ASTM D5482 Standard Test Method for Vapor Pressure of Petroleum Products (Mini Method - Atmospheric)
8. Sampling
8.1 General Requirements:
8.1.1 The extreme sensitivity of vapor pressure measurements to losses through evaporation and the resulting changes in composition is such as to require the utmost precaution and the most meticulous care in the handling of samples.

8.1.2 Obtain a sample and test specimen in accordance with 10.3 of Practice D4057, except do not use 10.3.1.8 of Practice D4057, Sampling by Water Displacement, for fuels containing oxygenates. Use a 1-L (1-qt) sized container filled between 70 to 80 % with sample.

8.1.3 Perform the vapor pressure determination on the first test specimen withdrawn from a sample container. Do not use the remaining sample in the container for a second vapor pressure determination. If a second determination is necessary, obtain a new sample.

8.1.4 Protect samples from excessive temperatures prior to testing. This can be accomplished by storage in an appropriate ice bath or refrigerator.

8.1.5 Do not test samples stored in leaky containers. Discard and obtain a new sample if leaks are detected.

8.1.6 Do not store samples in plastic (polyethylene, polypropylene, and so forth) containers since volatile materials may diffuse through the walls of the container.

8.2 Sampling Temperature - Cool the sample container and contents in an ice bath or refrigerator to the 0 to 1°C (32 to 34°F) range prior to opening the sample container. Allow sufficient time to reach this temperature. Verify the sample temperature by direct measurement of the temperature of a similar liquid in a similar container placed in the cooling bath or refrigerator at the same time as the sample.

8.3 Verification of Sample Container Filling - With the sample at a temperature of 0 to 1°C, take the container from the cooling bath or refrigerator and wipe dry with an absorbent material. If the container is not transparent, unseal it and using a suitable gage, confirm that the sample volume equals 70 to 80 % of the container capacity (see Note 3). If the sample is contained in a transparent glass container, verify that the container is 70 to 80 % full by suitable means (see Note 3).
8.3.1 Do not perform a vapor pressure test on the sample if the container is filled to less than 70 volume % of the container capacity.

8.3.2 If the container is more than 80 volume % full, pour out enough sample to bring the container contents within the 70 to 80 volume % range. Do not return any sample to the container once it has been withdrawn.

NOTE 3 - For non-transparent containers, one way to confirm that the sample volume equals 70 to 80 % of the container capacity is to use a dipstick that has been pre-marked to indicate the 70 and 80 % container capacities. The dipstick should be of such material that it shows wetting after being immersed and withdrawn from the sample. To confirm the sample volume, insert the dipstick into the sample container so that it touches the bottom of the container at a perpendicular angle, before removing the dipstick. For transparent containers, using a marked ruler or comparing the sample container to a like container that has the 70 and 80 % levels clearly marked, has been found suitable.

8.3.3 Reseal the container, if necessary, and return the sample container to the cooling bath or refrigerator.

8.4 Air Saturation of the Sample in the Sample Container:
8.4.1 Non-transparent Containers - With the sample again at a temperature between 0 and 1°C, take the container from the cooling bath or refrigerator, wipe it dry with an absorbent material, remove the cap momentarily, taking care that no water enters, reseal, and shake it vigorously. Return it to the cooling bath or refrigerator for a minimum of 2 min.

8.4.2 Transparent Containers - Since 8.3 does not require that the sample container be opened to verify the sample capacity, it is necessary to unseal the cap momentarily before resealing it so that samples in transparent containers are treated the same as samples in non-transparent containers. After performing this task, proceed with 8.4.1.

8.4.3 Repeat 8.4.1 twice more. Return the sample to the bath or refrigerator until the beginning of the procedure.

8.5 Verification of Single Phase Samples - After drawing a test specimen and injecting it into the instrument for analysis, check the remaining sample for phase separation. If the sample is contained in a transparent container, this observation can be made prior to sample transfer. When the sample is contained in a non-transparent container, mix the sample thoroughly and immediately pour a portion of the remaining sample into a clear glass container and observe for evidence of phase separation. A hazy appearance is to be carefully distinguished from separation into two distinct phases. The hazy appearance shall not be considered grounds for rejection of the fuel. If a second phase is observed, discard the test and the sample. Hazy samples may be analyzed (see Report section).

9. Preparation of Apparatus
9.1 Prepare the instrument for operation in accordance with the manufacturer's instructions.

9.2 Prepare the sample introduction accessories, if required, in accordance with the manufacturer's instructions.

9.3 Chill the sample syringe to between 0 and 4.5°C (32 and 40°F) in a refrigerator or ice bath. Avoid water contamination of the syringe reservoir by suitably sealing the outlet of the syringe during the cooling process.

9.4 Clean and dry the test chamber in accordance with the manufacturer's instructions. With the test chamber sealed, observe that the instrument display is stable and does not exceed 0.00 +/- 0.20 kPa (0.00 +/- 0.03 psi).

9.5 If in doubt of the cleanliness of the cell, refer to the cleaning procedure in the manufacturer's instructions, or if the display does not return to zero, refer to the calibration procedure in the manufacturer's instructions.

9.6 Verify that the temperature of the test chamber is within the required range from 37.8 +/- 0.1°C (100 +/- 0.2°F).

10. Calibration
10.1 Pressure Transducer:
10.1.1 Check the calibration of the transducer in accordance with the manufacturer's instructions on a monthly basis or when needed as indicated from the quality control checks (see Section 11). The calibration of the transducer shall be checked using two reference points, ambient barometric pressure, and a pressure above ambient pressure, determined by the operator, which is at least 80 % of the expected maximum pressure encountered during the test.

10.2 Temperature Measuring Device - Check the calibration of the temperature measuring device used to monitor the temperature of the test chamber at least every six months against a thermometer traceable to a national standard.

11. Quality Control Checks
11.1 Use a verification fluid with known volatility as an independent check against the instrument calibration each day the instrument is in use. For pure compounds (see 7.1), multiple test specimens may be taken from the same container over time, provided the pure compound is air saturated in accordance with the procedure given in 8.4, and the spent test specimens are not re-used, in whole or in part. If the observed vapor pressure differs from the reference value by more than 1.0 kPa (0.15 psi), then check the instrument calibration (Section 9).

11.2 Some possible materials and their corresponding vapor pressures, as found in DS 4B, include: cyclopentane, 68.3 kPa (9.91 psi); 2,2-dimethylbutane, 68.0 kPa (9.86 psi); 2,3-dimethylbutane, 51.1 kPa (7.41 psi); 2-methylpentane, 46.7 kPa (6.77 psi); and toluene, 7.1 kPa (1.03 psi).

NOTE 4 - It is recommended that at least one type of control sample used in 10.1 be representative of the samples regularly tested by the laboratory. The total vapor pressure measurement process (including operator technique) can be checked periodically by performing this test method on previously prepared samples from one batch of product, in accordance with the procedure described in 8.1.2. Samples should be stored in an environment suitable for long term storage without sample degradation. Analysis of results from these quality control samples can be carried out using control chart techniques 7 or other statistically equivalent techniques.