Precision environmental analysis

The duration of acclimation is affected by several environmental factors, such as temperature, pH, aeration status, and nutrients. The concentration of the compound that is being metabolized greatly affects the length of time before a decline in its concentration is detectable. The rate of biodegradation of trace compounds increases with concentration, but because compound loss is usually determined and not C02 or product formation, the low precision of analysis leads to data indicating a longer acclimation at higher concentration [104,106,113,128]. 

As the most important inorganic mass spectrometric technique, ICP-MS is also employed for the precise and accurate isotope ratio measurements of a multitude of elements (such as Li, B, S, Fe, Sr, Pb, U, Pu) in environmental samples (see Chapter 8).9,88-90 Isotope ratio measurements of environmental samples require special careful sample preparation techniques including trace/matrix separation and enrichment procedures if the analytes are at the trace and ultratrace level. As an example, the schematic diagrams of the separation and enrichment procedures for the precise isotope analysis of Pu, U and Sr in water samples from the Sea of Galilee using double-focusing... 

The determination of precision and accuracy is an important part of environmental analysis because it indicates the degree of bias or any error in the measurement. 

Understanding the nature of the environmental sample and the limitations it places on accuracy and precision of analysis is a critical factor in selecting what type of data to collect. Some matrices are so inherently indefinite that the analytical data produced for them even with the most accurate and precise methods cannot be called definitive, as illustrated in Example 2.4. 

The isotope 40K can be analyzed in natural water samples with the Cherenkov counting technique.2 3 Because of the lack of a suitable radiotracer for K and the similarity between the chemistries of rubidium and potassium, 86Rb can be used as a tracer for K.4 Also, thermal ionization mass spectrometry (TIMS) has been used to determine 40K in environmental samples. The interference of mass 40 can be solved by double spiking with 43Ca/48Ca the procedure for the routine high-precision isotope analysis of the K-Ca system will then be free of Ca fractionations.5... 

The major quality parameters to be addressed during sample preparation are listed in Table 1.4. These are accuracy, precision, extraction efficiency (or recovery), and contamination control. These quality issues also need to be addressed during the analysis that follows sample preparation. Accuracy is determined by the analysis of evaluation samples. Samples of known concentrations are analyzed to demonstrate that quantitative results are close to the true value. The precision is measured by running replicates. When many samples are to be analyzed, the precision needs to be checked periodically to ensure the stability of the process. Contamination is a serious issue, especially in trace measurements such as environmental analysis. The running of various blanks ensures that contamination has not occurred at any step, or that if it has, where it occurred. As mentioned before, the detection limits, sensitivity, and other important parameters depend on the recovery. The efficiency of sample preparation steps such as extraction and cleanup must be checked to ensure that the analytes are being recovered from the sample. 

Basic Mechanisms. Finally, further work is necessary on fundamental mechanisms of individual fire retardants. These mechanisms are a function of the particular chemicals involved and the environmental conditions of the fire exposure. There is a need to establish common methods and conditions for determining these mechanisms in order to compare different treatments. This would give us a better understanding of how these compounds work in action and would provide a more efficient approach for formulating fire-retardant systems than a trial and error approach. Correlations also need to be established between rapid precise thermal analysis methods and standard combustion tests. Retardant formulations could be evaluated initially on smaller (research and development size) samples. The more promising treatments could be tested for flame-spread index, heat release rate, and toxic smoke production. 

Much is made of detection limits in environmental analysis. Much of the modern concern about chemicals in the environment stems from the ability of the analytical chemist to analyse ever lower concentrations. Less attention is given to a limit of determination. Usually the RSD is the best possible for the given method, and because intra-laboratory precision, or even simple repeatability, is quoted, this is usually accepted. 

Quality assurance is about getting the correct result. In environmental analysis and monitoring, this involves several steps, including sample collection, treatment and storage, followed by laboratory analysis. A complete environmental protocol is shown in Figure 2.1. It is likely that the variation in the final measurement is more influenced by the work external to the analytical laboratory than that within the laboratory. Two important terms in quality assurance are accuracy and precision. 

This chapter has considered the various aspects of planning the experimental work, introducing the concepts of quality assurance, accuracy and precision, and certified reference materials. It is now time to consider the initial phase of any environmental analysis procedure, i.e. sampling, and this will be discussed in the next chapter. 

Chapter 2 is concerned with the concept of quality assurance and all that it involves with respect to obtaining reliable data from environmental samples. Particular emphasis is placed on the definitions of accuracy and precision. Finally, details on the use of certified reference materials in environmental analysis are provided. 

The first of the separation techniques to be used in process measurement was gas chromatography (GC) in 1954. The GC has always been a robust instrument and this aided its transfer to the process environment. The differences between laboratory GC and process GC instruments are important. With process GC, the sample is transferred directly from the process stream to the instrument. Instead of an inlet septum, process GC has a valve, which is critical for repetitively and reproducibly transferring a precise volume of sample into the volatiliser and thence into the carrier gas. This valve is also used to intermittently introduce a reference sample for calibration purposes. Instead of one column and a temperature ramp, the set up involves many columns under isothermal conditions. The more usual column types are open tubular, as these are efficient and analysis is more rapid than with packed columns. A pre-column is often used to trap unwanted contaminants, e.g. water, and it is backflushed while the rest of the sample is sent on to the analysis column. The universal detector - thermal conductivity detector (TCD)-is most often used in process GC but also popular are the FID, PID, ECD, FPD and of course MS. Process GC is used extensively in the petroleum industry, in environmental analysis of air and water samples" and in the chemical industry with the incorporation of sample extraction or preparation on-line. It is also applied for on-line monitoring of volatile products during fermentation processes" ... 

Good Laboratory Practice (GLP) requires that a quality control (QQ protocol for trace environmental analysis be put in place. A good laboratory QC protocol for any laboratory attempting to achieve precise and aeeurate TEQA requires the following eonsiderations ... 

Coulometry. Two methods of coulometry are used coulometry at controlled potential and coulometric titrations. The main advantage of the coulometric method is the elimination of the necessity of standardization as the Faraday constant is a standard. In analysis of complicated samples encountered in environmental analysis the coulometric titrations are more advantageous where 100% current efficiency can be more readily attained by suitable choice of the reagent-solvent system. Coulometric titrations are suitable for determining the amount of substance in the range 0.01 to 100 mg (and sometimes below 1 iJg). Under optimum conditions these titrations can be carried out with a precision and accuracy of 0.01%. Automatic coulometric analyzers for the determination of gaseous pollutants (SO2, O3, NO, etc.) have proven to be useful in environmental chemistry. 

However, online alternatives developed for environmental analysis are commonly direct adaptations of traditional analytical methods conducted in batch. Main limitations for most of these methods are sensitivity or precision problems due to the low concentrations of the individual species to be analyzed... 

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