ASTM E542-2001 Standard Practice for Calibration of Laboratory Volumetric Apparatus《试验室量器校准的标准规程》.pdf

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1、Designation: E 542 01Standard Practice forCalibration of Laboratory Volumetric Apparatus1This standard is issued under the fixed designation E 542; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number

2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 the calibrationo

3、f 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 temperature of 20C

4、 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 methodology describedher

5、ein.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 pipets, and tran

6、sfer 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 user of this stan

7、dard 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:E 1 Specification for ASTM Thermometers2E 694 Specification for Volumetric Ware3SI 10 Standard for Use of the International Sys

8、tem of Units(SI) (the Modernized Metric System)33. Summary of Practice3.1 This practice is based upon 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 thew

9、eight to the appropriate standard volume.4. Significance and Use4.1 The primary purpose of this practice 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

10、-dures are followed faithfully. Accordingly, the practice shouldprovide a means for checking the original 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

11、not exposed to hydrofluoricacid, hot phosphoric acid, or strong, hot alkalis, and that it isnot heated 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 t

12、he glassware be recalibratedafter ten years of service regardless of its appearance.4.3 Soda-lime 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.

13、It is recommended,therefore, that it be recalibrated after five years of serviceunless frosting (viewed 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 c

14、ubic centimetre, cm3, is used and willbe employed in this practice. The unit, millilitre, mL, may 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 ne

15、cessary to work at higherambient temperatures, such as is the case in tropical countries,calibration 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

16、desired.1This practice is under the jurisdiction of ASTM Committee E41 on LaboratoryApparatus, and is the direct responsibility of Subcommittee E41.01 on Apparatus.Current edition approved Octo. 10, 2001. Published January 2002. Originallypublished as E 542 79. Last previous edition E 542 00.2Annual

17、 Book of ASTM Standards, Vol 14.03.3Annual Book of ASTM Standards, Vol 14.04.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Apparatus6.1 Balance, having sufficient capacity to weigh the loadedvessel. The sensitivity of the balanc

18、e 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 weightsmust be calibrated with adequate accuracy. Ordinarily, weightswith NBS Class S-1 tolerances ar

19、e 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 calibration will depend upon theaccuracy requirement of the volumetric calibration (see Section14 for tolera

20、nces).6.3 Barometer, capable of providing atmospheric pressuremeasurements, consistent with the tolerances given in Section14. Alternatively, the existing barometric pressure may beobtained from the local weather service.6.4 Distilled or Deionized Water, suitable for general labo-ratory purposes.7.

21、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 volumetric ware be thoroughlycleaned before being tested or used. Glass apparatus must besufficiently clean

22、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, however, will not be wetted.(Follow the instructions of the manufacturer. Do not usematerials which wi

23、ll 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 dichromatic-sulfuric acid cleaning solu-tion (commercially available from laboratory supply houses),nitric

24、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 water, the vessel should be rinsedwith distilled water.7.2.2 After cleaning, the vessel should be r

25、insed 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 fillthem with cleaning solution by suction, using a vacuum line, ifavailable, or a small rubber bulb, bu

26、t 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 cleaningflasks, pour in enough cleaning solution while rotating so thata film of solution will cover the en

27、tire 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 stopcock to drain.Regardless of the type of vessel, always rinse thoroughly, firstwith tap water an

28、d 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 calibratedby this procedure, the reading is made on the lowest point ofthe meniscus. In order that th

29、e lowest point may be observed,it is necessary to place a shade of some dark materialimmediately below and behind the meniscus, which renders theprofile of the meniscus dark and clearly visible against a lightbackground. A convenient device for this purpose is a collar-shaped section of thick black

30、rubber tubing, cut open at oneside and of such size as to clasp the tube firmly. Alternatively,black paper may be used. “Short line” graduated vessels wherethe lines are less than one half of the circumference may beread more accurately by placing a mirror against the rear of thevessel to reflect th

31、e front line.7.3.2 Setting the MeniscusSetting of the meniscus shallbe performed by one of the two methods detailed below.Wherever practical the meniscus should descend to the positionof setting.7.3.2.1 The position of the lowest point of the meniscuswith reference to the graduation line is horizont

32、ally 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 position of the lowest point of the meniscuswith reference to the graduation line is such that it is in t

33、heplane 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 tube as observed by having the eye slightly below theplane of the graduation line. The setting is acc

34、urate 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 observethe approach of the meniscus from either above or below theline to its proper setting.NOTE 1The dif

35、ference 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 capacityis read as the difference between two meniscus readings (for example ona buret), then no error re

36、sults 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 working to the highest attainable accuracy, thedifference between the two methods of adjustment is unlik

37、ely 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 stand; alsoclamp a plain glass test tube, large enough to hold a thermom-eter, near the buret if the

38、buret is of such a size that it is notlarge enough to insert a thermometer in the top for observingthe temperature of the water. Fill the buret from a reservoir orstorage bottle, in which the water has reached equilibrium withroom temperature, and check to verify that there is neitherleakage from th

39、e tip nor from the stopcock plug. Drain andrecord the delivery time. Delivery time is determined by theunrestricted outflow of the water from the zero mark to theE 5422lowest graduation mark with the stopcock fully open. Refill theburet to approximately 10 mm above the zero mark and fill thetest tub

40、e that holds the thermometer; record the temperature.Set the meniscus on the zero mark using the buret stopcock tolower the liquid level and touch the tip with the wetted wall ofa beaker to remove any excess water. A weighing flask that hasbeen tightly stoppered and weighed empty is placed with thei

41、nside of the neck in contact with the tip of the buret (the flaskwill be at a slight angle).8.2 Fully open the stopcock until the water is only a fewmillimetres above the line being tested and then the stream isslowed so as to make an accurate setting. When the setting hasbeen completed, move the fl

42、ask 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 interval inthe same manner as the first onefrom the zero mark to thenext interval needed.8.4 For burets with a specif

43、ied 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 graduation line for calibration. Afterthe specified waiting time (for example, 30 s), adjust themeniscus to the graduation line

44、, 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 tip in contact withthe glass surface of the internal side of a beaker. Refill bysuction slightly above the index line

45、. 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 filling is completed. Thenslowly lower the meniscus to the index using either a stopcockor hose clamp for “fine control

46、.” 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 vertical position and deliver waterinto a previously weighed weighing flask with the tip in contactwith the inside wall

47、 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.10. Calibration of Flasks (to Contain)10.1 After cleaning and drying, weigh the empty flaskincluding the stopper. Pl

48、ace 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 stopper. Let stand for about 2 min to allow thewalls to drain.10.1.1 After cleaning and drying, weigh the empty flaskincl

49、uding 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 beused to adjust the meniscus instead of the buret. Determine thetemperature by placing a thermometer in the filling be