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
11. Quality Control Checks
11.1 Confirm the instrument is in statistical control at least once a week when it is in use, by analyzing a quality control (QC) sample that is representative of samples typically analyzed. Analysis of a single QC sample can be sufficient. Analysis of QC sample results can be carried out using control chart techniques. If the QC sample result determined causes the lab to be in an out-of-control situation, such as exceeding the lab's control limits, instrument recalibration or adjustment is required. An ample supply of QC sample material should be available for the intended period of use, and must be homogeneous and stable under the anticipated storage conditions. Prior to monitoring the measurement process, the user of the method needs to determine the average and control limits of the QC sample. The QC sample precision should be checked against the method precision to ensure data quality.
11.2 Although not mandatory, it is recommended that periodic analyses of certified density standards (i.e., traceable to national standards) that are separate from those that may be used in calibrating the instrument, be used to confirm testing accuracy.
