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

- 7 -

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.

- 8 -

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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