Standards or reference material

The usual way to perform calibration is to subject known amounts of the parameter (e.g. using a measurement standard or reference material) to the measurement process and monitor the measurement response... 

A measurement of a specified property in an unknown material is a quantitative comparison by ratio or difference made of that property between a reference standard or reference material and the unknown or between relevant settings in an instrument, preferably in the appropriate unit for the quantity under investigation, provided ... 

A reference standard, or reference material, is a substance prepared for use as the standard in an assay, identification, or purity test. 

Information on impurities, including their structure, acceptance limits, and control, is to be briefly described. For control of a drug substance, specifications (including justifications) and analytical procedures (including validation information) used for testing are to be summarized. Data on reference standards or reference materials used for drug substance testing are to be provided. Information on batches and the results of batch analyses are to be described. 

There are no recognized enzyme standards or reference materials. The accepted basis for measurement is the rate of reduction of the substrate, commonly nicotinamide adenine dinucleotide (NAD) for many reactions. The reduced form, NADH, absorbs at 340 nm, and the rate of change of this absorbance is measured in an enzyme-activity assay. The absorptivity a in Beer s law) is known for NADH from this and the rate of change of absorbance per unit time, the activity of the enzyme can be calculated in micromoles of substrate converted per minute. This is referred to as an International Unit (lU), expressing the activity as lU/liter. Therefore, an accurate, absolute absorbance scale must be established in each case in order to make a valid assay. 

The attainment of these required characteristics is often not straightforward. Conformance with the requirements is usually obtained by a twofold process. First, substantial experience with the system and attention to important technical details is required. Second, certain statistical diagnostic tests may be used, the most impt>rtant being control charts, which arc defined in Section 7, using standard or reference materials subjected to the same testing protocol as the experimental materials. Independence of individual measurements can be compromised if there is any carryover effect or correlation between one test measurement (sample or specimen) and the next measurement. Calibration operations, to be discussed later, can also be a source of problems in test measurement independence if they arc not conducted in an organized or standardized manner. 

An entirely distinct approach to estimating uses control chart principles (see Chapter 4). We have seen that these charts can be used to monitor the quality of laboratory methods used repeatedly over a period of time, and this chapter has shown that a single calibration line can in principle be used for many individual analyses. It thus seems natural to combine these two ideas, and to use control charts to monitor the performance of a calibration experiment, while at the same time obtaining estimates of The procedure recommended by ISO involves the use of q =2 OT 3) standards or reference materials, which need not be (and perhaps ought not to be) from among those used to set up the calibration graph. These standards... 

Calibration is usually done with ultrapure acetanilide [36] as the ratio between carbon and nitrogen of this standard is similar to that of phytoplankton. The efficiency of the oxidation-reduction reactors has to be frequently checked by analyzing standards or reference materials every 10-12 samples. 

If we put a sample next to one thermocouple and a "standard" or reference" next to the other, we can follow any thermal changes that may take place as both are heated since each TC generates Its own EMF as the temperature changes. Thus, If we put a reference material, R, directly in contact with the "TC(1)" thermocouple junction (hereinafter, we will refer to this thermocouple junction as "R") and a sample, S, at TC(2), l.e.- S , then we can detect any thermal change that may occur if either R or S undergoes a transformation as it is heated. 

Third, in order to ensure that a collaborated method is being performed properly, and that resultant data obtained is sound, an appropriate set of controls or reference materials is needed to test the method as it is being used (Chase and Long 1997). However, there is a difference in how one views the aforementioned concepts. For example, analytical method development is a process-oriented approach in which each step of the process is continually tested whereas, the use of a RM, standard control or comparison with another method is a result-oriented view (Taimer et al. 1995). 

Where standards, calibrants, or reference materials are certified, copies of the certificate are available for inspection. 

The standard details will be given to architects and engineers as criteria or reference material for new construction or modification design for munitions production base modernization. 

The laboratory shall have procedures for safe handling, transport, storage and ttse of reference standards and reference materials in order to prevent contamination or deterioration and in order to protect their integrity. 

If agreement is not reached between a properly calibrated apparatus and a reference standard, the reference material must be questioned. All too often materials used as standards for surface area or pore volume prove to be inadequate for a wide variety of reasons, some of which are listed below. 

After calibration of the HPLC, a food-based quality control material or reference material should be analyzed on a routine basis to validate the performance of the method. The chromatograms illustrated in the following sections of this chapter are of a food matrix created from a mixture of baby foods and infant formula however, a similar standard food reference material (SRM 2383) may be directly purchased from the National Institute of Standards and Technology (NIST). 

In physical science there are occasionally instances where measurements need to be more reproducible than the lowest achievable uncertainty relative to the true value in SI units. Chemists, not just occasionally but as a rule, must achieve traceability of measurements by use of some standard, a reference material, a reference instrument, or a reference method [18], The spread of these measurements made in different laboratories is often required to be smaller than the uncertainty with respect to true value. Nevertheless, one should state any such measurement in moles along with an assessment of the quality of its reproducibility. Such a statement will be different depending on its applicability within a laboratory, between laboratories, for a given method and environment, or in relation to an RM. When an RM is used, one must also include its often larger uncertainty of traceability to the SI unit. This uncertainty of the value of the RM must be included in the total uncertainty of the unknown. 

Let us begin with the ISO definition [9] A calibration is a set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or reference material, and the corresponding values realized by standards. Applied to amount measurements, the standards would then be the values assigned to the RMs (of defined composition) at the stated uncertainty relative to the true value of the property, expressed in SI units, or relative to an internationally recognized, certified standard RM for the relevant property, range, and matrix composition. 

A firm link must exist to the national institute, in metrology in chemistry to the national standards network, at the primary level via transfer standards (e.g. reference measurements and/or reference materials) or other means by which traceability to the national standards is ensured. 

The principal services include provision of high level calibration services (Fig. 3) and/or standards to suppliers offering secondary services or standards, preparation of standards and reference materials, and limited services direct to field... 

Control charts are used for monitoring the variability and to provide a graphical display of statistical control. A standard, a reference material of known concentration, is analyzed at specified intervals (e.g., every 50 samples). The result should fall within a specified limit, as these are replicates. The only variation should be from random error. These results are plotted on a control chart to ensure that the random error is not increasing or that a... 

Most of the instrumental direct methods, which are employed in routine analyses, are highly matrix-dependent, therefore methods must be validated with certified standard reference materials. Standard plant reference materials (SRMs), with certified elemental contents can be obtained from NIST, National Institute of Standards and Technology of the United States Department of Commerce or from BCR, Community Bureau of Reference, Commission of the European Community (Colinet et al., 1982 Criepink, 1990 Horwitz and Albert, 1991). 

In order to ensure comparability, it is possible to advance in one of two directions either to use perfectly standard apparatus of a type possessed by all, or to calibrate one s home-made apparatus by use of a standard or reference catalyst available to all. There is much to be said in favor of the former approach, but it implies the use of commercially available equipment, which is unlikely to be cheap and is not yet widely employed. However, experience teaches that there is little difficulty in reproducing measurements concerning the physical properties of catalytic materials (XPS, XRD, TEM, etc.) when, as is usually the case, standard instrumental methods are used. The alternative is to accept that for some time to come many laboratories will continue to use home-made facilities for chemisorption and catalysis, and that there will therefore be a need for a number of standard catalysts that may be tested to ensure the proper functioning of the equipment (and of the operator ). 

Lack of representativeness at the step of collecting a sample from an examined material object Uncertainties associated with the applied standards and/or reference materials... 

The presence of the distinct XRD patterns provides us new opportunities for precisely monitoring various physico-chemical phenomena that take place inside the well-defined carbon pores or at the pore walls such as adsorption, impregnation, framework changes, formation of metal clusters and grafted frmctional groups. The materials constructed with such well defined and controllable pore diameters are suitable as standards or references for the characterization of porosity of the carbons, similar to the already well-known case of the MCM-41 silica. 

Record all operating details and conditions, including yields, product or compound names, lot numbers of standards and reference materials, suppliers, and anyexpiration dates. 

In 1999, WHO published requirements for production and control of Haemophilus influenzae type b (Hib) conjugate vaccine and the acellular perussis component of monovalent or combined vaccines. The requirements for oral polio vaccine (OPV) were also revised in 1999, with several additions. WHO published new and replacement International Standards and Reference Materials covering a wide range of products.f ... 

So, the methods characteristic of each test, comprising taken together a type of tests, must undergo validation testing of their results. This is the implementation of the method, and the establishment of a standard for its performance. For the standardization of quantitative methods, this consists at a minimum of a determination of trueness when blank utilization, certified reference materials (or reference materials, or spiking materials) or collaborative trials are used, repeatability (r) with repetition,... 

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