ASTM D7622 Standard Test Method for Total Mercury in Crude Oil Using Combustion and Direct Cold Vapor Atomic Absorption Method with Zeeman Background Correction
6. Apparatus
6.1 General configuration of the instrument shall have the following functional components: temperature controlled sample heating and decomposition furnace, measuring cuvettes, mercury lamp placed in strong magnetic field, polarization modulator to separate analytical and reference lines, and detector. The following requirements are specified for all approved instruments.
NOTE 2 - The 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 Zeeman Mercury Spectrometer - Atomic absorption spectrometer with Zeeman background correction, operating with the mercury resonance absorption wavelength of 253.7 nm.
6.1.2 The atomizer 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 600 °C.
6.1.3 The heated analytical cell shall be capable to prevent mercury loses due to deposition to cold parts and to prevent mercury recombination with chlorine. The suggested operating temperature of the analytical cell is at least 700 °C.
6.1.4 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 Boats, quartz, stainless steel, porcelain, or other material as recommended and convenient size suitable for use in the instrument being used.
6.4 Micropipetters, one or more units of variable volume to cover a range from 10 µL to 250 µL, NIST traceable. Appropriately sized tips should also be available.
6.5 Ultrasonic Homogenizer - A bath-type ultrasonic homogenizer is used to dissociate particulate mercury and thoroughly mix the sample.
6.6 Glassware, volumetric flasks of various capacities and Class A 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 of the bulk container is obtained.
7.2 To prevent loss of mercury during storage and handling of samples, follow Practice D7482. Samples 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.
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 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 A standard sample of mercury ions solution (concentration C1 = 1.0 g/L).
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).
8.5 Nitric Acid, concentrated, Trace Metal Grade or better.
8.6 Combustion Reagents, activated charcoal, 30 x 50 mesh.
8.7 Potassium Dichromate Solution, 4 % (mass) - Place a 4 g portion of potassium dichromate in a volumetric flask (volume of 100 mL), dissolve in distilled water and dilute with the distilled water up to the mark. The solution is to be stored in a reservoir made of dark glass with a plug stopper. Storage time is 3 months.
8.8 Dilution Solution - Place 500 mL to 600 mL of distilled water in a heat-resistant glass and pour in carefully 50 mL of concentrated nitric acid (d = 1.37 g/mL). Stir constantly while pouring in the acid. Transfer to a volumetric flask of 1000 mL volume, add 5 mL of 4 % potassium dichromate solution and add up with distilled water up to the mark. The solution is to be stored in a reservoir made of dark glass with a plug stopper. Storage time is 3 months.
8.9 All CRMs, reference crude oils, or calibrating agents shall 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.
