ASTM D7303 Standard Test Method for Determination of Metals in Lubricating Greases by Inductively Coupled Plasma Atomic Emission Spectrometry
7. Apparatus
7.1 Analytical Balance, capable of weighing to 0.001 g or 0.0001 g, capacity of 150 g.
7.2 Inductively Coupled Plasma Atomic Emission Spectrometer - Either a sequential or simultaneous spectrometer is suitable, if equipped with a quartz ICP torch and RF generator to form and sustain the plasma. Suggested wavelengths for the determination of elements in dissolved grease solutions are given in Table 2.
7.3 Peristaltic Pump, (Recommended) - A peristaltic pump is strongly recommended to provide a constant flow of solution. The pumping speed must be in the range of 0.5 to 3 mL/min. The pump tubing must be able to withstand at least 6 h exposure to solutions.
7.4 Specimen Solution Containers, of appropriate size, glass or polyolefin vials or bottles, with screw caps without metal liners.
8. Reagents and Materials
8.1 Purity of Reagents - Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
8.2 Sulfuric Acid, concentrated sulfuric acid, H2SO4. (Warning - Causes severe burns. Corrosive.)
8.3 Nitric Acid, concentrated nitric acid, HNO3. (Warning - Causes severe burns. Corrosive.)
8.4 Hydrochloric Acid, concentrated hydrochloric acid, HCl. (Warning - Causes burns.)
8.5 Hydrofluoric Acid, concentrated hydrofluoric acid, HF. (Warning - Causes severe burns.)
8.6 Aqueous Standard Solutions, individual aqueous elemental standards with 100 mg/L concentrations ofelements of interest. These can be prepared by dissolving pure metal compounds in water or dilute acids, or may be purchased from commercial sources.
8.6.1 Multi-element aqueous standards may be advantageous to use.
8.6.2 Internal Standard, aqueous cobalt, indium, scandium, yttrium or other single element standard, not a component of the grease test specimen or calibration standard, nominal 500 mg/kg concentration.
8.7 Water, distilled or deionized water, unless otherwise indicated, references to water shall be understood to mean Type II reagent grade water as defined in Specification D1193.
8.8 Quality Control (QC) Samples, preferably are portions of one or more grease materials that are stable and representative of the samples of interest. These QC samples can be used to check the validity of the testing process as described in Section 15.
8.9 Microwave Oven, commercially available laboratory microwave digestion oven of sufficient power (for example, at least 1000 W) is suitable. The microwave digestion dishes are also commercially available. (Warning - Take all necessary precautions to prevent exposure to radiofrequency radiation.)
8.10 Microwave Sample Digestion System, with closed-vessel silicon-free polytetrafluoroethylene (PTFE) digestion vessels. The vessels need to be capable of withstanding the pressure generated from the digestion of 0.2 g of sample (pressure achieved with a 100 mL vessel and 0.2 g of sample could be in excess of 100 psi). Microwave digestions systems with temperature and pressure monitoring are recommended for safety and accuracy of sample preparation.
8.11 The test method requires essentially microwave transparent and reagent resistant suitably inert polymeric materials (examples are PFA or TFM) to contain acids and samples. For higher pressure capabilities the vessel may be contained within layers of different microwave transparent materials for strength, durability, and safety. The vessels internal volume should be at least 45 mL, capable of withstanding pressures of at least 30 atm (30 bar or 435 psi), and capable of controlled pressure relief. These specifications are given to provide an appropriate, safe, and durable reaction vessel of which there are many adequate designs by many suppliers.
8.12 Rotating Turntable, to insure homogeneous distribution of microwave radiation within most systems. The speed of the turntable should be a minimum of 3 rpm.
8.13 Combustion Dishes, Vycor or platinum evaporation dishes of 250 mL size.
8.14 Volumetric Flasks, polypropylene or similar material of 25 and 50 mL sizes.
8.15 Electric Muffle Furnace, capable of maintaining 525 +/- 25°C and sufficiently large to accommodate several 250 mL beakers. The capacity of an oxygen bleed is advantageous and optional. (Warning - Take all necessary precautions to prevent exposure to very hot surfaces.)
8.16 Heating Lamp, commercial infrared heating lamp.
