ASTM D7318 Standard Test Method for Existent Inorganic Sulfate in Ethanol by Potentiometric Titration
6. Apparatus
6.1 Potentiometric Titration Assembly - A titration assembly consisting of an automatic titrator fitted with a lead ion-selective electrode, a double-junction reference electrode, buret, and stirring is used. Stirring may be accomplished by means of magnetic or propeller type stirrer mechanisms. The buret size should ideally be 10 or 20 mL.
6.2 Reference Electrode - A double junction reference electrode with the inner electrode composed of silver/silver chloride with a potassium chloride solution as internal electrolyte. The external solution is composed of 1 M lithium chloride in ethanol. This configuration is used to prevent silver ion, a lead electrode poison, from leaching into the analyte solution during titration. Preferred electrolytes for use in double junction electrodes may vary with the manufacturer; use the manufacturer's recommended electrolytes for the application. Other types of reference electrodes may be considered with some caveats (for example, single junction, combination, or glassy carbon), but the data presented in this test method were generated using exclusively a double junction electrode, which is the best choice for this determination.
6.3 Lead Electrode - A lead sulfide–based crystalline sensor type lead ion selective electrode (ISE) is used.
6.4 Drying Oven - A drying oven for drying sodium sulfate at 110°C is required.
6.5 Pipets or Volumetric Transferring Devices - Class A glass pipets or their equivalent.
6.6 Polishing Material - Lead sulfide based crystalline sensor electrodes require polishing to remove oxidation products. These materials are supplied with the electrode from the manufacturer.
6.7 pH Test Strips - Test strips in the range of pH 1 to pH 7.
6.8 Titration Vessels - Standard glass beakers or titration vessels supplied with titration equipment.
7. Reagents and Materials
7.1 Lead Nitrate - Reagent grade, 99% minimum purity. (Warning - Poison, harmful by inhalation and if ingested. Avoid contact with the skin.) Dispose of this material in accordance with accepted local requirements.
7.2 Sodium Sulfate - Anhydrous, reagent grade, 99% minimum purity. (Warning - Do not ingest. Avoid unnecessary exposure.)
7.3 Perchloric Acid 70% - A.C.S. reagent grade, minimum purity with sulfate concentration <0.001% (m/M). Dispose of this material in accordance with accepted local requirements. It must contain no measurable sulfate. (Warning - Corrosive; keep away from skin and eyes. Perchloric acid is a strong oxidizer.)
7.4 Ethanol - Denatured with methanol, formula 3A or histological grade ethanol, anhydrous, denatured with ethyl acetate, methyl isobutyl ketone and hydrocarbon naphtha. It must be free of any measurable sulfate. (Warning - Flammable, toxic, may be harmful or fatal if ingested or inhaled. Avoid skin contact.)
7.5 Ethanol - Absolute, 200 proof, 99.5%, A.C.S. reagent grade.
7.6 Lithium Chloride - 99+%, A.C.S. reagent grade.
7.7 Water - Type III reagent water conforming to Specification D1193.
7.8 Anhydrous Calcium Sulfate Desiccant.
