1、Designation: D 6855 03Standard Test Method forDetermination of Turbidity Below 5 NTU in Static Mode1This standard is issued under the fixed designation D 6855; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the static determination ofturbidity in water (see 4.1).1.2 This test method is applicable to the measur
3、ement ofturbidities under 5.0 nephelometric turbidity units (NTU).1.3 This test method was tested on municipal drinkingwater, ultra-pure water and low turbidity samples. It is theusers responsibility to ensure the validity of this test methodfor waters of untested matrices.1.4 This standard does not
4、 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 regulatory limitations prior to use. Refer to theMSDSs for all chemicals used
5、 in this procedure.2. Referenced Documents2.1 ASTM Standards:2D 1129 Terminology Relating to WaterD 1192 Guide for Equipment for Sampling Water andSteam in Closed ConduitsD 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Methods of Committee D
6、19 on WaterD 3370 Practices for Sampling Water from Closed ConduitsD 5847 Practice for Writing Quality Control Specificationsfor Standard Test Methods for Water AnalysisE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Other Referenced Standards:USE
7、PA Method 180.1 Methods for Chemical Analysis ofWater and Wastes, Turbidity3ISO 7027 (The International Organization for Standardiza-tion) Water Qualityfor the Determination of Turbidity43. Terminology3.1 DefinitionsFor definitions of terms used in thismethod refer to Terminology D 1129.3.2 Definiti
8、ons:3.2.1 calibration turbidity standarda turbidity standardthat is traceable and equivalent to the reference turbiditystandard to within statistical errors, including commerciallyprepared 4000 NTU Formazin, stabilized formazin (see 9.2.3),and styrenedivinylbenzene (SDVB) (see 9.2.4). These stan-dar
9、ds may be used to calibrate the instrument.NOTE 1Calibration standards may be instrument specific.3.2.2 calibration verification standardsdefined standardsused to verify the accuracy of a calibration in the measurementrange of interest. These standards may not be used to performcalibrations, only ca
10、libration verifications. Included standardsare opto-mechanical light scatter devices, gel-like standards, orany other type of stable liquid standard.NOTE 2Calibration verification standards may be instrument specific.3.2.3 nephelometric turbidity measurementthe measure-ment of light scatter from a s
11、ample in a direction that is at 90with respect to the centerline of the incident light path. Unitsare NTU (Nephelometric Turbidity Units); when ISO 7027technology is employed units are in FNU (Formazin Nephelo-metric Units).3.2.4 ratio turbidity measurementthe measurement de-rived through the use of
12、 a nephelometric detector that serves asthe primary detector and one or more other detectors used tocompensate for variation in incident light fluctuation, straylight, instrument noise, or sample color.3.2.5 reference turbidity standarda standard that is syn-thesized reproducibly from traceable raw
13、materials by a skilledanalyst. All other standards are traced back to this standard.The reference standard for turbidity is formazin (see 9.2.2).3.2.6 seasoningthe process of conditioning laboratoryglassware with the standard to be diluted to a lower value. The1This test method is under the jurisdic
14、tion of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-phology, and Open-Channel Flow.Current edition approved Jan. 10, 2003. Published April 2003.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Se
15、rvice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from United States Environmental Protection Association (EPA),Ariel Rios Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460.4Available from A
16、merican National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.process reduces contamination and dilution errors. See Appen-dix X2 for the suggested procedure
17、.3.2.7 stray lightall light reaching the detector other thanthat contributed by the sample. For example: ambient lightleakage, internal reflections and divergent light in opticalsystems.3.2.8 turbidimeteran instrument that measures light scat-ter using a nephelometric detector. Examples include phot
18、o-electric nephelometers and ratio photoelectric nephelometers.3.2.9 turbidityan expression of the optical properties of asample that causes light rays to be scattered and absorbedrather than transmitted in straight lines through the sample.Turbidity of water is caused by the presence of suspended a
19、nddissolved matter such as clay, silt, finely divided organicmatter, plankton, other microscopic organisms, organic acids,and dyes.4. Summary of Test Method4.1 The optical property expressed as turbidity is measuredby the scattering effect that suspended particulate material haveon light; the higher
20、 the intensity of scattered light, the higherthe turbidity. In samples containing particulate material, themanner in which sample interferes with light transmittance isrelated to the size, shape and composition of the particles in thewater, and also to the wavelength of the incident light.4.2 The me
21、thod is based upon a comparison of the intensityof light scattered by the sample with the intensity of lightscattered by a reference suspension. Turbidity values aredetermined by a nephelometer, which measures light scatterfrom a sample in a direction that is at 90 with respect to thecenterline of t
22、he incident light path.5. Significance and Use5.1 Turbidity is undesirable in drinking water, plant effluentwaters, water for food and beverage processing, and for a largenumber of other water-dependent manufacturing processes.Removal is often accomplished by coagulation, settling, andfiltration. Me
23、asurement of turbidity provides a rapid means ofprocess control for when, how, and to what extent the watermust be treated to meet specifications.5.2 This test method is suitable to turbidity such as thatfound in drinking water, process water, and high purityindustrial water.6. Interferences6.1 For
24、this application, bubbles, color and large particles,although they cause turbidity, may result in interferences inmeasured turbidity as determined by this method. Bubblescause a positive interference and color typically causes anegative interference. Dissolved material that imparts a colorto the wat
25、er may cause errors in pure nephelometric reading-s,unless the instrument has special compensating features toreduce these interferences. Certain turbulent motions alsocreate unstable reading conditions of nephelometers.6.2 Color is characterized by absorption of specific wave-lengths of light. If t
26、he wavelengths of incident light aresignificantly absorbed, a negative interference will result un-less the instrument has special compensating features.6.3 Scratches, finger marks, or dirt on the walls of thesample cell may give erroneous readings. Sample cells shouldbe kept scrupulously clean both
27、 inside and outside and dis-carded when they become etched or scratched. The samplecells must not be handled where the light strikes them whenpositioned in the instrument well.6.3.1 Sample cell caps and liners must also be scrupulouslyclean to prevent contamination of the sample.6.4 Ideally, the sam
28、e indexed sample cell should be usedfirst for standardization followed by unknown (sample) deter-mination. If this is not possible, then sample cells must bematched. Refer to the instrument manual for instructions onmatching sample cells.NOTE 3Indexing of the sample cell to the instrument well is ac
29、com-plished by placing a mark on the top of the sample cell and a similar markon the upper surface of the well so that the sample cell can be placed inthe well in an exact position each time.NOTE 4Sample cells can be matched by first filling with dilutionwater (see 8.2).Allow the sample cell to stan
30、d for 5 to 10 min to allow forbubbles to vacate the sample. This is followed by cleaning and polishingthe outside of the cell. Cells are then measured on the same turbidimeterand should read no different than 0.01 NTU.6.5 Condensation of optical elements or sample cells canlead to severe errors in m
31、easurement.7. Apparatus7.1 Two types of instruments are available for the nephelo-metric method, the nephelometer and ratio nephelometer (seeFigs. 1 and 2).7.2 The resolution of the instruments should permit detec-tion of differences of 0.01 NTU or less in waters havingturbidities of less than 5.0 N
32、TU. The instrument must measurethe range from #0.02 to 5.0 NTU. See 12.1 for calibration ofinstruments. Calibration verification in the immediate range ofinterest must be performed using acceptable, defined verifica-tion standards (see 12.2).NOTE 5Consult manufacturers instructions for guidance asso
33、ciatedwith verification methods and verification devices.7.2.1 Consult the manufacturer to ensure that your instru-ment meets or exceeds the specifications of this method.7.3 Photoelectric Nephelometer:7.3.1 This instrument uses a light source for illuminating thesample and a single photodetector wi
34、th a readout device toindicate the intensity of light scattered at right angle(s) (90) tothe centerline of the path of the incident light. The photoelec-tric nephelometer should be designed so that minimal straylight reaches the detector in the absence of turbidity and shouldbe free from significant
35、 drift after a short warm-up period. Thelight source shall be a Tungsten lamp operated at a colortemperature between 2200 and 3000 K (USEPA Method180.1). Light Emitting Diodes (LEDs) or laser diodes indefined wavelengths ranging from 400 to 900 nm may also beused if accurately characterized to be eq
36、uivalent in perfor-mance to tungsten using calibration and calibration verificationstandards. If LEDs or laser diodes are used, then the LED orLaser diode should be coupled with a monitor detection deviceto achieve a constant output . LEDs and laser diodes should becharacterized by a wavelength of b
37、etween 400 and 900 nmD6855032with a bandwidth of less than 60 nm. (Examples of LEDsinclude: White light with a defined bandwidth and 860 6 30nm per ISO 7027.) The total distance traversed by incidentlight and scattered light within the sample is not to exceed 10cm. The angle of light acceptance to t
38、he detector shall becentered at 90 to the centerline of the incident light path andshall not exceed 6 10 from the 90 scatter path center line.The detector must have a spectral response that is sensitive tothe spectral output of the incident light used.7.3.2 Differences in physical design of photoele
39、ctricnephelometers will cause slight differences in measured valuesfor turbidity even though the same suspension is used forcalibrations. Comparability of measurements made using in-struments differing in optical and physical design is notrecommended. To minimize initial differences, the followingde
40、sign criteria should be observed (see Fig. 1).7.4 Ratio Photoelectric Nephelometer:7.4.1 Ratio Photoelectric Nephelometer(see Fig. 2 forsingle beam design; see Fig. 3 for multiple beam design.) Thisinstrument uses the measurement derived through the use of anephelometric detector that serves as the
41、primary detector andone or more other detectors used to compensate for variation inincident light fluctuation, stray light, instrument noise, orsample color. As needed by the design, additional photodetec-tors may be used to sense the intensity of light scattered atother angles. The signals from the
42、se additional photodetectorsmay be used to compensate for variations in incident lightfluctuation, instrument stray light, instrument noise and/orsample color. The ratio photoelectric nephelometer should beso designed that minimal stray light reaches the detector(s),and should be free from significa
43、nt drift after a short warm-upperiod. The light source should be a tungsten lamp, operated ata color temperature between 2200 and 3000 K (USEPAMethod 180.1). LEDs and laser diodes in defined wavelengthsranging from 400 to 900 nm may also be used. If an LED or alaser diode is used in the single beam
44、design, then the LED orlaser diode should be coupled with a monitor detection deviceto achieve a consistent output. The distance traversed byincident light and scattered light within the sample is not toexceed 10 cm. The angle of light acceptance to the nephelo-metric detector(s) should be centered
45、at 90 to the centerline ofthe incident light path and should not exceed 610 from theFIG. 1 Photoelectric NephelometerFIG. 2 Ratio Photoelectric Nephelometer (Single Beam Design)D6855033scatter path center line. The detector must have a spectralresponse that is sensitive to the spectral output of the
46、 incidentlight used. The instrument calibration (algorithm) must bedesigned such that the scaleable reading is from the nephelo-metric detector(s), and other detectors are used to compensatefor instrument variation described in 7.3.1.7.4.2 Differences in physical design of ratio photoelectricnephelo
47、meters will cause slight differences in measured valuesfor turbidity even when the same suspension is used forcalibrations. Comparability of measurements made using in-struments differing in optical and physical design is notrecommended. To minimize initial differences, the followingdesign criteria
48、should be observed (see Figs. 2 and 3).7.5 Sample Cells:7.5.1 The sample cells used in calibration and samplemeasurement must be the following:7.5.1.1 Clear, colorless glass or optically clear plastic, bekept scrupulously clean, both inside and out, and discardedwhen it becomes etched or scratched (
49、see non mandatoryAppendix X1 for sample cell cleaning procedure).7.5.1.2 Index marked so that repeated exact placements intothe instrument sample cell compartment for measurement canbe made. See 11.4.2.1.7.5.1.3 Handled where the light path does not pass duringmeasurement. Provision should be made in design to give thesample cell a proper place in which to handle the cell duringcalibration or sample measurement procedure. Instrument andsample cell design criteria are given in 7.3.1.7.5.1.4 The outside surface of a glass sample cell may beoiled, using silicone
