DETERMINATION OF THORIUM IN SOLUTION BY USING STANDARD ADDITION METHOD OF X-RAY SPECTROMETRY
A. ZARARSIZ , R. KIRMAZ , N. EFE , P. ARIKAN
TAEK-Ankara Nuclear Research and Training Center, 06100, Besevler -ANKARA
In present study, thorium content was determined in thorium bearing solution employing standard addition method. Samples were excited with 22-25 keV Ag X-rays from Cd-109 radioisotope source and obtained spectra were evaluated by AXIL programme. Correction factor was calculated in accordance to volume difference caused by standard addition.
The corrected results were compared with the results of standard calibration method and good agreement was observed for data.
1. INTRODUCTION
Rapid depletion of world uranium ore reserves emphasizes the significance of thorium as a possible future source of nuclear fuel.
X- ray fluorescence technique has been applied for analytical determination of thorium concentrations retained in leach solutions obtained from chemical treatment of thorium bearing ores1,2. The main advantages of this technique are simple sample preparation as compared to other analytical methods, short analysis time, and sensitivity with a minimum cost. Therefore, this technique was used by several workers to determine Th and other elements in aqueous and organic solutions. Arikan1 and Woltermann2 determined thorium in liquid samples. Zimmerman3 used the XRF method for the determination of thorium in solutions.
In present study, thorium content was determined in thorium bearing solution employing standard addition and standard calibration method and XRF spectrums were evaluated by AXIL software.
2. DESCRIPTION OF METHODS 2.1 Quantitative X-ray fluorescence analysis
The approach to quantification in XRF analysis is usually different for thin, intermediate thickness and infinitely thick samples;
a) Thin sample technique
h) Intermediate thickness samples
- Emission transmission method
c) Infinitely thick samples
- Use of calibration curves
- Use of internal standards
- Dilution methods fundamental parameter method
- Binary influence coefficient algorithms
- Algorithms with variable coefficients
- Empirical coefficients
- Standard addition methods
2.1.1 Standard addition method
If the analyte element is present in low concentration and no suitable standards are available and if only one or two elements are to be assessed, the standard addition technique can be applied. It involves the addition of known amounts of analyte to known amounts of sample, intimate mixing and production of a set of targets under identical conditions. The added element portion will, in principle, undergo the same matrix effect as the originally present fraction, and from the intensity increase due to the addition of the standard spike, one can directly convert the characteristic X-ray signal of the analyte into a concentration. Of course, different amounts of internal standards can be added to different samples to plot the intensity measured versus the concentration and to extrapolate, with better statistical significance, the line to the intercept on the concentration axis, which will represent the analyte concentration.
2.1.2 Formulation o f Standard Addition Method
Essentially, a weighed portion of the sample X is treated with analyte to increase the analyte concentration by AX , say 1% absolute, from Cx to Cx+AX. The analyte -line net intensity is then measured from the untreated Ix and treated Ix+AX sample. Then,
x x + A x
C x
C
x + A x(1)
In practice, a weighed portion of the sample X is treated with a weighed portion of a standard material S having known analyte concentration Cs to form a mixture XS containing
concentrations C(x) and C(s) of sample and standard, respectively. Incidentally, C(x) is actually
the dilution factor: weight of X/weight of X+S, or weight of X/ weight of XS. In the standard addition method, analyte-line intensity is measured from the untreated sample Ix and mixture Ix s.
C x
(I
X
/ I
XS)
• C ( S )1
-[(I
x/ I
x s)
•C
s ]where, C is weight fraction or percent. For analysis of liquids,
Cx
(I
x/ I
xs
) • C
(S
)(P
s/ P
x) +
K
v
x/ V )• [1 - (I
x/ I
x s)]]
(2 )
(3)
C is weight/volume fraction or percente (g/ml ); px and ps are densities of sample and standard, respectively; and vx and vy are volumes of sample and added standard.
3. EXPERIMENTAL
Thorium analysis of the solution samples were carried out using energy dispersive X-ray fluorescence spectrometry. The system employs annular Cd-109 radioisotope source for excitation of samples and the resulting photons are detected by a Si(Li) detector coupled to a multichannel analyzer and computer as described in Ref.4 Photons of 22 - 25 keV energy from Cd-109 source are used to induce fluorescence L X-rays of thorium from samples. The net peak intensities of thorium were calculated using an AXIL software program.
0.5, 1.0 ,1.5 , 2.0 ml standard solutions of 500 qg/ml Th- concentration were added to each thorium solutions samples (STh-01, STh-02, STh-03, STh-04, STh-05). Fluorescence analysis was accomplished by using the Addition Method.
The net peak intensities of thorium were calculated using an AXIL5 software program. Standard addition calibration curves for STh-01, STh-02, STh-03 are represented in Fig.2.
X-ray fluorescence analysis of thorium liquid samples were accomplished by calibration standardization procedure. Aliquots of a pure standard of thorium solution from Th(NO3)4 5H2O were used different concentrations (100, 200, 300, 400, 500 qg/ml). Fig. 3 shows the calibration curve with a good correlation coefficient of 0.998. 4
4. RESULTS AND DISCUSSION
The analysis of trace elements in liquid is very essential and sensitivity of analysis depends on mass density of the fluorescent element in the sample, matrix composition, fluorescent X-ray lines, design of detecting system and excitation energy. The result of Th analysis of five different solution by standard addition are given in Table. 1. Furthermore, for comparison the result of analysis by calibration standardization method of X-ray fluorescence for same samples are also listed in Table.1.
Students t-test have shown that the means of standard addition and calibration standardization measurements were identical within %95 confidence interval analysis by both methods. XRF technique by used the analysis of solution samples given a good performance.
Table.1 Analysis results by Standard addition and standard calibration
Samples No Standard addition (pg/ml) Standard Calibration (pg/ml) STh-01 143±11 147±12 STh-02 277±11 284±9 STh-03 303±8 298±9 STh-04 345±11 348±10 STh-05 413±9 404±1 5- REFERENCE
1. P. Arikan, A. Zararsiz and N. Efe, J. of Radioanal. And Nuclear Chem., Articles, 100(1986)303
2. M. F. Garbauskas and J. Wong, X-Ray Spetrometry, 12(1983)119
3. J. B. Zimmerman, C.R. Lalonde, Can. J. Spectrosc., 23(1978)157
4. A. Zararsiz, R.Kirmaz, P.Arikan, Nucl. Instr. Meth., B108(1996)
5. P. Van Espen, K.Janssens, I. Swenter, AXIL X-Ray Analysis Software (Packard, Canberra, 1986)
