ASTM D6849-02(2007)

LPG samples can change composition during storage and use from preferential vaporization of lighter (lower molecular weight) hydrocarbon components, dissolved inert gases (N₂, Ar, He, and so forth) and other dissolved gases/liquids (NH₃, CO₂, H₂S, H₂O, etc.). Careful selection of cylinder type, cylinder volume, and use of inert gas for pressurizing cylinders is required to ensure that composition changes are small enough to maintain the integrity of LPG when used as a QC reference material for various LPG test methods.

Monitoring of ongoing precision and bias on QC materials using control chart techniques in accordance with Practice D 6299 can be used to establish the need for calibration or maintenance.

1.1 This practice covers information for the storage and use of LPG samples in standard cylinders of the type used in sampling method, Practice D 1265 and floating piston cylinders used in sampling method, Practice D 3700.

1.2 This practice is especially applicable when the LPG sample is used as a quality control (QC) reference material for LPG test methods, such as gas chromatography (GC) analysis (Test Method D 2163) or vapor pressure (Test Method D 6897) that use only a few mL per test, since relatively small portable Department of Transportation (DOT) cylinders (for example, 20 lb common barbecue cylinders) can be used. This practice can be applied to other test methods. However, test methods that require a large amount of sample per test (for example, manual vapor pressure Test Method D 1267) will require QC volumes in excess of 1000 L if stored in standard DOT cylinders or American Society of Mechanical Engineers (ASME) vessels.