Kruidhof, H.

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Analytica Chimica Acta, 102 (1978) I U-180 u Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands Short Communication A GENERAL X-RAY FLUORESCENCE SPECTROMETRIC TECHNIQUE BASED ON SIMPLE CORRECTIONS FOR MATRIX EFFECTS H. KRUIDHOF Twuente University of Technology. Department of Chemical Engineering. Labomtory for Inorganic Chemistry and Materials Science, Enschede (The Netherlands) (Received 14th Februaty 1978) X-ray fluorescence spectrometxy is highly selective but, as is well known, problems arise when the x-rays are absorbed in different ways by the samples and standards. When the composition of the samples is approximately known, these mat& effects can bc prevented by preparing standards and samples in the same way, e.g. by a bora>i fusion technique [l--5] _ This procedure, when it is used correctly, ensures sufficient compensation of matrix effects. If, how- ever, almost nothing is known about the composition of the samples, this method is not applicable. Even when it is applied, much work is involved in the preparation of new standards. Accordingly, several methods of correcting for matri. effects have been suggested [6-111 ; some of them give good results but arc rather complicated, while others may be restricted to certain wavelengths. The method reported here, which is relatively simple and generally appli- cable for most materials, involves a combination of borax fusion with matrix effect corrections. The latter are done with algorithms, which are derived from the intensity formulae, together with empirical coefficients. Experimental Sample preparation. Accurately weigh two different amounts of the same sample (S, g and S2 g on an ignited base) into Pt-5% Au crucibles: and add 6.000 g (dry weight) of boras. b1i.s well and fuse in a furnace at about 1000°C. Cast the melt into Pt--5% Au moulds, maintained at about SOO%, to produce glass discs of 30-mm diameter. For the determination of an elementj, measure the intensities at a certain wavelength (Xi) and correct for the backs?ound and dead-time; the corrected intensities are Iis,* and Iis,, respectively. Standard preparation. If possible, use only the anhydrous oxides of the required elements, although other inorganic anhydrous compounds may be used at need. For element j, weigh two different amounts of its compound (m, g and m2 g on an ignited base) and prepare glass discs as described above. The respective corrected measured intensities are ljm, and ljm,. Matrix absorption corrections Excitation by the total primary spectrum of an x-ray tube can be repiaccd by excitation by a hypothetical effective wavelength (A,). The absorption coefficients for this wavelength, pi(he), are then used to calculate the primary absorption of the sample. The total sample absorption for element j is given by: CiNi fpi(Xje) + Api(Xj)l, where the first term indicates the absorp- tion for the effective wavelength of clement j, and the second term the absorption for the characteristic wavelength. Let the absorption coefficients for the borax be Ki for the effective wave- length and KY for the characteristic wavelength of element j, and let the absorption coefficients for the sample be a; and a: for the effective wave- length and characteristic wavelength of elementj, respectively. The absorption for the glass disc with S I g of sample (see sample preparation) can’ then be described by The terms (Ki + AK;) and (a; + Aa,r’) depend on the wavelength, but are constants for element j measured under fixed conditions. A is an apparatus constant. Thus new combined absorption coefficients for primary and sec- ondary radiation can be introduced. If (K,’ -+- .4Ky) = Kj and (u; -!- AU;‘) = A,, the expression becomes (6Ki + S,Aj)/(6 + S,). Analogously, the absorption of the glass disc with S2 g of sample CZIII be described by (6Kj + S,Aj)/(6 +Sx), and the absorptions of the standard discs (see standard preparation) by (6Kj + RI &)f(6 + m ,) and (6Kj + mzBj)/(6 i m2), respectively. Here, Bj is the so-called combined absorp- tion coefficient for primary and secondary absorption of the compound used for making standard discs of element j. ~a~culatio~ of absorption coefficients. For the sample the following expression now holds: 6Kj cS,A, _ Szljs, (6 +SX) (6 +S,) - S,l,s, (6 +S,) “2 .$pi Thus Aj can be calculated in terms of Kj; and the re*aI value of Kj is not important, because all the absorption coefficients are in terms of Kj. If Ki is taken as a constant parameter of 1 for every wavelength, rearrangement gives for A, (and analogousfy for _tl): Aj = 6(Slljs, - s21jS,)lsIs2 <rjS, -rjS,) Bj = 6(~1_lirn,-~~~jrn,)f~t~~ (ljm, -fjm,) The amount of elementj in the disc with S, g sample is then given by C, = bm,Ijs, (6 +SiAi) (6 + ml) 16 +Si) = brnl lis, (6 +S,Aj) f I im, (6 +S,) (6 +miBj)(G +ml) ljs, (6 + m $3) 179 where b is a conversion factor for the compound of elementj which is used for making standards. The concentration of elementj in the sample can then be easily calculated. Results and discussion Several ceramic materials were analysed as described above. The amounts weighed for the sample (S, g and S2 g, respectively), were about 0.5 g and 0.3 g, while the weights (m, g and m2 g) of the oxides used for making the standard discs were about 0.12 g and 0.07 g, respectively. To prevent loss of lead, samples and standards containing lead were fused first at 800°C and then at 1000°C. The results are shown in Table 1. Some B.C.S. alloys were also anaiysed (Table 2). These alloys were dissolved in acid, and two different aliquots of the same solution were transferred to platinum crucibles, evaporated to dryness and ignited. Glass discs were prc- pared from the ignited materials. A synthetic mixture of Fe, Cr and Ni solutions was also analysed (Table 3). TABLE 1 Results (in %) for some ceramic samples Sample 1 Sample 2 Sample 3 Present Found Present Found Present Found Pb 57.6 57.7 57.6 57.4 - - Ti 17.08 17.02 17.16 17.20 - - Sm 8.02 7.95 8.03 7.97 48.38 48.50 Zr -. - - - 32.52 32.63 TABLE 2 Results (in %) for some B.C.S. alloys Alloy B.C.S. 21812 B.C.S. 263/l B.C.S. 330 B.C.S. 23512 Prrsxxt Found Prcscn t Found Present Found Present Found Fe - - 0.35 0.36 - - - - Cr 0.10 0.11 0.24 0.26 - - 18.60 18.57 Ni 0.18 0.18 - - - - 9.38 9.58 Mn 0.63 0.63 0.36 0.36 0.45 0.46 - - TABLE 3 Results (in mg) for a synthetic Fe-Ct-2% solution FC Cr Ni Present 886 102.8 609.7 Found 885 102.5 607.2 i80 The influence of possible enhancement on this technique is not known exactly, but in practice good results are obtained, where enhancement could be expected, so that probably only slight interference will occur. it is clear that, for every wavelength measured, the discs must be infinitely thick. It can be concluded that the method described is reliable with an acceptable accuracy for most materials. The applicability of the technique to specific materials is under investigation and will be reported later. The author thanks Dr. IS. J. de Vries and Professor A. J. Burggraaf for their stimulating interest and valuable discussions. REFERENCES 1 K. G. Carr-Brian, Analyst, 89 (1964) 556. 2 R. Jenkins and J. L. de Vries, Practical X-ray Spectrometry, Philips Technical Library, 1968, p_ 150. 3 A. Strasheim and $1. P. Brandt, Spectrochim. Acta, Part B, 23 (1967) 183. 4 F. F. Rinddi and P. E. Aguzzi, Spectrochim. Acta, Part B, 23 (X967) 15. 5 J. H. H. G. van Wiliigen, H. Kruidhof and E. A. M. F. Dahmen, Talanta, 18 (1971) 450. 6 $1. L. Salmon and J. P. Blackledge, Nor&o Rept., 3 (1956) 68. 7 K. Norrish and R. M. Taylor, Clay Miner. Bull., 5 (1962) 98. 8 G. Anderman and J. IV. Kemp, Anal. Chem.. 30 (1958) 1306. 9 D. A. Stephenson, Anal. Chem., 43 (1971) 310. 10 J. H. I-i. G. van Willigen, H. Kruidhof and E. A. 31. F. Dahmen, Anal. Chim. Acta, 62 (1972) 279. 11 W. K. de Jong, X-ray Spectrom., 2 (1973) 151. 

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A general x-ray fluorescence spectrometric technique based on simple corrections for matrix effects

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A general x-ray fluorescence spectrometric technique based on simple corrections for matrix effects

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