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CHAPTER 1
Introduction
1.1 THE ENVIRONMENT
The environment is the sum total of human surroundings consisting of the atmosphere, the hydrosphere, the lithosphere, and the biota. Human beings are totally dependent on the environment for life itself. The atmosphere provides us with the air we breathe, the hydrosphere provides the water we drink, and the soil of the lithosphere provides us with the vegetables that we eat. In addi- tion, the environment provides us with the raw materials to fulfill our other needs: the construction of housing, the production of the numerous consumer goods, etc. In view of these important functions, it is imperative that we main- tain the environment in as pristine a state as is possible. Fouling of the envi- ronment by the products of our industrial society ( i.e. pollution) can have many harmful consequences, damage to human health being of greatest concern. In addition to the outdoor environment, increasing concern is being expressed about the exposure of individuals to harmful pollutants within the indoor environment , both at home and at work. Levels of harmful pollutants can often be higher indoors than outdoors, and this is especially true of the workplace where workers can be exposed to fairly high levels of toxic sub- stances. Occupational health , occupational medicine , and industrial hygiene are subjects that deal with exposure at the workplace. Pollution is mainly, although not exclusively, chemical in nature. The job of the environmental analyst is therefore of great importance to society. Ultimately, it is the environmental analyst who keeps us informed about the quality of our environment and alerts us to any major pollution incidents, which may warrant our concern and response.
1.1.1 Biogeochemical Cycles
The different components of the biosphere and their interactions are illus- trated in Figure 1.1. The biosphere is that part of the environment where life
exists. It consists of the hydrosphere (oceans, rivers, and lakes), the lower part of the atmosphere, the upper layer of the lithosphere (soil), and all life forms. The concept of the biosphere was first introduced by the Russian sci- entist Vladimir Vernadsky (1863–1945) as the “sphere of living organisms distribution”. Vernadsky was among the first to recognise the important role played by living organisms in various interactions within the biosphere, and he established the first-ever biogeochemical laboratory specifically dedi- cated to the study of these interactions. He expounded his theories in an aptly entitled book, “Biosphere”, published in 1926. The various spheres act as reservoirs of environmental constituents and they are closely linked through various physical, chemical, and biological processes; there is constant exchange of material between them. Chemical substances can move through the biosphere from one reservoir to another, and this transport of constituents is described in terms of a biogeochemical cycle. Biogeochemical cycles of many elements are closely linked to the hydrological cycle. The hydrological cycle acts as a vehicle for moving water-soluble nutrients and pollutants through the environment. If all the components of the cycle are identified and the amounts and rates of material transfer quantified, the term budget is used. Both beneficial nutrients and harmful pollutants are transported through biogeochemical cycles with far- reaching consequences. The more commonly discussed biogeochemical cycles are those of important macronutrients such as carbon, sulfur, nitrogen, and phosphorus, but, in principle, a biogeochemical cycle could be drawn up for any substance. The cycle is usually illustrated as a series of compartments (reservoirs) and pathways between them. Each reservoir can be viewed in terms of a box model shown in Figure 1.2.
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Figure 1.1 Interactions between component parts of the biosphere
to natural emissions to the environment is 3:1 for arsenic, 5:1 for cadmium, 10:1 for mercury, and 28:1 for lead.
1.1.2 Environmental Pollution
Pollution is commonly defined as the addition of a substance by human activity to the environment, which can cause injury to human health or dam- age to natural ecosystems. This definition excludes “natural pollution”, although natural processes can also release harmful substances into the envi- ronment. There are different categories of pollution: chemical, physical, radioactive, biological, and aesthetic. This book is concerned primarily with chemical pollutants and their determination in environmental matrices. Most substances that are considered as pollutants are actually natural con- stituents of the environment, albeit at concentrations which are generally harmless. It is the increase in the concentration of these natural constituents, usually by industrial activity, to levels at which they may have harmful effects that is of concern. There are, however, a few pollutants that are entirely synthetic and would not be present in the environment if it were not for human activity ( e.g. chlorofluorocarbons). Sources of pollution can be:
● (^) Domestic ● (^) Industrial ● (^) Agricultural ● (^) Transportation ● (^) Warfare
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Table 1.1 Human impacts on biogeochemical cycles
Cycle Human interference Environmental consequence
Carbon Fossil fuel combustion, clearing of forests Global warming Sulfur Fossil fuel combustion Acid rain Nitrogen Fossil fuel combustion, fertilizers Acid rain, eutrophication Phosphorus Detergents and fertilizers Eutrophication
Table 1.2 Relative contributions of anthropogenic and natural sources (approximate)
Emissions to the atmosphere (% of total) Pollutant Natural Anthropogenic
Sulfur dioxide 50 50 Oxides of nitrogen 50 50 Carbon dioxide 95 5 Hydrocarbons 84 16
Pollution can be classified according to its geographical scale as local, regional, or global. Local pollution may affect only a single field, small stream, or a city ( e.g. photochemical smog). Regional pollution may affect a part of a country, a whole country, or even an entire continent. Global warm- ing due to the greenhouse effect of CO 2 is an example of a pollution problem on a global scale. However, the distinction between these different categories is not always clear-cut. For example, many contemporary megacities extend over enormous areas and many urban conurbations may consist of several cities (Metro Manila, Los Angeles area, north-eastern seaboard of the US, etc. ). In such areas, photochemical smog is a regional problem. Acid rain was, until lately, considered a regional problem as it affects almost all of Europe and North America. However, acid rain has recently been identified at locations throughout the world, from tropical rainforests in Asia, Africa, and South America to the polar ice caps in the Arctic. Therefore, acid rain may now be viewed as a global problem. The number of pollution sources is constantly rising throughout the world as a consequence of growing industrial development. The driving force behind the increase in pollution is the rapidly growing population of the world (Figure 1.3). The world’s population has more than doubled over the last 40 years, and over the next 30 years it is expected to increase by another
Introduction 5
Figure 1.3 The world’s population growth
care, provided protection against many natural disasters, increased the stan- dard of living, eliminated many dangerous jobs, improved safety at work, etc. On the other hand, we now have the ability not only to destroy isolated ecosystems but all life on the earth, including human life, and not just by means of weapons of mass destruction, but also by our polluting influence on the environment. The “globalisation” of what were previously minor, local environmental problems ( e.g. acid rain), as well as the emergence of new global threats ( e.g. destruction of stratospheric ozone, global warming) seems to indicate that we are well on our way to accomplishing this. It would be a sad indictment on the human race if it were to undo, in a small fraction of the geological time scale, what took nature millions of years to achieve: life in its many forms. Clearly, the real-world experiment, which we are con- ducting, needs to be carefully controlled if we are to slow down, or reverse, this trend. Major environmental problems of the 21st century will include:
● (^) Global warming and climate change ● (^) Stratospheric ozone depletion ● (^) Acid rain ● (^) Urban pollution ● (^) Haze from forest fires ● (^) Declining water resources ● (^) Eutrophication ● (^) Desertification ● (^) Solid and toxic waste disposal ● (^) Radioactive waste disposal ● (^) Depletion of resources
However, it is not all gloom and doom; there have been many environ- mental success stories over the years. Unfortunately, these successes have so far been mainly limited to the developed nations. For example, air quality of most cities in Western Europe and North America has significantly improved as compared to half a century ago. Concentrations of SO 2 and smoke have decreased steadily since the 1950s and catastrophic smog episodes are no longer a menace to urban populations. More recently, the introduction of cat- alytic converters has reduced the emissions of automotive air pollutants and improved urban air quality even further. “Car-free” zones have been intro- duced in some cities and improvements in public transport have been imple- mented. DDT, organotin compounds, phosphate-containing detergents, and many other harmful chemicals have been banned in most developed nations. Water quality has improved in some countries compared to what it was dur- ing the Industrial Revolution. Many countries have phased out the use of lead
Introduction 7
in petrol. Strict controls have been imposed on the transport and disposal of toxic wastes. Increasing emphasis is being placed on the so-called “clean technologies”. Re-cycling, re-use, life-cycle analysis, sustainable develop- ment, energy conservation, “eco-safe”, environmental impact assessment (EIA), and other such concepts and methods are being increasingly imple- mented. Considerable research has gone into developing alternative, non- polluting energy sources (solar, wind, etc. ). The greater general awareness of environmental problems has resulted in the public raising environmental issues and demanding greater environmental accountability from industries and governments. Unfortunately, similar improvements are not evident in developing countries where development has been accompanied by increas- ing environmental devastation. Over the past 20 years, the relatively unspoiled environment of these countries has regressed to a state on par with that of the developed countries during the Industrial Revolution. However, there is cause for optimism. As these countries increasingly adopt pollution control tech- nologies, much as they have adopted other technologies pioneered by the developed nations, the quality of the environment could yet improve.
1.1.3 Effects of Pollution
Effects of pollution are multifarious; however, those of greatest concern are the impacts on human health. Other concerns include impacts on natural ecosystems, effects on weather and climate, and economic and sociopolitical impacts of pollution and its abatement. Many of the substances considered as pollutants may act as beneficial nutrients in small doses, and the effect of dose or concentration on health is described by means of a dose–response curve. For many elements ( e.g. F, Se, Cu, Cr, Mn), there is a window of dose (or concentration) that is beneficial to health, while levels above this window may be toxic leading to illness or even death. On the other hand, for many essential nutrients, concentrations below the beneficial window may lead to deficiency and consequent illness. Similar dose–response curves exist for plant nutrients (see Figure 6.2). For many substances there is a threshold level below which harmful effects are not apparent. However, for many environmental toxins, especially carcino- gens such as benzene, there is no threshold and any concentration can be harmful. Additional problems in evaluating the toxic effects of pollutants include additive effects of several pollutants and synergism. Synergism results in the combined effects of several pollutants producing an effect greater than the sum of the effects of the individual pollutants. Health effects of pollutants can be classified as acute or chronic. Acute effects result from short-term exposure, usually to high concentrations of pollutants and are common following industrial exposure or accidental
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technology are made by environmental engineers. Environmental analysts may be required to assess the efficiency of the control technology, and once installed, to confirm that the problem has been eliminated and that legislative standards are being adhered to. International and national guidelines and stan- dards for air, water, soil, sludge, crops, and foods are listed in Appendix C.
1.2 ENVIRONMENTAL ANALYSIS
1.2.1 Aims of Analysis
The purpose of environmental analysis is two-fold:
● (^) To determine the background and natural concentrations of chemical constituents in the environment ( background monitoring ). ● (^) To determine the concentration of harmful pollutants in the environment ( pollution monitoring ).
Background monitoring is useful in studies of general environmental processes and for establishing concentrations against which any pollution effects could be assessed. It is, however, a fact that pollution has now affected even the most remote areas of the globe, and true background levels of many substances are becoming increasingly difficult to determine. The objectives of pollution monitoring are:
● (^) To identify potential threats to human health and natural ecosystems. ● (^) To determine compliance with national and international standards. ● (^) To inform the public about the quality of the environment and raise pub- lic awareness about environmental issues. ● (^) To develop and validate computer models, which simulate environmental processes and are extensively used as environmental management tools. ● (^) To provide input data for Geographical Information Systems (GISs) used in conjunction with expert systems as an aid to environmental man- agement. ● (^) To provide inputs to policy-making decisions (land-use planning, traffic, etc. ). ● (^) To assess the efficacy of pollution control measures. ● (^) To investigate trends in pollution and identify future problems.
Environmental analysis is often used in EIA studies. These studies are car- ried out before any major industrial development is given a go-ahead by the authorities, and their aim is to assess any potential impacts of the development on environmental quality. As part of EIA, it is often necessary to establish the baseline concentrations of various substances at the proposed site so that potential impacts may be assessed. Environmental analysis is also integral to
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the field of environmental forensics , which forms an important part of envi- ronmental law. Environmental forensics involve fingerprinting pollutant releases to determine the source and cause of contamination.
1.2.2 Types of Analysis
The chemical substance being determined in a sample is called an analyte ( i.e. atom, ion, molecule). Samples are “analysed” whereas analytes are “determined”. We can broadly define two categories of chemical analysis:
● (^) Qualitative analysis – concerned with the identification ( i.e. determin- ing the nature) of a chemical substance. ● (^) Quantitative analysis – concerned with the quantification ( i.e. deter- mining the amount) of a chemical substance.
The former answers the question: “Which substance is present?” while the latter answers the question: “How much is present?” Results of quantitative analysis are generally expressed in terms of concentration. Concentration is the quantity of analyte (in grams or moles) per unit amount of sample (grams or litres). Obviously, quantitative analysis involves identification as well as quantification since a numerical value must be ascribed to a particular sub- stance. For example, qualitative analysis may simply tell us whether mercury is present in a sample of waste effluent, whereas quantitative analysis will tell us exactly how much mercury is present in the effluent. Often, the so- called “spot tests” based on distinctive colour-forming reactions, or complex schemes of analysis, can be used for purposes of identification. There is, however, a hidden quantitative aspect in qualitative analysis. If a result of a qualitative analysis is negative ( i.e. the substance in question was not identi- fied) this does not mean that the substance is absent; it merely implies that the substance is present at a level below that at which the spot test, or analy- sis scheme, responds. For example, mercury is present in seawater at a level of 3 10 ^5 ppm (parts per million). It is unlikely that a routine spot test would be able to identify this. The development of evermore-sensitive instru- ments capable of quantifying even the minutest traces of substances has exposed the shortcomings of many of the cruder and insensitive schemes of qualitative analysis. Nevertheless, qualitative spot tests still remain useful in many situations where substance levels are high, and they are particularly useful where routine analyses are required, such as in industry. Chemical analysis may also be categorised with respect to the type of sub- stance being analysed. Inorganic analysis is concerned with the determina- tion of atoms and inorganic compounds, whereas organic analysis involves the determination of organic compounds.
Introduction 11
1.3 SAMPLING AND STORAGE
1.3.1 Sampling
A sample is that portion of the physical environment, which is withdrawn for chemical analysis. A sample can be aqueous ( e.g. river water), gaseous ( e.g. air), or solid ( e.g. soil). The chemical substance being analysed in the sample, whether an atom, ion, or molecule, is referred to as the analyte ( e.g. Pb in dust). Sampling is the process by which a sample is obtained, and this can be done in one of the two ways:
● (^) Batch sampling involves taking a sample from the environment and per- forming an analysis either on site or later on in the laboratory. For exam- ple, batch sampling of a wastewater effluent for pH analysis would imply that a volume ( e.g. 100 mL) of the effluent is collected and then analysed for pH. These samples are collected at a specific time and place and are also called grab samples. ● (^) Continuous sampling involves continuously monitoring the environ- mental parameter of interest. In the above example, continuous analysis of the effluent pH would involve placing a pH electrode directly into the effluent stream and recording the pH on a chart recorder or a data log- ger. In this way a continuous record of the effluent pH is obtained. This kind of sampling could detect important changes in the effluent that would be missed by batch sampling.
Batch sampling is the easiest and most common method of obtaining a sample and it is widely used in environmental surveys. Continuous sampling is generally combined with an instrumental method of analysis, and the term given to this combination is continuous monitoring. This method of analysis is being adopted more extensively in many applications ( e.g. effluent moni- toring, air monitoring). Usually, the method is combined with some kind of alarm system to alert the operator when standards are being exceeded. For example, if the level of pollutant in an effluent stream is found to exceed the emission standard, an alarm may be activated and the plant personnel could switch off the process and attempt to resolve the problem. In many cities, continuous monitoring of air quality is carried out by the municipal authori- ties. This allows for alerts to be broadcast to the public via the media when air quality standards are observed to have been breached. The public is then asked to stay indoors, refrain from outdoor exercise, and so on, until the air quality improves. Such a fast response would not be possible in the case of batch sampling, which involves laboratory analysis at some later time. Another type of sample is a composite sample, prepared by mixing several batch samples, usually collected at the same place but at different times. These are used to evaluate the average concentration in a medium in which
Introduction 13
the concentration may vary with time. For example, batch samples of waste- water are collected every 2 h over a 24-h period and pooled into one container. The concentration in the mixture is supposed to reflect a 24-h average. Composite samples can also be prepared by mixing samples collected at dif- ferent places at the same time. For example, in soil surveys, samples collected from different locations in a field are pooled together to give an area average. Although sampling appears to be a relatively straightforward matter, it is generally one of the most problematic stages of an environmental analysis. The main difficulty lies in obtaining a representative sample. The sample represents only a small portion of the system under investigation and it is important that the sample is representative of the whole system as much as possible. In environmental analysis this is not always possible to achieve. Usually, it is easier to obtain representative samples from homogeneous than from heterogeneous systems. An environmental analyst faces unique prob- lems of obtaining representative samples from water, air, effluent gases, dust, and soil. Some of the questions that need to be addresses are:
● (^) When and where should the sample be taken? ● (^) How many samples should be taken? ● (^) How much sample is required?
Some quite sophisticated statistical sampling procedures have been devel- oped that can help the analyst answer some of these questions, nevertheless most sampling is carried out without reference to these statistical considera- tions. The analyst will usually decide on the best location, time, and number of samples to be taken (the so-called random sampling ). Considerations of site accessibility, time, and expense are often more influential factors than purely scientific considerations. Anyway, several samples are collected at each site in order to obtain some indication of variability in analyte concen- tration at the site, and in case some of the samples are lost, spoilt, or incor- rectly analysed. Obtaining as representative a sample as possible is paramount since the analyst cannot obtain the same sample again. The envi- ronment is a dynamic system, which is constantly changing, and returning to the same site at a later date may give completely different results.
1.3.2 Storage
Once the sample has been collected, it is transported to the laboratory for analysis. Sometimes it is possible to carry out the analysis at the site using portable test kits, or inside on-site laboratories (see Section 1.5.4), but most often the sample has to be transported some distance. It is desirable to perform the analysis as soon as possible after sample collection. On many occasions this is not possible and the sample has to be stored until the analysis can be performed. During transportation and storage, it is important to preserve the
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Appendix B. The bottles should be thoroughly rinsed with laboratory water to remove any traces of cleaning agent and filled with laboratory water when not in use.
1.4 SAMPLE TREATMENT
Although some samples may be analysed directly, most often the sample has to be prepared for analysis. A variety of sample-treatment methods are used depending on the type of sample, the analyte to be determined, and the kind of analytical method to be used. The purposes of sample treatment are three-fold:
● (^) To convert the sample and analyte into a form suitable for the analysis by the chosen method. ● (^) To eliminate the interfering substances. ● (^) To concentrate the sample.
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Table 1.3 Recommended storage conditions for some analytes in water samples. All samples should be stored in a refrigerator at 4 ° C
Analyte Bottle material a^ Preservative Maximum storage time
Alkalinity P None 2 weeks Ammonia P HNO 3 to pH 2 4 weeks BOD P, G None 2 days Calcium P None 4 weeks COD P, G H 2 SO 4 to pH 2 4 weeks Chloride P None 4 weeks Conductivity P None 1 week Dissolved oxygen G MnSO 4 Analyse as soon as possible Fluoride P None 4 weeks Hardness P None 4 weeks Magnesium P None 4 weeks Nitrate P H 2 SO 4 to pH 2 4 weeks Nitrite P None Analyse as soon as possible Pesticides G pH 5–9 1 week to extraction, 6 weeks after extraction pH P None Analyse as soon as possible Phenols G NaOH to pH 12 1 week to extraction, 6 weeks after extraction Phosphate P None 2 days Potassium P None 4 weeks Sodium P None 4 weeks Sulfate P None 4 weeks Suspended solids P, G None 1 week Total solids P, G None 1 week Trace metals P HNO 3 to pH 2 6 months ( e.g. Pb, Fe) Volatile solids P, G None 1 week
aP polyethylene; G pyrex glass.
Typical sample-treatment methods include:
● (^) Dissolution/digestion. A solid sample has to be dissolved in a solution before it can be analysed by most analytical methods. Various methods for decomposing and dissolving solid samples are available: acid digestion on a hot plate, refluxing, ultrasonic digestion, and microwave digestion. ● (^) Filtration. Aqueous samples are usually filtered. For example, when determining soluble components it is customary to filter out the sus- pended particles from solution as these may interfere in the analysis. ● (^) Solvent extraction. Organic analytes are usually extracted into an organic solvent. This can also serve to concentrate the sample. Various other treatments can also be applied: drying, sieving, ignition, boiling, precipitation, complexation, reduction, oxidation, etc. Solid samples are usually dried in an oven to remove any water before carrying out any other treatment. An important consideration when treating the sample is to avoid contam- ination. Impurities present in many of the reagents can contaminate the sam- ple or cause interferences.
1.5 ANALYTICAL METHODS
1.5.1 Selection of Method
The analyst can use either a classical method (titrimetry, gravimetry) or one of the many instrumental methods. The selection of the appropriate method is based on the following criteria:
● (^) Expected concentration of analyte in the sample ● (^) Number of samples to be analysed ● (^) Time that can be devoted to the analysis ● (^) Cost of the analysis
Analytical methods employed in environmental analysis are summarised in Table 1.4. More details about the methods used in this book are given in Appendix B. Methods may be classified as specific, selective, or universal. Specific methods respond to only one analyte and are therefore not prone to interference from other substances. Selective methods respond to certain classes of analytes and may be prone to some interference. Universal meth- ods respond to all classes of analytes.
1.5.2 Classical Analysis
Titrimetry (also called volumetric analysis) is simple, inexpensive, rapid, and accurate. It requires the most rudimentary of laboratory glassware (burettes,
Introduction 17
pipettes, and volumetric flasks) available in all laboratories. Titrations are generally useful for determining analyte concentrations at levels 1 mg L^1 and are of limited use for trace component analysis. Gravimetry is inexpensive and accurate but tedious and slow. It, too, requires the minimum of laboratory equipment and can be carried out in all laboratories.
1.5.3 Instrumental Analysis
Instrumental methods in environmental analysis generally involve spec- troscopy and chromatography. Spectroscopic methods used in the analysis of environmental samples include UV/visible, atomic absorption or emission, and infrared (IR). Most laboratories would be equipped with a colorimeter (for visible spectrophotometry) and a flame photometer (for atomic emission spectrophotometer (AES)), but some may also have an atomic absorption spectrophotometer (AAS) and more advanced UV/visible instruments. Other advanced spectroscopic techniques which may not be generally available in all laboratories are: inductively coupled plasma (ICP) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and Fourier-transform infrared (FTIR) spectroscopy. Chromatographic methods available in many laborato- ries include gas chromatography (GC) and high-pressure liquid chromatog- raphy (HPLC) including ion chromatography (IC). These are all very useful for analysing environmental samples. A variety of electrochemical techniques can be used for environmental analysis. The most common are ion selective electrodes (ISE), an example of which is the widely used pH electrode found in all laboratories. Other tech- niques such as coulometry, polarography, and voltammetry, although useful for some environmental analyses, may not be found in many laboratories. More advanced techniques that may be used for environmental analysis but may not be available in many laboratories are: gas chromatography/mass spectrometry (GC/MS), X-ray methods, ICP spectroscopy, and a variety of radiochemical techniques. Experiments in this book require only an AAS, an IC, and a colorimeter or UV/visible spectrophotometer.
1.5.4 Test Kits and Portable Laboratories
In many instances, it is necessary to analyse pollution on the spot in the field rather than taking the sample back to the laboratory. This may be necessary for the following reasons:
● (^) To avoid any changes in the sample composition due to chemical or bio- logical reactions during transport to the laboratory.
Introduction 19
● (^) To obtain results immediately as, for example, during an emergency fol- lowing a spillage of hazardous chemicals, when a delay in analysis could have grave consequences.
Many test kits and portable systems are commercially available for the on- site analysis of pollutants. These can vary in sophistication from simple col- orimetric methods involving visual comparisons to portable laboratories and instruments. Kits suitable for rapid and easy determination of various compounds have been developed, and these generally involve adding premeasured reagents supplied in powder or pill form to the sample and matching the developed colour with colour discs, which can be rotated to obtain a colour match with the reacted sample. There are several variations of this methodology avail- able for water testing. Indicator tubes based on visual colorimetry have been developed for determining on-site air pollution (see Section 3.2.6). Test kits are also available for testing acid rains by means of visual colour compar- isons after addition of a reagent. Visual methods are suitable for quick spot checks, and although they provide quantitative information, they are not of much use in serious environmental research. Many different portable instruments are commercially available for the determination of numerous water and air pollutants. Instruments can range from those capable of measuring only one parameter to multisubstance analysers. Portable, battery-operated laboratories consisting of colorimeters and spectrophotometers for comprehensive on-site analysis of a suite of pol- lutants can also be purchased on the market. More advanced techniques such as GC/MS and XRF are also available as portable instruments.
1.6 STANDARDISATION AND CALIBRATION
1.6.1 Standardisation
In titrimetric analysis, a standard solution is added to the sample and the con- centration of analyte is determined from the volume and the standard solu- tion used up. The exact concentration of the standard solution is not known at the onset but it can be found by titrating the standard solution with another solution called a primary standard. The primary standard is prepared from reagents of high purity and stability. For example, in the determination of water hardness, the standard EDTA solution used as a titrant is first titrated against an accurately prepared solution of CaCO 3. Standardisation is the name given to this process of accurately determining the concentration of a standard solution.
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