Analytical protocols traceability

For operationally defined parameters (e.g. extractable forms of elements using a specific extraction method), results are obviously linked to the methods used, which hence requires that these methods are standardized if comparability of data has to be ensured. This justifies standard methods for these parameters to be made mandatory. In this context, given that analytical results are directly linked to the analytical protocol, standard methods will represent a key element in the traceability chain. In other words, the traceability chain is broken if the protocol is not strictly followed (Quevauviller, 2004b). 

Traceability is also a foundation of method validation. When a method is validated, it means that, properly applied, the method will produce reliable and trustworthy data with a known performance and known limitations. This does not mean that each sample will be the same, but the analytical protocols will be, thereby ensuring optimal performance and comparability of data. Novel samples may require novel approaches, but a standardized and validated method will, at the very least, provide a starting point. Method validation is one of the key components of total quality management in a laboratory. 

The process of providing an answer to a particular analytical problem is presented in Figure 2. The analytical system—which is a defined method protocol, applicable to a specified type of test material and to a defined concentration rate of the analyte —must be fit for a particular analytical purpose [4]. This analytical purpose reflects the achievement of analytical results with an acceptable standard of accuracy. Without a statement of uncertainty, a result cannot be interpreted and, as such, has no value [8]. A result must be expressed with its expanded uncertainty, which in general represents a 95% confidence interval around the result. The probability that the mean measurement value is included in the expanded uncertainty is 95%, provided that it is an unbiased value which is made traceable to an internationally recognized reference or standard. In this way, the establishment of trace-ability and the calculation of MU are linked to each other. Before MU is estimated, it must be demonstrated that the result is traceable to a reference or standard which is assumed to represent the truth [9,10]. 

Abstract The authors propose definitions and terminology for protocols on traceability links, generally to the international system of units, for specific chemical-analytical measurements in accordance with recognized principles of science. These definitions and terms could be useful in science, technology, commerce or law. A chain of such links leads from a measurand in a sample up to a unit in the International System of Units or, if unavailable, to a value on an internationally recognized measurement scale. The quality of such a chain is quantified by combining all recognized uncertainties estimated for all its links. These uncertainties of... 

Previously the authors have brought into discussion principles for traceability in chemical analysis [1], In this Journal is also the first part of this contribution [2] on protocols for traceability of analytical-chemical measurements. This first part is intended mainly for specialists who develop such protocols. It deals with terminology and definitions used when describing protocols for traceability1. These terms are mostly taken from recognized literature sources [3-7], Analysts, who want to judge the applicability of an established protocol and to use it, will be familiar with most of these terms and find others self explanatory. They may, nev-... 

CDC and the CRMLN established a traceability scheme (Fig. 1). The CRMLN uses this approach in a certification program for manufacturers. In this program, NCCLS protocol EP9-A is used as a basis for comparison using fresh serum samples [31]. The manufacturer collects a minimum of 40 specimens and analyzes them in duplicate in five separate runs. The specimens are then shipped to a CRMLN laboratory for analytical and statistical analysis. When the NCEP performance criteria for bias and precision are met, the manufacturer is issued a Certificate of Traceability for the... 

Some specialty gas mixture laboratories use NIST-traceable standards for instmment calibration requiring high levels of accuracy, such as EPA protocol mixtures. Where such standards are not available, suppliers typically make their own primary standards using gravimetric techniques. This can provide highly accurate standards of stable components. The grade of the desired mixture will determine the degree of analytical effort required. 

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