Determination of Phosphonate Concentration in Water
|Publication Date:||6 April 2018|
This standard test method is a colorimetric determination of low concentrations of phosphonate residuals in water from oil and gas production, water injection/disposal, and other industrial applications.
This test method is applicable to determination of phosphonate concentrations in the range of 0.1 to 5 mg/L.
For samples containing more than 5 mg/L phosphonate, the sample must first be diluted with a known quantity of deionized water so that the phosphonate concentration is within the applicable range of this test method. The quantity of deionized water added is used to compute the Laboratory Dilution Factor described in Section 10.1.
Analyses of water samples containing less than 0.5 mg/L phosphonate shall follow the modification in Paragraph 8.1.1.
Additional information can be found in API(1) RP 45.2
This test method is intended to analyze low phosphonate concentrations in waters that contain interferences. Typical interferences include calcium, barium, strontium, sulfate, sulfide, orthophosphate, silicate, and iron (Fe+2/Fe+3). Other interferences include oil droplets, turbidity, and high total dissolved solids (> 100,000 mg/L). [out of place - moved to 1.5]
This standard test method is comprised of three steps: (1) the first step is to digest the sample digestion to convert all phosphonate to orthophosphate; (2) the second step is to convert the orthophosphate conversion to a to a phosphomolybdate (PO3Mo12O36) complex,by adding a molybdate reagentthe third step is to extraction of the complex into an organic liquid phase, and color development, and (3) colorimetric determination of its concentration.
This test method has been successfully tested for and is considered valid when used for analyzing the phosphonate concentration and has been used successfully with reagent water, produced water, and synthetic brines. It is the responsibility of the user to ensure the validity of this test method when used for water of untested matrices.
Personnel using this standard must have good analytical skills.
(1) American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005-4070.