ASTM D7343 Standard Practice for Optimization, Sample Handling, Calibration, and Validation of X-ray Fluorescence Spectrometry Methods for Elemental Analysis of Petroleum Products and Lubricants
8. Procedure
8.1 Cup Preparation and Measurement (Open Cell):
8.1.1 Prepare the cups in strict accordance with the manufacturer's recommendations. When attaching the support film ensure that the film is not torn or left with any creases. (Warning - Do not touch the analytical surface of the film. This includes both sides of the film area that are subject to excitation and detection (the bigger of these two areas if they are not equal).)
8.1.2 Place the prepared cup film face down on a clean, lint-free, tissue-covered surface, ready for use, or on a sample tray specifically designed to hold cups during the sample preparation process.
8.1.3 Pour either a sample or standard into the prepared sample cup so that it is level to any recommended mark on the cup. Ifthere is no mark, then fill the cups about two-thirds full. It is important that all samples and standards used for a particular application contain approximately the same quantity of sample.
8.1.4 Verify that the prepared cup does not leak as in 5.1.3.5 for the first time a new sample type is analyzed. After that, look at each prepared cup for any signs of a leak. If a leak is detected, prepare another cup, fill it, and check again for leaks.
8.1.5 Use instrument autosamplers only if repeatability data demonstrates that the sample and sample cup (including film) integrity do not change during the waiting time on the autosampler and during the analysis time.
8.1.6 When the measurement is complete, remove the sample/standard, and check for leaks that may have occurred during the measurement. If the sample shows signs of leakage, repeat the measurement with a new cup, and discard the leaking sample's measurement.
8.2 Cup Preparation and Measurement (Closed Cell):
8.2.1 Place a new sample cell on a supporting surface, and pour the liquid to be analyzed into the cell to the recommended level or two-thirds full. It is important that all samples and standards used for a particular application contain approximately the same quantity of sample.
8.2.2 Seal the film over the open end of the cell using the provided sleeve or snap-on ring. (Warning - Take care not to touch the film to avoid contamination. Take care to avoid wrinkles in the film.) Ideally the film surface will be taut and flat.
8.2.3 Avoid puncturing the film during the sealing process. Check the completed cell for leaks. This can be done immediately after attaching the film by inverting the cell and reinverting. If a leak is present, a liquid front can be seen migrating from the leak across the outside film surface. This can also be done by placing the cell on a clean tissue, film side down, and observing the appearance of liquid on the tissue. Use extreme care with the tissue method to avoid contamination.
8.2.4 Immediately after the cell is sealed and it has been determined that it does not leak, pierce the top of the plastic cup for a vent to avoid pressure buildup and bulging of the film. This can be accomplished by placing the cell into the sample holder and using a push pin or other such tool to puncture the plastic.
8.2.5 Place the cup in the analysis position of the instrument, and measure it promptly. Use instrument autosamplers only if repeatability data demonstrates that the sample and sample cup (including film) integrity do not change during the waiting time on the autosampler and during the analysis time.
8.2.6 When the measurement is complete, remove the sample/standard, and check for leaks that may have occurred during the measurement. If the sample shows signs of leakage, repeat the measurement with a new cup, and discard the leaking sample's measurement.
8.3 Sealed Sample Holders (Closed Cells) - There are special sealed cups available to analyze high vapor pressure liquids. These cups are necessary when the liquid could contaminate the optical path of the spectrometer and are useful when analyzing so called winter gas. They are also necessary when using a spectrometer with tube above optics. They function by displacing the air bubble from the cell. Without any head space for vapors to expand into, the sample may be analyzed without undue fear of rupture.
