Tolerance pipet

Accuracy tolerances for volumetric transfer pipets are given by ASTM standard E969 and Federal Specification NNN-P-... 

Using the tolerance values for pipets and volumetric flasks given in Table 4.2, the overall uncertainties in Ma and Mb are... 

I. 000 X 10- 1.000 X 10-k 1.000 X 10-k and 1.000 X 10- M from a 0.1000 M stock solution. Calculate the uncertainty for each solution using a propagation of uncertainty, and compare to the uncertainty if each solution was prepared by a single dilution of the stock solution. Tolerances for different types of volumetric glassware and digital pipets are found in Tables 4.2 and 4.4. Assume that the uncertainty in the molarity of the stock solution is 0.0002. 

It is possible to check the calibration of a pipet, flask, or buret. The process involves weighing with a calibrated analytical balance. The volume of water (temperature noted) delivered or contained by the glassware is weighed. Then the analyst converts this weight to volume (using the density of water at the temperature noted), corrects the result to 20°C (the usual temperature of the factory calibration), and compares it to the factory calibration. If the difference is not tolerable, the piece of glassware is either not used for accurate work or a correction factor is applied. It should be pointed out that the thermometers used must be properly calibrated and that the timer used to measure the delivery time for the burets and pipets must also be calibrated. 

Pipets deliver known volumes of liquid. The transfer pipet in Figure 2-1 la is calibrated to deliver one fixed volume. The last drop does not drain out of the pipet and should not be blown out. The measuring pipet in Figure 2-1 lb is calibrated like a buret. It is used to deliver a variable volume, such as 5.6 mL, by starting delivery at the 1.0-mL mark and terminating at the 6.6-mL mark. The transfer pipet is more accurate, with tolerances listed in Table 2-4. 

Each instrument that we use has a scale of some sort to measure a quantity such as mass, volume, force, or electric current. Manufacturers usually certify that the indicated quantity lies within a certain tolerance from the true quantity. For example, a Class A transfer pipet is certified to deliver 10.00 0.02 mL when you use it properly. Your individual pipet might always deliver 10.016 0.004 mL in a series of trials. That is, your pipet delivers an average of 0.016 mL more than the indicated volume in repeated trials. Calibration is the process of measuring the actual quantity of mass, volume, force, electric current, and so on, that corresponds to an indicated quantity on the scale of an instrument. 

Acids could be delivered by transfer pipets whose tolerances are given in Table 2-4. So 2 mL means 2.000 0.006 mL... 

Standards of Accuracy The capacity tolerances for volumetric flasks, transfer pipets, and burets are those accepted by the National Institute of Standards and Technology (Class A),1 as indicated in the accompanying tables. Use Class A volumetric apparatus unless otherwise specified in the individual monograph. For plastic volumetric apparatus, the accepted capacity tolerances are Class B.2... 

The capacity tolerances for measuring (i.e., graduated ) pipets of up to and including 10-mL capacity are somewhat larger than those for the corresponding sizes of transfer pipets, namely, 0.01, 0.02, and 0.03 mL for the 2-, 5-, and 10-mL sizes, respectively. 

Accuracy tolerances for volumetric transfer pipettes are given by ASTM Standard E969.02 Standard Specification for Glass Volumetric (Transfer) Pipets, West Conshohodcen, PA American Society for Testing of Material, 2003 and Federal Specification NNN-P-395. 

Triturate the cell suspension thoroughly with a plastic pipet to give a complete single cell suspension. F-9 cells are tough and will tolerate much up and down pipeting. 

Figure 2 8 (a) Class A glass volumetric flask showing proper position of the meniscus—at the center of the ellipse formed by the front and back of the caiibration mark when viewed from above or below. Volumetric flasks and transfer pipets are calibrated to this position. [A. H. Thomas Co., Philadelphia, PA.] (b) Class B polypropylene plastic volumetric flask for trace analysis. [Fisher Scientific, Pittsburgh, PA.) Class A flasks meet tolerances of Table 2-2. Class B tolerances are twice as big as Ciass A tolerances. 

A transfer pipet is more accurate than a measuring pipet. Tolerances for Class A (the most accurate grade) transfer pipets in Table 2-3 are the allowed error in the volume that is actually delivered. 

Also calibrate the entire apparatus. Put 400 mL of dry (0.02 % water maximum) xylene in the apparatus and test in accordance with Section 9. When complete, discard the contents of the trap and add 1.00 0.01 mL of distilled water from the buret or micro-pipet, at 20 C, directly to the distillation flask and test in accordance with Section 9. Repeat 8.1.2 and add 4.50 0.01 mL directly to the flask.The assembly of the apparatus is satisfactory only if trap readings are within the tolerances specified here ... 

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