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Atomic Energy of Canada Limited
ANALYSIS FOR GADOLINIUM IN HEAVY WATER
BY FLAME EMISSION
by
M. HURTEAU, J.P. MISLAN and R.W. ASHLEY
Chalk River Nuclear Laboratories
Chalk River, Ontario
March 1974
AECL-4772
ANALYSIS FOR GADOLINIUM IN HEAVY WATER BY FLAME EMISSION
M. H u r t e a u , J . P . M i s l a n , R.W. A s h l e y
Abstract
Methods are described for the determination of
gadolinium in water by flame emission techniques. High con-
centrations (50-10,000 ug/ml) are determined by direct
aspiration into the flame. Medium concentrations (1-50 yg/ml)
can be determined after concentration by evaporation or with
signal enhancement by addition of perchloric acid. For con-
centrations less than 1 yg/ml, solvent extraction with
1-(2-Pyridylazo)-2-Naphthol (PAN) is used for preconcentration,
Interference from boron can be suppressed by addition of NH^Cl,
General Chemistry BranchAtomic Energy of Canada LimitedChcilk River Nuclear Laboratories
Chalk River, Ontario
March 1974
AECL-4 77 2
Analyses pour déterminer le gadolinium dans l'eaulourde par émission de flamme
par
M. Hurteau, J.P. Mislan, R.W. Ashley
Résumé
On décrit des méthodes permettant de
déterminer le gadolinium dans l'eau par émission de
flamme. Les hautes teneurs (50-10 000 yg/ml) sont
déterminées par une aspiration directe dans la flamme.
Les teneurs moyennes (1-50 yg/ml) peuvent être déter-
minées après concentration par evaporation ou au moyen
d'un renforcement notoire par l'addition d'acide
perchlorique. Pour les teneurs inférieures à 1 ug/ml,
on a recours à une extraction par solvant avec
l-(2-Pyridylazo)-2-Naphthol (PAN) pour la préconcen-
tration. L'interférence du bore peut être supprimée
par l'addition de NH,Cl.4
L'Energie Atomique du Canada, LimitéeLaboratoires Nucléaires de Chalk River
Chalk River, Ontario
Mars 1974AECL-4772
ANALYSIS FOR GADOLINIUM IN HEAVY WATER BY FLAME EMISSION
M. Hurteau, J.P. Mislan, R.W. Ashley
INTRODUCTION
Emergency shutdown (800 milliseconds) of the Gentilly
Boiling Light Water (B.L.W.) power reactor is achieved by rapid
injection of concentrated gadolinium nitrate solution into the
heavy water moderator system. Normal operation is resumed
after removal of the Gd on ion exchange columns. Monitoring
of the Gd concentration over several orders of magnitude is
required to ensure that the icn exchange column utilized for Gd
removal operates efficiently.
The standard method of analysis is a rather lengthy
solvent extraction - spectrophotometric procedure (1). A need
for a simpler, faster procedure exists. The use of nitrous oxide
flames and long path pre-mix burners has increased the potential
of flame emission for this analysis. Flame emission spectroscopy
using these conditions has been investigated for this purpose
and found to be an attractive alternative technique. Samples can
be analyzed quickly over a wide dynamic range (0.1 ppm - 10,000 ppm)
using simple, straight-forward sensitivity enhancement procedures.
The depressant action of boron, as boric acid which is added to
the moderator system for long-term reactivity control, can be
minimized b/ addition of a chemical buffer (NHi,Cl) .
- 2
EQUIPMENT AND REAGENTS
The instrument used in these studies was a "Techtron"
AA-5 model with standard flame emission attachments (Techtron
FE-5 chopper and Techtron #70 wavelength scanner). A Techtron
NzO-C2H2 burner head (Techtron #AB-50) with a slot length of
5.5 cm was used for all measurements.
A strip chart recorder (Varian #G-2000) was used for
emission signal readout. This recorder has a 10-position cali-
brated span switch with vernier control to allow the operator a
choice of spans from 1 millivolt to 1 volt.
The concentrator was a rotary evaporator driven by com-
pressed air. The assembly is shown in Fig. 1.
Stock gadolinium solutions (1) 10,000 yg/ml - 1.15 29 g
Gd2O3 were dissolved in 50 ml of 2M HNO3 by heating and stirring
and diluted to 100 ml; (2) 1000 yg/ml - 1.1529 g Gd2O3 were
dissolved in 50 ml 2M HNO3 as above and diluted to 1000 ml.
5N HClOit - 55 ml of reagent grade acid were diluted
to one liter.
IN IICICU - 11 ml of reagent grade acid were diluted
to one liter.
Ammonium chloride stock solution - A 1M NH14CI solution
was prepared by dissolving 53.5 g of NHUC1 in 500 ml of H 20.
After dissolution, the solution was cooled and diluted to one
liter.
ROTARYDRIVE UNIT
VACUUMPUMP
COMPRESSEDAIR INLET
CONDENSER SAMPLE FLASKCONCENTRATERECEIVER
TWO ml MARK
H" HOLE ONBOTH SIDES OFTHE GLASSTUBING (V'l.D.)
1OOO ml ROUNDBOTTOM FLASK
ONE ml MARK
100 ml ROUNDBOTTOM FLASK
GLAS5 TUBING~7mm I.D.
FIGURE I ROTARY EVAPORATOR
. 4 -
Methanol - reagent grade
Buffer solution - 55 g of ammonium chloride were
dissolved in 300 ml of water. 300 ml of ammonium hydroxide (281)
were added and the solution diluted to one liter. The pH value
is ̂ 9.5.
1-(2-Pyridylazo)-2-Naphthol (PAN) - 0.1 g of PAN was
dissolved in 90 ml methanol. This solution was filtered through
a Whatman paper #40 (12.5 cm) and washed with methanol. The
filtrate was collected in a 100 ml volumetric flask and diluted
to the mark with methanol.
Methyl Iso-Butyl Ketone (MIBK) - reagent grade
EXPERIMENTAL
Preparation of Standard Solutions
Three sets of standards were prepared from the gadolinium
stock solution, as follows:
ij-~) High range - Aliquots of the 10,000 ug/ml stock solu-
tion were diluted to give standard solutions ranging in con-
centration from 1000 to 10,000 ug/ml.
ii) Medium range - Aliquots of the 1000 ug/ml stock solu-
tion were diluted to give standards with a concentration range
of 1 to 50 ug/ml.
Low range - Standards containing from 0.01 to 1.0 ug/ml
- 5 -
Gd were prepared by diluting 100 ml aliquots of the 1 to 10 ppm
standards to one liter.
Instrument Conditions
Choice of wavelength - Flame emission has not been used
extensively for gadolinium analysis. Some general studies have
been made^ •'*•'. The gadolinium emission spectrum CC2H2-N2O
flame) was re-examined over the region 4621 A. - 6220 A. Several
bands and lines were recorded in this region and the one with the
o
most sensitivity air. least interference was found to be at 4621 A.
This wavelength was used in all the subsequent experimental work.
A portion of the spectrum is shown in Fig. 2.
Instrument parameters - The general operating conditions
for the Techtron AA-5 were as follows:
1-10,000 ug/ml Gd 0.1-1 yg/ml Gd
CzUz
N20
Slit
Wavelength
Burner height
Recorder span
12 psi
18 psi
300 y
4621 A
7 mm
10 mV
13 psi
21 psi
300 y
4621 A
7 mm
2 mV
A gadolinium solution was aspirated and the conditions
for maximum intensity of the emission were established by varying
- 6 -
FIGURE 2 Gd SPECTRUM (4575 - 6275A)
Gd SPECTRUM
BACKGROUND
BACKGROUND\
Gd SPECTRUM
r-- IA
•J3
IA
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fuel rates, slit opening and burner height. Burner height was
found to be very important. The "red feather" region of the
flame is relatively small O 2 mm), and the maximum emission for
gadolinium is found in this region.
Electronic signal expansion was obtained in two ways.
Firstly, with the coarse gain set at 3, the recorder span was
changed from 10 mV to 2 mV to give a five-fold expansion of
signal. Secondly, the instrument gain was adjusted to give lOO"; T
for a 10 ppm gadolinium solution, the zero being set on a reagent
blank solution. Signal expansion in the latter case was two-fold.
Analysis Conditions
i) High rang;e - The standard solutions covering the range 50
to 10,000 yg/ml were aspirated directly into the flame under the
optimum conditions and emission intensities measured. Water was
used as reference. With concentrations up to ^500 yg/ml, the
full flame path length (5.5 cm) could be used. Above thi>, it was
necessary to rotate the burner to reduce the effective flame
length and hence the emission intensity to a measurable level.
ii) Medium range - (1-50 yg/ml). Two approaches were in-
vestigated, (1) signal enhancement by reagent addition,
(2) concentration by pre-evaporation.
In the first, additions of various acids and alcohols
were made to standard solutions and emission intensities measured.
Maximum signal expansion was required for these solutions.
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The second approach was to concentrate the 1-50 yg/ml
standard solutions ten-fold in the rotary flash evaporator. A
20 ml aliquot of solution is reduced to less than 2 ml in 25-30
minutes.
iii) Low range - (0.1 to 1.0 yg/ml). For these low concentra-
tions a larger concentration factor was required to bring the
solutions within a measurable emission intensity range. A
solvent extraction preconcentration technique using the PAN
complex^ ' was examined. The procedure followed was to transfer
a 100 ml of standard solution to a 125 ml separatory funnel, add
5 ml buffer solution and 1 ml PAN solution and mix. After five
minutes, 10 ml of MIBK were added and the mixture shaken for at
least one minute. The phases were allowed to separate for 3 to
4 minutes after which the lower aqueous layer was removed and
discarded. Five milliliters of 0.1N HCIO* were added to the
organic phase and the mixture was shaken for one minute. Back ex-
traction with acid was required because of the low solubility of
the Gd-PAN complex in MIBK; precipitation occurs at concentrations
>3 yg/ml. After the phases had separated, the acid solution
(lower phase) was collected. This solution was aspirated and
emission intensity measured. A reagent blank was carried through
the same extraction procedure and run with the standards.
Interferences
The development of these procedures was directed primarily
towards the analysis of heavy water samples that contain only
- 9 .
traces of impurities and therefore no investigation was made of
effects of cations and anions in general. Boron is the only
likely interference to be met since it may be added in concentra-
tions of 1 to 10 ug/ml to the reactor system as a soluble poison.
The effect was checked by aspiration of standard Gd solutions
containing known amounts of boron.
Precision and Sensitivity
The precision of the analyses was checked for the low
concentration range only. Standard solutions containing 250 ppb,
500 ppb and 750 ppb gadolinium were analyzed in replicate. The
reagent blank was also run in replicate at the same time.
Sensitivities were calculated as amount of gadolinium
giving a response of one chart division (always greater than 2X
noise signal) under the specific conditions used for analysis,
i.e. expanded or non-expanded signal.
RESULTS AND DISCUSSION
i) High Concentration Range
The calibration curve obtained for concentrations of
gadolinium up to 250 ppm is shown in Fig. 3. Net intensities
(sample minus blank) were used. A wide dynamic range of con-
centrations (up to 10,000 yg/ml) can be covered by rotating the
burner head. This has the same effect as diluting the solution
since the proportion of excited atoms in the optical path is
- 10 -
reduced. Results were very satisfactory and this direct deter-
mination of high concentrations of gadolinium is a very sample
procedure for rapid analysis of such solutions.
ii) Medium Concentration Range
The effect of various acids and alcohols on emission
intensities is shown in Table 1. Of the acids examined, only
perchloric gave an enhanced signal. All three alcohols enhanced
the emission intensity but with ethanol and propanol the response
was too noisy to be useful. The combination of perchloric acid
and methanol gave the same response as perchloric acid alone.
Both the HCIO4 addition and the preconcentration technique
gave good results. The first is a simpler, more rapid procedure
whereas the latter can cover a larger concentration range but
requires considerably more time, e.g. 50-fold volume reduction
requires about one hour. For concentrations from 1 to 10 Mg/rnl
the preconcentration method is recommended. For concentrations
of 10-50 ug/ml the direct determination xvit.h HClOi, addition is
satisfactory.
iii) Low Concentration Range
The results for the analysis of the standard solutions
containing 0.1 to 1 ppm gadolinium are shown in Fig. 4.
The results of the replicate analyses of standard
gadolinium solutions are shown in Table 2.
EMISSION INTENSITY (ARBITRARY UNITS)
o
INJOoo
4ooo
ooo
O-OOO
33
O
CD
a)
o
ID3
a
tn
Io
U1o
z n "D anto M to co 1 —I 33
3^
oz3D
ro -* r̂o -• m
oo
~xl C
^ m -i 1
o3 t
*E> 0
tvi\_nO
" II
CDX.
oto
Ul
UJ
1 1
FIGURE 4
-.6000
-. 5000
-.4000
-.3000
f^~- BLANK
-.1000
1 1
1 1
CALIBRATION CURVE FOR
1 1
1
LOW CONCENTRAT
i
I
ION
XTO
f
1
RANGE
I I
—
AA-5 PARAMETERS ~
WAVELENGTH
SLIT
BURNER HEIGHT
C 2H 2 13 psi
N 20 21 psi
RECORDER
I
4621A
300A
7mm —
-fc.O
-7.252mV
I Ippb Gd 100 200 300 400 500 600 700 800 900 1000
- 13 -
TABLE ]
Effect of Various Chemical Reagents on Emission Intensityof 100 ppm Gd Solutions
Reagent Concentration Emission Intensity % Enhancement
Aqueous Medium
HNO3 - 0.2N0.4N0.6N
H2SO1, - 0.2N0.4N0.6N
HC1 - 0.3N0.6N0.9N
HClOi, - 0.1N0.2N0.3N
Methanol (4 0% v/v)
Ethanol (40% v/v)
Propanol (40% v/v)
40% Methanol, 0. 2N HClOi,
40% Ethanol, 0.2N HCIO4
40% Propanol, 0.2N HC1CU
0.
0.0.0.
0.0.0.
0.0.0.
0.0.0.
0.
0.
0.
0.
0.
0.
320
30030029 5
128130133
280325330
583585587
370
390*
370*
585
580
635
0
- 7
-60
- 3
+ 81
+ 15
+ 22
+ 47
+ 81
+ 81
+ 98
.0
.0
.0
.0
.0
.0
. 0
.0
.0
.0
ft
gave noisy signal
- 14 .
TABLE 2
Results of Replicate Analyses of StandardGadolinium Solutions
Concentra-tion of Gd
(ug/ml)
250
500
7 50
Blank
No. ofDetermina-
tions
6
6
6
6
iv) Sensitivity
AverageIntensityReading
0.2475
0.3542
0.4400
0.1350
StandardDeviation
0.0227
0.0111
0.0275
0.015 2
Coefficientof
Variation {%)
9. 2
3.1
6.3
11.3
Sensitivities for the three concentration levels, defined
as amount to give a response equal to twice the background, were
as follows:
Range
50 - 10,000 yg/ml
1 - 50 yg/ml
0 . 1 - 1 yg/ml
Sensit ivity
4 yg/ml
0.15 yg/ml
0.02 yg/ml
v) Interferences
In low concentrations, boron does not affect, the Gd
analysis. The repression at 40 ppm boron is less than 5% and
increases only gradually to about 151 at 200 ppm boron. SrCl 2
and Nf-UCl were examined as suppressants for the boron effect and.
- 15
the latter found to eliminate the interference at least up to
200 ppm boron when added to give a solution 0.2°0 in NIUC1 .
CONCLUSIONS
Simple, rapid methods have been developed to analyze
for gadolinium in heavy water over a large range of concentra-
tions. Maximum analysis time is about 30 minutes compared to
3-4 hours for the spectrophotometric procedure. A coefficient of
variation of ±9%, or better, was obtained for concentrations of
Gd below 1 ug/ml. These methods permit monitoring of gadolinium
concentration changes during reactor operation rapidly and
conveniently.
REFERENCES
(1) "Determinatioi of Rare Earth Metals with 1 - (2-Pyridylazo)-
2-Naphthol", Anal. Chim. Acta 28_ (1963), p. 388-392.
(2) "Atomic Absorption Studies on Rare Earth and Refractory
Metals", Anal. Chim. Acta 37_ (1967), p. 239,
R.J. Jaworowski, R.P. Weberling and D.J. Bracco.
(3) "Flame Spectra of the Rare Earth Elements", Spectro-Chimica
Acta, 1962, Vol. 18, p. 1127, V.A. Fassel, R.H. Curry,
R.N. Kniseley.
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