Standard reference material processing

The establishment of performance criteria for a given tumor marker test is not a simple process because accuracy and precision are unique for each type of analyte and its application. Establishing methodological limits for accuracy, precision, sensitivity, and specificity often requires standard reference materials, quality control materials, comparative studies, and actual clinical specimens. Accuracy and precision must be measured over the analyte reportable range for which the device is intended to be used. Sensitivity and specificity must be considered with respect to the intended clinical use of the device. Also, the indications for use should be carefully considered in the design of the study protocol. The indications for class II should be to monitor residual tumor after surgery (or radiation), the recurrence of tumor, or response to therapy. A 510(k) must provide clear evidence that the device is accurate, safe, effective, and substantially equivalent to a device legally marketed in the United States. 

In order to measure the exact amount of a specific protein (analyte) by IHC signal intensity, a critical requirement is the availability of a standard reference material (present in a known amount by weight) that can be used to calibrate the assay (IHC stain). It is then possible to determine the amount of test analyte (protein) by a translation process from the intensity of IHC signals. In this respect it is helpful to consider the IHC stain as a tissue based ELISA assay (Enzyme Linked ImmunoSorbent Assay), noting that ELISA is used in the clinical laboratory as a standard quantitative method for measuring protein by weight in fluids, by reference to a calibrating reference standard. 

Multidimensional Data Intercomparisons. Estimation of reliable uncertainty intervals becomes quite complex for non-linear operations and for some of the more sophisticated multidimensional models. For this reason, "chemometric" validation, using common, carefully-constructed test data sets, is of increasing importance. Data evaluation intercomparison exercises are thus analogous to Standard Reference Material (SRM) laboratory intercomparisons, except that the final, data evaluation step of the chemical measurement process is being tested. 

A QC assessment was done for all samples. De-ionized water field blanks were collected on seven different days to evaluate process contamination. Site duplicates were taken at eight sites to evaluate repeatability and site variation. Instrumental precision was constrained by analysis of laboratory duplicate solutions, and is typically less than 5%. Finally, standard reference material (SRM) water standards were analyzed with sample batches, to assess instrumental accuracy. 

Control charts are used in many different applications besides analytical measurements. For example, in a manufacturing process, the control limits are often based on product quality. In analytical measurements, the control limits can be established based on the analyst s judgment and the experimental results. A common approach is to use the mean of select measurements as the centerline, and then a multiple of the standard deviation is used to set the control limits. Control charts often plot regularly scheduled analysis of a standard reference material or an audit sample. These are then tracked to see if there is a trend or a systematic deviation from the center-line. 

In 2005, De Laeter discussed the role of isotope reference materials for the analysis of non-traditionaT stable isotopes. At present, no isotopically certified reference materials exist for a large number of elements, including Cu, Zn, Mo and Cd, and it is important that this situation be rectified as soon as practicable. Before the isotopically certified reference materials become available for selected elements, suitable reference materials can be created as a standard if sufficient and reliable isotope data have been obtained by interlaboratory comparisons. For example, the Hf/ Hf isotope ratio was measured using hafnium oxide from Johnson Matthey Chemicals, JMC-475, for hafnium isotope ratio measurements with different multi-collector mass spectrometers (ICP-MS and TIMS) as summarized in Table 8.1. However, no isotope SRM is certified for the element Mo either. Mo isotope analysis is relevant, for example, for studying the isotope fractionation of molybdenum during chemical processes or the isotope variation of molybdenum in nature as the result of the predicted double (3 decay of Zr or 18.26-28 spectroscopically pure sample from Johnson Mattey Specpure is proposed as a laboratory standard reference material if sufficient and reliable isotope data are collected via an interlaboratory comparison. 

Of additional benefit to enantioselective POP separations is the quantification of enantiomer compositions in standardized reference materials, available from sources such as the US National Institute of Standards and Technology (NIST) and Environment Canada [105, 106]. Such materials are intended for quality assurance/quality control in sample processing and instrumental analysis of their respective matrices, and enantiomer quantification extends this use to enantioselective studies. 

Sample preparation is much the same as for other GD couplings to instruments. Metal or alloy discs, and compacted conducting samples, are the most frequently used. Solution samples have been examined by deposition onto graphite, aluminium and copper cathodes. Quantitative analyses are usually performed by using a calibration graph run from standard reference materials, a process that takes considerably more time than preparing a solution-based curve. Conversely, time is saved in the direct analysis of solids also, the inert atmosphere of a GD cell reduces the spectral interferences frequently encountered in flame atomizers. 

TiC>2 Degussa P25 (presently Evonik) is the most used material for CO2 reduction, normally used as a standard reference material in thermodynamically downhill photocatalytic processes. It is a mixture of two polymorphs of titanium dioxide, namely anatase (80%) and rutile (20%) and the particle size up to some nanometers. Recently, Ohtani et al found that Degussa P25 also contains trace amount of amorphous titanium dioxide [165]. 

This is the most widely used method for the determination of the phase composition of powders. The x-ray diffractometer contains a source of monochromatic x-rays that irradiate the sample and are diffracted from atomic planes and detected. The angle of diffraction of x-rays by the crystalline planes is characteristic of the crystal structure, and the intensity of scattered radiation is characteristic of the atomic composition. In recent years, automated data processing has enabled higher accuracy and speed. A number of problems are encountered in the quantitative determination of phases in fine powders. Some of these are overlap of phase peaks (e.g., in silicon nitride), orientation of grains, and presence of coarse particles. The last produces distortion of the diffraction data. A number of standard reference materials for XRPD have been developed for use in improving the quality of data [37]. 

Most work discussed here regarding standard Antek on-line/at process analyzers, laboratory based equipment, and the High Speed Sulfur (HSS) on-line analyzer was carried out in the PAC Houston R D Laboratory and Production facility. Other data were collected from various industry and public sources and are so identified in the associated text and graphics. Various solvents, sulfur sources, and standard reference materials were used in association with both historical and new data. Solvents and chemicals, such as iso-octane, toluene, and dibutyl sulfide, were of typically reagent grade purity and were obtained from readily available commercial sources, such as Aldrich chemicals. When appropriate, these materials were analyzed before use. 

The focus of this paper is on the technique of Combustion CVAAS and its applicability to some of the samples encountered in the petroleum industry. It describes the equipment and test procedure adopted by our laboratory for the determination of total mercury in crude oil, condensate, and other process stream samples. Validation of this technique using standard reference materials (SRM), certified standards, and spiked samples is addressed. Instrument response to various organic mercury species and precision data derived from actual crude oil samples is presented. 

This should not be considered as a drawback when one realizes that FIA is a technique essentially performed under physically and chemically non-equilibrium conditions, and that reproducibility of the reaction process rather than its completeness is the key issue of the technique. With proper calibration, good results may be obtained under nonequilibrium conditions for the precipitation. This has been pfewen experimentally in the coprecipitation of cobalt and nickel with Fe(lI)-HMDTC [22]. Although the analyte collection efficiency was onl approximately 50%, good sensitivity and precision were achieved. with excellent agreement of analytical results with certified values of standard reference materials, covering a large variety of different sample matrices. 

The facility should have a separate room for storing radioactive standard and stock solutions. This room usually is located near the sample receiving and processing area. Radioactive standards and solutions must be kept separate from other laboratory operations to prevent cross-contamination. The room should have cold storage capabilities and lockable cabinets. It should be designed to the same specifications as other sample preparation rooms, with a fume hood and computer access to permit dilution and other processing of radioactive standard reference materials and stock solutions. 

Many of the data published today are either erroneous or apply to inadequately characterized materials. Unrecognized systematic errors are frequently present in the measurement process, and consequently the data do not represent the property purportedly measured within the stated uncertainty. In other instances, the property measured is especially sensitive to unreported characteristics of the material. For example, the transport properties of pure metals and crystalline dielectric solids at low temperatures are determined almost entirely by the physical and chemical defects in them, rather than by their chemical or generic identification, such as copper, aluminum, etc. Great care must be exercised to characterize such materials, if reported data are to have any usefulness. Both the study of systematic errors and specimen characterization are of the utmost importance to the reliability and usefulness of data. This paper only considers the use of standard reference materials (SRMs) to reduce systematic errors in the measuring system. The problem of insufficient material characterization is an extensive subject in itself and will not be discussed further here. 

C means certified values, A refers to assigned values (not certified), and I corresponds to data given for information. (Adapted from Gills TE (1999) NIST standard reference materials for measurement assurance - practices, issues and perspectives. In Fajgelj A and Parkany M (eds.) The Use of Matrix Reference Materials in Environmental Analytical Processes, Cambridge The Royal Society of Chemistry, pp. 57-64.)... 

B. Candidate Biological Standards and Reference Materials Processed at NIBSC... 

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