General

This standard test method covers the colorimetric determination of phosphonate in the range of 0.1 to 5 mg/L in brines from oil and gas production operations, water injection/disposal operations, and other industrial applications. If the brine contains more than 5 mg/L phosphonate, the sample shall be diluted and analyzed by this procedure. Additional information can be found in API⁽³⁾ RP 45²

This standard is intended for use in analyzing low concentrations of phosphonate in brine containing interfering elements. This standard is most useful for analyzing phosphonate at 0.1 to 1 mg/L in brines with interfering elements. Typical interfering elements in high total dissolved solids (100,000 mg/L) brines include insoluble salts of calcium, barium, strontium, sulfate, sulfide, silicate, iron (Fe⁺²/Fe⁺³), oil droplets, orthophosphate, and turbidity. Personnel using this standard must have good analytical skills.

This standard includes a digestion step to break down the phosphonate materials to orthophosphate. The orthophosphate is then reacted with molybdate to form a phosphomolybdate (PO₃Mo₁₂O₃₆) complex. The complex is extracted into an organic phase and measured colorimetrically.

This standard is useful for the determination of phosphonate residuals. Treating chemicals that contain phosphonates are used as mineral scale and corrosion inhibitors in oil and gas production, water injection/disposal operations, and other industrial applications.

This standard has been used successfully with reagent water and both field and synthetic brines. It is the user's responsibility to ensure the validity of this standard for waters of untested matrices.

⁽³⁾ American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005-4070.

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