Class A glassware

Measurement Errors for Class A Glassware Class B Glassware... 

Some volumetric glassware products have a large A imprint on the label. This designates the item as a class A item, meaning that more stringent calibration procedures were undertaken when it was manufactured. Class A glassware is thus more expensive, but it is most appropriate when highly precise work is important. This imprint may be found on both flasks and pipets. 

It is important to remember that whatever volume measurement device is used, the analyst depends on it to deliver the indicated volume, i.e., it must be properly calibrated. Analytical chemists and technicians often depend on class A glassware to represent accurate calibration and hence do not usually feel the need for independent calibration. However, where non-class A glassware and alternative transfer devices are used, there is legitimate concern over their proper calibration. 

Contrary to common belief, it is safe to place borosilicate volumetric ware in a drying oven. While there has not been a study indicating the effects of heating on Type I, Class B or Type II glass, there was a study on Type I, Class A volumetric ware. The study was done by Burfield and Hefter,6 and the results (which are shown in Table 2.8) clearly indicate that any variations from the original volume are within tolerances even for Class A glassware. 

Clinical chemistry procedures require accurate volumetric measurements to ensure accurate results. For accurate work, only Class A glassware should be used. Class A glassware is certified to conform to the specifications outlined in NIST circular C-602. ... 

Glassware types include Class A and Class B. Class A glassware is manufactured to the highest tolerances from Pyrex, borosilicate, or Kimax glass (see tables on pages 41 and 42). Class B (economy ware) tolerances are about twice those of Class A. 

Class A glassware is accurate enough for most analyses. It can be calibrated to NIST specifications. 

We commonly measure liquid volumes with precision volumetric glassware such as burets, pipets, and volumetric flasks. The National Institute of Standards and Technology in the United States has established specifications for Class A glassware two examples are listed in Table 2.2 on the next page. We may accurately determine the volume of a vessel at one temperature from the mass of a liquid of known density, such as water, that fills the vessel at this temperature. 

Uncertainty is often taken to be half a division on either side of the smallest unit on the scale. However, the accuracy of measurements also depends on the quality of the glassware used, for example. Class A and Class B glassware. Class B volumetric glassware usually has ml errors or random uncertainties greater (often twice) than those of Class A glassware. For example, for Class A and Class B 100 cm volumetric flasks the uncertainties are Class A 0.08 ml and Class B 0.20 ml (Figure 11.7). 

Volumetric Flasks. 1-L capacity. These flasks should be Class A glassware. 

Microburets. 2.00 or 5.00-mL capacity. The microburets should be Class A glassware with 0.01 or 0.02-mL divisions or less. It is advisable to have the buret s tip end equipped with a syringe needle to dispense very small drops of titrant. 

Specifications for class A and class B glassware are taken from American Society for Testing and Materials E288, E542 and E694 standards. 

As with other graduated glassware, burettes are produced to both Class A and Class B specifications in accordance with the appropriate standard [BS 846 (1985) ISO 385 (1984)], and Class A burettes may be purchased with BST Certificates. All Class A and some Class B burettes have graduation marks which completely encircle the burette this is a very important feature for the avoidance of parallax errors in reading the burette. Typical values for the tolerances permitted for Class A burettes are ... 

What is essential in establishing traceability is that the measurand is specified unambiguously. This may be, e.g. in terms of extractable cadmium from soil by using a named acid mix or the concentration of a metal in a particular oxidation state, e.g. Fe(n) or Fe(m). The units used to report the result should also be known and acceptable SI units are preferred. The method used will be validated and if used in accordance with the written procedures should produce results that are fit for purpose . The class of glassware to be used will be specified in the method procedure, e.g. Class A pipettes and volumetric flasks, as these are manufactured to a specified tolerance. Instruments will be regularly calibrated and their performance verified daily. In terms of the chemicals used, these will... 

Ware. This glassware is calibrated not only to Class A tolerances, but to each mark on the glass. This calibration ensures high accuracy for every measurement. It needs to be specially ordered and calibrated. 

Class A. This code is for the highest-class glassware that is production... 

Resistance to Chemicals. Exposure to all alkalines should be kept to a minimum (minutes). Exposure to hydrofluoric and perchloric acid should be limited to seconds. Volumetric ware used once for these materials should be downgraded (glassware that was Class A should now be considered Class B) or not used at all. If measurements of these acids or alkalines are required, use plastic ware because it is resistant to these chemicals. 

Copper 327.4 air/acetylene For the determination of major alloying elements the use of Class A volumetric glassware is recommended... 

All chemicals and reagents used in this work were ACS reagent grade, all volumetric glassware was class-A, and all beakers, bottles, and volumetric glassware were washed with aqua regia and rinsed with deionized, double-distilled water before use. 

TABLE 1 Capacity tolerances of precision (class A) volumetric glassware... 

Caution. The residues on the glassware and the frit may contain sodium-potassium alloy and/or tris(trimethylsilyl)arsine and should not be exposed to air until disposal. tert-Butyl alcohol and isopropyl alcohol can be used to destroy these pyrophoric compounds however, this should be performed in a fume hood, as arsine gas may be generated. The solid on the frit can be mixed with class D metal fire extinguisher and subsequently treated with either of the aforementioned alcohols. 

Aside from the fact that the reactions in Scheme 9.6 were performed in small wells instead of traditional flasks and glassware, the chemical reactions are no different from the types of reactions performed in a traditional introductory organic chemistry class. The reagents are mixed into a common solvent so that they may react with one another in solution. 

The work of such a class should be biased towards producing the more simple types of glassware used in the science laboratories. The emphasis should be on the quality and quantity of the items made, and on the economical use of the materials and accessories employed. 

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