Certified Standard Reference Materials CRMs

If available, run one or more certified standard reference materials (CRMs) to check the accuracy of the overall method (use eqn [7]). 

Certified (Standard) Reference Materials (CRM/ SRM) Real-world samples, as similar as possible to the unknown samples to be analyzed, for which the concentra-tion(s) of analyte(s) have been certified by expert laboratories using several independent analytical methods under strict international conditions (Section 2.2.1). Such materials are rare and expensive, and if available are used only occasionally to check on the performance of the method and/or to validate reference materials prepared in-house. 

Procedures for the analysis of some organochlorines in environmental samples (e.g., chlorinated dioxins - EPA Method 1613) [68] also require the use of surrogate standards (usually 13C-labeled) and certified or standard reference materials (CRMs or SRMs). At present there are no stable isotope labeled reference materials and no reference materials have yet been certified for PCA... 

Zambia, Thailand and USA (Florida) were analyzed by using the X-ray fluorescence method for elemental composition. These rock phosphates have also been evaluated for their agronomic effectiveness by means of radioisotope techniques (Zapata and Axmann, 1991). The samples were prepared as pellets and analyzed using the emission transmission method for trace elements (Markowicz and Haselberger, 1992). All samples were excited using an Mo tube with an Mo secondary target. For quality control of concentration data analysis of standard reference material CRM 032 (phosphate rock) produced by CEC, Brussels, has been used. Satisfactory agreement between certified and measured values was obtained. 

Reference materials are used to demonstrate the accuracy, reliability and comparability of analytical results. A certified or standard reference material (CRM or SRM) is a reference material, the values of one or more properties of which have been certified by a technically valid procedure and accompanied by a traceable certificate or other documentation issued by a certif5dng body such as the... 

Many of these are also available as BCS Certified Reference Materials (CRM) supplied by the Bureau of Analysed Samples Ltd, Newham Hall, Middles borough, UK, who also supply EURONORM Certified Reference Materials (ERCM), the composition of which is specified on the basis of results obtained by a number of laboratories within the EEC. BCS Reference Materials are obtainable from the Community Bureau of Reference, Brussels, Belgium. In the USA similar reference materials are supplied by the National Bureau of Standards. 

ID-TIMS has frequently been used for certification of Standard Reference Materials by NIST (ex NBS) and IRMM (ex BCR), as in case of the Polymer Elemental Reference Material (PERM) project for the production of PE standards with certified concentrations of eight elements, namely Cd, Cr, Hg, Pb, As, S, Cl and Br [1], Also certification of the VDA-001 to -004 PE/Cd CRMs has taken advantage of both ID-TIMS [224,425] and... 

In analytical practice, they are best recognized by the determination of xtest as a function of the true value xtrue, and thus, by analysis of certified reference materials (CRMs). If such standards are not available the use of an independent analytical method or a balancing study may provide information on systematic errors (Doerffel et al. [1994] Kaiser [1971]). In simple cases, it may be possible, to estimate the parameters a, / , and y, in Eq. (4.5) by eliminating the unknown true value through appropriate variation of the weight of the test portions or standard additions to the test sample. But in the framework of quality assurance, the use of reference materials is indispensable for validation of analytical methods. 

Some reference material producers/suppliers use different names to describe their materials. For example, a Standard Reference Material (SRM) is a certified reference material issued by the National Institute of Standards and Technology (NIST), while European Reference Materials (ERMs) are CRMs produced under a joint collaboration between three European reference materials producers, i.e. BAM (Federal Institute for Materials Research and Testing, Germany), IRMM (European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Belgium) and LGC (UK). 

SRM stands for standard reference material. It is a standard chemical manufactured and certified by the National Institute of Standards and Technology (NIST) as being exactly as labeled. It is the ultimate standard. CRM stands for certified reference material. It is a standard chemical manufactured and certified by a vendor as being exactly as labeled. It is traceable to a SRM, meaning it has been compared to and certified with the use of an ultimate standard. 

In the above discussion, standard reference materials (SRMs) were mentioned often. A reference material (RM) is a material or substance suitable for use in calibrating equipment or standardizing solutions. A certified reference material (CRM) that a vendor indicates, via a certificate, is an RM. A standard reference material (SRM) is one that is distributed and certified by a certifying body, such as NIST. The SRM is the material to which all calibration and standardization materials should be traceable. A standard material becomes one when it is compared to or prepared from another. Ultimately, it all rests on the SRM — meaning all standard materials are traceable to an SRM (see Figure 5.10). 

Standard reference material (SRM) for wavelength accuracy, stray light, resolution check, and photometric accuracy can be purchased from NIST. Certified reference materials (CRMs) which are traceable to NIST and recertification services can be purchased from instrument manufacturers and commercial vendors [12]. The cost of neutral-density filters and prefabricated standard solutions in sealed cuvettes can be substantial. When purchasing performance verification standards from a secondary supplier other than a national standard organizations such as NIST in the United States and National Physical Laboratory (NPL) in the United Kingdom, make sure that the traceability of the standards are available in the certificates. The traceability establishes the relationship of individual results to the national standard through an unbroken chain of comparisons. 

To an increasing extent, the isotope dilution technique is being applied in the certification of standard reference materials, e.g., for Hg determination in a polyethylene certified reference material (CRM 680 and 681), or Cd and T1 determination in high purity Zn (CRM 325/2R), where ID-ICP-MS yields the most accurate data.45... 

The development and improvement of analytical methodologies for mycotoxins has been greatly improved by the increased availability of matrix matched certified reference materials (CRMs) (Boenke, 1995) (Table 11.6). The type of matrix CRMs and concentration of the specified mycotoxin are based on the natural occurrence pattern of the toxin in specific foods and feeds. The recent availability of suitable CRMs, while being a prerequisite for the implementation of regulations and standards, will also be invaluable in many ways for the validation of new methods, solving trade disputes and for harmonising proficiency schemes. 

Abstract Since the uncertainty of each link in the traceability chain (measuring analytical instrument, reference material or other measurement standard) changes over the course of time, the chain lifetime is limited. The lifetime in chemical analysis is dependent on the calibration intervals of the measuring equipment and the shelf-life of the certified reference materials (CRMs) used for the calibration of the equipment. It is shown that the ordinary least squares technique, used for treatment of the calibration data, is correct only when uncertainties in the certified values of the measurement standards or CRMs are negligible. If these uncertainties increase (for example, close to the end of the calibration interval or shelf-life), they are able to influence significant-... 

According to the definition [1] the traceability chain is the unbroken chain of comparisons or calibrations from the result of a measurement or the value of a measurement standard to the national or international standards, all having stated uncertainties. The uncertainty of each link in this chain (measuring analytical instrument, reference material or other measurement standard) changes over the course of time. Therefore, the calibration intervals of measuring equipment used in testing (analytical) laboratories [2, 3] and of measurement standards used for their calibration are very important. The same applies to the shelf-life of a certified reference material (CRM) as a measurement standard. So, taking into account these... 

Analyses are performed in accordance with standardized methods issued under the responsibility of a Technical Committee within the Health Ministry. Usually such measurements rely on a comparison of the measured quantity in the unknown sample with the same quantity in a standard , i.e. an RM, according to a specific measurement equation [6], after calibrating the instrument. Calibration of a photometric system for clinical analyses usually means the set of operations that establish, under specific conditions, the relationship, within a specified range, between values indicated by the instrument and the corresponding values assigned to the RMs at the stated uncertainty. Calibration of the photometer itself implies the calibration of wavelength and absorbance scale by means of proper wavelength and absorbance RMs [5], traceable to national standards. A calibration of the instrument is still needed in concentration units to check the indicated provided value. The measurement result is then verified by application of that method of measurement to a certified reference material (CRM). Both the comparator - a photometric device with narrow or wide bandwidth, and the RMs should thus be validated. 

This example is of a traceability [1] protocol [2] for the chemical measurement of an element by a primary method of measurement [3]. It can be used for the certification of a single-element reference material by a national reference laboratory. This protocol relates to a very pure strontium nitrate solution, stabilized by 10% (by volume) nitric acid1. This solution is to be certified for the amount of strontium substance n(Sr) per unit mass of aqueous solution m (sol). The general measurement method described is based in part on the experience of certifying a currently available certified reference material (CRM) [4], Standard Reference Material (SRM) 3153a [5],... 

Abstract Some problems arising in the establishment of the traceability of the certified reference material (CRM) CZ 6007a (total protein, creatinine and stress indicators) are discussed. Bovine serum albumin is recommended as a calibration standard for total protein determination... 

Certified reference materials (CRMs) should be used to ensure comparability of results, traceability of measurements at different levels in the traceability chain and support implementation of legislation, standardization programmes, research programmes, accreditation of laboratories and industrial production processes [1]. 

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. 

Use of reference materials traceable to SI. In the majority of measurements, the certified reference materials (CRM) traceable to SI are by far the best definable reference points and they are most frequently used as measurement standards in chemical and other measurements. These materials are the means of achieving reliable measurements and they are available from the internationally recognized organizations for a wide range of users. 

In order to combine the capability of these commercial producers and the capability of the certification of NMI, CENAM has launched a program called Certified Traceable Reference Materials, MRTC in Spanish. This is a similar initiative to NTRM of NIST. It is intended primarily to promote the capability of domestic industries to produce and certify CRMs in those fields where there exist enormous demand and absolute lack. This program is under development in the field of gas standards for vehicular emissions, Fig. 3, and pH measurements with domestic industries. 

The traceability of the value carried by a reference material (RM) should be demonstrated by the RM producer [13]. The producer shall provide the traceability of results of its measurements to the national or international measurement standards. Where this is not possible, the correlation of results with the values of national or international certified reference materials (CRMs) is required. Ideally, the values of the CRMs should themselves be traceable [2]. 

To check the accuracy of the analytical procedure, the following Certified Reference Materials (CRMs) were used Peach Leaves, NIST SRM 1547 Tomato Leaves, NIST SRM 1573 Pine Needles, NIST SRM 1575 and Wheat Flour, NIST SRM 1567. All of them are produced by the National Institute of Standards and Technology (NIST Gaithersburg, MD, USA). 

Some refractory elements cannot be determined by ET-AAS at the levels usually present in waters. That is the case with M. El Himri et al. [28] developed a fast and accurate procedure, without any prior treatment, to analyze tap and mineral waters from Spain and Morocco for this highly toxic element. ICP-MS was employed. The analytical isotope selected was 238U, with Rh as internal standard. An LoD of 2ngl 1 was obtained. The estimated repeatability was 3 percent at the concentration level of 73 ng l-1. The method was validated by comparison with a radiochemical procedure devised for natural samples and by analysis of a Certified Reference Material (CRM). Multi-element capabilities of ICP-AES have also been employed for surveys of trace elements. Al-Saleh and Al-Doush [29] reported the concentrations of dissolved Be, Cd, Cr, Cu, Fe, Mg, Mn, Hg, Ni, Se, Sr, V, and Zn in 21 samples of retail bottled waters from Riyadh, Saudi Arabia. It was found that Cd, Fe, Hg, Ni, and Zn were present at concentrations higher than the limits recommended by the EU and World Health Organization (WHO) guidelines. 

Suppliers. BCR, Institute for Reference Materials and Measurements (IRMM), Belgium NIST, National Institute of Standards and Technology, United States NRCC, National Research Council of Canada. Classifications CRM, Certified Reference Material DORM, Dogfish Muscle Reference Materials for Trace Metals LUTS, Nondefatted Lobster Hepatopancreas Reference Material for Trace Metals SRM, Standard Reference Material TORT, Lobster Hepatopancreas Marine Reference Material for Trace Metals. 

---