ASTM: D6501: Phosphonates in Brines

Summary
Analytes
Revision
Data and Sites

Official Method Name

Standard Test Method for Phosphonate in Brines

Current Revision

Current edition approved Dec. 10, 1999. Published April 2000.

Media

WATER

Instrumentation

Spectroscopy (Colorimetry; Photometry)

Method Subcategory

Inorganic

Method Source

ASTM

Citation

Annual Book of ASTM Standards, Section 11, Water and Environmental Technology, Volume 11.01, Water (I)

Brief Method Summary

Phosphonate materials are converted to orthophosphate by potassium persulfate digestion. The orthophosphate is then reacted with ammonium molybdate to form a phosphomolybdate complex. The complex is extracted with a methyl isobutyl ketone/cyclohexane mixture and measured colorimetrically.

Scope and Application

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. This phosphonate method is intended for use to analyze low concentration of phosphonate in brine containing interfering elements.

Applicable Concentration Range

0.1-5 mg/L

Interferences

Sulfide interferes in this test method, but techniques described in the procedure (see Section 9.1.2) eliminate this interference. Concentrations less than 1000 mg/L copper (Cu⁺²) and silica (SiO₂/SiO₃^-2/Si⁺⁴); and less than 200 mg/L of iron (Fe⁺²/Fe⁺³ can be tolerated.
Produced brines can contain high concentrations of dissolved solids. Some of these dissolved solids tend to precipitate when produced brines reach new equilibria at atmospheric temperature and pressure. Phosphonate will coprecipitate or adsorb onto these newly formed solids and become unavailable for analysis. This problem can be minimized by acidifying the brine sample on-site with hydrochloric acid to pH below 2.
Glassware must be cleaned with phosphate free detergent and rinsed with 0.1 N hydrochloric acid to remove all residual phosphate or phosphonate.
The standard addition method in Section 12.6 is recommended for brine with high matrix interference.

Quality Control Requirements

Minimum quality control requirements are initial demonstration of proficiency, plus analysis of method blanks, quality control samples, and recovery spikes and, duplicate samples. For a general discussion of quality control and good laboratory practices, see Practices D 4210 and D 5789 and Guide D 3856.

Sample Handling

Collect the sample in accordance with Specification D 1192 or Practices D 3370, as applicable.
Preserve the samples immediately at the time of collection by adding 4 mL of 6 N hydrochloric acid per 100-mL brine.

Maximum Holding Time

Relative Cost

Unknown

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Phosphonate(N-55583) Phosphonate	0.100 mg/L	106% Rec (ML)	9.50			0.80 mg/L

Precision Descriptor Notes:	An interlaboratory study was conducted that involved eight laboratories analyzing samples at three different concentrations of phosphonate, each in a different brine concentration. The difference in brines was not expected to have any effect on the analytical results for phosphonate, but simulated different typical matrices. Each laboratory analyzed each sample in triplicate to provide a basis for estimating the single-operator standard deviation. It is recognized that the design of this study does not meet the requirements of D2777, but it is believed that the following statistical results are adequate to give the user's legitimate estimates of the precision and bias of the test method and for use as a basis for establishing generic quality control criteria to be used in the test method.
Detection Level Note:	None.

Precision Descriptor Notes:

An interlaboratory study was conducted that involved eight laboratories analyzing samples at three different concentrations of phosphonate, each in a different brine concentration. The difference in brines was not expected to have any effect on the analytical results for phosphonate, but simulated different typical matrices. Each laboratory analyzed each sample in triplicate to provide a basis for estimating the single-operator standard deviation. It is recognized that the design of this study does not meet the requirements of D2777, but it is believed that the following statistical results are adequate to give the user's legitimate estimates of the precision and bias of the test method and for use as a basis for establishing generic quality control criteria to be used in the test method.

Detection Level Note:

None.

Revision	PDF/Link
Current edition approved Dec. 10, 1999. Published April 2000.

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ASTM: D6501: Phosphonates in Brines

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