scope:

This standard covers the colorimetric determination of phosphonate in the range of 0.1 to 5 mg/L in brines from gas and oil 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(footnote 4) RP 45.

This test method is intended for use in analyzing low concentrations of phosphonate in brine containing inter- fering elements. This test method 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, orthophos- phate, and turbidity. Personnel using this test method must have good analytical skills.

This test method 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 color- imetrically.

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

This test method 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 test method for waters of untested matrices.

Footnote 4 - American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005.