Secondary standard working

Secondary standard (working standard). A material of high purity that has been characterized against a primary or compendial standard. A secondary standard is often used to conserve the amount of primary standard. 

Master standards calibrated by reference to primary standards and usnally in the form of porcelain or opaque glass panels, ceramic tiles, acrylic painted chips, etc. These are maintained with extreme care, nsually at the standards institutes, and are used only to calibrate other secondary standards. Working standards used as a reference for a group of laboratory iirstrumetrt standards. These are usually ceramic or porcelain tiles. 

For scientific work the fundamental standard of mass is the international prototype kilogram, which is a mass of platinum-iridium alloy made in 1887 and deposited in the International Bureau of Weights and Measures near Paris. Authentic copies of the standard are kept by the appropriate responsible authorities in the various countries of the world these copies are employed for the comparison of secondary standards, which are used in the calibration of weights for scientific work. The unit of mass that is almost universally employed in laboratory work, however, is the gram, which may be defined as the one-thousandth part of the mass of the international prototype kilogram. 

In a multi-year, multi-laboratory situation it is unlikely that the amount of primary standard (PS) will suffice to cover all requests. The next best thing is to calibrate a larger amount of lower-quality secondary standard (SS) against the PS, and to repeat the calibration at specified intervals until both the PS and the SS have been consumed. In this way, consistency can be upheld until a new lot of PS has been prepared and cross-validated against the previous one. In practice, a working standard will be locally calibrated against the SS and be used for the daily method calibration runs. (See Section 4.32.)... 

The problems with various primary calibration standards are still being resolved. The earlier discussion of DeMore et al, indicates the work undertaken by the carb in comparing oxidant calibration procedures. It was recommended that all oxidant analyzers in the California network be calibrated by a secondary standard consisting of an ultraviolet ozone analyzer. The primary standard recommended is ultraviolet photometry. These recommendations have been adopted by the cars. Potassium iodide, indicated as a second choice, requires the application of a correction factor of 0.78. 

Reference materials are often real samples that have been carefully prepared and analyzed by many laboratories by many different methods. In this way, their known value and accompanying confidence limits are determined. The regular use of reference materials not only provides for calibration and standardization, but it also can demonstrate an analyst s proficiency with a method. It should be noted that SRMs are expensive, however, and are not often used for routine calibration and standardization work. Usually, primary and secondary standards are used for that. Another important fact about RMs is that they are considered to have a finite shelf life and cannot be confidently used as RMs after a certain period of time. 

Thiocyanate standard solution the stock standard is made from KSCN. The secondary and working standards are prepared from this. See the preceding section under Colorimetric Method. 

The concepts of calibration and especially of metrological traceability were elaborated by physicists as mentioned above. The reference or top of the calibration hierarchy preferably is the definition of an SI unit, which is realized or embodied as a primary measurement standard. By direct comparison, the quantity value of a secondary measurement standard can be established. Subsequent comparisons may furnish quantity values of reference measurement standard, working measurement standard, and routine measurement standard with which the object carrying the measure and is compared to obtain its measurement result which then retrospectively is metrologically traceable to the SI unit. The primary measurement standard, as the definition of metrological traceability says, is preferably an international or national measurement standard. 

Hierarchies, such as primary, secondary, and working level, or certified RMs and RMs are extensively used in describing traceability chains. Whilst such terms can be useful in explaining processes and links, they can also be confusing. For this reason their use has been limited in this paper. It is considered preferable to describe hierarchies in terms of the associated uncertainties. It can also be noted that, whereas in physical measurement it is common to have a hierarchy of references of the same basic type (e.g., a series of mass standards), this is rare in chemical measurement where the chain usually contains only one chemical RM, linked to a higher reference by a measurement process. 

Secondary standard Stock solution Working standard... 

Since the early work of Ricardo [7], it has been recognized that some fuels, including many aromatics and ethers, knock less easily than isooctane. This presents no difficulty for an assessment based on the HUCR, or the critical compression ratio (CCR), widely featured in Lovell s comprehensive review of fuel properties in 1948 [10]. However, it does present difficulty for one based on the octane number, because some fuels have octane numbers larger than 100. The octane number scale has been extrapolated in a way which is necessarily arbitrary, and there are secondary standards based on iso-octane containing the anti-knock, lead tetra-ethyl, discussed in Section 7.2.6 [9]. 

In 1968 the IAEA with the participation of WHO conveyed a panel of experts to discuss the dosimetric requirements of radiotherapy centres. The panel recommended the setting up of dosimeter calibration centres (later called Secondary Standard Dosimetry Laboratories—SSDLs) in developing countries. In 1974 experts, mainly from the large national standard laboratories, discussed the concept of SSDLs and their role in metrology. An SSDL was defined as a laboratory designated by the competent national authority to undertake dosimetry calibrations. For the proper function of the SSDLs, the need for dose intercomparison and for coordination of the work of individual laboratories was recognised. This ultimately led to the establishment of the international lAEAAVHO Network of SSDLs. 

These collaborative studies have led to the establishment of European working standards. Consequently, the titers and potencies of biological products will be expressed with respect to the same reference standard. The existence of reference standards recognized throughout Europe enables national control agencies and manufacturers to avoid costly duplications of work on secondary standards that could otherwise lead to disagreements. 

The first five of these characteristics are essential to minimize the errors involved in analytical methods. The last three characteristics are just as important as the first five in most analytical laboratories. Because primary standards are often costly and difficult to prepare, secondary standards are often used in day-to-day work. 

Secondary standards are employed in industrial, academic, and clinical laboratories. Calibrated at appropriate intervals against primary standards at the National Bureau of Standards, secondary standards are used to calibrate working instruments in the local institution. It is well known, but should nevertheless be emphasized, that there is an accumulation of errors in the progression down the calibration chain. Consequently, for the highest-accuracy work, calibrations should be performed by the primary standards laboratories. 

Secondary or working standards may be established by the application of appropriate tests and checks at regular intervals to ensure standardization. All in-house reference standards should be based on official reference standards, when available. 

These tables were originally published as the final report to the U.S. Atomic Energy Commission as Report NYO-10586 in partial fulfillment of Contract AT(30-1 )-2543. The tables were later reproduced in Review of Modem Phyeics. The data may also be obtained from the Superintendent of Documents, U.S. Government Printing Office, Washington, D. C. 20402 in the publication NSRDS-NBS 14. Persons seeking discussion of the experimental work, conventions, secondary standards, etc. will find these in Review of Modem Physics, Vol. 39, No. 1, 78-124, January 1967. 

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