This test method is useful for the determination of trace level phosphonate residues in brines. Chemical treatment which contain phosphonates are used as mineral scale and corrosion inhibitors in gas and oil drilling and production operations; and other industrial applications. Often, the decision for treatment is based on the ability to measure low phosphonate concentration and not upon performance criteria. Phosphonate concentrations as low as 0.16 mg/L have been shown effective in carbonate scale treatment. This test method enables the measurement of sub-mg/L phosphonate concentration in brines containing interfering elements.

The procedure includes measuring total (see 12.3.8) and free orthophosphate (see 12.4.3) ions and the difference in concentration is the phosphonate concentration. The sample could contain orthophosphate naturally, or from decomposition of the phosphonate during processing or well treatment or from treating compounds containing molecular dehydrated phosphates.

1.1 This test method covers the colorimetric determination of phosphonate (PNA) in brines from gas and oil production operations in the range from 0.1 to 5 mg/L.

1.2 This phosphonate method is intended for use to analyze low concentration of phosphonate in brine containing interfering elements. This test method is most useful for analyzing phosphonate at 0.1 to 1 mg/L range in brines with interfering elements; however, it requires personnel with good analytical skill.

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

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific hazard statements, see 9.1.3.