Balances, analytical, calibration

Certain variables— water quality, calibration of analytical balances, calibration of volumetric glassware and pipettes, stability of electrical power, and the temperature of heating baths, refrigerators, freezers, and centrifuges—should be monitored on a laboratorywide basis because they wiU affect many of the methods in the laboratory (see Chapter 1). In addition, there wiU be certain variables that relate more directly to individual analytical methods, and these require... 

WEIGHT.dat Thirty high-precision calibration measurements carried out on each of two analytical balances (LSD 0.01 mg) in the course of less than one hour using the calibration weight 30 g , cf. Ref. 25. 

Analytical standards are prepared for two purposes for fortifying control matrices to determine the analytical accuracy and for calibrating the response of the analyte in the mass spectrometer detector. The purity of all standards must be verified before preparation of the stock solutions. All standards should be refrigerated (2-10 °C) in clean amber-glass bottles with foil/Tefion-lined screw-caps. The absolute volume of the standard solutions may be varied at the discretion of the analyst, as long as the correct proportions of the solute and solvent are maintained. Calibrate the analytical balance before weighing any analytical standard material for this method. 

Instrument/Equipment Effects Examples include the calibration and precision of an analytical balance, the specified tolerance for volumetric glassware and a temperature controller that maintains a mean temperature which is different (within specification) from its indicated value. 

If it is established that a measuring device provides a value for a known sample that is in agreement with the known value to within established limits of precision, that device is said to be calibrated. Thus, calibration refers to a procedure that checks the device to confirm that it provides the known value. An example is an analytical balance, as discussed above. Sometimes the device can be electronically adjusted to give the known value, such as in the case of a pH meter that is calibrated with solutions of known pH. However, calibration can also refer to the procedure by which the measurement value obtained on a device for a known sample becomes known. An example of this is a spectrophotometer, in which the absorbance values for known concentrations of solutions become known. We will encounter all of these calibration types in our studies. 

Any device routinely checked for calibration can be monitored in this way. For example, an analytical balance can be tested with a known weight, the value of the known weight being the desirable value and the expected range of precision dictating the warning and action limits (Experiment 1). 

Note This experiment assumes that a permanent log and a quality control chart are constantly maintained for each analytical balance in use in the laboratory. Each day you use a given analytical balance and log in with your name and date. The following calibration check should be performed weekly on all balances. If, according to the log, the calibration of the balance you want to use has not been checked in over a week, perform this procedure. Review Section 3.3 for basic information concerning the analytical balance. 

Check the calibration of the analytical balance you have chosen to use by weighing this standard weight on this balance. When finished, store the standard weight in the specified protected location. 

An analyst determines that the analytical balance he used in a given analytical test is wrongly calibrated. Is this a determinate or an indeterminate error Explain. 

Briefly explain the differences between calibrating an analytical balance and calibrating a pH meter and what happens if the measured standard does not give the correct result. 

In the case of an analytical balance, the standard is a known weight. This weight is measured and if this result and the known value are the same, the balance is calibrated. If they are not the same, the balance is taken out of service and repaired. In the case of a pH meter, the standard is a buffer solution. The pH of this buffer solution is measured and if the known pH and the measured pH are the same, the meter is calibrated. If they are not the same, the readout is electronically tweaked until it gives the correct result. It is then said to be calibrated. 

Quality assurance measures such as pre-analytical checks on instrumental stability, wavelength calibration, balance calibration, tests on resolution of chromatography columns, and problem diagnostics are not included. For present purposes they are regarded as part of the analytical protocol, and IQC tests their effectiveness together with the other aspects of the methodology. 

As we have seen that the volumetric analysis essentially requires the precise and accurate measurement of weights and volumes of interacting solutions. However, the weights are measured upto the fourth place of decimal by using a manually operated good analytical balance or a single-pan electrical balance that need to be calibrated periodically with the help of a standard weight box. 

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. 

Write an SOP for the calibration of an analytical balance. Include a revision number, an indication of what SOP it replaces, the effective date, the purpose, the scope, the outline of the procedure, and references. Also include your name under "prepared by" and another name for "approved by."... 

This balance is a high-grade analytical balance. It carries out internal calibration but as a double check it is checked with certified check weights. Any deviation of the check weight values from those expected indicates need for servicing of the balance. Check weight calibration should be carried out once a week according to the instructions in SOP/OOIC/OI. 

Laboratory personnel commonly give one of three common responses to someone who points out the traceability requirements of ISO/fEC 17025 Its ok we have our balances calibrated every year, and when it is further pointed out that calibration extends to the chemical aspects of the measurement, I am sure it is ok to use this analytical-reagent-grade material to make a calibration solution, or we make measurements in such complex matrices, a suitable CRM just does not exist. The first comment stems from the rather physical or engineering flavor of the section in ISO/IEC 17025 (section 5.6) (ISO/IEC 2005), although traceability of calibration materials is mentioned. 

Prepare neat (solvent-free) trans calibration standards by weighing accurately, on an analytical balance (to the nearest 0.0001 g), 0.3 -x g of a trans-free reference fat and x g of trielaidin (TE) into each of a series of 10-mL beakers, where x equals 0.0015, 0.0030, 0.0150, 0.0300, 0.0600, 0.0900, 0.1200, and 0.1500 g. Store calibration standards in plastic screw-cap vials. 

Analytical balances must be regularly checked against reference weights provided by the US National Institute of Technology and Standards (the old National Bureau of Standards). Other countries have similar calibration services. Some balances have an internal calibration standard, which periodically resets crucial software parameters that control the front-panel display. 

Class 2 weights are used as working standards for calibration, built-in weights for analytical balances, and laboratory weights for routine analytical work. 

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