIG. 3 ELECTRICAL CIRCUIT FOR CRAMER PROGRAMMER
b!_3S- S •« U M
o
o
i
S - .ass
F I G U R E 5 T Y P I C A L RECORDER READOUT
2 min.CYCL
2 min.CYCLE
Cr - 0 . 2 5 p p m I N AQUEOUS
- 2 . 5 p p m I N AQUEOUS
2 min.CYCLE
i.
N i - 2. 5 p p m I N A Q U E O U S
W A V E L E N G T H S E L E C T O R F U L L C Y C L E
2 m i n .CYCLE
- 2 . 5 p p m I N A Q U E O U S
2 m i n .CYCLE C u - 1 p p m I N A Q U E O U S
25sec|"NEW |qYCLE"
j_1
. .L.
5
Tlu International Standard Serial Number
ISSN 0067-0367
has been assigned to this series of reports.
To identify individual documents in the serieswe have assigned an AECL—number.
Please refer to the AECL-number whenrequesting additional copies of this document
from
Scientific Document Distribution OfficeAtomic Energy of Canada Limited
Chalk River, Ontario, Canada
KOJ I JO
Price S2.00 per copy
39-76