ASTM D6501-99

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An American National Standard
Designation: D 6501 – 99
Standard Test Method for
Phosphonate in Brines
This standard is issued under the fixed designation D 6501; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E 275 Practice for Describing and Measuring Performance
of Ultraviolet, Visible, and Near Infrared Spectrophotom-
1.1 This test method covers the colorimetric determination
eters
of phosphonate (PNA) in brines from gas and oil production
operations in the range from 0.1 to 5 mg/L.
3. Terminology
1.2 This phosphonate method is intended for use to analyze
3.1 Definitions—For definitions of terms used in this test
low concentration of phosphonate in brine containing interfer-
method, refer to Terminology D 1129.
ing elements. This test method is most useful for analyzing
3.2 Definitions of Terms Specific to This Standard:
phosphonate at 0.1 to 1 mg/L range in brines with interfering
3.2.1 phosphonate, n—a group of organophosphorus com-
elements; however, it requires personnel with good analytical
pounds typically used for mineral scale and corrosion control,
skill.
as cleaning agents, dispersants, and chelants. Typical phospho-
1.3 This test method has been used successfully with
nate compounds include, but are not limited to, the following
reagent water and both field and synthetic brine. It is the user’s
phosphonic acid and their neutralized salts: Aminotri(methyl-
responsibility to ensure the validity of this test method for
enephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic
waters of untested matrices.
acid, ethylenediaminetetra (methylenephosphonic acid), hex-
1.4 This standard does not purport to address all of the
amethylenediaminetetra (methylenephosphonic acid), and di-
safety concerns, if any, associated with its use. It is the
ethylenetriaminepenta (methylenephosphonic acid).
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Summary of Test Method
bility of regulatory limitations prior to use. For specific hazard
4.1 Phosphonate materials are converted to orthophosphate
statements, see 9.1.3.
by potassium persulfate digestion. The orthophosphate is then
reacted with ammonium molybdate to form a phosphomolyb-
2. Referenced Documents
date complex. The complex is extracted with a methyl isobutyl
2.1 ASTM Standards:
2 ketone/cyclohexane mixture and measured colorimetrically.
D 1129 Terminology Relating to Water
D 1192 Specification for Equipment for Sampling Water
5. Significance and Use
and Steam in Closed Conduits
2 5.1 This test method is useful for the determination of trace
D 1193 Specification for Reagent Water
level phosphonate residues in brines. Chemical treatment
D 2777 Practice for Determination of Precision and Bias of
2 which contain phosphonates are used as mineral scale and
Applicable Test Methods of Committee D-19 on Water
corrosion inhibitors in gas and oil drilling and production
D 3370 Practices for Sampling Water from Closed Con-
2 operations; and other industrial applications. Often, the deci-
duits
sion for treatment is based on the ability to measure low
D 3856 Guide for Good Laboratory Practices in Laborato-
2 phosphonate concentration and not upon performance criteria.
ries Engaged in Sampling and Analysis of Water
Phosphonate concentrations as low as 0.16 mg/L have been
D 4375 Terminology for Basic Statistics in Committee
2 shown effective in carbonate scale treatment. This test method
D-19 on Water
enables the measurement of sub-mg/L phosphonate concentra-
D 5810 Guide for Spiking into Aqueous Samples
tion in brines containing interfering elements.
D 5847 Practice for Writing Quality Control Specifications
5.2 The procedure includes measuring total (see 12.3.8) and
for Standard Test Methods for Water Analysis
free orthophosphate (see 12.4.3) ions and the difference in
concentration is the phosphonate concentration. The sample
This test method is under the jurisdiction of ASTM Committee D19 on Water could contain orthophosphate naturally, or from decomposition
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
Current edition approved Dec. 10, 1999. Published April 2000.
Annual Book of ASTM Standards, Vol 11.01.
3 4
Annual Book of ASTM Standards, Vol 11.02. Annual Book of ASTM Standards, Vol 03.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6501–99
of the phosphonate during processing or well treatment or from ety . Other grades may be used, provided it is first ascertained
treating compounds containing molecular dehydrated phos- that the reagent is of sufficiently high purity to permit its use
phates. without lessening the accuracy of the determination.
8.2 Purity of Water—Unless otherwise indicated, references
6. Interferences to water shall be understood to mean reagent water conforming
to Specification D 1193, Type III.
6.1 Sulfide interferes in this test method, but techniques
8.3 Alcoholic Sulfuric Acid Solution—Cautiously add 20
described in the procedure (see 9.1.2) eliminate this interfer-
mL concentrated H SO (sp. gr. 1.89) to 900 mL methyl
+2 2 4
ence. Concentrations less than 1000 mg/L copper (Cu ) and
alcohol and dilute to 1 L with methyl alcohol. It is recom-
–2 +4
silica (SiO /SiO /Si ); and less than 200 mg/L of iron
2 3
mended to dispense the liquid with a bottle top liquid dis-
+2 +3
(Fe /Fe ) can be tolerated.
penser, which dispenses a 10-mL volume.
6.2 Produced brines can contain high concentrations of
8.4 Ammonium Molybdate Solution—Dissolve 39.1 g
dissolved solids. Some of these dissolved solids tend to
(NH ) Mo O ·4H O in 200 mL water. Cautiously add 210
6 7 24 2
precipitate when produced brines reach new equilibria at
mL concentrated HCl (sp. gr. 1.19) to 400 mL water. Cool, add
atmospheric temperature and pressure. Phosphonate will co- molybdate solution, and dilute to 1 L. It is recommended to
precipitate or adsorb onto these newly formed solids and
dispense the liquid with a liquid dispenser, which dispenses a
become unavailable for analysis. This problem can be mini- 10-mL volume.
mized by acidifying the brine sample on-site with hydrochloric 8.5 Glycerol—Reagent grade, 99 % or greater.
acid to pH below 2. 8.6 Hydrochloric Acid (6N)—Add 500 mL of concentrated
HCl (sp. gr. 1.19) to 500 mL of water.
6.3 Glassware must be cleaned with phosphate free deter-
8.7 Methyl Alcohol—Reagent grade, 99 % or greater.
gent and rinsed with 0.1 N hydrochloric acid to remove all
8.8 Methyl Isobutyl Ketone/Cyclohexane Solvent—Mix
residual phosphate or phosphonate.
equal volumes of methyl isobutyl ketone (MIBK) and cyclo-
6.4 The standard addition method in 12.6 is recommended
hexane.
for brine with high matrix interference.
NOTE 1—Warning: This solvent is highly flammable.
7. Apparatus
It is recommended to dispense the liquid with a bottle top
7.1 Pressure Cooker or Sterilizer (Autoclave) . liquid dispenser, which dispenses a 20-mL volume.
8.9 Phosphate Solution, standard (1.00 mL = 0.05 mg PO ).
7.2 Spectrophotometer , for measurement above 650 nm 4
Dissolve 71.6 mg anhydrous KH PO in water and dilute to 1
with 4-cm light path cells. A longer light path will yield a 2 4
L.
corresponding higher sensitivity (see 12.5.1). Spectrophotom-
8.10 Phosphonate Solution, (50-mg/L phosphonate)—If the
eter practices prescribed in this test method shall conform to
standard addition procedure (see 12.6) is to be used, a stock
Practice E 275.
solution of 50 mg/L, as phosphonate, should be prepared. To
7.3 Bottle Top Liquid Dispenser , 20-mL capacity, <1 %
prepare this solution, a concentrated sample of the phosphonate
accuracy, and <0.1 % precision.
to be measured along with the wt/wt percent phosphonate
7.4 Pipetter, automated , 10-mL capacity with 0.2 to 0.5 %
concentration must be obtained from the manufacturer. The
accuracy.
wt/wt percent phosphonate concentration also can be calibrated
9 10
7.5 Glass Bottles , 60 mL and 240 mL with Teflony lined by this procedure as described in 12.2 and 12.3.
screw cap closure. 8.11 Potassium Persulfate,K S O .
2 2 8
8.12 Sodium Chloride Solution (1.0 M, Synthetic Brine)—
8. Reagents and Materials Dissolve 58.44 g. NaCl in 800 mL water and dilute to 1 L. This
solution is used as a synthetic brine.
8.1 Purity of Reagents—Reagent grade chemicals shall be
8.13 Sodium Hypochlorite, (5.65–6 %).
used in all tests. Unless otherwise indicated, it is intended that
8.14 Stannous Chloride Solution—Mix 0.4 g SnCl ·2H O
2 2
all reagents shall conform to the specifications of the Commit-
in 100 mL glycerol. This reagent is stable for at least six
tee on Analytical Reagents of the American Chemical Soci-
months. The solution is stored in a dropper bottle.
9. Hazards
Fisher Scientific No. 14-141-S has been satisfactory for this purpose, or
9.1 Precautions:
equivalent, should be used.
Varian DMS-100 has been satisfactory for this purpose, or equivalent, should
be used.
Fisher Scientific No. 13-687-21 REPIPET has been satisfactory for this
purpose, or equivalent, should be used. Reagent Chemicals, American Chemical Society Specifications, American
Fisher Scientific No. 21-279-25 Eppendorf Maxipipetter has been satisfactory Chemical Society, Washington, DC. For suggestions on the testing of Reagents not
for this purpose. listed by the American Chemical Society, see Analar Standards for Laboratory
Fisher Scientific No. 03-326-3C and 03-326-3G have been satisfactory for this Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
purpose. and National Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville,
MD.
D6501–99
9.1.1 Most phosphonate inhibitors are strongly adsorbed to of solution is critical in procedure 12.2.3. At this point in the
glass or metal; therefore, polyethylene beakers, flasks, pipets, procedure, all of the phosphonate has been oxidized to phos-
etc., should be used to contain and transfer brine solutions from phate.
the field.
12.3 Color development and extraction procedure:
9.1.2 A glass bottle is recommended for use in the color
12.3.1 The timings specified in procedures 12.3.3, 12.3.4,
development steps (see 12.2 and 12.3) for better visualization
and 12.3.7 are critical to the test. It is recommended to run
of the reaction. Since the reaction media is acidic, phosphonate
small numbers of samples at a time in order to manage the
will not adsorb to the glass surface.
timing.
9.1.3 Personnel performing this test must be familiar with
12.3.2 Standard addition method (see 12.6) should be used
all precautions for handling strong sulfuric acid, hydrochloric
for data quality control.
acid and sulfide-containing brine. Personnel should consult the
12.3.3 Add 20 mL MIBK/Cyclohexane solvent and 10 mL
material safety data sheet for handling strong acids. Protective
ammonium molybdate solution to the sample bottles, and
clothing and latex gloves should be worn. The sulfide brine
immediately, vigorously shake each bottle for 15 s. At this
should be handled in the hood with good ventilation. Sulfide
point, the clear, and electrically-neutral phosphomolybdate
containing brine can be treated with sodium hypochlorite prior
complex has been formed and extracted into the organic
to analysis to oxidize the hydrogen sulfide.
solvent phase.
12.3.4 Wait exactly five minutes to allow the aqueous and
10. Sampling
organic solvent phases to be separated, and withdraw 10.0 mL
10.1 Collect the sample in accordance with Specification
of liquid from the organic solvent layer into a clean 60-mL
D 1192 or Practices D 3370, as applicable.
glass bottle using an automatic pipetter. Care should be taken
10.2 Preserve the samples immediately at the time of
not to disturb the solvent/water interface or accidentally
collection by adding 4 mL of 6 N hydrochloric acid per
withdraw some aqueous solution, since the excess molybde-
100-mL brine.
num in the aqueous phase can also be reduced by stannous
chloride to form a deep blue color.
11. Calibration and Standardization
12.3.5 Add 10 mL alcoholic H SO solution to the samples,
2 4
11.1 Prepare standards by adding 2.0, 4.0, 6.0, 8.0, 10.0 mL
and swirl to mix.
each of phosphate standard solution (1.00 mL = 0.05 mg PO )
12.3.6 Add four drops stannous chloride solution to each
to separate 100-mL volumetric flasks. Dilute to 100 mL with 1
sample, and mix thoroughly.
M sodium chloride solution. These solutions will contain 1.0,
12.3.7 After 10 minutes, but before 20 minutes, pour each
2.0, 3.0, 4.0, 5.0 mg/L phosphate as PO . If the procedure in
sample into a 4-cm cell and read the absorbance against the
12.5 is used for samples with low phosphonate concentrations,
blank at 725 nm. Absorbance readings also can be taken at 650
then solutions containing 0.2, 0.4, 0.6, 0.8, 1.0 mg/L phosphate
or 700 nm, but with reduced sensitivity. Use the sample blank
as PO should be used.
as reference solution in measuring the sample.
11.2 Follow the procedure in 12.2 and 12.3 to develop color,
and determine the absorbance at 725 nm.
12.3.8 Read the total phosphate concentration (C – )
T PO4
11.3 Prepare a calibration curve showing phosphate ion from a calibration curve prepared by analyzing known phos-
concentration in mg/L on the X axis with the corresponding phate standards, as described in Section 11.
absorbance (A) reading of the spectrophotometer on the Y axis
12.4 Procedure for Analyzing Orthophosphate Concentra-
of linear graph paper.
tion in the Brine:
12.4.1 Pipet 20 mL of the acidified brine sample to a
12. Procedure
separate 60-mL glass bottle.
12.1 The procedures in 12.2 and 12.3 are applicable to
12.4.2 Follow the procedure in 12.3.3-12.3.7 to develop
samples containing 0.5 to 5 mg/L phosphonate. For samples
phosphomolybdate complex and to extract the complex to the
containing less than 0.5 mg/L phosphonate, a larger sample
organic liquid phase.
volume or a different light path cell can be used (see 12.5).
12.4.3 Read the orthophosphate concentration (C – )
F PO4
12.2 Persulfate Digestion Procedure:
from a calibration curve prepared in Section 11.
12.2.1 Pipet 20 mL of the following samples (a, b, c) into
12.5 Procedure for brines containing phosphonate concen-
separate 60-mL glass bottles, each containing 200 mg of
trations outside the range(s) specified.
potassium persulfate. Multiple samples can be digested at the
12.5.1 The above concentration range is spec
...