D4294_16e1_8

If you employ reusable cups, clean and dry cells before use. Disposable sample cups are not to be reused. Window material usually has less than 10 micrometer polyester or polycarbonate film (See section 7.6). Polycarbonate is preferred due to its high transmissivity of sulfur x-rays. Renewal of the window of the sample cup is essential for the measurement of each sample. Avoid touching the inside of the sample cup or portion of the window film in the cup or in the instrument window 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 number of sulfur x-rays transmitted. Therefore, the importance of the film smoothness and cleanliness cannot be over stressed to ensure reliable results. The analyzer will need recalibration if the type or thickness of the window film is changed. Impurities which may affect the measurement of low levels of sulfur have been found in polyester films and may vary from lot to lot. Therefore, if using a polyester film, the calibration should be checked after starting each new roll. Samples of high aromatic content may dissolve polyester, polypropylene and polycarbonate films. In these cases, other materials besides these films may be used for x-ray windows, provided that they do not contain any elemental impurities. An optional window material is 6-micrometer-thick polyimide foil. While polyimide foil absorbs sulfur x-rays more than other films, it may be a preferred window material as it is much more resistant to chemical attack by aromatics and exhibits higher mechanical strength.