More E The techniques are simple in concept and can provide reliable results, provided the procedures are followed faithfully. Accordingly, the practice should provide a means for checking the original calibration of glassware and similar apparatus and for periodic rechecks as the need should arise. A frosting of the glass surface viewed when dry indicates that chemical attack has occured, and recalibration may be in order. As a precaution, however, it is recommended that the glassware be recalibrated after ten years of service regardless of its appearance.
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You are on page 1of 7 Search inside document Standard Practice for Calibration of Laboratory Volumetric Apparatus1 This standard is issued under the fixed designation E ; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision.
A number in parentheses indicates the year of last reapproval. A superscript 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. Scope volume of water either contained in or delivered by the vessel. It is based on the gravimetric determination of the quantity of 4. Significance and Use water either contained or delivered, and the conversion of this value to true volume at the standard temperature of 20C by 4.
Calibration uniform procedures that may be used to accurately calibrate a using mercury is excluded. Calibration may be performed wide variety of volumetric ware. The techniques are simple in using alternative gravimetric methodology, provided that it is concept and can provide reliable results, provided the proce- demonstrated and documented that the results obtained are dures are followed faithfully. Accordingly, the practice should equivalent to those obtained using the methodology described provide a means for checking the original calibration of herein.
Typical products 4. A frosting of the glass capacity pipets. As a precaution, apparatus with capacities below 0. It is the with time because of attack from moisture in the atmosphere as responsibility of the user of this standard to establish appro- well as from the chemicals mentioned above.
In addition, it priate safety and health practices and determine the applica- should not be heated above 90C when dry. It is recommended, bility of regulatory limitations prior to use. Referenced Documents 5. Units of Measurement 2. Rather, the cubic centimetre, cm3, is used and will SI the Modernized Metric System 3 be employed in this practice.
The unit, millilitre, mL, may be considered as equivalent to the cubic centimetre. Summary of Practice 5. The procedures described provide for such a calibration. When it is necessary to work at higher 1 ambient temperatures, such as is the case in tropical countries, This practice is under the jurisdiction of ASTM Committee E41 on Laboratory Apparatus, and is the direct responsibility of Subcommittee E Published January Equa- published as E Last previous edition E Apparatus ware should be cleaned in an appropriate manner before 6.
The sensitivity of the balance will be a limiting factor 7. Either a single-pan, 7. In either case the weights the meniscus. In order that the lowest point may be observed, must be calibrated with adequate accuracy. Ordinarily, weights it is necessary to place a shade of some dark material with NBS Class S-1 tolerances are required. The balance must immediately below and behind the meniscus, which renders the have physical dimensions to accept the size of the vessels profile of the meniscus dark and clearly visible against a light which need to be weighed.
A convenient device for this purpose is a collar- 6. The accuracy of this calibration will depend upon the side and of such size as to clasp the tube firmly.
Alternatively, accuracy requirement of the volumetric calibration see Section black paper may be used. Short line graduated vessels where 14 for tolerances. Alternatively, the existing barometric pressure may be 7. General Considerations with reference to the graduation line is horizontally tangent to the plane of the upper edge of the graduation line.
The position 7. Glass apparatus must be plane of the middle of the graduation line. This position of the sufficiently clean to permit uniform wetting of the surface. The clean of the tube as observed by having the eye slightly below the walls of some plastic apparatus, however, will not be wetted. The setting is accurate if, as the Follow the instructions of the manufacturer. Do not use eye is raised and the ellipse narrows, the lowest point of the materials which will attack, discolor, or swell the plasticware.
By this method it is possible to observe ing the water surface. The liquids usually used for cleaning the approach of the meniscus from either above or below the glassware are sodium dichromatic-sulfuric acid cleaning solu- line to its proper setting. The choice NOTE 1The difference between meniscus positions resulting from the alternative methods of adjustment is the volume equivalent of one half the of cleaning agent to be used depends on the nature of the thickness of the graduation line.
In the case of articles where the capacity contaminant. After cleaning with the cleaning solution and is read as the difference between two meniscus readings for example on thoroughly rinsing with tap water, the vessel should be rinsed a buret , then no error results if the article is manufactured using one with distilled water. It is not large flasks , when working to the highest attainable accuracy, the difference between the two methods of adjustment is unlikely to exceed necessary to dry any vessel marked to deliver.
The 8. Calibration Procedure for Burets solution should be drawn through the pipet several times until 8. Rinse thoroughly clamp a plain glass test tube, large enough to hold a thermom- with tap water and then with distilled water. For cleaning eter, near the buret if the buret is of such a size that it is not flasks, pour in enough cleaning solution while rotating so that large enough to insert a thermometer in the top for observing a film of solution will cover the entire interior surface.
A break the temperature of the water. Fill the buret from a reservoir or in the film indicates a contaminated area. For filling a buret storage bottle, in which the water has reached equilibrium with with cleaning solution, it should be held in a vertical position room temperature, and check to verify that there is neither and filled by pouring into the top.
Open the stopcock to drain. Drain and Regardless of the type of vessel, always rinse thoroughly, first record the delivery time. Delivery time is determined by the with tap water and then with distilled water. Plastic volumetric unrestricted outflow of the water from the zero mark to the 2 E lowest graduation mark with the stopcock fully open. Refill the and weigh. A pipet or dropper with a finely drawn tip may be buret to approximately 10 mm above the zero mark and fill the used to adjust the meniscus instead of the buret.
Determine the test tube that holds the thermometer; record the temperature. The tempera- lower the liquid level and touch the tip with the wetted wall of ture may be taken after final weighing by placing a thermom- a beaker to remove any excess water. A weighing flask that has eter directly in the flask, provided the flask is of sufficient size been tightly stoppered and weighed empty is placed with the to accommodate it.
Calibration of Flasks to Deliver 8. Fill the flask to approximately the index line and slowed so as to make an accurate setting. When the setting has empty rapidly by gradually inclining the flask so as to avoid been completed, move the flask horizontally, breaking the splashing on the walls as much as possible. When the main contact with the buret. Recheck the setting. Place a watch glass or plastic the same manner as the first onefrom the zero mark to the cap on the flask to reduce evaporation and weigh immediately.
Take a water temperature reading, fill the flask, and make the 8. Place the same cap or watch glass on the open the stopcock until the meniscus has reached a position a filled flask and weigh. The reverse of this procedure may be few millimetres above the graduation line for calibration.
After used, if desirable. Calibration of Other Volumetric Glassware Calibration Procedure for Pipets One Mark brated by a similar procedure as described in Section 8, except 9.
Refill by measuring pipet. Record the temperature of Then slowly lower the meniscus to the index using either a stopcock Weighing Procedure or hose clamp for fine control. The tip must be in contact Normally, index line. Do not remove any water remaining on the tip at IE and IL are observed under the same conditions, hence a this time.
Hold the pipet in a vertical position and deliver water precise zero adjustment of the balance is not necessary. Either into a previously weighed weighing flask with the tip in contact a single-pan or double-pan balance may be used. For the latter with the inside wall of the neck of the flask. After the water has case, during both weighings, place on the opposite pan a ceased to flow, wait 2 s, then remove the pipet from contact vessel, similar to the one being weighed to serve as a tare.
The flask is now stoppered and weighed with its Complete both of the required weighings in as short a time contained load. Record the temperature of the air in Calibration of Flasks to Contain the balance case and the barometric pressure for use in Place an appropriate sized funnel in the Fill from beaker requisite measurements. Weighings should be made with care or supply line, maneuvering the funnel so as to wet the entire and made expeditiously to minimize evaporation losses which neck below the stopper.
Let stand for about 2 min to allow the would constitute a source of error. The balance used should be walls to drain.
22. ASTM E-542 Standard Practice for calibration of laboratory volumetric apparatus.pdf