A method for characterizing a sample with respect to the presence of a specified element, the sample having a surface and characterized by a bulk, the method comprising: a. illuminating the surface of the sample with x-ray excitation radiation; b. measuring a first intensity of a first characteristic emission line of the specified element at a first energy; c. measuring a second intensity of a second characteristic emission line of the specified element at a second energy; wherein the first characteristic emission line is the K α -line of the specified element and the second characteristic emission line is the K β -line of the specified element or wherein the first characteristic emission line is the L α -line of the specified element and the second characteristic emission line is the L β -line of the specified element; the method being characterized by d. comparing a measured ratio R of the second intensity to the first intensity to empirically-determined minimum and maximum ratio values R min and R max, wherein a measured ratio of R equal to R min indicates that the specified element is located in a surface layer, a measured ratio of R max > R > R min indicates that the specified element is located in the bulk; e. selecting a concentration calculation method from a plurality of distinct concentration calculation methods based on the result of the comparing step, wherein in the case where the result of the comparing step indicates that the specified element is disposed in a surface layer, the selected concentration calculation method includes determining an areal density of the specified element; and f. wherein in the case where the result of the comparing step indicates that the specified element is located within the bulk of the sample, the selected concentration calculation method includes determining a volumetric concentration of the specified element within the sample; and g. calculating the concentration in accordance with the selected concentration calculation method and outputting at least one of the areal density and volumetric concentration of the specified element. a. illuminating the surface of the sample with x-ray excitation radiation; b. measuring a first intensity of a first characteristic emission line of the specified element at a first energy; c. measuring a second intensity of a second characteristic emission line of the specified element at a second energy; wherein the first characteristic emission line is the K α -line of the specified element and the second characteristic emission line is the K β -line of the specified element or wherein the first characteristic emission line is the L α -line of the specified element and the second characteristic emission line is the L β -line of the specified element; the method being characterized by d. comparing a measured ratio R of the second intensity to the first intensity to empirically-determined minimum and maximum ratio values R min and R max, wherein a measured ratio of R equal to R min indicates that the specified element is located in a surface layer, a measured ratio of R max > R > R min indicates that the specified element is located in the bulk; e. selecting a concentration calculation method from a plurality of distinct concentration calculation methods based on the result of the comparing step, wherein in the case where the result of the comparing step indicates that the specified element is disposed in a surface layer, the selected concentration calculation method includes determining an areal density of the specified element; and f. wherein in the case where the result of the comparing step indicates that the specified element is located within the bulk of the sample, the selected concentration calculation method includes determining a volumetric concentration of the specified element within the sample; and g. calculating the concentration in accordance with the selected concentration calculation method and outputting at least one of the areal density and volumetric concentration of the specified element.