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D4530_8 (15)

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Determine the mass of each clean sample vial being used in the sample analysis and record the mass to nearest 0.1 milligrams. During weighing and filling, handle vials with forceps to help minimize weighing errors. Discard the sample vials after use. It is assumed that a representative sample of the stock or process has been obtained for laboratory use following practice D4057 or similar standard. Stir the sample to be tested, first warming, if necessary, to reduce its viscosity. Samples that are homogeneous liquids can be transferred directly to vials using a rod, syringe, or eyedropper. Solid materials may also be heated or frozen with liquid nitrogen, and then shattered to provide manageable pieces. Transfer an appropriate mass of the sample-- see Table 1 of the written standard-- into a tared sample vial. Reweigh to nearest 0.1 milligrams and record. Place the loaded sample vials into vial holder-- up to 12-- noting position of each sample with respect to index mark. A control sample can be included in each batch of samples being tested. This control sample should be a typical sample that has been tested at least 20 times in the same equipment in order to define an average percent carbon residue and standard deviation. Results for each batch are deemed acceptable when results for the control sample fall within the average percent carbon residue, plus or minus three standard deviations. Control results that are outside these limits indicate problems with the procedure or the equipment. With the oven at less than 100 degrees Celsius, place the vial holder into the oven chamber and secure lid. Purge with nitrogen for at least 10 minutes at 600 milliliters per minute, then decrease the purge to 150 milliliters per minute. And heat the oven slowly to 500 degrees Celsius at 10 to 15 degrees Celsius per minute. If the sample foams or spatters, causing loss of sample, discard and repeat the test. Spattering may be due to water that can be removed by prior gentle heating in a vacuum, followed by a nitrogen sweep. Alternatively, a smaller sample size can be used. Hold oven at 500, plus or minus 2 degrees Celsius, for 15 minutes. Then, shut off furnace power and allow oven to cool freely while under nitrogen purge of 600 milliliters per minute. When oven temperature is less than 250 degrees Celsius, remove the vial holder for further cooling in desiccator. After the samples are removed from the oven, the nitrogen purge may be shut off. Warning, do not open oven to air at any time during the heating cycle. The introduction of air-- oxygen-- will likely cause the sample to ignite and spoil the test. Because of the oven design and materials, such an ignition is normally not a hazard to the operator. Open the oven only after oven temperature falls below 250 degrees Celsius during the cooling step. Maintain nitrogen flow until after the vial holder has been removed from the oven. Warning, locate the cooking oven in laboratory exhaust hood for safe venting of smoke and fumes. Alternatively, install vent line from MCRT of an exhaust to laboratory exhaust system. Warning, if a vent line is used, do not connect directly to exhaust chimney to avoid creating negative pressure in the line. To reduce oven temperature for the next run, remove the oven lid to allow faster cooling, as required by the procedure. The subsequent test can be started when the oven has been cooled to below 100 degrees Celsius. Transfer sample vials maintained in place in the vial holder to desiccator, and allow vials to cool to room temperature. Weigh the cooled vials to the nearest 0.1 milligrams and record. Handle the vials with forceps. Discard the used glass sample vials. Occasionally, examine the condensate trap at the bottom of the oven chamber. Empty if necessary and replace. Warning, the condensate trap residue may have some carcinogenic materials present. Avoid contact with the trap residue. Dispose of it in accordance with local laboratory practice.

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Duration: 5 minutes and 33 seconds
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Language: English
License: Dotsub - Standard License
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Views: 5
Posted by: abuckmaster on Aug 23, 2018

D4530_8 (15)

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