Spot analysis of light elements by X-ray emission spectrography

Abstract

The applicability of the X-ray emission spectrography to the spot analysis have been pointed out and actively studied. However, the discussions have been concentrated mostly on the analysis for heavy elements and not for light elements. Here we studied the fundamental considerations for the analysis of light elements and, as one of the applications, determined the quantity of sulfur in heavy oil and of aluminum in the cement.
In the spot analysis, the fundamental equation {eq. (1)} for the intensity of fluorescent X-rays can be approximated to eq. (2), which is the basic relation for the spot analysis, where the element to be analyzed can be determined not being suffered from other coexisting elements. However, it is found from the calculation of absorption coefficients that this approximation holds for the heavy elements, but not for the light elements. For the latter case, it is found that the equation {eq. (3)} of the intensity for the specimen with infinite thickness can be rather applied, because the mass absorption coefficient of filter paper for soft X-rays relatively increases as compared with the case of heavy elements (Table I). In this case, it can be calculated that, when the quantity of the droplet is very little, the denominator in eq. (3) can be attributed mostly from filter paper but not from the solute under the normal concentration. So we were convinced, that the spot analysis can be a practical and convenient method where X-ray intensity of the element to be analyzed is hardly suffered from other co-existing elements for the light elements as well as heavy elements.
There might be the possibility that the sulfur-contained compounds would be vaporized or decomposed when the X-rays is applied to heavy oil in the vacuum, and so we studied changes of SK_α intensity with irradiation time, for various conditions (Figs. 14). Moreover, the SK_α intensity variation, which is due to the difference of the spot quantity, (Figs. 5 & 6) and the error at the measurements (Table II) were investigated.
From those observations, we have fixed the analysis procedures as follows:
At first, we make the specimen pieces in the sequential procedures, where we add xylene to the heavy oil sample in each same amount, obtain the quantity of 10 μl from thus obtained solution and then spot on the No. 7 filter paper. We prepare three specimen pieces for the same solution. The measurement of the X-ray intensity is done twice for each specimen piece and so we obtain the value as its average. The standard deviation of the error from the chemical analysis is 0.04% (Table III).
Using the aluminum chloride solution as a standard, the quantity of aluminum oxide in the cement (the standard sample for chemical analysis, containing Al₂O₃ 5.10%) is determined as 5.28%, and that aluminum content in potassium alum (for the commercially available reagent, the calculated ratio of Al is 5.66%) is 5.42%.