Intercomparison of results

In the field of electrophoresis, standardization is yet to be achieved in many areas. In laboratories throughout the world, variations of techniques exist. Interlaboratory intercomparisons of results are not widespread and there are apparent needs to have better control of electrophoretic results. Also, many techniques need to be validated for experimental appropriateness. Taylor (2) expressed the need for test validation "A plethora of methods, procedures, and protocols based on the same measurement principle can arise for a given analytical determination. Usually, they are worded differently, and they may contain subtle or major differences in technical details. The extent to which each needs to be validated is a matter of professional Judgment. It is evident some validation tests could be merely a matter of experimentally testing the clarity of the written word. ... 

Class reactions for many of the compounds are either few or non-existent and thus an evaluation of recoveries or reproducibility of the analyses is difficult. A review of the literature concerning natural lipids in seawater high-l hts the fact that detailed information has been gathered at the expense of any wide aerial surveys of the levels of these compounds in ocean waters. The concentration ranges found by various workers vary widely and in the absence of standardised methods of extraction and analysis, intercomparison of results is often impossible. 

In general, most researchers rely on reporting between 15 and 30 PAH-compounds for characterising specific emissions. In order to facilitate intercomparison of results between the large number of laboratories which are engaged in the analysis of PAH and POM emissions and to permit a comprehensive assessment and evaluation of analytical data in terms of environmental, occupational and health impact, a concensus on a minimum number of representative compounds to be reported in all PAH emissions is highly desirable. 

Dupont trade name of Teflon, or in Grum and Saltzman s original work. Allied Halon G-80) powder, packed to a density of 1.0 g/cm. Grum and Saltzman s work was rapidly followed by papers by Jack Hsia and Vic Weidner (1981) of the National Bureau of Standards (now NIST) that thoroughly characterized packed PTFE. The initial Weidner and Hsia paper reported absolute reflectance data for packed PTFE powder from 200 to 2500 nm (0.2-2.5 /an) and established this material as the standard of choice for diffuse reflectance measurements in the UV-VIS-NIR region of the spectrum. A follow-up study involving a laboratory intercomparison of results showed that even as much as a 20% error in compression of the powder gave excellent results in consistency of reflectance (Fig. 3). 

A final consistency test for the present impurity kinetic model requires an intercomparison of results at 1000 and 10,000 Torr. Based upon the above described procedure, the 0,16 0.02 10,000 Torr result for Y° corresponded to an estimated Ha impurity mole fraction in the CsFg of O.OOO9 0.0001, in semiquantltatlve agreement with the corresponding 0.0012 O.OOOlf- 1000 Torr result. 

Electrolytic tin plate is ideal for an intercomparison of the three methods, not only because of its great importance, but also because the value of a for tin is near 400, which corresponds to a relatively large linear range (Equation 6-9). Such an intercomparison was carried out10 with satisfactory results on standard samples on which the tin thickness was established by a chemical method. 

Buesseler KO, Bauer JE, Chen RF, Eglinton TI, Gustafsson O, Landing W, Mopper K, Moran SB, Santschi PH, Vernon Clark R, Wells ML (1996) An intercomparison of cross-flow filtration techniques used for sampling marine colloids overview and organic carbon results. Marine Chem 55 1-31 Buffle J, Perret D, Newman M (1992) The use of filtration and ultrafiltration for size fractionation of aquatic particles, colloids, and macromolecules. In Enviroiunental particles. Buffle J, van Leeuwen HP (eds) Lewis Publishers, Boca Raton FL, pl71-230... 

Commission of the European Communities., Results of the Second CEC Intercomparison of Active and Passive Dosemeters for the Measurement of Radon and Radon Decay Products, EUR Report 10403 EN (1986). ... 

Miles, J.C.H. and Sinnaeve, J., Results of the second CEC intercomparison of active and passive dosemeters for the measurement of radon and radon decay products (1984)... 

Most of the reference materials discussed are based on natural matrices (seawater, algal cells, sediment) and would initially only be certified for a limited number of constituents. Nevertheless, it is apparent that such materials provide a resource for the investigation of a much wider variety of constituents, and it is important that the ocean science community be encouraged to investigate these materials further. In particular, the existence of these materials would facilitate a wide variety of necessary interlaboratory method comparisons that have been neglected to date. Eventually these intercomparisons will result in consensus values for other constituents, which can then be assigned to the reference materials. 

To monitor the laboratory performance against both its own requirements and the norms of peer laboratories there is a need for intercomparison of laboratory results. This is usually done by participating in proficiency testing (PT), i.e. an external quality assessment. In this way, the laboratory performance at national or international level are monitored and, furthermore, the reproducibility is highlighted. 

A number of intercomparisons of chemical submodels have been carried out. Figure 16.18, for example, shows some of the results from one such intercomparison for conditions chosen to be representative of moderately polluted conditions (Kuhn et al., 1998). The average final 03 predicted by the models was 148 ppb, but there are clearly significant differences between the models. Thus the highest, the EMEP model (European... 

It is difficult to envision that balloon-borne techniques will be able to satisfy the demand for more complex and frequent measurements. Therefore it is critical for maximizing the scientific return of balloon-borne flights to include simultaneous measurements of the right mix of species and photolysis rates. In the absence of frequent balloon-borne measurements it is nonetheless very gratifying to have achieved the coalescence of results by independent techniques as a zero-order substitute for intercomparisons. A possible direction for future stratospheric research with a new platform, remotely piloted aircraft, that alleviates some disadvantages of balloon-borne platforms is discussed in the last section of this chapter. 

One procedure that is widely used to circumvent these complications is to remove ambient ammonia from the sampled air without removing particles by inserting one of several types of diffusion denuders upstream from the filter(s). In fact, in a recent Environmental Protection Agency (EPA)-sponsored intercomparison of methods for determination of strong acid content of aerosols, all but one protocol utilized an ammonia denuder (63), and all used an impactor or cyclone to remove coarse particles. The presence of this denuder clearly prevents neutralization of acidic aerosols by ammonia but also disturbs the gas-aerosol equilibrium between sulfate-nitrate aerosols and gaseous species. Ammonia and nitric acid are released from the depositing particles (64, 65) and must be collected downstream if accurate particulate ammonium and nitrate determinations are to be made. If equal amounts of ammonia and nitric acid are released, then the absolute [H+] (neq/m3) will not be altered. No specific evidence is available in the literature to demonstrate alteration of the observed [H+] as the result of reequilibration, but this area deserves further study. 

Completion of Field Studies in the Troposphere with Better Spatial Coverage. All of the examples of tropospheric measurements in this chapter were made at surface sites with the instrument inlets within 4 to 10 m of the ground. With the important influences of the surface on the near-surface concentrations of some atmospheric species and the lack of spatial information from surface studies, it is important to coordinate the surface measurements with aircraft (or balloon) measurements. Some aircraft measurements of nitrogen species in the troposphere have been made, but it is important to ensure that the measurement techniques on the surface and in the air give equivalent results. This assurance can only be accomplished through careful intercomparison of instruments utilized in each platform. 

All but one of the seven laboratories that recently participated in a intercomparison of niacin assays chose to use microbiological assays (42). The results from the lone HPLC determi-nation/UV absorbance determination were rejected due to lack of chromatographic resolution. 

The numerical and approximate analytical treatments using the Samuel-Magee model and an intercomparison of the results have been presented in an excellent review of diffusion kinetics by Kuppermann (19). He has pointed out that there is a quantitative inconsistency between the model and experiment although the agreement can be... 

In this section we describe the various experimental techniques which have been used to measure aT and we include a critical evaluation of their limitations so as to aid in the intercomparison of the various sets of data. Many experimental groups have contributed to this field, but the aim here is not to discuss every technique in great detail but rather to select a representative subset in order to illustrate the most interesting features. Discussions of the results obtained are given in sections 2.5 and... 

When intercomparisons between results obtained by these two illumination systems were made, no significant differences were noted. Therefore, the rotary photoreactor (7) was used in the large majority of these studies. 

Intercomparison of the top and bottom sections of Tables XII, XIII, and XIV shows that for the L = 0 approximations the best set gives much better results than the Chebyshev at low orders, while the Cheby-shev at lower temperatures gradually improves as the order increases. It is obvious that the better approximations obtained by the Chebyshev (L = 5) for n = 1 and 2 are because of accidental cancellation of errors. We do not expect the Chebyshev (L = 5) generally to yield as good an approximation as the best set for a system. Such an example is illus-... 

Zagyguai, P., Parr, R.M. and Nagy, L.G., Additional results for the G-1 IAEA intercomparison of methods for processing Ge(Li) gamma-ray spectra. J. Radioanal. Nucl. Chem., 89 (1985) 589. 

As part of the evaluation of results of the intercomparison exercises for major and trace elements, NRC assigns a performance evaluation criteria based on the number of times results reported by a laboratory fall within acceptable criteria. The percentage of laboratories achieving superior or good performances has increased since 1991 from 46% to 83% (Figure 13.3). Superior-rated laboratories submitted results for most analytes within the 95% confidence intervals goodrated laboratories submitted many results within the accepted range with a minimum number of outliers (16). 

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