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Introduction to environmental analysis - Reeve R.

Reeve R. Introduction to environmental analysis - Wiley publishing , 2002. - 312 p.
ISBN 0-471-49295-7
Download (direct link): introductiontoenvironmental2002.pdf
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There is the possibility, with suitable equipment, of continuous monitoring in the field. This is obviously not possible with laboratory analyses.
An advantage of field sampling which you would probably not have considered is that it may be possible to analyse for species in situ which are so reactive that they would not survive transportation to the laboratory. This is particularly the case with reactive atmospheric components.
Field analysis could use the following equipment:
(i) Portable monitors for specific ions or compounds. Simple monitors (mg/l concentration range) have been available for water samples for many years and have found large-scale use with organizations which need rapid and simple tests for water quality. Newer types of monitors can determine pollutants at ^g/l concentrations and are often used for screening samples to minimize the number of expensive laboratory analyses. Portable gas monitors are standard for health monitoring and for site analysis. Instruments are available to detect specific pollutants in contaminated and reclaimed land.
(ii) More complex instruments which can be left at secure locations or used in mobile laboratories. These have long been used in air analysis where they can be part of networks for monitoring air quality. Mobile laboratories find use in urban atmosphere investigations and for contaminated and reclaimed land. Continuous monitoring is sometimes undertaken on major rivers, e.g. the Thames and the Rhine. You could also include in this category ship-board laboratories used for marine investigations.
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Introduction to Environmental Analysis
(iii) On-line monitors for discharge pipes or flue gases. These may be used to warn of high concentrations in flue gases or aqueous discharges for compliance with the relevant legislation.
You should not underestimate the degree of sophistication needed for instruments which must operate automatically in the field. At the design stage, you would have to consider minimization of the use of consumables, ensuring that the sampling system never becomes blocked and that the measurement device (often spectrometric or electrochemical) can be kept continuously clean. The instrument should be self-calibrating and the results should be automatically logged or transmitted to a remote location.
Although the main route for chemical analysis is by laboratory analysis, field analysis is playing an important and increasing role, particularly for screening. Examples are described in subsequent chapters following discussions of the laboratory methods.
2.9 Quality Assurance
We have already learnt that pollutants can have concentrations in the environment of <^g/l and these concentrations can vary widely. Samples for analysis can be water, the atmosphere, solids or living organisms. Whatever the sample or concentration, it is important to be confident in the analytical method and the result produced.
Let us now consider think what the term ‘confidence’ could mean.
(i) The method used should have been validated prior to the analytical investigation. i.e. thoroughly tested to show that the method gives accurate results for the type of sample being analysed. Ideally, the method itself would include procedures to confirm its reliability for each fresh batch of samples.
(ii) There is some indication of the error inherent in the method.
DQ 2.6
Why do you have to confirm reliability for each fresh batch of samples? Answer
Potential interferences may change from sample to sample. There may also have been changes in the reagents used or procedures within the laboratory which may affect the result.
If we are concerned about the accuracy of a result it is obvious that concern should extend all the way from sampling to the publication of the final analytical result.
Transport and Analysis of Pollutants
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DQ 2.7
What areas would you consider to be important in producing an accurate
analysis?
Answer
• The sampling procedure should produce a representative sample.
• The sample should not become contaminated or alter chemically during storage.
• There should be no contamination of the sample within the laboratory or during the analysis.
• Any losses in extraction, separation and concentration procedures should be minimized.
• There should be no interference in the final analysis from other components in the sample.
• Results should be correctly calculated and archived for future reference.
Most of these concerns would be applicable to any area of analytical chemistry but the potential contamination of the sample during sampling, sample storage or in the analytical determination is of particular importance in environmental analysis. Many of the compounds are universal contaminants and so will be found in the materials used for sample containers, the apparatus used, solvents and even in the laboratory atmosphere. It may be surprising for you to realize that reliable data for the concentrations of trace metals in sea water have only been available for the last two decades. The values that are now accepted can be an order of magnitude lower than the previous ‘best’ figures. The earlier values were very largely due to the metal ions picked up during the analytical procedure.
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