ASTM D6508-2000(2005)e2 288 Standard Test Method for Determination of Dissolved Inorganic Anions in Aqueous Matrices Using Capillary Ion Electrophoresis and Chromate Electrolyte《用毛.pdf

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1、Designation: D 6508 00 (Reapproved 2005)e2Standard Test Method forDetermination of Dissolved Inorganic Anions in AqueousMatrices Using Capillary Ion Electrophoresis and ChromateElectrolyte1This standard is issued under the fixed designation D 6508; the number immediately following the designation in

2、dicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEWarning notes were moved into the text in Jan

3、uary 2005.e2NOTEAdded research report reference to Section 17 editorially in March 2008.1. Scope1.1 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 otheraqueous matrices u

4、sing 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 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 t

5、o 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 1The highest accepted anion concentration submitted forprecision and bias extend the anion concentration range for the followinganions: Chlori

6、de to 93 mg/L, Sulfate to 90 mg/L, Nitrate to 72 mg/L, andortho-phosphate to 58 mg/L.1.4 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 an

7、d determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 9.2. Referenced Documents2.1 ASTM Standards:2D 1066 Practice for Sampling SteamD 1129 Terminology Relating to WaterD 1193 Specification for Reagent WaterD 2777 Practice for Determination

8、 of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3370 Practices for Sampling Water from Closed Conduits1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Curren

9、t edition approved Jan. 1, 2005. Published April 2005.Originally approved in 2000. Last previous edition approved in 2000 asD 6508 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume info

10、rmation, refer to the standards Document Summary page onthe ASTM website.FIG. 1 Electropherogram of Mixed Anion Working Solution andAdded Common Organic AcidsFIG. 2 Electropherogram of 0.2 mg/L Anions Used to DetermineMDL1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoh

11、ocken, PA 19428-2959, United States.D 3856 Guide for Good Laboratory Practices in Laborato-ries Engaged in Sampling and Analysis of WaterD 5810 Guide for Spiking into Aqueous SamplesD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisD 5905 Practice

12、for the Preparation of Substitute Wastewa-terF 488 Test Method for On-Site Screening of HeterotrophicBacteria in Water3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 capillary ion elec

13、trophoresis, nan electrophoretictechnique in which a UV-absorbing electrolyte is placed in a 50m to 75 m fused silica capillary. Voltage is applied across thecapillary causing electrolyte and anions to migrate towards theanode and through the capillarys UV detector window.Anionsare separated based u

14、pon the their differential rates of migra-tion in the electrical field. Anion detection and quantitation arebased upon the principles of indirect UV detection.3.2.2 electrolyte, na combination of a UV-absorbing saltand an electroosmotic flow modifier placed inside the capillary,used as a carrier for

15、 the analytes, and for detection andquantitation. The UV-absorbing portion of the salt must beanionic and have an electrophoretic mobility similar to theanalyte anions of interest.3.2.3 electroosmotic flow (EOF), nthe direction and ve-locity of electrolyte solution flow within the capillary under an

16、applied 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 cationicquaternary amine in the electrolyte that dynamically coats thenegatively charged silica

17、wall giving it a net positive charge.This reverses the direction of the electrolytes natural elec-troosmotic flow and directs it towards the anode and detector.This modifier augments anion migration and enhances speed ofanalysis. Its concentration secondarily effects anion selectivityand resolution,

18、 (see Fig. 7).3.2.5 electrophoretic mobility, nthe specific velocity of acharged analyte in the electrolyte under specific electroosmoticflow conditions. The mobility of an analyte is directly relatedto the analytes equivalent ionic conductance and appliedvoltage, and is the primary mechanism of sep

19、aration.3.2.6 electropherogram, na graphical presentation of UV-detector response versus time of analysis; the x axis isFIG. 3 Electropherogram of Substitute WastewaterFIG. 4 Electropherogram of Drinking WaterFIG. 5 Electropherogram of Municipal Wastewater TreatmentPlant DischargeFIG. 6 Electrophero

20、gram of Industrial WastewaterD 6508 00 (2005)e22migration time, which is used to qualitatively identify theanion, and the y axis is UV response, which can be convertedto time corrected peak area for quantitation.3.2.7 hydrostatic sampling, na sample introduction tech-nique in which the capillary wit

21、h electrolyte is immersed in thesample, and both are elevated to a specific height, typically 10cm, above the receiving electrolyte reservoir for a presetamount of time, typically less than 60 s. Nanolitres of sampleare siphoned into the capillary by differential head pressure andgravity.3.2.8 indir

22、ect UV detection, na form of UV detection inwhich the analyte displaces an equivalent net charge amount ofthe highly UV-absorbing component of the electrolyte causinga net decrease in background absorbance. The magnitude of thedecreased absorbance is directly proportional to analyte con-centration.

23、Detector output polarity is reversed in order toobtain a positive mV response.3.2.9 midpoint of peak width, nCIE peaks typically areasymmetrical with the peak apex shifting with increasingconcentration, and the peak apex may not be indicative of trueanalyte migration time. Midpoint of peak width is

24、the midpointbetween the analyte peaks 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. Themigration time in capillary ion electrophoresis is analogous toretention time in chromat

25、ography.3.2.11 time corrected peak area, nnormalized peak area;peak area divided by migration time. CE principles state thatpeak area is dependent upon migration time, that is, for thesame concentration of analyte, as migration time increases(decreases) peak area increases (decreases). Time correcte

26、dpeak area accounts for 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 in t

27、heelectrolyte 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 modi

28、fied EOF incombination with a negative power supply augments theFIG. 7 Pictorial Diagram of Anion Mobility and ElectroOsomotic Flow ModifierFIG. 8 Selectivity Diagram of Anion Mobility Using Capillary IonElectrophoresisFIG. 9 Pictorial Diagram of Indirect UV DetectionD 6508 00 (2005)e23mobility of t

29、he 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 species move towardthe detector at the same rate as the EOF. The neutral speciesmigrate

30、 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 electrolyteis immersed in the sample and the height of the sample raised10 cm for 30 s where

31、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 based upon the principles of indirectUV detection. The UV-absorbing electrolyte an

32、ion is displacedcharge-for-charge by the separated analyte anion. The analyteanion zone has a net decrease in background absorbance. Thisdecrease in UV absorbance in quantitatively proportional toanalyte anion concentration (see Fig. 9). Detector outputpolarity is reversed to provide positive mV res

33、ponse to the datasystem, and to make the negative absorbance peaks appearpositive.4.4 The analysis is complete once the last anion of interestis detected. The capillary is vacuum purged automatically bythe system of any remaining sample and replenished with freshelectrolyte. The system now is ready

34、for the next analysis.5. Significance and Use5.1 Capillary ion electrophoresis provides a simultaneousseparation and determination of several inorganic anions usingnanolitres of sample in a single injection. All anions present inthe sample matrix will be visualized yielding an anionic profileof the

35、sample.5.2 Analysis time is less than 5 minutes with sufficientsensitivity for drinking water and wastewater applications.Time between samplings is less than seven minutes allowingfor high sample throughput.5.3 Minimal sample preparation is necessary for drinkingwater and wastewater matrices. Typica

36、lly, only a dilution withwater is needed.5.4 This test method is intended as an alternative to othermulti-analyte methods and various wet chemistries for thedetermination of inorganic anions in water and wastewater.Compared to other multi-analyte methods the major benefits ofCIE are speed of analysi

37、s, simplicity, and reduced reagentconsumption and operating costs.6. Interferences6.1 Analyte identification, quantitation, and possible 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 t

38、he concentration differen-tial is less than 100:1. As the resolution between two anionpeaks increase so does the tolerated concentration 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 Disso

39、lved carbonate, detected as HCO3-1, is an anionpresent in all aqueous samples, especially alkaline samples.Carbonate concentrations greater than 500 mg/L will interferewith PO4quantitation.6.3 Monovalent organic acids, except for formate, andneutral organics commonly found in wastewater migrate late

40、rin the electropherogram, after carbonate, and do not interfere.Formate, a common organic acid found in environmentalsamples, migrates shortly after fluoride but before phosphate.Formate concentrations greater than 5 mg/L will interfere withfluoride identification and quantitation. Inclusion of 2 mg

41、/Lformate into the mixed anion working solution aids in fluorideand formate identification and quantitation.6.4 Divalent organic acids usually found in wastewatermigrate after phosphate. At high concentrations, greater than10 mg/L, they may interfere with phosphate identification andquantitation.FIG

42、. 10 General Hardware Schematic of a Capillary Ion Electrophoresis SystemD 6508 00 (2005)e246.5 Chlorate also migrates after phosphate and at concen-trations greater than 10 mg/L will interfere with phosphateidentification and quantitation. Inclusion of 5 mg/L chlorateinto the mixed anion working so

43、lution 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 perpendicularbetween them to the baseline. This causes a decrease in pe

44、akarea 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 Electrophoresis Systemthe system con-sists of the following components, as shown in

45、 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 prevent environmentalcontamination of the samples and electrolytes duri

46、ng a multi-sample batch analysis.7.1.3 Sample Introduction Mechanism, capable of hydro-static 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 pr

47、evious sample matrix, and to clean thecapillary with other reagent, such as sodium hydroxide.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

48、a polymercoating for flexibility, and noncoated section to act as the cellwindow for UV detection.37.1.7 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 migra

49、tion 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-centration units.3NOTE 2It is recommended that integrators or standard chromato-graphic data processing not be used with this test method.7.3 Anion Exchange Cartridges in the Hydroxide Form.3,47.4 Plastic Syringe, 20-mL, dispo