Sampling important norms

In concluding this section, it is pertinent to take note of a special kind of isotopic fractionation ubiquitous, often quite severe, and arguably the most important source of fractionation that must be taken into consideration in noble gas geochemistry. This fractionation arises in mass spectrometric analysis contributory effects can and do arise in gas extraction and transport through the vacuum system, in the ion source (especially when a source magnet is used), in beam transmission, and in ion collection and detection (especially when an electron multiplier is used). As noted in Section 1.3, sample data are corrected for instrumental (and procedural) discrimination, which is calibrated by analysis of some standard gas (usually air). This is a roundabout and imperfect near-equivalent to the 8 value convention, which is the norm in stable isotope geochemistry (O, C, H, S, N, etc.). The reproducibility of instrumental discrimination inferred from repeated calibration analysis is usually quite satisfactory, but seldom is any care taken to try to match operating conditions in samples and calibration analyses. It is thus a matter of faith - undoubtedly quite... 

Various approaches have been used to define detection limit for the multivariate situation [24], The first definition was developed by Lorber [19]. This multivariate definition is of limited use because it requires concentration knowledge of all analytes and interferences present in calibration samples or spectra of all pure components in the calibration samples. However, the work does introduce the important concept of net analyte signal (NAS) vector for multivariate systems. The NAS representation has been extended to the more usual multivariate situations described in this chapter [25-27], where the NAS is related to the regression vector b in Equation 5.11. Mathematically, b = NAS/ NAS and NAS = 1/ b. Thus, the norm of the NAS vector is the same as the effective sensitivity discussed in Section 5.4.9.1 A simple form of the concentration multivariate limit of detection (LOD) can be expressed as LOD = 3 MINI, where e denotes the vector of instrumental noise values for the m wavelengths. The many proposed practical approaches to multivariate detection limits are succinctly described in the literature [24],... 

Four Dutch norms, important for the determination of alpha or beta emitters, have been validated. Gross-alpha and gross-beta measurements are very useful for fast and easy screening of environmental samples after a nuclear accident. 

Variability in ecotoxicity testing can have important implications, especially if we are using the data to make a decision about the acceptability (or otherwise) of a chemical, site, waste stream or process on the basis of the result. Thus, whenever we compare the outcome of a test with a threshold, there is a chance that a sample will appear to have exceeded the threshold simply because, on a particular occasion, the test yielded higher toxicity than the norm. Conversely, a bioassay may produce a result that indicates lower toxicity than the threshold, but only because the test on this occasion yielded an EC50 that was particularly high. In both cases, the same test on another occasion, or the same test performed by another laboratory, could result in a different outcome. 

These can be performed successfully with AES. Indeed, the unambiguous detection and identification of a single non-interfered atomic spectral line of an element is sufficient to testify to its presence in the radiation source and in the sample. The most intensive line under a set of given working conditions is known as the most sensitive line. These elemental lines are situated for the various elements in widely different spectral ranges and may differ from one radiation source to another, as a result of the excitation and ionization processes. Here the temperatures of the radiation sources are relevant, as the atom and ion lines of which the norm temperatures (see Section 1.4) are closest to the plasma temperatures will be the predominant ones. However, not only will the plasma temperatures but also the analyte dilutions will be important, so as to identify the most intensive spectral lines for a radiation source. Also the freedom from spectral interferences is important. 

When evaluating lab values in pediatric patients, it is imperative to nse age- and sex-adjnsted norms. It is also important to know that many blood samples are capillary samples, snch as heel- or flngersticks, that may have slightly different resnlts than venons samples. 

On the other hand, a series of technical norms have been developed to guarantee the quality and characteristics and/or properties of paints and coating materials these are provided by international organizations such as the ASTM (American Society for Testing and Materials) and ISO (International Standard Organization). Concerning the control tests that are currently appHed to paint samples. Table 2 summarizes the most important properties of paints and the techniques employed in their evaluation. 

Since the nature of these chemicals in water varies from polar compounds like phenol to very nonpolar compounds such as pentachlorophenol (PCP), it is a challenge to analytical chemists to determine them collectively. Conventional analytical methods for these compounds are often extensive as they require numerous analytical steps to obtain significant results. The first and also one of the most important requirements is to find a suitable sample preparation technique that allows the separation of the substances of interest from the sample matrix. The analysis of phenols in water is normed by EPA Method 625 [9]. A main disadvantage of this time-consuming and cost-intensive method is the large sample volume required for the extraction and use of large volumes of toxic organic solvents. Therefore, current developments in the field of sample preparation aim for fast and low-cost treatment of enviromnental samples. 

Where samples are at least two years old, a lack of secular equilibrium between "Pb and °Po would immediately call into question the accuracy of the analyses the most likely source of error being under-estimation of Pb. Under normal circumstances this would trigger more detailed examination of scale composition and re-analysis by gamma spectrometry. It is important to emphasise, however, that the discrepancy would only be apparent if data for Po were available from alpha spectrometry. As noted above, for reasons of cost and time, this is often not the case in routine analysis of industrial NORM. 

Finally, for Fq = 2.7 (corresponding to a probability of failure of 8.2 x 10 ) and a tolerance of 2 % for the Euclidean norm of the MPP, the procedure described in section Relationship with Monte Carlo Simulation yields M = 4 and a partition of F into 48 elements leading to an overall effort of 768 deterministic FE runs for the reliability estimation problem. This is considerably lower than 10" runs for importance sampling and 10 mns for a direct Monte Carlo simulation. 

In order to minimize errors arising from such effects, a number of guidelines have been laid down in industry norms or specifications. It is useful to consult such a norm or specification when faced with the task of determining solids concentration and size distribution by on-line sampling. We mention some of the most important points below, enough to carry out a reasonably accurate sampling, and refer to, for example, the norm ISO 9096 for more information. 

The comparability of MALDI results obtained in different laboratories can only be ensured by using standardized conditions of measurement, and identical sample and matrix preparation methods. Therefore, national and international MALDI-TOF MS round robin tests have been jjetfotmed. Their results were used to create national and international norms (ASTM, DIN, and ISO) for the determination of molecular masses and mass distributions of important polymer classes (PS, PMMA, and PEO). The classification of MALDI as an equitable (standardized) method relating to other established methods of polymer characterization may give an important push for increasing the application of MALDI MS. 

---