ASTM D6508-00(2005)e1

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e1
Designation: D 6508 – 00 (Reapproved 2005)
Standard Test Method for
Determination of Dissolved Inorganic Anions in Aqueous
Matrices Using Capillary Ion Electrophoresis and Chromate
Electrolyte
This standard is issued under the fixed designation D 6508; 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.
e NOTE—Warning notes were moved into the text in January 2005.
1. Scope
1.1 This test method cover the determination of the inor-
ganic anions fluoride, bromide, chloride, nitrite, nitrate, ortho-
phosphate, and sulfate in drinking water, wastewater, and other
aqueous matrices using capillary ion electrophoresis (CIE)
with indirect UV detection. See Figs. 1-6.
1.2 The test method uses a chromate-based electrolyte and
indirect UV detection at 254 nm. It is applicable for the
determination or inorganic anions in the range of 0.1 to 50
mg/L except for fluoride whose range is 0.1 to 25 mg/L.
1.3 It is the responsibility of the user to ensure the validity
of this test method for other anion concentrations and untested
aqueous matrices.
NOTE 1—The highest accepted anion concentration submitted for
FIG. 1 Electropherogram of Mixed Anion Working Solution and
precision and bias extend the anion concentration range for the following
Added Common Organic Acids
anions: Chloride to 93 mg/L, Sulfate to 90 mg/L, Nitrate to 72 mg/L, and
ortho-phosphate to 58 mg/L.
Applicable Test Methods of Committee D19 on Water
1.4 This standard does not purport to address all of the
D 3370 PracticesforSamplingWaterfromClosedConduits
safety concerns, if any, associated with its use. It is the
D 3856 Guide for Good Laboratory Practices in Laborato-
responsibility of the user of this standard to establish appro-
ries Engaged in Sampling and Analysis of Water
priate safety and health practices and determine the applica-
D 5810 Guide for Spiking into Aqueous Samples
bility of regulatory limitations prior to use. For specific hazard
statements, see Section 9.
2. Referenced Documents
2.1 ASTM Standards:
D 1066 Practice for Sampling Steam
D 1129 Terminology Relating to Water
D 1193 Specification for Reagent Water
D 2777 Practice for Determination of Precision and Bias of
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
Current edition approved Jan. 1, 2005. Published April 2005.
Originally approved in 2000. Last previous edition approved in 2000 as
D 6508 – 00.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on FIG. 2 Electropherogram of 0.2 mg/L Anions Used to Determine
the ASTM website. MDL
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D 6508 – 00 (2005)
FIG. 3 Electropherogram of Substitute Wastewater
FIG. 6 Electropherogram of Industrial Wastewater
3. Terminology
3.1 Definitions—For definitions of terms used in this test
method, refer to Terminology D 1129.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 capillary ion electrophoresis, n—an electrophoretic
techniqueinwhichaUV-absorbingelectrolyteisplacedina50
µmto75µmfusedsilicacapillary.Voltageisappliedacrossthe
capillary causing electrolyte and anions to migrate towards the
anode and through the capillary’s UVdetector window.Anions
are separated based upon the their differential rates of migra-
tion in the electrical field.Anion detection and quantitation are
based upon the principles of indirect UV detection.
3.2.2 electrolyte, n—a combination of a UV-absorbing salt
FIG. 4 Electropherogram of Drinking Water andanelectroosmoticflowmodifierplacedinsidethecapillary,
used as a carrier for the analytes, and for detection and
quantitation. The UV-absorbing portion of the salt must be
anionic and have an electrophoretic mobility similar to the
analyte anions of interest.
3.2.3 electroosmotic flow (EOF), n—the direction and ve-
locity of electrolyte solution flow within the capillary under an
applied electrical potential (voltage); the velocity and direction
of flow is determined by electrolyte chemistry, capillary wall
chemistry, and applied voltage.
3.2.4 electroosmotic flow modifier (OFM), n—a cationic
quaternary amine in the electrolyte that dynamically coats the
negatively charged silica wall giving it a net positive charge.
This reverses the direction of the electrolyte’s natural elec-
troosmotic flow and directs it towards the anode and detector.
Thismodifieraugmentsanionmigrationandenhancesspeedof
analysis. Its concentration secondarily effects anion selectivity
FIG. 5 Electropherogram of Municipal Wastewater Treatment
Plant Discharge
and resolution, (see Fig. 7).
3.2.5 electrophoretic mobility, n—the specific velocity of a
D 5847 Practice for Writing Quality Control Specifications charged analyte in the electrolyte under specific electroosmotic
for Standard Test Methods for Water Analysis flow conditions. The mobility of an analyte is directly related
D 5905 Practice for the Preparation of Substitute Wastewa- to the analyte’s equivalent ionic conductance and applied
ter voltage, and is the primary mechanism of separation.
F 488 Test Method for On-Site Screening of Heterotrophic 3.2.6 electropherogram, n—a graphical presentation of UV-
Bacteria in Water detector response versus time of analysis; the x axis is
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D 6508 – 00 (2005)
FIG. 7 Pictorial Diagram of Anion Mobility and ElectroOsomotic Flow Modifier
migration time, which is used to qualitatively identify the
anion, and the y axis is UV response, which can be converted
to time corrected peak area for quantitation.
3.2.7 hydrostatic sampling, n—a sample introduction tech-
nique in which the capillary with electrolyte is immersed in the
sample, and both are elevated to a specific height, typically 10
cm, above the receiving electrolyte reservoir for a preset
amount of time, typically less than 60 s. Nanolitres of sample
aresiphonedintothecapillarybydifferentialheadpressureand
gravity.
3.2.8 indirect UV detection, n—a form of UV detection in
which the analyte displaces an equivalent net charge amount of
the highly UV-absorbing component of the electrolyte causing
FIG. 8 Selectivity Diagram of Anion Mobility Using Capillary Ion
anetdecreaseinbackgroundabsorbance.Themagnitudeofthe
Electrophoresis
decreased absorbance is directly proportional to analyte con-
centration. Detector output polarity is reversed in order to
obtain a positive mV response.
3.2.9 midpoint of peak width, n—CIE peaks typically are
asymmetrical with the peak apex shifting with increasing
concentration, and the peak apex may not be indicative of true
analyte migration time. Midpoint of peak width is the midpoint
between the analyte peak’s start and stop integration, or the
peak center of gravity.
3.2.10 migration time, n—the time required for a specific
analyte to migrate through the capillary to the detector. The
migration time in capillary ion electrophoresis is analogous to
retention time in chromatography.
3.2.11 time corrected peak area, n—normalized peak area;
peak area divided by migration time. CE principles state that
peak area is dependent upon migration time, that is, for the
same concentration of analyte, as migration time increases
FIG. 9 Pictorial Diagram of Indirect UV Detection
(decreases) peak area increases (decreases). Time corrected
peak area accounts for these changes.
electrolyte when an electrical field is applied through the open
4. Summary of Test Method
tubular fused silica capillary. The electrolyte’s electroosmotic
4.1 Capillary ion electrophoresis, see Figs. 7-10, is a free low modifier dynamically coats the inner wall of the capillary
zone electrophoretic technique optimized for the determination changing the surface to a net positive charge. This reversal of
of anions with molecular weight less than 200. The anions wall charge reverses the natural EOF. The modified EOF in
migrate and are separated according to their mobility in the combination with a negative power supply augments the
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D 6508 – 00 (2005)
FIG. 10 General Hardware Schematic of a Capillary Ion Electrophoresis System
mobility of the analyte anions towards the anode and detector 5.3 Minimal sample preparation is necessary for drinking
achieving rapid analysis times. Cations migrate in the opposite water and wastewater matrices. Typically, only a dilution with
directiontowardsthecathodeandareremovedfromthesample water is needed.
during analysis. Water and other neutral species move toward
5.4 This test method is intended as an alternative to other
the detector at the same rate as the EOF. The neutral species
multi-analyte methods and various wet chemistries for the
migrate slower than the analyte anions and do not interfere
determination of inorganic anions in water and wastewater.
with anion analysis (see Figs. 7 and 8).
Compared to other multi-analyte methods the major benefits of
4.2 The sample is introduced into the capillary using hydro-
CIE are speed of analysis, simplicity, and reduced reagent
staticsampling.Theinletofthecapillarycontainingelectrolyte
consumption and operating costs.
is immersed in the sample and the height of the sample raised
10 cm for 30 s where low nanolitre volumes are siphoned into
6. Interferences
thecapillary.Aftersampleloading,thecapillaryisimmediately
6.1 Analyte identification, quantitation, and possible comi-
immersed back into the electrolyte. The voltage is applied
gration occur when one anion is in significant excess to other
initiating the separation process.
anions in the sample matrix. For two adjacent peaks, reliable
4.3 Anion detection is based upon the principles of indirect
quantitation can be achieved when the concentration differen-
UVdetection.The UV-absorbing electrolyte anion is displaced
tial is less than 100:1. As the resolution between two anion
charge-for-charge by the separated analyte anion. The analyte
peaks increase so does the tolerated concentration differential.
anion zone has a net decrease in background absorbance. This
In samples containing 1000 mg/L Cl, 1 mg/L SO can be
decrease in UV absorbance in quantitatively proportional to
resolved and quantitated, however, the high Cl will interfere
analyte anion concentration (see Fig. 9). Detector output
with Br and NO quantitation.
polarityisreversedtoprovidepositivemVresponsetothedata
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6.2 Dissolved carbonate, detected as HCO , is an anion
system, and to make the negative absorbance peaks appear
present in all aqueous samples, especially alkaline samples.
positive.
Carbonate concentrations greater than 500 mg/L will interfere
4.4 The analysis is complete once the last anion of interest
with PO quantitation.
is detected. The capillary is vacuum purged automatically by
6.3 Monovalent organic acids, except for formate, and
the system of any remaining sample and replenished with fresh
neutral organics commonly found in wastewater migrate later
electrolyte. The system now is ready for the next analysis.
in the electropherogram, after carbonate, and do not interfere.
5. Significance and Use
Formate, a common organic acid found in environmental
samples, migrates shortly after fluoride but before phosphate.
5.1 Capillary ion electrophoresis provides a simultaneous
Formate concentrations greater than 5 mg/Lwill interfere with
separation and determination of several inorganic anions using
fluoride identification and quantitation. Inclusion of 2 mg/L
nanolitres of sample in a single injection.All anions present in
formate into the mixed anion working solution aids in fluoride
the sample matrix will be visualized yielding an anionic profile
and formate identification and quantitation.
of the sample.
5.2 Analysis time is less than 5 minutes with sufficient 6.4 Divalent organic acids usually found in wastewater
sensitivity for drinking water and wastewater applications. migrate after phosphate. At high concentrations, greater than
Time between samplings is less than seven minutes allowing 10 mg/L, they may interfere with phosphate identification and
for high sample throughput. quantitation.
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D 6508 – 00 (2005)
6.5 Chlorate also migrates after phosphate and at concen- 7.5 Vacuum Filtration Apparatus, capable for filtering 100
trations greater than 10 mg/L will interfere with phosphate mL of reagent through a 0.45 µm aqueous filter.
identification and quantitation. Inclusion of 5 mg/L chlorate
into the mixed anion working solution aids in phosphate and 8. Reagents and Materials
chlorate identification and quantitation.
8.1 Purity of Reagents—Unless otherwise indicated, it is
6.6 As analyte concentration increases, analyte peak shape
intended that all reagents shall conform to the reagent grade
becomes asymmetrical. If adjacent analyte peaks are not
specification of the Analytical Reagents of the American
baseline resolved, the data system will drop a perpendicular
Chemical Society, where such specifications are available.
between them to the baseline. This causes a decrease in peak
Other grades may be used, provided it is first ascertained that
area for both analyte peaks and a low bias for analyte amounts.
the reagent is of sufficient high purity to permit its use without
For optimal quantitation, insure that adjacent peaks are fully
lessening the performance or accuracy of the determination.
resolved, if they are not, dilute the sample 1:1 with water.
Reagent chemicals shall be used for all tests.
NOTE 3—Calibration and detection limits of this test method are biased
7. Apparatus
by the purity of the reagents.
7.1 Capillary Ion Electrophoresis System—the system con-
8.2 Purity of Water—Unless otherwise indicated, references
sists of the following components, as shown in Fig. 10 or
to water shall be understood to mean Type I reagent water
equivalent:
conforming or exceeding specification D 1193. Freshly drawn
7.1.1 High Voltage Power Supply, capable of generating
water should be used for preparation of all stock and working
voltage (potential) between 0 and minus 30 kV relative to
standards, electrolytes, and solutions. Performance and detec-
ground with the capability working in a constant current mode.
tion limits of this test method are limited by the purity of
7.1.2 Covered Sample Carousel,
...