D2622_8 (16)

Samples shall be taken in accordance with the instructions and practices D4057 or D4177 when applicable. When reuseable sample cells are used, clean and dry cells before each use. Disposable sample cells shall not be reused. For each sample, an unused piece of x-ray film is required for the sample cell. Avoid touching the inside of the sample cell, the portion of the window film in the cell, or the instrument window (if the instrument is so equipped) that is exposed to x-rays. Oil from fingerprints can affect the reading when analyzing for low levels of sulfur. Wrinkles in the film will affect the intensity of the sulfur x-rays transmitted. Therefore, it is essential that the film be taut and clean to ensure reliable results. The analyzer may need recalibration if the type or thickness of the window film is changed. After the sample cell is filled, create a small vent hole except when the cell is of the sealed type. Employ adequate storage, mixing, and sampling procedures. Refrigerate gasolines or other similar volatile materials to retain sample integrity in storage, but allow them to return to room temperature before testing. Expose these materials to ambient conditions only as long as necessary to obtain a sample for analysis. Impurities or thickness variations, which may affect the measurement of low levels of sulfur, have been found in polyester films and may vary from lot to lot. Therefore, the calibration should be checked after starting each new lot of film. See practice D7343 for more detailed sample handling and preparation information.