ASTM D5188 Standard Test Method for Vapor-Liquid Ratio Temperature Determination of Fuels (Evacuated Chamber and Piston Based Method)
8. Sampling
8.1 General:
8.1.1 Conduct bulk sampling to obtain the laboratory samples in accordance with Practice D4057 except for gasoline-oxygenate blends where water displacement is not used. The extreme sensitivity of T(V/L) 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. (Warning - Extremely flammable, harmful if inhaled or ingested. Skin irritant on repeated contact. Aspiration hazard.)

8.1.2 The size of the sample container from which the sample is taken shall be 1 L (1 qt). It shall be 70 % to 80 % filled with sample.

8.1.3 The precision statement will be derived using samples in 1 L (1 qt) containers. However, samples taken in containers of other sizes as prescribed in Practice D4057 can be used if it is recognized that the precision could be affected. In the case of referee testing, the 1 L (1 qt) sample is mandatory.

8.1.4 Perform the T(V/L) determination on the first test specimen withdrawn from the sample container. Do not use the remaining sample in the container for a second T(V/L) determination. If a second determination is necessary, obtain a new sample.

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

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

8.2 Sampling Handling Temperature - Place the sample container and contents in an ice bath or refrigerator to the 0 °C to 1 °C (32 °F to 34 °F) range prior to opening the sample container. Allow sufficient time to reach this temperature.

NOTE 6 - One way to verify the sample temperature is 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. Alternatively, temperature-monitoring studies conducted by laboratories have determined the minimum amount of time necessary to achieve the required temperature requirements stated in 8.2, based upon typical sample receipt temperatures and cooling capacities of the instrumentation employed by the laboratory on samples included in such studies. The results of such studies have subsequently been applied to additional samples submitted for analysis. Typical minimum time durations reported by laboratories have ranged between approximately 30 min and 45 min, however, laboratories choosing this option need to determine the minimum cooling time required for their specific operation by conducting their own temperature-monitoring study.

8.3 Verification of Sample Container Filling:
8.3.1 With the sample at a temperature of 0 °C to 1 °C, take the container from the cooling bath or refrigerator and wipe dry with 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 7). If the sample is contained in a transparent glass container, verify that the container is 70 % to 80 % full by suitable means (see Note 7).

8.3.2 Discard the sample if the container is filled to less than 70 % by volume of the container capacity.

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

NOTE 7 - 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 by comparing the sample container to a like container which has the 70 % and 80 % levels clearly marked, has been found suitable.

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

8.4 Air Saturation ofthe Sample in the Sample Container:
8.4.1 Transparent Container Only - Since 8.3.1 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. 8.4.2 With the sample again at a temperature of 0 °C to 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 vigorously. Return it to the bath or refrigerator for a minimum of 2 minutes.

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

9.2 Clean and dry, or rinse the test chamber to avoid contamination of the test sample.

9.3 When a vacuum pump is used for evacuation prior to sample introduction, visually determine from the instrument display that the test chamber pressure is stable and does not exceed 0.1 kPa (0.01 psia). If the pressure is not stable or exceeds this value, check that the chamber contains no volatile materials from a previous sample, the seals are satisfactory, the calibration of the transducer is correct, and the apparatus does not leak.

9.4 If a syringe is used for introduction of the sample specimen, chill the syringe to between 0 °C and 1.0 °C (32 °F to 34 °F) such as in a refrigerator or ice bath before drawing in the sample specimen. Water contamination of the syringe reservoir during this cooling procedure shall be avoided. One way to achieve this is by sealing the outlet of the syringe during the cooling process.

9.5 When a vacuum pump is used for evacuation prior to introduction of the test specimen, set the temperature of the test chamber to close to the expected result, if known; or 40 °C (104 °F), if unknown.

9.6 When a moveable piston is used for evacuation, set the temperature of the test chamber to close to 20 °C (68 °F) prior to introduction of the test specimen.

10. Calibration
10.1 Perform a calibration check of the pressure transducer as indicated by the performance check (see 10.3). The calibration of the transducer is accomplished using two reference points, zero pressure, and ambient barometric pressure.

NOTE 8 - Calibration frequency of the pressure transducer may vary with instrument type and frequency of use. A calibration check of the pressure transducer at least once every six months is recommended.

NOTE 9 - Pressure transducers can be sensitive to working temperature. Calibration should be performed at the test chamber temperature most frequently used.

10.1.1 Connect a McLeod gage or a calibrated electronic vacuum measuring device to the vacuum source in line with the test chamber. Apply vacuum to the test chamber. When the vacuum measuring device registers a pressure less than 0.1 kPa (0.8 mm Hg) adjust the indicator to zero or to the actual reading on the vacuum measuring device as dictated by the instrument design or manufacturer's instructions.

10.1.2 Open the test chamber to the atmosphere and observe the indicator reading. If the pressure reading is not equal to the ambient barometric pressure, adjust the indicator span control until the appropriate reading is observed. Ensure that the instrument is set to display the total pressure and not a calculated or corrected value.

10.1.3 Repeat 10.1.1 and 10.1.2 until the zero and barometric pressure read correctly without further adjustments.

10.2 Calibrate the platinum resistance thermometer and indicator used to monitor the temperature of the test chamber at least every six months against a National Institute of Standards and Technology (NIST) traceable thermometer.

10.3 Check the performance of the instrument each day it is in use by running one of the air saturated reference materials shown in Table 1. Handle the performance check material in the same manner as a sample (see Sections 8 and 12), except that for pure compounds (see 7.1), multiple test specimens may be taken from the same container over time, provided the test specimen is air-saturated according to the procedure given in 8.4 and the spent test specimens are not reused in whole or in part. Table 1 provides the accepted reference value (ARV) and acceptable testing range (at least 95 % confidence interval with 90 % coverage) of reference fluids tested in the 2015 ILS. If values outside the acceptable testing range intervals are obtained, verify the quality of the reference fluids and re-check the calibration of the instrument (see Section 10). Two component blends may be more sensitive to variations in the V/L setting than pure components.

NOTE 10 - Other pure compounds having vapor pressures within the range of fuels to be tested may be used.

11. Quality Control Checks
11.1 After having verified that the instrument is performing properly, use a quality control (QC) sample that is representative of the fuel(s) routinely tested by the laboratory to confirm that the instrument is in statistical control following the guidelines given in Practice D6299.

11.2 Record the T(V/L) temperature and compare this to the decision criteria for statistical control. If the result is found to be outside the decision criteria for statistical control, initiate an investigation for root causes.

11.3 Store the QC sample in an environment suitable for long-term storage without sample degradation.