Products and Services
X-Ray Fluorescence
Primary X-rays generated from the X-ray tube irradiate the sample. This produces secondary X-rays also known as fluorescence X-rays which are characteristic of the elements in the sample. This is the basis of X-ray spectrochemical analysis. A portion of this radiation emitted from the sample is collimated onto an analyzing crystal of known crystal lattice [d] spacing. This crystal diffracts the fluoresced beam into its component wavelengths through the angular movement of the spectrometer's goniometer. This varies the X-ray beam angles (theta) of incidence and emergence which detect the diffracted peaks. These peaks of X-ray intensity can be scanned and measured. Quantitative element analysis is usually made by the comparison of the element peak of interest with the peak from an appropriate standard.
SAMPLE FORM:
Samples of metals and alloys should have at least one flat surface for quantitative analysis. The surface to be measured should fill an area 1 inch in diameter. This will provide the maximum irradiation of the sample leading to a shorter analysis time. However, smaller surface area samples may be analyzed. The surface of the sample may have to be polished in order to provide an optically flat surface. Acid resistant materials evaluated as a fused glass button. The usual fluxing agent is a mixture of lithium carbonate and lithium tetraborate. The sample weight should be at least 2 grams for routine single element quantitative analysis.
METHOD ADVANTAGES AND LIMITATIONS:
Samples may be analyzed nondestructively. Thus, the sample can be recovered for reuse or for additional analyses. The standards against which the samples are measured should be closely matched not only in the analyte concentration but in the sample matrix, because of the interelement effects that are present in XRF. Also, the porosity of a solid sample has a large effect on the signal obtained. Therefore, it is a rapid and precise technique for analyzing well known samples such as in a production environment, but it may be difficult to analyze research or unknown samples because well matched standards may not be available.
QUALITATIVE USE:
Can quickly and nondestructively detect elements from uranium (atomic no. 92), decreasing in atomic number to sodium (atomic no. 11). Beyond sodium, detection limits rise dramatically as you continue down in atomic number.
QUANTITATIVE USE:
The detection limit of the elements is dependent on the element, sample matrix, and instrument operating conditions, but is generally at low parts per million. Analysis precision of 0.2 to 0.3 percent of the intensity is routinely obtained for a single line, devoid of any overlap from interferents. Accuracy of +/- 5 percent of the amount of the analyte present is obtained when using established methods of analysis. Quantitative analysis requires relatively long measurement times for each element and background because a large number of counts are required to obtain a precise value of the fluorescence intensities.
NSL Analytical Services, 7650 Hub Parkway, Cleveland, OH 44125. Tel: 216-447-1550; Fax: 216-447-0716.
