ASTM D7623 Standard Test Method for Total Mercury in Crude Oil Using Combustion-Gold Amalgamation and Cold Vapor Atomic Absorption Method
6. Apparatus
6.1 There are several configurations of the instrumental components that can be used satisfactorily for this test method. Functionally, the instrument shall have the following components: sample heating furnace, decomposition furnace, gold amalgamator, amalgamator furnace, measuring cuvettes, mercury lamp, and detector. The following requirements are specified for all approved instruments.
NOTE 2 - Approval of an instrument with respect to these functions is paramount to this test method, since such approval tacitly provides approval of both the materials and the procedures used with the system to provide these functions.
6.1.1 The instrument shall be capable of drying the sample once it is weighed and introduced.
6.1.2 The instrument shall have a decomposition tube, which shall be operated at a temperature high enough to completely decompose the sample. The suggested operating temperature is at least 700 °C.
6.1.3 The catalyst shall be capable of completing the oxidation of the sample and trapping halogens as well as nitrogen and sulfur oxides. The suggested operating temperature of the catalytic tube is 850 °C.
6.1.4 The instrument shall contain one or more gold amalgamator fixed to an inert material and shall be capable of trapping all mercury.
6.1.5 The amalgamator shall contain a furnace capable of rapidly heating the amalgamator to release all trapped mercury.
6.1.6 The instrument shall have an absorption cell through which the elemental mercury released from the gold amalgamator flows. The cell shall be heated to avoid any condensation of water or other decomposition products.
6.1.7 The light source for the atomic absorption process shall be a low pressure mercury lamp.
6.1.8 A narrow bandpass interference filter or monochromator, capable of isolating the 253.65 nm mercury line, shall be used.
6.1.9 The system may contain a computer for controlling the various operations of the apparatus, for recording data, and for reporting results.
6.2 Analytical Balance, with a sensitivity of 0.1 mg.
6.3 Sample Combustion Boats, porcelain, quartz, or other material as recommended and of convenient size suitable for use in the instrument being used.
6.4 Crucibles, porcelain, high-form, 40 mL capacity or suitable size for heating reagent in furnace.
6.5 Micropipettes, one or more units of variable volumes to cover a range of 10 µL to 250 µL. Appropriately sized tips should also be available.
6.6 Ultrasonic Homogenizer - A bath type ultrasonic homogenizer is used to dissociate particulate mercury and thoroughly mix the sample.
6.7 Electric Muffle Furnace, capable of maintaining 750 °C +/- 25 °C and sufficiently large to accommodate the sample boats and reagent containers.
6.8 Glassware, class A, volumetric flasks and pipettes of various capacities. All glassware must be thoroughly cleaned with freshly prepared 10 % nitric acid solution and rinsed with water. It is recommended that dedicated glassware be maintained to minimize cross contamination.
7. Sample
7.1 Obtain the analysis sample of crude oil in accordance with Practice D4057 or D4177. Crude oil should be collected in a manner that ensures a representative sample from the bulk container is obtained.
7.2 To prevent loss of mercury during storage and handling of samples, follow Practice D7482. Sample should not be collected in metal containers. Precleaned, glass volatile organic analysis (VOA) vials have been found to be suitable for this purpose.
7.3 Samples should be analyzed as quickly as possible after collection. Sample containers should be kept tightly capped and stored in a cool location free from direct sunlight.
8. Reagents
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 use without lessening the accuracy of the determination.
8.2 Purity of Water - Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to Type II of Specification D1193. Water must be checked for potential mercury contamination before use.
8.3 Air or Oxygen - Filtered, purified air or high purity oxygen, as specified by the instrument manufacturer, shall be used. The air must be mercury-free. Some instruments process incoming combustion air with filters and driers before it is used for the analysis.
8.4 Certified Reference Materials (CRMs) - Use Certified Reference Material (CRM) crude oils with mercury values for which confidence limits are issued by a recognized certifying agency such as the National Institute of Standards and Technology (NIST).
8.4.1 All CRMs, reference crude oils, or calibrating agents must have precision values of less than or equal to method repeatability. Such CRMS, reference crude oils, or calibrating agents must be stable and must be mixed thoroughly before each use.
8.5 L-cysteine, 99+ % purity. Reagents must be evaluated for mercury content by checking blank solutions for response on the instrument.
8.6 Nitric Acid, concentrated, Trace Metal Grade or better.
8.7 Mercuric Chloride, 99.99+ % purity. A commercially prepared mercury stock standard may be used.
8.8 Phosphate Buffer, pH 7.2. Some phosphate buffers use mercury compounds as preservative. The buffer must be mercury-free. Check with the instrument manufacturer for sources of suitable buffer.
8.9 Combustion Reagents:
8.9.1 Additive 1 or B (Aluminum Oxide), ground, available from instrument manufacturer.
8.9.2 Additive 2 or M, 40/60 m % mixture of calcium hydroxide and sodium carbonate available from instrument manufacturer.
8.9.3 Calcium Hydroxide, 99.5 % minimum purity.
8.9.4 Sodium Carbonate, 99.99 % minimum purity.
8.10 Glassine Weighing Paper.
