ASTM D2158 Standard Test Method for Residues in Liquefied Petroleum (LP) Gases
7. Apparatus
7.1 Centrifuge Tube, 100-mL graduated, conforming to dimensions given in Fig. 1. The first 0.5 mL shall be graduated in 0.05-mL increments. The shape of the lower tip of the tube is especially important. The taper shall be uniform and the bottom shall be rounded as shown in Fig. 1. Tubes shall be made of thoroughly annealed heat-resistant glass. Volumetric graduation tolerances, based on air-free water at 20°C, are given in Table 1. Detailed requirements for centrifuge tubes appear in Test Methods D96 and D1796.
7.2 Cooling Coil and Cooling Bath, a minimum length of 6 m of 5 to 7-mm outside diameter copper tubing wound to a diameter of 63.5 +/- 1.5-mm outside diameter, and assembled in a suitable cooling bath. (See Fig. 2 as an example.)
7.2.1 Mechanical refrigeration is permitted provided that the coolant temperature is below -43°C. If dry ice is used, a non-glass dewar or vessel is recommended.
7.3 Syringe, 2-mL graduated in 0.1 mL and equipped with a needle 200 +/- 5 mm long. The needle may be either a sharp needle (ordinary medical syringe needle) or a safe, non-sharp syringe needle to avoid a puncture hazard. Alternatively, an equivalent liquid dispensing device capable of delivering 0.1-mL increments may be used, such as a 0.1-mL pipette.
7.4 Temperature Measuring Device, that is intrinsically safe, with accuracy equal to or better than Specification E1 or IP Test Methods - Appendix A shall be used. Thermometers conforming to Specification E1 or IP Appendix A have been found to be satisfactory.
Low Range, -38°C to + 50°C, IP 1C/ASTM 5C or IP 2C/ASTM 6C
High Range, -20°C to + 50°C, ASTM 57C
NOTE 1 - When a thermometer or a water bath, or both, are not available, for example when conducting a field test, a satisfactory alternative for screening purposes is to warm the tip of the centrifuge tube with the hand.
7.4.1 For routine testing, a general purpose thermometer with 0.5°C subdivisions and a maximum scale error of 0.5°C may be used.
7.5 Absorbent Paper, white, at least 100-mm diameter. Medium grade or rapid filter paper has been found to be satisfactory. In this test method, the paper will be referred to as "filter paper".
7.6 Solvent Wash Bottle, typically polyethylene.
7.7 Water Bath, controlled at 38 +/- 2°C.
7.8 Copper Wire, 1 to 2-mm diameter, at least 10 mm longer than the centrifuge tube's height.
7.9 Clamp, suitable for holding the centrifuge tube during weathering.
8. Reagents and Materials
8.1 Solvent - HPLC-grade pentane or cyclopentane. Another grade of solvent may be used provided that it meets the requirements of 10.2.
8.1.1 Although pentane is the preferred solvent for use in this test method, cyclopentane may be substituted for pentane whenever the ambient temperature or altitude is too high to enable the convenient handling of pentane.
8.1.2 Storage of solvent in a polyethylene wash bottle for several days contaminates the solvent. Therefore, do not use any solvent that has remained in a polyethylene wash bottle for more than one day.
9. Hazards
9.1 Note that there is a significant fire hazard from LPG vapors, and since the boiling point of LPG can be as low as -41°C, there is a risk of freezing "burns". Take appropriate safety precautions to prevent ignition or fire, and wear suitable protective equipment to protect against skin contact with liquid or vaporizing LPG.
9.2 Operators should wear a grounded antistatic wrist strap. The use of an antistatic floor mat and grounding the sample cylinder are also advised.
