1、Designation: D6508 10Standard Test Method forDetermination of Dissolved Inorganic Anions in AqueousMatrices Using Capillary Ion Electrophoresis and ChromateElectrolyte1This standard is issued under the fixed designation D6508; the number immediately following the designation indicates the year ofori
2、ginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the inor-ganic a
3、nions fluoride, bromide, chloride, nitrite, nitrate, ortho-phosphate, and sulfate in drinking water, wastewater, and otheraqueous matrices using capillary ion electrophoresis (CIE)with indirect UV detection. See Figs. 1-6.1.2 The test method uses a chromate-based electrolyte andindirect UV detection
4、 at 254 nm. It is applicable for thedetermination or inorganic anions in the range of 0.1 to 50mg/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 validityof this test method for other anion concentrations and untestedaqueous matrices.NOTE 1T
5、he highest accepted anion concentration submitted forprecision and bias extend the anion concentration range for the followinganions: Chloride to 93 mg/L, Sulfate to 90 mg/L, Nitrate to 72 mg/L, andortho-phosphate to 58 mg/L.1.4 The values stated in SI units are to be regarded asstandard. No other u
6、nits of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of re
7、gulatory limitations prior to use. For specific hazardstatements, see Section 9.2. Referenced Documents2.1 ASTM Standards:2D1066 Practice for Sampling SteamD1129 Terminology Relating to WaterD1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test
8、 Methods of Committee D19 on WaterD3370 Practices for Sampling Water from Closed ConduitsD3856 Guide for Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of WaterD5810 Guide for Spiking into Aqueous Samples1This test method is under the jurisdiction of ASTM Committee D19 o
9、n Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Sept. 1, 2010. Published October 2010. Originallyapproved in 2000. Last previous edition approved in 2005 as D6508 00 (2005)2.DOI: 10.1520/D6508-10.2For referenced ASTM standards
10、, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.FIG. 1 Electropherogram of Mixed Anion Working Solution andAdded Common Organic AcidsFIG. 2
11、 Electropherogram of 0.2 mg/L Anions Used to DetermineMDL1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.D5847 Practice for Writing Quality Control Specificationsfor S
12、tandard Test Methods for Water AnalysisD5905 Practice for the Preparation of Substitute Wastewa-terF488 Test Method for On-Site Screening of HeterotrophicBacteria in Water33. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D1129.3.2 Definitions of Ter
13、ms Specific to This Standard:3.2.1 capillary ion electrophoresis, nan electrophoretictechnique in which a UV-absorbing electrolyte is placed in a 50m to 75 m fused-silica capillary.3.2.1.1 DiscussionVoltage is applied across the capillarycausing electrolyte and anions to migrate towards the anodeand
14、 through the capillarys UV detector window. Anions areseparated based upon the differential rates of migration in theelectrical field. Anion detection and quantitation are basedupon the principles of indirect UV detection.3.2.2 electrolyte, na combination of a UV-absorbing saltand an electroosmotic-
15、flow modifier placed inside the capil-lary, used as a carrier for the analytes, and for detection andquantitation.3.2.2.1 DiscussionThe UV-absorbing portion of the saltmust be anionic and have an electrophoretic mobility similar tothe analyte anions of interest.3.2.3 electroosmotic flow (EOF), nthe
16、direction and ve-locity of electrolyte-solution flow within the capillary under anapplied electrical potential (voltage); the velocity and directionof flow is determined by electrolyte chemistry, capillary-wallchemistry, and applied voltage.3.2.4 electroosmotic-flow modifier (OFM), na cationicquater
17、nary amine in the electrolyte that dynamically coats thenegatively charged silica wall giving it a net positive charge.3.2.4.1 DiscussionThis modifier reverses the direction ofthe electrolytes natural electroosmotic flow and directs ittowards the anode and detector. This modifier augments anion3With
18、drawn. The last approved version of this historical standard is referencedon www.astm.org.FIG. 3 Electropherogram of Substitute WastewaterFIG. 4 Electropherogram of Drinking WaterFIG. 5 Electropherogram of Municipal Wastewater TreatmentPlant DischargeFIG. 6 Electropherogram of Industrial WastewaterD
19、6508 102migration and enhances speed of analysis. Its concentrationsecondarily affects anion selectivity and resolution, (see Fig.7).3.2.5 electropherogram, na graphical presentation of UV-detector response versus time of analysis; the x-axis is migra-tion time, which is used to identify the anion q
20、ualitatively, andthe y-axis is UV response, which can be converted to time-corrected peak area for quantitation.3.2.6 electrophoretic mobility, nthe specific velocity of acharged analyte in the electrolyte under specificelectroosmotic-flow conditions.3.2.6.1 DiscussionThe mobility of an analyte is d
21、irectlyrelated to the analytes equivalent ionic conductance andapplied voltage, and is the primary mechanism of separation.3.2.7 hydrostatic sampling, na sample-introduction tech-nique in which the capillary with electrolyte is immersed in thesample, and both are elevated to a specific height, typic
22、ally 10cm, above the receiving-electrolyte reservoir for a presetamount of time, typically less than 60 s.3.2.7.1 DiscussionNanolitres of sample are siphoned intothe capillary by differential head pressure and gravity.3.2.8 indirect UV detection, na form of UV detection inwhich the analyte displaces
23、 an equivalent net-charge amount ofthe highly UV-absorbing component of the electrolyte causinga net decrease in background absorbance.3.2.8.1 DiscussionThe magnitude of the decreased absor-bance is directly proportional to analyte concentration.Detector-output polarity is reversed in order to obtai
24、n apositive mV response.3.2.9 midpoint of peak width, nCIE peaks typically areasymmetrical with the peak apexs shifting with increasingconcentration, and the peak apex may not be indicative of trueanalyte-migration time.3.2.9.1 DiscussionMidpoint of peak width is the midpointbetween the analyte peak
25、s start and stop integration, or thepeak center of gravity.3.2.10 migration time, nthe time required for a specificanalyte to migrate through the capillary to the detector.3.2.10.1 DiscussionThe migration time in capillary ionelectrophoresis is analogous to retention time in chromatogra-phy.3.2.11 t
26、ime-corrected peak area, nnormalized peak area;peak area divided by migration time.3.2.11.1 DiscussionCE principles state that peak area isdependent upon migration time, that is, for the same concen-tration of analyte, as migration time increases (decreases) peakarea increases (decreases). Time-corr
27、ected peak area accountsfor these changes.4. Summary of Test Method4.1 Capillary ion electrophoresis, see Figs. 7-10, is a freezone electrophoretic technique optimized for the determinationof anions with molecular weight less than 200. The anionsmigrate and are separated according to their mobility
28、in theelectrolyte when an electrical field is applied through the opentubular fused silica capillary. The electrolytes electroosmoticlow modifier dynamically coats the inner wall of the capillarychanging the surface to a net positive charge. This reversal ofwall charge reverses the natural EOF. The
29、modified EOF incombination with a negative power supply augments themobility of the analyte anions towards the anode and detectorachieving rapid analysis times. Cations migrate in the oppositedirection towards the cathode and are removed from the sampleduring analysis. Water and other neutral specie
30、s move towardthe detector at the same rate as the EOF. The neutral speciesmigrate slower than the analyte anions and do not interferewith anion analysis (see Figs. 7 and 8).4.2 The sample is introduced into the capillary using hydro-static sampling. The inlet of the capillary containing electrolytei
31、s immersed in the sample and the height of the sample raised10 cm for 30 s where low nanolitre volumes are siphoned intothe capillary.After sample loading, the capillary is immediatelyimmersed back into the electrolyte. The voltage is appliedinitiating the separation process.4.3 Anion detection is b
32、ased upon the principles of indirectUV detection. The UV-absorbing electrolyte anion is displacedFIG. 7 Pictorial Diagram of Anion Mobility and ElectroOsomotic Flow ModifierD6508 103charge-for-charge by the separated analyte anion. The analyteanion zone has a net decrease in background absorbance. T
33、hisdecrease in UV absorbance in quantitatively proportional toanalyte anion concentration (see Fig. 9). Detector outputpolarity is reversed to provide positive mV response to the datasystem, and to make the negative absorbance peaks appearpositive.4.4 The analysis is complete once the last anion of
34、interestis detected. The capillary is vacuum purged automatically bythe system of any remaining sample and replenished with freshelectrolyte. The system now is ready for the next analysis.5. Significance and Use5.1 Capillary ion electrophoresis provides a simultaneousseparation and determination of
35、several inorganic anions usingnanolitres of sample in a single injection. All anions present inthe sample matrix will be visualized yielding an anionic profileof the sample.5.2 Analysis time is less than 5 minutes with sufficientsensitivity for drinking water and wastewater applications.Time between
36、 samplings is less than seven minutes allowingfor high sample throughput.5.3 Minimal sample preparation is necessary for drinkingwater and wastewater matrices. Typically, only a dilution withwater is needed.5.4 This test method is intended as an alternative to othermulti-analyte methods and various
37、wet chemistries for thedetermination of inorganic anions in water and wastewater.Compared to other multi-analyte methods the major benefits ofCIE are speed of analysis, simplicity, and reduced reagentconsumption and operating costs.6. Interferences6.1 Analyte identification, quantitation, and possib
38、le comi-gration occur when one anion is in significant excess to otheranions in the sample matrix. For two adjacent peaks, reliablequantitation can be achieved when the concentration differen-tial is less than 100:1. As the resolution between two anionpeaks increase so does the tolerated concentrati
39、on differential.In samples containing 1000 mg/L Cl, 1 mg/L SO4can beresolved and quantitated, however, the high Cl will interferewith Br and NO2quantitation.6.2 Dissolved carbonate, detected as HCO3-1, is an anionpresent in all aqueous samples, especially alkaline samples.Carbonate concentrations gr
40、eater than 500 mg/L will interferewith PO4quantitation.6.3 Monovalent organic acids, except for formate, andneutral organics commonly found in wastewater migrate laterin the electropherogram, after carbonate, and do not interfere.Formate, a common organic acid found in environmentalsamples, migrates
41、 shortly after fluoride but before phosphate.Formate concentrations greater than 5 mg/L will interfere withfluoride identification and quantitation. Inclusion of 2 mg/Lformate into the mixed anion working solution aids in fluorideand formate identification and quantitation.6.4 Divalent organic acids
42、 usually found in wastewatermigrate after phosphate. At high concentrations, greater than10 mg/L, they may interfere with phosphate identification andquantitation.6.5 Chlorate also migrates after phosphate and at concen-trations greater than 10 mg/L will interfere with phosphateidentification and qu
43、antitation. Inclusion of 5 mg/L chlorateinto the mixed anion working solution aids in phosphate andchlorate identification and quantitation.6.6 As analyte concentration increases, analyte peak shapebecomes asymmetrical. If adjacent analyte peaks are notbaseline resolved, the data system will drop a
44、perpendicularbetween them to the baseline. This causes a decrease in peakarea for both analyte peaks and a low bias for analyte amounts.For optimal quantitation, insure that adjacent peaks are fullyresolved, if they are not, dilute the sample 1:1 with water.7. Apparatus7.1 Capillary Ion Electrophore
45、sis Systemthe system con-sists of the following components, as shown in Fig. 10 orequivalent:7.1.1 High Voltage Power Supply, capable of generatingvoltage (potential) between 0 and minus 30 kV relative toground with the capability working in a constant current mode.7.1.2 Covered Sample Carousel, to
46、prevent environmentalcontamination of the samples and electrolytes during a multi-sample batch analysis.FIG. 8 Selectivity Diagram of Anion Mobility Using Capillary IonElectrophoresisFIG. 9 Pictorial Diagram of Indirect UV DetectionD6508 1047.1.3 Sample Introduction Mechanism, capable of hydro-stati
47、c sampling technique, using gravity, positive pressure, orequivalent.7.1.4 Capillary Purge Mechanism, to purge the capillaryafter every analysis with fresh electrolyte to eliminate anyinterference from the previous sample matrix, and to clean thecapillary with other reagent, such as sodium hydroxide
48、.7.1.5 UV Detector, having the capability of monitoring 254nm, or equivalent, with a time constant of 0.3 s.7.1.6 Fused Silica Capillarya 75 m (inner diameter) x375 m (outer diameter) x 60 cm (length) having a polymercoating for flexibility, and noncoated section to act as the cellwindow for UV dete
49、ction.4,57.1.7 Constant Temperature Compartmentto keep thesamples, capillary, and electrolytes at constant temperature.7.2 Data Systema computer system that can acquire dataat 20 points/s minimum, express migration time in minutes tothree decimal places, use midpoint of the analyte peak width,or center of gravity, to determine the analyte migration time,use normalized migration times with respect to a referencepeak for qualitative identification, use time corrected peak arearesponse for analyte quantitation, and express results in con-centrat
