Providing adequate samples for Chemical Analysis

February 11, 2011

How big must the sample be for Atomic Emission Spectroscopy?

Adequate chemical analysis AES samples

Ideally a sample for chemical analysis by atomic emission spectroscopy (AES) should be at least 1’ square and 0.050’ thick to prevent leaking of light and gas from the aperture during excitation and to prevent the sample from melting during excitation. AES samples of other configurations may be used if they can be mechanically altered to conform to this size requirement:

  • Tubing with a 0.040” wall thickness or better and bar or rod down to 0.25” diameter can be flattened to yield a suitable AES sample. Similarly Round Pipe can be flattened to an accommodating flatness.
    Flattened AES chemistry sample

    Sample flattened for AES chemical analysis

     

     

     

  • Shaped samples may also be flattened for chemical analysis by atomic emission spectroscopy, if they will yield a sample of appropriate size.

There are circumstances which will not allow a sample to be flattened, some of these are hardness, carburization, nitriding, and brittle alloys.

How much weight do I need for ICP-AES Carbon/Sulfur/Nitrogen analysis?

The required weight for Inductively-Coupled Plasma Atomic Emissions Spectroscopy (ICP-AES) carbon/sulfur/nitrogen analysis will depend on the sample and material being tested. Generally, we would like to have at least 5 grams of material for ICP-AES analysis, which is the weight of a nickel. Whenever possible, more is better, to have extra material for rechecks, if a material is found to be out of specification, or for re-sampling, if a problem is encountered during sample preparation.

The sample can be a powder, several small parts (e.g. screws, nuts, springs), or a machining product such as chips or drillings. If the sample is to be a machining product, care must be taken to provide only the material to be tested.

  • Paint and corrosion as well as scale from the surface of parts should not be allowed to co-mingle with the sample, as this will lead to erroneous results.
  • Large amounts of cutting oil should be avoided.
  • Over heating the sample, resulting in blue or heat tinged chips can lead to false readings, especially in elements like carbon and sulfur.

The sample should be placed in a container that will not allow the sample to be lost in transit.  Plastic bags with a seal lock are especially good for this, particularly for powders.  If using plastic bags be sure the sample is cool before placing it in the bag.

Tagged as: AES, atomic emission spectroscopy, Chemical Analysis, ICP-AES

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Element Analysis by Atomic Emission Spectroscopy

November 19, 2010

Element analysis using atomic emission spectroscopy

Atomic emission spectroscopy for element analysis

Atomic Emission Spectroscopy (AES) is an instrumental method for performing elemental chemical analysis or determining the elemental composition of a sample solid material. The basic principle of AES is that when free atoms are put into an energetic environment, they emit light in a series of wavelength bands, similar to the diffraction of light into a rainbow. These wavelength bands or emission lines form a pattern that is characteristic of the atom that produced it. Generally, the intensities of the various emission lines are proportional to the number of atoms in the test sample that produced the lines. If an element is present in a sample, its characteristic spectrum lines also will be present. The concentration of that particular element can be determined by measuring the intensities of the characteristic lines and comparing them to the same lines from known standards. Thus, element analysis can qualitatively identify the type of element by the emission spectrum and quantitatively measure the amount of the element by the intensities of the emission lines.

When performing the atomic emission spectroscopy test with an AES system that  has a spark source, the sample is put in the spectrometer as a cathode and a tungsten pin is the anode. The gap between the pin and the sample is filled with the inert gas Argon. When the spark strikes the sample, rapid heating of the sample occurs causing vaporization of a small amount of sample from the surface, and forming a plasma (high energy gas cloud). The plasma produces the spectrum of lines from the elements that are present in the sample. The spectra are analyzed using mirrors and a diffraction grating to separate the analytical lines, as well as a set of photomultiplier tubes to quantify the light emitted from the elements and to measure their concentrations. Then, a computer compares the amount of light from the sample to that of known standards to identify the element, and calculates the quantity of the element. Spectrographic spark source instruments are very rapid and are often used in production applications such as steel mills and foundries.

Tagged as: AES, atomic emission spectroscopy, element analysis

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