ASTM D6508-00(2005)e2

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
´2
Designation: D6508 – 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 D6508; 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 (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Warning notes were moved into the text in January 2005.
´ NOTE—Added research report reference to Section 17 editorially in March 2008.
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.
1.4 This standard does not purport to address all of the
D2777 Practice for Determination of Precision and Bias of
safety concerns, if any, associated with its use. It is the
Applicable Test Methods of Committee D19 on Water
responsibility of the user of this standard to establish appro-
D3370 Practices for Sampling Water from Closed Conduits
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. For specific hazard
statements, see Section 9.
2. Referenced Documents
2.1 ASTM Standards:
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
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. 13, 2005. Published April 2005.
Originally approved in 2000. Last previous edition approved in 2000 as
D6508 – 00. DOI: 10.1520/D6508-00R05E02.
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
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
´2
D6508 – 00 (2005)
FIG. 3 Electropherogram of Substitute Wastewater
FIG. 6 Electropherogram of Industrial Wastewater
F488 Test Method for On-Site Screening of Heterotrophic
Bacteria in Water
3. Terminology
3.1 Definitions—For definitions of terms used in this test
method, refer to Terminology D1129.
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
FIG. 4 Electropherogram of Drinking Water
based upon the principles of indirect UV detection.
3.2.2 electrolyte, n—a combination of a UV-absorbing salt
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-
FIG. 5 Electropherogram of Municipal Wastewater Treatment
Plant Discharge troosmotic flow and directs it towards the anode and detector.
Thismodifieraugmentsanionmigrationandenhancesspeedof
analysis. Its concentration secondarily effects anion selectivity
and resolution, (see Fig. 7).
D3856 Guide for Good Laboratory Practices in Laborato-
3.2.5 electrophoretic mobility, n—the specific velocity of a
ries Engaged in Sampling and Analysis of Water
charged analyte in the electrolyte under specific electroosmotic
D5810 Guide for Spiking into Aqueous Samples
flow conditions. The mobility of an analyte is directly related
D5847 Practice for Writing Quality Control Specifications
for Standard Test Methods for Water Analysis
D5905 Practice for the Preparation of Substitute Wastewa-
Withdrawn. The last approved version of this historical standard is referenced
ter on www.astm.org.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
´2
D6508 – 00 (2005)
FIG. 7 Pictorial Diagram of Anion Mobility and ElectroOsomotic Flow Modifier
to the analyte’s equivalent ionic conductance and applied 4. Summary of Test Method
voltage, and is the primary mechanism of separation.
4.1 Capillary ion electrophoresis, see Figs. 7-10, is a free
3.2.6 electropherogram, n—a graphical presentation of UV- zone electrophoretic technique optimized for the determination
detector response versus time of analysis; the x axis is
of anions with molecular weight less than 200. The anions
migration time, which is used to qualitatively identify the migrate and are separated according to their mobility in the
anion, and the y axis is UV response, which can be converted
electrolyte when an electrical field is applied through the open
to time corrected peak area for quantitation. tubular fused silica capillary. The electrolyte’s electroosmotic
low modifier dynamically coats the inner wall of the capillary
3.2.7 hydrostatic sampling, n—a sample introduction tech-
changing the surface to a net positive charge. This reversal of
nique in which the capillary with electrolyte is immersed in the
wall charge reverses the natural EOF. The modified EOF in
sample, and both are elevated to a specific height, typically 10
combination with a negative power supply augments the
cm, above the receiving electrolyte reservoir for a preset
mobility of the analyte anions towards the anode and detector
amount of time, typically less than 60 s. Nanolitres of sample
achieving rapid analysis times. Cations migrate in the opposite
aresiphonedintothecapillarybydifferentialheadpressureand
directiontowardsthecathodeandareremovedfromthesample
gravity.
during analysis. Water and other neutral species move toward
3.2.8 indirect UV detection, n—a form of UV detection in
the detector at the same rate as the EOF. The neutral species
which the analyte displaces an equivalent net charge amount of
migrate slower than the analyte anions and do not interfere
the highly UV-absorbing component of the electrolyte causing
with anion analysis (see Figs. 7 and 8).
anetdecreaseinbackgroundabsorbance.Themagnitudeofthe
4.2 The sample is introduced into the capillary using hydro-
decreased absorbance is directly proportional to analyte con-
staticsampling.Theinletofthecapillarycontainingelectrolyte
centration. Detector output polarity is reversed in order to
is immersed in the sample and the height of the sample raised
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
(decreases) peak area increases (decreases). Time corrected
FIG. 8 Selectivity Diagram of Anion Mobility Using Capillary Ion
peak area accounts for these changes. Electrophoresis
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
´2
D6508 – 00 (2005)
quantitation can be achieved when the concentration differen-
tial is less than 100:1. As the resolution between two anion
peaks increase so does the tolerated concentration differential.
In samples containing 1000 mg/L Cl, 1 mg/L SO can be
resolved and quantitated, however, the high Cl will interfere
with Br and NO quantitation.
-1
6.2 Dissolved carbonate, detected as HCO , is an anion
present in all aqueous samples, especially alkaline samples.
Carbonate concentrations greater than 500 mg/L will interfere
with PO quantitation.
6.3 Monovalent organic acids, except for formate, and
neutral organics commonly found in wastewater migrate later
in the electropherogram, after carbonate, and do not interfere.
Formate, a common organic acid found in environmental
samples, migrates shortly after fluoride but before phosphate.
FIG. 9 Pictorial Diagram of Indirect UV Detection
Formate concentrations greater than 5 mg/Lwill interfere with
fluoride identification and quantitation. Inclusion of 2 mg/L
10 cm for 30 s where low nanolitre volumes are siphoned into
formate into the mixed anion working solution aids in fluoride
thecapillary.Aftersampleloading,thecapillaryisimmediately
and formate identification and quantitation.
immersed back into the electrolyte. The voltage is applied
6.4 Divalent organic acids usually found in wastewater
initiating the separation process.
migrate after phosphate. At high concentrations, greater than
4.3 Anion detection is based upon the principles of indirect
10 mg/L, they may interfere with phosphate identification and
UVdetection.The UV-absorbing electrolyte anion is displaced
quantitation.
charge-for-charge by the separated analyte anion. The analyte
6.5 Chlorate also migrates after phosphate and at concen-
anion zone has a net decrease in background absorbance. This
trations greater than 10 mg/L will interfere with phosphate
decrease in UV absorbance in quantitatively proportional to
identification and quantitation. Inclusion of 5 mg/L chlorate
analyte anion concentration (see Fig. 9). Detector output
into the mixed anion working solution aids in phosphate and
polarityisreversedtoprovidepositivemVresponsetothedata
chlorate identification and quantitation.
system, and to make the negative absorbance peaks appear
6.6 As analyte concentration increases, analyte peak shape
positive.
becomes asymmetrical. If adjacent analyte peaks are not
4.4 The analysis is complete once the last anion of interest
baseline resolved, the data system will drop a perpendicular
is detected. The capillary is vacuum purged automatically by
between them to the baseline. This causes a decrease in peak
the system of any remaining sample and replenished with fresh
area for both analyte peaks and a low bias for analyte amounts.
electrolyte. The system now is ready for the next analysis.
For optimal quantitation, insure that adjacent peaks are fully
5. Significance and Use resolved, if they are not, dilute the sample 1:1 with water.
5.1 Capillary ion electrophoresis provides a simultaneous
7. Apparatus
separation and determination of several inorganic anions using
nanolitres of sample in a single injection.All anions present in
7.1 Capillary Ion Electrophoresis System—the system con-
the sample matrix will be visualized yielding an anionic profile
sists of the following components, as shown in Fig. 10 or
of the sample.
equivalent:
5.2 Analysis time is less than 5 minutes with sufficient
7.1.1 High Voltage Power Supply, capable of generating
sensitivity for drinking water and wastewater applications.
voltage (potential) between 0 and minus 30 kV relative to
Time between samplings is less than seven minutes allowing
ground with the capability working in a constant current mode.
for high sample throughput.
7.1.2 Covered Sample Carousel, to prevent environmental
5.3 Minimal sample preparation is necessary for drinking
contamination of the samples and electrolytes during a multi-
water and wastewater matrices. Typically, only a dilution with
sample batch analysis.
water is needed.
7.1.3 Sample Introduction Mechanism, capable of hydro-
5.4 This test method is intended as an alternative to other
static sampling technique, using gravity, positive pressure, or
multi-analyte methods and various wet chemistries for the
equivalent.
determination of inorganic anions in water and wastewater.
7.1.4 Capillary Purge Mechanism, to purge the capillary
Compared to other multi-analyte methods the major benefits of
after every analysis with fresh electrolyte to eliminate any
CIE are speed of analysis, simplicity, and reduced reagent
interference from the previous sample matrix, and to clean the
consumption and operating costs.
capillary with other reagent, such as sodium hydroxide.
6. Interferences
7.1.5 UV Detector, having the capability of monitoring 254
nm, or equivalent, with a time constant of 0.3 s.
6.1 Analyte identification, quantitation, and possible comi-
gration occur when one anion is in significant
...