Volumetric equipment, calibration

When solution must be pumped, consideration should be given to use of holding tanks between the dry feed system and feed pumps, and the solution water supply should be controlled to prevent excessive dilution. The dry feeders may be started and stopped by tank level probes. Variable-control metering pumps can then transfer the alum stock solution to the point of application without further dilution. Means should be provided for calibration of the chemical feeders. Volumetric feeders may be mounted on platform scales. Belt feeders should include a sample chute and box to catch samples for checking actual delivery with set delivery. Gravimetric feeders are usually furnished with totalizers only. Remote instrumentation is frequently used with gravimetric equipment, but seldom used with volumetric equipment. 

For other sources this experimental approach is not possible. E.g. for the purity of a material, the traeness of a balance or a volumetric equipment or similar uncertainties om knowledge is purely based on other information like certificates published by the manufacturer or a calibration laboratory. In some cases the only available information is the analyst s experi-... 

In physics, the use of calibration hierarchies is well established and is used in any laboratory, e.g. for balances, volumetric equipment, spectrometer wavelengths, cuvette light path lengths, thermometers, barometers and clocks. 

Uncertainty associated with the use of volumetric equipment at a temperature different from that of calibration, (7-Temp. 

Volumetric equipment is marked by the manufacturer to indicate not only the manner of calibration (usually TD for to deliver or TC for to contain ) but also the temperature at which the calibration strictly applies. Pipets and burets are ordinarily calibrated to deliver specified volumes, whereas volumetric flasks are calibrated on a to-contain basis. 

The top surface of a liquid confined in a narrow tube exhibits a marked curvature, or meniscus. It is common practice to use the bottom of the meniscus as the point of reference in calibrating and using volumetric equipment. This minimum can be established more exactly by holding an opaque card or piece of paper behind the graduations (Figure 2-21). 

Instrumental Errors. Instrumental errors are caused by nonideal instrument behavior, by faulty calibrations, or by use under inappropriate conditions. Typical sources of instrumental errors include drift in electronic circuits leakage in vacuum systems temperature effects on detectors currents induced in circuits from llO- power lines decreases in voltages of batteries with use and calibration errors in meters, weights, and volumetric equipment. 

General principles for preparation of calibration solutions and matrix matched calibrators are described in Section 9.8.1 and similarly for QC samples in Section 9.8.2. Records to support the preparation, storage conditions (location and temperature) and use of these samples must be maintained at the analytical site, together with SOPs and information for all relevant apparatus including freezers and refrigerators, analytical balances, volumetric equipment etc. 

Calibration is the process of relating the actual quantity (such as mass, volume, or electric current) to the quantity indicated on the scale of an instrument. Volumetric glassware can be calibrated to measure the volume that is actually contained in or delivered by a particular piece of equipment. Calibration is done by measuring the mass of water contained or delivered and using Table 2-5 to convert mass to volume ... 

Volumetric procedures incorporate several important sources of systematic error. Chief amongst these are the drainage errors in the use of volumetric glassware, calibration errors in the glassware, and indicator errors. Perhaps the commonest error in routine volumetric analysis is to fail to allow enough time for a pipette to drain properly, or a meniscus level in a burette to stabilize. Pipette drainage errors have a systematic as well as a random effect the volume delivered is invariably less than it should be. The temperature at which an experiment is performed has two effects. Volumetric equipment is conventionally calibrated at 20°C, but the temperature in... 

Some typical experimental setups for volume and density measurement are given in Fig. 6.3. Rarely is it possible to make a volume determination by finding the appropriate lengths. Almost always, the volume measurement will be based on a mass determination, as described in Chapter 7. For routine liquid volume measurement, common in the chemical laboratory, one uses volumetric equipment in the form of calibrated flasks, cylinders, burettes, and pipettes, as well as pycnometers. These instruments are usually calibrated for use at one temperature only. Their quality and use are described in many laboratory handbooks. Calibration is always done by weighing the instrument filled with water or mercury, or weighing the liquid delivered when the instrument is emptied. 

A modern adsorption microcalorimeter was built for the simultaneous measurement of isotherms and adsorption heats, establishing its correct functioning through adequate calibration of both the calorimeter part and the volumetric equipment of the adsorption part. For this purpose, the microcalorimeter calibration constant was found with values that go from 134.11 0.19 WV" to 156.67 0.23 WV. The adsorption isotherm was determined for a type NAZSM-5 zeolite as a reference solid to establish the correct functioning of the equipment. Micropore volume and superficial area were determined to be 0.20 cmVg and 296 m /g, respectively. These results agree very well with those obtained with commercial equipment. Finally, the differential heats of adsorption, for the same solid, were measured. The analysis of results gives valuable information about the studied C02/NaZSM-5 system, which is in concordance with other studies in the literature. 

To ensure that S eas is determined accurately, we calibrate the equipment or instrument used to obtain the signal. Balances are calibrated using standard weights. When necessary, we can also correct for the buoyancy of air. Volumetric glassware can be calibrated by measuring the mass of water contained or delivered and using the density of water to calculate the true volume. Most instruments have calibration standards suggested by the manufacturer. 

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. 

Standardization of a Titrant For wet chemistry analytical methods, a titration is often used and the titrant, or the solution to which an unknown sample is compared, must be standardized. This can be done by comparing it with another standard. The important thing here is that the standard with which it is compared is ultimately traced to a SRM. The procedure utilizes volumetric glassware heavily, and thus the analyst must be assured that these are properly calibrated, as discussed above. Auto-titrators can be used (Figure 5.4). In this case, the automated equipment can be calibrated against manual equipment, i.e., volume readings obtained with the auto-titrator must match the volume readings obtained with a calibrated buret for the same sample. If they do not match (within accepted limits), the auto-titrator must be taken out of service and repaired, just like the defective balance. 

C. Large-scale oxidation protocol. The large-scale oxidations reactions were carried out in a 300mL Parr autoclave equipped with an injection port, a thermocouple port, a septa sealed addition port and port connected to the volumetric measurement and gas supply module. The module consists of a forward pressure regulator and a calibrated ballast reservoir. The pressure in the reactor and in the ballast reservoir is monitored constantly and the pressure drop in the ballast reservoir is constantly converted into moles of oxygen uptake recorded vs. the time. 

Select calibration hierarchy. By selecting a working calibrator, its calibration hierarchy is determined by the available documentation. Attention should also be paid to the calibration and metrological traceability of measurement results for input quantities to a measurement function measured by accessory equipment such as balances, thermometers, and volumetric ware. 

The home-made heat-flow calorimeter used consisted of a high vacuum line for adsorption measurements applying the volumetric method. This equipment comprised of a Pyrex glass, vacuum system including a sample holder, a dead volume, a dose volume, a U-tube manometer, and a thermostat (Figure 6.3). In the sample holder, the adsorbent (thermostated with 0.1% of temperature fluctuation) is in contact with a chromel-alumel thermocouple included in an amplifier circuit (amplification factor 10), and connected with an x-y plotter [3,31,34,49], The calibration of the calorimeter, that is, the determination of the constant, k, was performed using the data reported in the literature for the adsorption of NH3 at 300 K in a Na-X zeolite [51]. 

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