When using certified calibrants

Very few laboratories (3) were rejected by statistical tests and this number remained about constant when laboratories used certified calibration solutions. This means... 

Description Certified reference materials (CRMs) may be used as calibrators or measurement trueness control material. When used as calibrator, a CRM permits traceable and thus comparable measurement results. 

Pauwels (1999) argues that the certified values of CRMs should be presented in the form of an expanded combined uncertainty according to the ISO Guide on the expression of uncertainty in measurement, so that coverage factor should always be clearly mentioned in order to allow an easy recalculation of the combined standard uncertainty. This is needed for uncertainty propagation when the CRM is used for calibration and the ISO Guide should be revised accordingly. The use of the expanded uncertainty has been pohcy in certification by NIST since 1993 (Taylor and Kuyatt 1994). 

The air sampler manufacturer, who will also supply certification, often performs calibration of certain kinds of air sampling equipment. Air pumps and blowers will always require calibration when used. This involves the use of flow meters certified for accuracy by the manufacturer. In the same way, analytical instrumentation will... 

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). 

Ensures that the inspection, measuring, and test equipment is capable of the accuracy and precision necessary Establishes, documents, and maintains calibration procedures, including details of equipment type, identification number, location, frequency of checks, check method, acceptance criteria, and the action to be taken when results are unsatisfactory Identifies, calibrates, and adjusts all inspection, measuring, and test equipment and devices that can affect product quality at prescribed intervals or, prior to use, against certified equipment having a known valid relationship to nationally recognized standards. Where no such standards exist, the basis used for calibration is documented. 

An individual analyst in most instances is concerned only with links from values in samples to similar values in certified RMs [9-13] or from calibrated instruments. When using an existing protocol, chemists must carefully follow all procedures, minimize errors, such as those resulting from contaminations, compled with the uncertainties in estimating these contaminations. Rigorously correct use of a protocol and aggressive self-criticism in its application constitute a professional challenge. 

In this scheme, the primary reference material is defined as a chemical substance of the highest (and known) purity, or a well-characterized substance in a matrix, This classification of materials is, however, fairly arbitrary. It is ideal when used in connection with standards characterized in terms of biological activity. Primary standards are thus the International Reference Preparations (IRP) produced by the World Health Organization (WHO). In this case the primary standard for a particular antibiotic is the WHO reference preparation which constitutes the unit of that antibiotic. When people wish to use it they have to prepare a large batch of samples calibrated to the primary. This is then called a secondary standard. However, for well-defined chemical parameters, the term certified reference material is preferred. 

The primary purpose of the new standards was to measure the linearity of calorimeter response over its entire range from 800 to 1200 Btu/SCF. Preliminary tests on three calorimeters show that there may be a bias of+1.5 Btu at the midrange of the calorimeter. That means that when standard B (certified heating value of 813.3 Btu/SCF) or standard C (certified heating value of 1186.1 Btu/SCF) are used to calibrate the calorimeter and the other two standards are used as a test gas, only standard A (certified heating value of 996.6 Btu/SCF) reads high by 1.5 Btu/SCF. This study will continue for other points within the 800-1200 Btu range in order to develop an accurate calibration curve for future use. 

Certified reference materials are intended primarily for calibration and in quality control of analytical techniques. A certified reference material is a reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure that establishes its traceability to an accurate realization of the unit in which the property values are expressed and for which each certified value is accompanied by an uncertainty at a stated level of confidence. They are used to test, validate, and optimize new analytical techniques as well as in quality control of routine laboratory work. Table 3 gives a list of environmental samples that provide certified values of PAH content. These are available from various bodies as certified reference materials. In measuring the concentration of a substance for certification purposes, more than two independent and reliable analytical methods are used. Certified reference materials when used for standardization of analytical methods will make comparisons between PAH data obtained by a variety of workers using... 

In most analytical procedures, calibration is carried out by means of a calibration curve using com-pound(s) prepared with chemicals of an appropriate purity and verified stoichiometry. Matrix effects must often be taken into account and, consequently, the calibration solutions should be matrix-matched. CRMs of pure compounds may be used for calibration. However, matrix CRMs should in principle not be used for the purpose of calibration unless no other suitable calibrants are available, with the exception of those methods (e.g., spark source mass spectrometry, wavelength-dispersive XRF, etc.) that require calibration with CRMs of a similar, fully characterized matrix (e.g., metal alloys, cements). For such methods, accuracy can only be achieved when certified RMs are used for the calibration. 

There are two broad classes of calibration solutions used in analyses of the kind discussed here. The first class, referred to as calibration solutions, corresponds to solutions of the analyte(s) in clean solvent, possibly also containing internal standard(s) such solutions can be certified calibration solutions (Section 2.2.2) or solutions prepared in the analyst s own laboratory according to procedures determined ahead of time to be fit for the purpose for which the analysis is to be undertaken. The other class of calibration solutions, which will be referred to as matrix-matched calibrators (sometimes just calibrators ), is prepared from aliquots of a blank (or control) matrix (identical or almost so to the matrix composing the analytical samples but devoid of the target anal54 e(s) to within the detection limits of the analytical method, see Section 9.4.7). When a suitable blank matrix is available, this is the preferred approach since many interferences and other effects are largely accounted for automatically. 

Spike calibration 2% relative standard deviation (RSD) was assumed. This value is very conservative, but it is based on a combination of replicate spike calibrations and an additional component to allow for uncertainties in the standard solutions used for calibration. When using three Ru solutions from three different companies, three significantly different Ru concentrations were obtained for the spike, despite the certified and traceable PGE concentrations (nominal 10 pg ml ) that they were supposed to have. 

Inspection tolerance can be divided into two major components the accuracy variability of the instruction and the repeatability of the measuring method. The calibration and accuracy of the instrument are documented and certified by its manufacturer, and it is periodically checked. Understanding the overall inspection process is extremely useful in selecting the proper method for measuring a specific dimension. When all the inspection methods available provide an acceptable level of accuracy, the most economical method should be used. 

The participants The range of participants should, whenever possible, be chosen in such a manner that widely different methods (based on different physical or chemical principles) can be used. The number of participants (recommended 15) should be sufficient to allow meaningful statistical processing of the results. When the laboratories feel the need for a CRM, either because the available calibrants are not comparable and a primary calibrant appears necessary for traceability, or because a reliable certified control material is needed but not available, then it is recommended that these laboratories do not plan a certification project entirely on their own, but that they involve laboratories having a background in traceability. 

But in order to understand what needs to be changed, we first need to understand the current situation. In order for a pharmaceutical company to use any analytical method for certifying the properties (efficacy, potency, etc.) of their products, the analytical method has to be validated. Validation , in the parlance of the FDA, is a far cry from what we usually call validation when developing a multivariate spectroscopic method. In fact, what we call validation in spectroscopic calibration (which usually means calculating an SEP, or an SECV) is a far cry from the dictionary definition of validate , which is to make legally valid , where valid is defined as having legal efficacy or force [11],... 

Ideally both the control materials and those used to create the calibration should be traceable to appropriate certified reference materials or a recognised empirical reference method. When this is not possible, control materials should be traceable at least to a material of guaranteed purity or other well characterised material. However, the two paths of traceability must not become coincident at too late a stage in the analytical process. For instance, if control materials and calibration standards were prepared from a single stock solution of analyte, IQC would not detect any inaccuracy stemming from the incorrect preparation of the stock solution. 

Each instrument that we use has a scale of some sort to measure a quantity such as mass, volume, force, or electric current. Manufacturers usually certify that the indicated quantity lies within a certain tolerance from the true quantity. For example, a Class A transfer pipet is certified to deliver 10.00 0.02 mL when you use it properly. Your individual pipet might always deliver 10.016 0.004 mL in a series of trials. That is, your pipet delivers an average of 0.016 mL more than the indicated volume in repeated trials. Calibration is the process of measuring the actual quantity of mass, volume, force, electric current, and so on, that corresponds to an indicated quantity on the scale of an instrument. 

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-... 

Temperature. Water temperature is an important parameter in calculations of oxygen solubility, calcium carbonate saturation and stabiUty, and various forms of alkalinity, as well as in determining basic hydrobiological characteristics. The temperature should be taken in situ for accuracy, and a standard mercury thermometer with readings to the nearest 0.1°C should be used. It should be calibrated against a precision thermometer certified by the National Bureau of Standards. A thermistor is preferable when attempting to measure temperature at different depths and for automated monitoring and surveillance, and should be similady calibrated (see TemperaTUREMEASUREMENT). 

It should be noted that when we used methods of measurement needing inorganic reference materials for calibration (such as flame photometry or atomic absorption spectrometry) the uncertainty due to the reference materials was considerably lower than that due to the photometric device. On the contrary, when we used a clinical reference material certified for its glucose concentration with a 10% (rel) uncertainty, this uncertainty exceeded twice the uncertainty due to the spec-trophotometric device. When we determined Mg by a spectrophotometric method with Titan Yellow, we found that the uncertainty due to the reference material was approximately twice that due the device, as we used a very accurate spectrophotometer. 

---