Intercalibration studies

Again, as in the case of the surface film samplers, information on the comparative merits of the various water samplers is largely anecdotal. Although such studies are not inspiring and require an inordinate amount of time, both on the hydrographical wire and in the laboratory, they are as necessary for a proper interpretation of data as are intercalibration studies of the analytical... 

While there have been very few intercalibration studies done between the various kinds of methods, the few available comparisons suggest that both the ultraviolet irradiation method and the various total combustion methods... 

Solyom [37] has carried out intercalibration studies on methods for the determination of total nitrogen in sludges. Nitrogen was determined by oxidation in alkaline solution with potassium peroxydisulphate, followed... 

Stability of calibrants and analytes is another frequently overlooked aspect of quality assurance, which is particularly relevant to surfactants. This aspect is discussed in Chapter 4.4. Very few intercalibration studies have been performed for the surfactant types of analytes (cf. Chapter 4.5). Currently, no certified reference material is available for surfactants. The European Commission has recently tendered for production of a reference material with certified surfactant concentrations [2]. We can conclude that quality assurance in quantitative surfactant analysis is still in its infancy when compared to analysis of PCB or chlorinated dioxins. Notwithstanding this, several important achievements have been made during recent years regarding improvement of the accuracy and reliability of qualitative analysis of surfactants, which will be the subject of the following chapters. 

Gagne, F., Blaise, C., van Aggelen, G., Boivin, P., Martel, P., Chong-Kit, R., Jonczyk, E., Marion, M., Kennedy, S.W., Legault, R. and Goudreault, J. (1999a) Intercalibration study in the evaluation of toxicity with rainbow trout hepatocytes, Environmental Toxicology 14 (4), 429-437. 

Estimation of Uncertainty in The determination of the total ion molal concentration of calcium from salinity measurement is relatively precise with a probable error of less than 0.3% under open ocean conditions. Dickson and Riley (37) have recently discussed the effect of analytical errors on the evaluation of the components of the aquatic carbon-dioxide system for seawater at 25°C and 1 atmosphere total pressure. Their conclusions Indicate that if alkalinity and total carbon dioxide are the measured parameters a probable combined uncertainty in the total carbonate ion molal concentration from 3 to 6 percent results, depending on Fco2 If pH and alkalinity are the measured parameters the uncertainty is approximately 4 percent. In addition to the probable error introduced by analytical precision, the absolute accuracy of the measurements introduces an error which is difficult to evaluate. The results of the GEOSECS intercalibration study (38) were indicative of this problem. A conservative guess is that accuracy introduces at least a one percent further uncertainty. It is also difficult to determine exactly what error is introduced through temperature and pressure corrections to situ conditions. For the deep sea this may introduce a further uncertainty of at least... 

Andrews P, Intercalibration Study on Toxaphene, Organized by Health Canada... 

Cooper, E.L., Valkovic, V., Strachnov, V., Dekner, R. and Danesi, P.R., Results of the intercalibration study of laboratories involved in assessing the environmental consequences of the Chernobyl accident. Appl. Radiat. Isot., 43 (1992) 149. 

Brewer, P. G., Spencer, D. W., Trace Element Intercalibration Study,"... 

For physical and chemical measurements it is essential that measurements are referenced to standards accepted by all the laboratories undertaking a particular type of measurement. In particular, the use of chemical analytical procedures validated through their application to certified reference materials (CRM) (26) is highly recommended. It is to be noted that a number of CRMs prepared with Antarctic matrices are already available, i.e., marine sediment and krill, or in preparation (26-29). These and other CRMs should be also used routinely by the participating laboratories to assure a periodical assessment of accuracy and repeatability of measurements. These laboratories should also undertake regular intercalibration studies. It is possible that in the first application of these exercises systematic errors will be found, but better results are expected in subsequent rounds together with a general improvement in the performance of laboratories and data quality. 

A method performance study may also be used to evaluate the performance of a new analytical method or an automated form of an already existing method [1,19]. Under certain circumstances a method performance study may be called intercalibration study. This should only concern exercises where the calibration of methods is investigated e.g. studies on calibrants, calibrant solutions, calibration procedures etc. Such studies are more frequent in physical measurements for metrological purposes. 

The GC analyses were performed on several glass capillary columns with various liquid phases (OV-101, SE-52, and SE-54) in a Hewlett-Packard 5840-A GC with splitless injection. Except for the intercalibration study, quantitation of chromatograms was based upon external standards. Areas from chromatograms were manually integrated using a digitizing planimeter. 

The results from the intercalibration study (Experiment 1) between the EPA Environmental Research Laboratory—Narragansett and the laboratory of James Quinn at the U.R.I. Graduate School of Oceanography agreed closely (Table II). This agreement also indicates that subsampling variability of the intercalibration sediments was quite low. The amount of material recovered from sediments by three extraction methods (Table III) was compared in Experiment 2. A considerable increase in the amount of hydrocarbon material returned from sediment samples was observed as the method of extraction became more vigorous. 

Application of AAS, MS, and ICP-MS Detection in an Intercalibration Study for Trimethyllead in Artificial Rainwater ... 

In this case, an intercalibration study served not only to test the ability of the various laboratories to perform an analysis, it also pointed out the steps in the determination which required further research. The high temperature catalytic oxidation (HTCO) technique has become much more common in this field, with several companies now supplying suitable instrumentation. This technique is not only simpler to run than the older wet oxidation methods, it also allows almost-real-time analyses at sea. The problem of the production of a proper blank, and therefore of a proper reference material for the DOC analysis, has yet to be solved at this time it is being patched by the use of low DOC deep water as a blank, or of water which has passed through the combustion chamber of the analyzer and subsequently condensed. Placing DOC and total nitrogen (TN) detectors in-line has made simultaneous determinations of both quantities on the same sample a routine procedure [53]. 

Colorimetric methods for the determination of DIP, nitrate, nitrite, ammonium, and silicate are well established, with both manual and automatic procedures well understood and able to provide adequate sensitivity for most purposes. These methods can readily be used at sea and in the future probably in situ. International intercalibration exercises have shown that many laboratories now have the analytical expertise to measure nutrient concentrations at ambient levels, but this is not true of all laboratories and the analysis still requires careful analytical procedures that recognize the importance of contamination control, blank correction, and the complications arising from the saltwater matrix. Although there have been a number of such intercalibration studies, there is no widely available standard reference material for nutrient analysis at present. 

No author has discussed the possible reasons for the discrepancy between the relatively low values found for lead in water in this region and the high theoretical amounts in the known discharges. Also, the potential sources of error, such as sampling procedures, sample preparation, and analysis have not been identified, and no intercalibration studies have been conducted. 

An intercalibration study involving five labs found that each lab was able to achieve linearity with its own choice of one or two ofthese three instruments. Differences between methods were larger than differences between labs for each method. Five samples were used ranging Ifom 200-3000 pg/g. An additional 15 soil samples were analyzed, and these are discussed in the following paragraphs. Although adequate instrumentation seems to be available for the laboratory analysis of lead and dust, sample preparation and extraction procedures still have problems to be resolved. 

The instrumentation and methodology for testing soils in the laboratory similar to those used for dust. Preliminary results of the intercalibration study designed to measure differences between labs and instrument methods indicate that differences between methods was greater than differences between labs for the same method. 

Murphy, K.R., Butler, K.D., Spencer, R.G.M., Stedmon, C.A., Boheme, J.R., and Aiken, G.R. (2010). Measurement of dissolved organic matter fluorescence in aquatic environments An intercalibration study. Environ. Sci. Technol, 44,9405-9412. 

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