ASTM D4052 for density, relative density and API gravity of liquids
ASTM D4052 standard test method for density, relative density, and API gravity of liquids by digital density meter
12. Procedure
12.1 Manual Injection:
12.1.1 Introduce a small amount (about 1 to 2 mL) of sample into the clean, dry sample tube of the instrument using a suitable syringe or alternative, as described in 6.4.
12.1.2 The sample can also be introduced by siphoning. Plug the external TFE-fluorocarbon capillary tube into the entry port of the sample tube. Immerse the other end of the capillary in the sample and apply suction to the other port using a syringe or vacuum line until the sample tube is properly filled (see Note 1).
12.1.3 Turn on the illumination light and examine the sample tube carefully. Make sure that no bubbles are trapped in the tube, and that it is filled to just beyond the suspension point on the right-hand side. The sample must be homogeneous and free of even the smallest bubbles. If bubbles are detected, empty and refill the tube and recheck for bubbles.
NOTE 4 - If the sample is too dark in color to determine the absence of bubbles with certainty, the density cannot be measured within the stated precision limits of Section 15.
12.1.4 For most instrument models, it is recommended to turn the illumination light off with minimal delay after sample introduction and checking for bubbles because the heat generated can affect the measurement temperature. For newer models however, the cell light may be left on without affecting results. Refer to the manufacturer's recommendations concerning whether to leave the illumination light off or on.
12.1.5 After the instrument displays a steady reading to four significant figures for density, relative density, or API Gravity, and five for T-values, indicating that temperature equilibrium has been reached, record the density, relative density, API Gravity or T-values, or both, as appropriate. For instruments that can print out results from the display, the print out can be used to meet the recording requirements.
12.1.6 Based on the 1999 ILS testing protocols (see Note 6), precision determinations involving a single manual injection, as well as taking the average of two manual injections, was evaluated. See the Precision and Bias section for more details. If the lab performs a single manual determination, the density, relative density, or API Gravity values recorded in 12.1.5, or a combination thereof, is to be used for reporting purposes. In most cases, a single manual injection determination is sufficient for sample analysis.
12.1.6.1 If the lab decides to perform a second manual injection determination for a given sample, repeat 12.1.1-12.1.5. If the two determinations do not differ by more than 0.0002 g/mL for density or 0.0002 for relative density, average the two determinations, otherwise, discard both determinations and repeat the analysis using two new test specimens until the acceptance criteria identified above is satisfied. With respect to API Gravity determinations of gasoline or RFG samples, if the two determinations do not differ by more than 0.05° API Gravity units, average the two determinations, otherwise, discard both determinations and repeat the analysis using two new test specimens until the acceptance criteria is satisfied. With respect to API Gravity determinations of distillates, basestocks, and lubricating oils, follow the protocol in the prior sentence except use 0.03° API Gravity units as the acceptance criteria. Averaged results meeting the criteria identified in this section is to be used for reporting purposes.
12.2 Automated Injection:
12.2.1 The use of an autosampler (see 6.5) is required when analyzing samples by automated injection. Follow manufacturer's instructions for ensuring the integrity of the test specimen prior to analysis, as well as transferring a representative test specimen into the instrument for analysis.
12.2.2 When using an autosampler, it is required, based on the results obtained in the 1999 ILS6 to analyze gasoline or RFG samples using two separate test specimens per sample, in order that errors due to potential sample handling of volatile materials and potential bubble formation may be detected and the system performance monitored. For all other sample types, a single determination using an autosampler is sufficient.
12.2.2.1 If the lab decides to perform a second automated injection determination for a given distillate, basestock, or lubricating oil (see Note 6 and the Precision and Bias section), use the same acceptance criteria in 12.1.6.1 for allowed differences between each determination for density (0.0002 g/mL), relative density (0.0002) and API Gravity units (0.03°) as for manually injected samples. Averaged results meeting the necessary acceptance criteria are to be used for reporting purposes.
12.2.3 For determining the density or relative density of gasoline or RFG samples analyzed by automated injection, average the results of the two separate test specimens analyzed in 12.2.2 if the two determinations are within 0.0002 mg/L of one another for density (or 0.0002 for relative density). If the two determinations fall outside this acceptance criteria, both determinations are to be discarded and 12.2.2 shall be repeated until the acceptance criteria identified in the previous sentence is satisfied. In cases where the acceptance criteria is not initially satisfied, the lab may need to investigate and take corrective actions before proceeding with subsequent analyses.
12.2.4 For determining the API Gravity of gasoline or RFG samples analyzed by automated injection, follow the same protocol defined in 12.2.3, except that the acceptance criteria for the results of the two determinations for API Gravity are to be within 0.05° API Gravity units before averaging and reporting the results.
12.2.5 Record the density, relative density, or API Gravity results, or a combination thereof, determined by the analyses as appropriate, such as by using the instrument print out of results to meet the recording requirements.
