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D1319_10 (15)

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Ensure that the silica gel is tightly packed in the column and charger section (up to the appropriate level), which includes the appropriate amount of dyed gel (3 millimeters to 5 millimeters) added to an approximately half-full separator section, prior to the start of sample analysis. See Note 3 for specific guidance. One way to prepare the column for analysis is to freely suspend the column from a loose-fitting clamp placed immediately below the pressuring gas connection of the charger section. While vibrating the column along its entire length, add small increments of silica gel through a glass funnel into the charger section until the separator section is half full. Stop the vibrator and add a 3 millimeter to 5 millimeter layer of dyed gel. Start the vibrator and vibrate the column while adding additional silica gel. Continue to add silica gel until the tightly packed gel extends approximately 75 millimeters into the charger section. Wipe the length of the column with a damp cloth while vibrating the column. This aids in packing the column by removing static electricity. Vibrate the column after filling is completed for at least 4 minutes. More than one column can be prepared simultaneously by mounting several on a frame or rack to which an electric vibrator is attached. Attach the filled column to the apparatus assembly in the darkened room or area, and when a permanently mounted meter rule is used, fasten the lower end of the column to the fixed rule. For samples that would meet volatility conditions of Group 2 or less of Test Method D86, chill the sample and a hypodermic syringe to less than 4ÂșC. Draw 0.75 milliliters, plus or minus 0.03 milliliters, of sample into the syringe and inject the sample approximately 30 millimeters below the surface of the gel in the charger section. Fill the charger section to the spherical joint with isopropyl alcohol. Connect the column to the gas manifold and apply 14 kilopascals plus or minus 2 kilopascals gas pressure for 2.5 minutes plus or minus 0.5 minutes to move the liquid front down the column. Increase the pressure to 34 kilopascals plus or minus 2 kilopascals, gauge for another 2.5 minutes plus or minus 0.5 minutes and then adjust the pressure required to give a transit time of about one hour. Usually a gas pressure of 28 kilopascals to 69 kilopascals gauge is needed for gasoline-type samples and 69 kilopascals to 103 kilopascals gauge for jet fuels. The pressure required will depend on the tightness of packing the gel and the molecular weight of the sample. A transit time of one hour is optimal; however, high-molecular weight samples may require longer transit time. After the red, alcohol-aromatic boundary has advanced approximately 350 millimeters into the analyzer section, make a set of readings by quickly marking the boundary of each hydrocarbon zone observed in ultraviolet light in the following sequence. (Warning Direct exposure to ultraviolet light can be harmful, and operators should avoid this as much as possible, particularly with regard to their eyes.) For the non-inflourescence saturate zone, mark the front of the charge and point where the yellow fluorescence first reaches its maximum intensity; for the upper end of the second, or olefin zone, mark the point where the first intense blue fluorescence occurs; finally, for the upper end of the third, or aromatic zone, mark the upper end of the first reddish or brown zone. Refer to Figure 3 as an aid in identifying the boundaries. With colorless distillates, the alcohol-aromatic boundary is clearly defined by a red ring of dye. However, impurities in cracked fuels often obscure this red ring and give a brown coloration, which varies in length, but which shall be counted as part of the aromatic zone, except that when no blue fluorescence is present, the brown or reddish rings shall be considered as part of the next distinguishable zone below it in the column. With some oxygenate blended fuel samples, another red band may appear several centimeters above the reddish or brown alcohol aromatic boundary (see Figure 4 of the written standard) and shall be ignored. Avoid touching the column with the hands while marking the zones. If the boundaries have been marked off with index clips, record the measurements. The first maximum intense yellow fluorescence is defined to be the center of the lowest intense yellow fluorescent band. When the sample has advanced at least another 50 millimeters down the column, make a second set of readings by marking the zones in reverse order as described in Section 10.5 of the written standard so as to minimize errors due to the advancement of boundary positions during readings. If the marking has been made with a glass writing pencil, two colors can be used to mark off each set of measurements and the distances measured at the end of the test with the analyzer section lying horizontally on the bench top. If the boundaries have been marked off with index clips, record the measurements. Erroneous results can be caused by improper packing of the gel or incomplete elution of hydrocarbons by the alcohol. With precision bore columns, incomplete elution can be detected from the total length of the several zones, which must be at least 500 millimeters for a satisfactory analysis. With standard wall tubing, this criterion of total sample length is not strictly applicable because the inside diameter of the analyzer section is not the same in all columns. For information regarding the cleaning process of precision bore columns, reference section 10.8 of the written standard.

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Duration: 6 minutes and 33 seconds
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Posted by: abuckmaster on Aug 23, 2018

D1319_10 (15)

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