ASTM E542-2001(2012) 2500 Standard Practice for Calibration of Laboratory Volumetric Apparatus《实验室容量仪器校准的标准方法》.pdf

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1、Designation: E542 01 (Reapproved 2012)Standard Practice forCalibration of Laboratory Volumetric Apparatus1This standard is issued under the fixed designation E542; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re

2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This practice covers procedures for use in t

3、he calibrationof volumetric ware, in accordance with Specification E694such as is in common use in chemical and clinical laboratories.It is based on the gravimetric determination of the quantity ofwater either contained or delivered, and the conversion of thisvalue to true volume at the standard tem

4、perature of 20C bymeans of suitable equations and standard tables. Calibrationusing mercury is excluded. Calibration may be performedusing alternative gravimetric methodology, provided that it isdemonstrated and documented that the results obtained areequivalent to those obtained using the methodolo

5、gy describedherein.1.2 This practice is intended to encompass capacity warebetween the limits of 0.1 cm3and 2000 cm3. Typical productsfalling within the purview of this practice are burets graduated“to deliver”, graduated cylinders, volumetric flasks, specificgravity flasks, measuring and dilution p

6、ipets, and transfer andcapacity pipets.1.3 The procedures are not recommended for calibration ofapparatus with capacities below 0.1 cm3, such as microglass-ware.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the us

7、er of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E694 Specification for Laboratory Glass Volumetric Appa-ratus3. Summary of Practice3.1 This practice is based u

8、pon a determination of thevolume of water either contained in or delivered by the vessel.Procedures are given for cleaning, setting the meniscus,manipulating the apparatus, weighing, and converting theweight to the appropriate standard volume.4. Significance and Use4.1 The primary purpose of this pr

9、actice is to provideuniform procedures that may be used to accurately calibrate awide variety of volumetric ware. The techniques are simple inconcept and can provide reliable results, provided the proce-dures are followed faithfully. Accordingly, the practice shouldprovide a means for checking the o

10、riginal calibration ofglassware and similar apparatus and for periodic rechecks asthe need should arise.4.2 Borosilicate volumetric glassware will hold its calibra-tion indefinitely provided that it is not exposed to hydrofluoricacid, hot phosphoric acid, or strong, hot alkalis, and that it isnot he

11、ated above 150C when dry. A frosting of the glasssurface (viewed when dry) indicates that chemical attack hasoccured, and recalibration may be in order. As a precaution,however, it is recommended that the glassware be recalibratedafter ten years of service regardless of its appearance.4.3 Soda-lime

12、volumetric glassware will become frostedwith time because of attack from moisture in the atmosphere aswell as from the chemicals mentioned above. In addition, itshould not be heated above 90C when dry. It is recommended,therefore, that it be recalibrated after five years of serviceunless frosting (v

13、iewed when dry) is observed sooner.5. Units of Measurement5.1 CapacityThe basic SI unit for volume is the cubicmetre, m3. Due to its large size, it is rarely used in volumetriccalibration. Rather, the cubic centimetre, cm3, is used and willbe employed in this practice. The unit, millilitre, mL, may

14、beconsidered as equivalent to the cubic centimetre.5.2 Standard TemperatureVolumetric ware is almost uni-versally calibrated at 20C. The procedures described providefor such a calibration. When it is necessary to work at higherambient temperatures, such as is the case in tropical countries,1This pra

15、ctice is under the jurisdiction of ASTM Committee E41 on LaboratoryApparatus and is the direct responsibility of Subcommittee E41.01 on Apparatus.Current edition approved Nov. 1, 2012. Published November 2012. Originallyapproved in 1979. Last previous edition approved in 2007 as E542 01(2007). DOI:1

16、0.1520/E0542-01R12.2For referenced ASTM standards, 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.Copyright ASTM International, 100 Barr Har

17、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1calibration may be required at the International StandardsOrganization (ISO) recommended temperature of 27C. Equa-tions are given to correct the calibrated volume to othertemperatures as this may be required or desired.6. Appara

18、tus6.1 Balance, having sufficient capacity to weigh the loadedvessel. The sensitivity of the balance will be a limiting factorin the accuracy of the measurements. Either a single-pan,direct-reading balance or an equal-arm balance of adequatesensitivity and capacity may be used. In either case the we

19、ightsmust be calibrated with adequate accuracy. Ordinarily, weightswith NBS Class S-1 tolerances are required. The balance musthave physical dimensions to accept the size of the vesselswhich need to be weighed.6.2 Thermometer, for measuring the temperature of thewater. The accuracy of this calibrati

20、on will depend upon theaccuracy requirement of the volumetric calibration (see Section14 for tolerances).6.3 Barometer, capable of providing atmospheric pressuremeasurements, consistent with the tolerances given in Section14. Alternatively, the existing barometric pressure may beobtained from the lo

21、cal weather service.6.4 Distilled or Deionized Water, suitable for general labo-ratory purposes.7. General Considerations7.1 This section describes manipulative techniques requiredto obtain accurate and reproducible volumetric measurements.7.2 Cleaning Procedures:7.2.1 It is important that volumetri

22、c ware be thoroughlycleaned before being tested or used. Glass apparatus must besufficiently clean to permit uniform wetting of the surface.When clean, the walls will be uniformly wetted and the waterwill adhere to the glass surface in a continuous film. The cleanwalls of some plastic apparatus, how

23、ever, will not be wetted.(Follow the instructions of the manufacturer. Do not usematerials which will attack, discolor, or swell the plasticware.)Lack of cleanliness causes irregularities in capacity by distort-ing the water surface. The liquids usually used for cleaningglassware are sodium dichroma

24、tic-sulfuric acid cleaning solu-tion (commercially available from laboratory supply houses),nitric acid, fuming sulfuric acid, alcohol, and water. The choiceof cleaning agent to be used depends on the nature of thecontaminant. After cleaning with the cleaning solution andthoroughly rinsing with tap

25、water, the vessel should be rinsedwith distilled water.7.2.2 After cleaning, the vessel should be rinsed with ethylalcohol and dried with clean air at room temperature. It is notnecessary to dry any vessel marked “to deliver.” Whencleaning small articles such as pipets, it is usually easier to fillt

26、hem with cleaning solution by suction, using a vacuum line, ifavailable, or a small rubber bulb, but never by mouth. Thesolution should be drawn through the pipet several times untilthe entire inside surface is evenly coated. Rinse thoroughlywith tap water and then with distilled water. For cleaning

27、flasks, pour in enough cleaning solution while rotating so thata film of solution will cover the entire interior surface. A breakin the film indicates a contaminated area. For filling a buretwith cleaning solution, it should be held in a vertical positionand filled by pouring into the top. Open the

28、stopcock to drain.Regardless of the type of vessel, always rinse thoroughly, firstwith tap water and then with distilled water. Plastic volumetricware should be cleaned in an appropriate manner beforecalibration.7.3 Reading and Setting a Liquid Meniscus:7.3.1 Reading the MeniscusFor all apparatus ca

29、librated bythis procedure, the reading is made on the lowest point of themeniscus. In order that the lowest point may be observed, it isnecessary to place a shade of some dark material immediatelybelow and behind the meniscus, which renders the profile ofthe meniscus dark and clearly visible against

30、 a light back-ground.Aconvenient device for this purpose is a collar-shapedsection of thick black rubber tubing, cut open at one side andof such size as to clasp the tube firmly. Alternatively, blackpaper may be used. “Short line” graduated vessels where thelines are less than one half of the circum

31、ference may be readmore accurately by placing a mirror against the rear of thevessel to reflect the front line.7.3.2 Setting the MeniscusSetting of the meniscus shall beperformed by one of the two methods detailed below. Wher-ever practical the meniscus should descend to the position ofsetting.7.3.2

32、.1 The position of the lowest point of the meniscuswith reference to the graduation line is horizontally tangent tothe plane of the upper edge of the graduation line. The positionof the meniscus is obtained by having the eye in the same planeof the upper edge of the graduation line.7.3.2.2 The posit

33、ion of the lowest point of the meniscuswith reference to the graduation line is such that it is in theplane of the middle of the graduation line. This position of themeniscus is obtained by making the setting in the center of theellipse formed by the graduation line on the front and the backof the t

34、ube as observed by having the eye slightly below theplane of the graduation line. The setting is accurate if, as theeye is raised and the ellipse narrows, the lowest point of themeniscus remains midway between the front and rear portionsof the graduation line. By this method it is possible to observ

35、ethe approach of the meniscus from either above or below theline to its proper setting.NOTE 1The difference between meniscus positions resulting from thealternative methods of adjustment is the volume equivalent of one half thethickness of the graduation line. In the case of articles where the capac

36、ityis read as the difference between two meniscus readings (for example ona buret), then no error results if the article is manufactured using onemethod of adjustment and is later used by the other method.Even in the most unfavorable cases of single-mark articles (for examplelarge flasks), when work

37、ing to the highest attainable accuracy, thedifference between the two methods of adjustment is unlikely to exceed30 % of the Class A (precision apparatus) limit of error and a correctioncan be calculated where necessary.8. Calibration Procedure for Burets8.1 Clamp the buret vertically on a support s

38、tand; alsoclamp a plain glass test tube, large enough to hold athermometer, near the buret if the buret is of such a size that itis not large enough to insert a thermometer in the top forE542 01 (Reapproved 2012)2observing the temperature of the water. Fill the buret from areservoir or storage bottl

39、e, in which the water has reachedequilibrium with room temperature, and check to verify thatthere is neither leakage from the tip nor from the stopcockplug. Drain and record the delivery time. Delivery time isdetermined by the unrestricted outflow of the water from thezero mark to the lowest graduat

40、ion mark with the stopcockfully open. Refill the buret to approximately 10 mm above thezero mark and fill the test tube that holds the thermometer;record the temperature. Set the meniscus on the zero markusing the buret stopcock to lower the liquid level and touch thetip with the wetted wall of a be

41、aker to remove any excesswater. A weighing flask that has been tightly stoppered andweighed empty is placed with the inside of the neck in contactwith the tip of the buret (the flask will be at a slight angle).8.2 Fully open the stopcock until the water is only a fewmillimetres above the line being

42、tested and then the stream isslowed so as to make an accurate setting. When the setting hasbeen completed, move the flask horizontally, breaking thecontact with the buret. Recheck the setting.8.3 Then stopper and weigh the flask a second time, afterwhich refill the thermometer tube and test the next

43、 interval inthe same manner as the first onefrom the zero mark to thenext interval needed.8.4 For burets with a specified waiting time, use thefollowing procedure: after adjustment to the zero mark, fullyopen the stopcock until the meniscus has reached a position afew millimetres above the graduatio

44、n line for calibration.Afterthe specified waiting time (for example, 30 s), adjust themeniscus to the graduation line, remove the flask, and weigh.9. Calibration Procedure for Pipets (One Mark)9.1 Fill the pipet with distilled water by suction to the indexmark and measure the delivery time with the

45、tip in contact withthe glass surface of the internal side of a beaker. Refill bysuction slightly above the index line. Record the temperature ofthe distilled water in the beaker from which the pipet is filled.Remove any water on the outside of the tip by a downwardwipe with filter paper after the fi

46、lling is completed. Thenslowly lower the meniscus to the index using either a stopcockor hose clamp for “fine control.” The tip must be in contactwith the wet wall of a beaker while the setting is made on theindex line. Do not remove any water remaining on the tip atthis time. Hold the pipet in a ve

47、rtical position and deliver waterinto a previously weighed weighing flask with the tip in contactwith the inside wall of the neck of the flask.After the water hasceased to flow, wait 2 s, then remove the pipet from contactwith the flask. The flask is now stoppered and weighed with itscontained load.

48、10. Calibration of Flasks (to Contain)10.1 After cleaning and drying, weigh the empty flaskincluding the stopper. Place an appropriate sized funnel in theflask to discharge the water below the stopper. Fill from beakeror supply line, maneuvering the funnel so as to wet the entireneck below the stopp

49、er. Let stand for about 2 min to allow thewalls to drain.10.1.1 After cleaning and drying, weigh the empty flaskincluding the stopper. Place an appropriate sized funnel orother filling device in the flask to discharge the water below thecapacity line. Fill from beaker or supply line taking care toavoid wetting neck above capacity line.10.1.2 Place the flask under a buret and complete filling andsetting the meniscus, taking care not to splash water on thewalls, after which place stopper in neck to lessen evaporationand weigh. A pipet or dropper with a finely drawn tip may