Standards, matching

In trace organic analysis there is usually an extraction or clean-up process, rather than a sample dissolution. Here not only must the matrix effect be considered, but also the recovery yield of the extraction. Frequently an external spike standard is added, but there is often no way of knowing if the recovery of the spike standard matches the analyte in question. There is considerable evidence that the U S E P A method for VOA analysis (Minnich 1993) is subject to such error, as reported by Schumacher and Ward (7997). The analyst must always consider the possibility of such an error, especially when using CRMs to control methods that are applied in routine mode. 

Care must be taken to ensure that the criteria or methods used closely match the site-specific conditions under study. Failure to do so may result in early elimination of at-risk buildings from the analysis pool. Further, when standard criteria are being applied, care must be taken to ensure that the objective of the standard matches the intent of the study. A standard developed for equipment protection or loss prevention may not be appropriate for personnel protection. 

Lithium tetraborate has been found to be an excellent fusion agent enabling complete dissolution of silicate materials in acid for the analysis of major and minor constituents in coal. Carefully prepared standards matching the approximate concentrations of both the silica and alumina present in unknown samples permit determinations to be made with precision and accuracy. This method is currently being used to analyze coal ash and related materials. 

ICP offers good detection limits and a wide linear range for most elements. With a direct reading instrument multi-element analysis is extremely fast. Chemical and ionization interferences frequently found in atomic absorption spectroscopy are suppressed in ICP analysis. Since all samples are converted to simple aqueous or organic matrices prior to analysis, the need for standards matched to the matrix of the original sample is eliminated. 

Use of quantitative external standards matched to the analytes-e. g. fetuin or antibody for glycoprotein analyses and the equivalent glycan libraries for oligosaccharide analyses. 

Measurement Emission response, calibration curve, sample/standard matching, etc. Same for all samples... 

A diffraction spectrum is considered a fingerprint for identifying examined materials. An acquired spectrum should be compared with the standard from an X-ray diffraction database. The standard spectrum has been collected from a pure powder sample with fine powder size, usually several micrometers in diameter. We would expect to match both peak locations and relative peak intensities between the acquired spectrum and the standard if the sample is the same substance as the standard. Matching relative intensities, however, is not always possible even when the examined specimen has the same crystalline stmcture as the standard. One reason for this discrepancy might be the existence of preferential crystal orientation in the sample. This often happens when we examine coarse powder or non-powder samples. Preferential orientation of crystals (grains in solid) may even make certain peaks invisible. 

Today, atomic emission spectroscopy always makes use of relative quantitation, i. e. unknown samples are quantitatively analysed after calibration with samples of known composition. The most common approach to calibration is internal standardisation. The underlying assumption, introduced by Gerlach in 1925, is that the ratio of the analyte mass to the mass of the internal standard, matching the analyte in its chemical properties, emission wavelength, energy of the line, and ionisation... 

DO ASSE/BCSP CURRICULUM STANDARDS MATCH EDUCATIONAL NEEDS ... 

Standardization matches the concept of calibration generally used in analytical chemistry. The number of radionuclides produced per unit time by irradiation of an infinitesimally thin target is determined by the balance of the increase due to nuclear reactions and the decrease due to radioactive decay ... 

O Equations (30.25) and (30.28) provide the basis for quantitative activation analysis, hence the unknown mass Wx of analyte x can be determined if all other parameters are accurately known. This is seldom the case, so a comparative analysis with a standard sample containing a known mass, nts, of the same element is usually performed. If the standard matches the size and composition of the unknown sample, the ratio of counts Ncjc/Nc,s can be used for the calculation of the unknown mass. Applying Eq. (30.25) one obtains ... 

Analytical advantages of the ICPAES technique are the simultaneous or sequential multielement capability, a relative absence of matrix interference, high precision, simplicity of calibration, and a wide dynamic range. Commonly employed pretreatments include dry ashing, acid extraction, wet mineralization, and the use of PPRs. Wet digestion is preferable for pretreatment of most biological material, with the exception of serum or plasma. Pretreatment with PPRs is the preferred method for plasma and serum samples. This then leaves only the metals in solution for analysis by ICPAES. Excellent results are obtained using the Mg emission line 279.553 nm [96]. Inconsistencies with this type of analysis are usually due to aerosol production and introduction into the plasma. It is also important that the viscosity and surface tension of the samples and standards match. 

It would appear that antimony electrodes can be used reliably in experiments on proximal renal tubules, where there is little change in the phosphate buffer concentration and probably no change in ionic strength, providing that the phosphate buffers and ionic strength of the standards match the unknown fluid. Questionable data should be expected with antimony microelectrodes in distal tubules, collecting ducts and in final urine, where ionic composition and buffer capacity vary widely. 

If dangerous failures of lEC standards match the unsafe failures above, this is not the case for safe failures. Indeed, in their current editions, any non-dangerous failure is considered safe. This allows the suppher to consider safe any kind of failure (e.g. SU failure) without any relationship to the safety function in question and to announce the SFF safe failure fraction, i.e. proportion) to be much higher than in reality. 

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