ASTM D7328 Standard Test Method for Determination of Existent and Potential Inorganic Sulfate and Total Inorganic Chloride in Fuel Ethanol by Ion Chromatography Using Aqueous Sample Injection
7. Apparatus
7.1 Analytical Balance, at least 2000 g capacity, capable of weighing accurately to 0.01 g.
7.1.1 Analytical Balance, at least 100 g capacity, capable of weighing accurately to 0.0001 g.
7.2 Drying Oven, controlled at 110 °C +/- 5 °C for drying sodium sulfate and sodium chloride.
7.3 Desiccator, containing freshly activated silica gel (or equivalent desiccant) with moisture content indicator.
7.4 Pipettes or Volumetric Transferring Devices, Class A glass pipettes or their equivalent of 2.0 cc capacity or automatic pipettes fitted with disposable polypropylene tips.
7.4.1 Plastic Syringe, 10 cc disposable, optionally fitted with a 0.2 µm syringe filter (must be chloride and sulfate-free).
7.5 Volumetric Flask, Class A of1 L capacity and Class A of 10 mL capacity.
7.6 Ion Chromatograph, Analytical system with all required accessories including syringes, columns, suppressor, gases, and detector.
7.6.1 Injection System, capable of delivering 25 µL with a precision better than 1 %.
7.6.2 Pumping System, capable of delivering mobile phase flows between 0.5 mL/min and 1.5 mL/min with a precision better than 5 %.
7.6.3 Guard Column, for protection of the analytical column from strongly retained constituents. Better separations are obtained with greater separating power.
7.6.4 Anion Separator Column, capable of producing satisfactory analyte separation (see Fig. 1).
7.6.5 Anion Suppressor Device, micro membrane suppressor or equivalent. A cation exchange column in the hydrogen form has been used successfully, but it will periodically need to be regenerated as required. This is indicated by a high background conductivity and low analyte response.
7.6.6 Conductivity Detector, low volume (<2 µL) and flow, temperature compensated, capable of at least 0 µS/cm to 1000 µS/cm on a linear scale.
7.6.7 Integrator or Chromatography Data System Software, capable of measuring peak areas and retention times, and correcting the data according to the baseline of the chromatogram.
7.7 Gloves, powder-free examination type.
7.8 Hot Block, aluminum, capable of being heated to 65 °C with suitable holes to hold 15 mL glass vials, with a method of flowing nitrogen over inserted samples.
7.9 Glass Vials, 15 mL with screw top.
8. Reagents
8.1 Purity of Reagents - Reagent grade or higher purity chemicals shall be used for the preparation of all samples, standards, eluents, and regenerator solutions. 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 Purity of Water - Unless otherwise indicated, reference to water shall be understood to mean reagent water as defined by Type I in Specification D1193. For eluent preparation and handling, comply with all ion chromatograph instrument and column vendor requirements (for example, filtering, degassing, etc.).
8.3 Eluent Buffer Solution - The eluent solution used depends on the systems or analytical columns that are used (contact instrument and column vendors). For the chromatograms in Fig. 1, the following eluent buffer was used: Sodium bicarbonate (NaHCO3) 1.7 mM and sodium carbonate (Na2CO3) 1.8 mM. Dissolve 2.8563 g +/- 0.0005 g of NaHCO3 and 3.8157 g +/- 0.0005 g of Na2CO3 in reagent water in a 1 L Type A volumetric flask and dilute to volume. Dilute 100 mL of this concentrate to 2000 mL with reagent water for the final working eluent solution. Other volumes of stock solution may be prepared using appropriate ratios of reagents. Follow the specific guidelines for this solution from the vendor of the column being used. Alternatively, this solution can be purchased from a qualified vendor.
8.4 Suppressor Solution for Membrane Suppressor, 0.025 N sulfuric acid. Carefully add 13.7 mL of reagent grade sulfuric acid (relative density 1.84) to approximately 500 mL reagent water in a 1 L volumetric flask. (Warning - This will generate a very hot solution. Allow it to cool before diluting to 1000 mL volume. Never add water to concentrated acid!) Dilute to 1000 mL with reagent water, and label this solution as 0.50 N sulfuric acid. Dilute 100 mL of this concentrate to 2000 mL with reagent water for the final working suppressor solution. Other volumes of stock solution may be prepared using appropriate ratios of reagents. Follow the specific guidelines for this solution from the vendor of the column being used.
8.5 Sodium Sulfate, anhydrous, reagent grade, 99 % minimum purity. (Warning - Do not ingest; avoid unnecessary exposure.)
8.6 Sodium Chloride, ACS reagent grade, 99 % minimum purity.
8.7 Ethanol, denatured with methanol, formula 3A or histological grade ethanol, anhydrous, denatured with ethyl acetate, methylisobutyl ketone and hydrocarbon naphtha. (Warning - Flammable; toxic; may be harmful or fatal if ingested or inhaled; avoid skin contact.)
8.8 Hydrogen Peroxide Solution, 30 %, commercially available 30 % hydrogen peroxide solution.
8.9 Nitrogen Gas, 99.99 mol % pure, free of hydrocarbons.
