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How to Determine Sulfur Using XRF

X-ray fluorescence -- or XRF -- spectroscopy is used by chemists, physicists and material science workers to identify the composition of a geologic sample -- primarily rocks and soils. This technique analyzes and measures the amount of the periodic table elements that have atomic numbers greater than 15. Sulfur is the lightest element that XRF is useful for -- measuring the energy of light emitted by a sample after excitation with x-rays. With sulfur, the energy of the emission lines are at 2.3 keV. The examination of the emission spectra of an XRF analysis indicates the presence or absence of sulfur in the analytical sample.

Things You'll Need

XRF instrument
Rock standards
Sample
Crusher
Grinder -- for solid samples such as geologic rocks

Instructions

- 1
  Turn on the XRF instrument, and allow a warm-up period to ensure stable operation. The emission source of x-rays must stabilize to provide consistent intensity for the illumination of the samples. Warm the instrument for a minimum of 30 minutes, prior to any analysis.
- 2
  Obtain the analysis of several rock standards that have a composition that includes sulfur. This provides a correlation between the amount of sulfur in the sample and the intensity of the emission signal from the sample.
- 3
  Pass your analytical sample through a grinder, to break it into pieces measuring 1 to 10 mm. The grinding step helps to homogenize the sample, providing pieces that represent the bulk sample.
- 4
  Separate a small portion of sample that measures between a few grams to 100 grams of crushed sample. Place it in a grinder, and grind it into a fine powder.
- 5
  Analyze the powdered sample, and obtain the spectral output of the XRF instrument. The spectra produced is a two-dimensional plot of intensity versus energy of x-rays emitted. The energy of the x-rays emitted identify the elements contained in the sample. And the intensity indicates the amount of each particular element.
- 6
  Examine the region around 2.3 keV for the presence of peaks that are representative of sulfur. The two main peaks for sulfur are 2.307 and 2.308 keV -- which correspond to the transition of K and L within sulfur. If one or both of these peaks are present in the spectra, then sulfur is present in the sample. The absence of both of these peaks indicates the sample doesn̵7;t contain sulfur.

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