Reference Materials and Chemical Standards

Out-of-laboratory measurements are undertaken across a broad range of industrial and analytical sectors for a variety of reasons in clinical and medical diagnostics for the control of chemical and petrochemical production processes and to monitor emissions and discharges to the environment. The validity of data derived from such measurements is clearly of vital importance, for example to demonstrate compliance with environmental legislation. However, it is particularly difficult to obtain valid and reliable measurements outside the laboratory. The inability to control the environment in which the measurements are made and the use of untrained operators both have potential to impact significantly on the reliability of data. The situation is made worse because of the lack of adequate QA and QC procedures, the shortage of reference materials and calibration standards, and... 

Analytical standards imply the existence of a reference material and a recommended test method. Analytical standards other than for fine chemicals and for the NIST series of SRMs have been reviewed (6). Another sphere of activity ia analytical standards is the geochemical reference standards maintained by the U.S. Geological Survey and by analogous groups ia France, Canada, Japan, South Africa, and Germany (7). 

When the American Type Culture Collection (ATCC) was founded in 1925, one of its chief roles was to be a source of standards. In this context we mean standard organisms, rather than standard materials or chemicals known as Reference Materials or Certified Reference Materials and issued in the USA by the National Bureau of Standards (NBS). The National Bureau of Standards evolved into NIST and the abbreviation SRM became a trade mark of NIST. 

In addition, a system for making sure staff are appropriately qualified and trained for the work that they are doing must be in place. This will enable an auditor to see clearly the demonstrated competence of the staff and how this has been checked. The requirements for all major items of equipment must be listed, to ensure that the equipment in use is suitable for the task, is in working condition and, where necessary, is calibrated. For all of the instrumentation there needs to be a documented schedule for maintenance. Measurements must be traceable, that is, the laboratory must be able to show how the calibration of measurement instruments is traceable to National or International Standards. Where this presents practical problems, as in some chemical measurements for example, interlaboratory comparison and the use of reference materials (and preferably Certified Reference Materials) will be required. 

Chemical and Physical Standards, Calibrants, Certified Reference Materials and Reagents... 

The percentages of Sn and Pb were obtained from electrochemical data using additions of Sn02 and PbCOs, ZnO as a reference material and 267 sibca brick (British Chemical Standards). Elec-trochemically calculated values from measurements at three pairs of potentials, using the Sn plus Pb stripping peak in acetate buffer (H), are compared with nominal compositions (nom) of the frits and the composition of the ceramic sample obtained from SEM/EDX analysis [242]... 

Abstract The basic concepts of traceability as they are defined by the Comite Consultatif pour la Quantite de Matiere (CCQM) are difficult to apply to some chemical results. For instance, for some environments or chemical analyses measurement results are expressed in conventional units. Such units are realized on conventional scales relying on two fundamental pillars reference materials and standard specification. The octane number of fuel or water turbidity measure-... 

It consists of three levels. At the top of the structure a network of national laboratories provides the primary chemical measurement standards and ensures that these are linked up with the international reference framework for chemical measurements. Via primary reference materials and reference measurements, a secondary level consisting of accredited chemical calibration laboratories, including verification authorities in the regulated area, is connected to the national standards level. 

This secondary or intermediate level has an important multiplier function. It is firmly linked to the national standards and provides traceable calibration means (mainly certified reference materials) and test samples to the workshop level, which consists essentially of chemical testing laboratories (including medical laboratories) which are required to give evidence to their customers that their measurement results are traceable to recognized references. In the case of medical laboratories, the traceability requirement also has a legal background. 

This suggested to CENAM the development of activities for the establishment of traceable chemical measurements in Mexico in two stages the first step from 1992 to 1997 [2] corresponded to the period of development of infrastructure and human resources of CENAM, which was possible thanks to the collaboration of other NMIs involved in developing reference materials and their later certification and the second period, from 1998 to 2002, in which a limited number of certified reference materials (CRM) were developed and certified for industrial application as well as to meet normative requirements, and also some of the primary methods of measurement were declared as national standards in a Federal Register, known as DOF. 

Results of analytical chemistry are only valid within a reference system. Reference materials are the standards of analytical chemistry. They may be characterised for Identity (chemical structure) and for Property values (specific chemical quantities). 

One of the remaining questions concerns the QA of chemical reference materials and the competence of RM producers. Whilst laboratory accreditation normally requires the use of physical measurement standards that have been produced in accredited calibration laboratories, the situation regarding chemical measurement standards is, so far, much less formal. General Requirements for the Competence of Reference Material Producers (3,4) have been available since 1996, but the implementation of accreditation based on these requirements is still in its infancy. There is a need for a more balanced approach to accreditation practice related to measurement standards. For example, should only reference materials produced by accredited producers be used as measurement standards in accredited test laboratories Or, does the whole system of the QA of measurement standards need to be re-examined ... 

Contract research, analysis and consultancy in the chemicals, environment, forensics, food, health, life sciences and pharmaceuticals sectors World-wide distribution of reference materials and standards following acquisition of the Promochem company. 

Generally physical, chemical, and ionization interferences are similar in terms of incidence and extent in all three flame analytical atomic spectrometric techniques, but they are not a severe problem provided the analyst is aware of their existence, and takes the necessary precautions. Spectral interferences are not regarded as a serious problem in flame AAS or flame AFS, but are potentially much more serious in FES. Unless the analyst is certain that a particular FES determination is spectral interference-free for the samples in question, scanning and careful scrutiny of emission spectra from samples and standards is advisable, together with reliability checks using certified reference materials and/or determination at more than one wavelength. 

May WE, Benner BA, Wise SA, et al. 1992. Standard reference materials for chemical and biological studies of complex environmental samples. Mutat Res 276 11-22. 

Grffnbfrg RR, Zfislfr R, Kingston HM and Sullivan TM (1988) Neutron activation analysis of the NIST Bovine Serum Standard Reference Material using chemical separations. Fresenius J Anal Chem 332 652-656. 

Sixteen years after the review by Engstrom Wright (1984), problems still remain with chemical characterization of sediment components. However, the development of new reference materials promises better standardization of analytical procedures, and brings nearer the goal of more generalized interpretations. 

The sample matrix problem has stimulated the development of two pragmatic solutions matrix reference materials and interlaboratory comparisons. The matrix-matched, certified reference material (CRM) is a unique type of chemical standard commonly used to validate complete measurement methods and sometimes for instrumental cafibration (e.g., in XRF). Such standards must be available for each required analyte/matrix combination. Similarly, interlaboratory comparisons are vmdertaken for each relevant analyte/matrix combination in order to establish comparability of data between laboratories. These comparisons range from rovmd robin studies, which collaboratively test a new method, to formal PT schemes that assess agreement between laboratories on an ongoing basis. 

Whenever possible, reference materials should be included in the experimental plan as a way of checking for bias [7. However, it is also important that the chemical state and environment of the analyte be as nearly identical as possible in both reference material and sample. The method of standard addition (where the spike should again be in the same chemical state as the native analyte) is particularly useful in a search for systematic errors, as is a comparison involving different analytical methods. 

These instrumental tools and visual workstation are just a few techniques used to characterize and measure structural and chemical properties of materials or cells cultured on them (Figure 3). Incorporating these advanced imaging techniques into our measurement toolkit allows us to translate this work into standard reference materials and methods to aid discovery, research, and regulatory issues. 

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