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The old saying is ‘you are what you eat’. You may, however, also be ‘you are what you drink’. Water chemistry has helped us to define the different currents and circulation of the world’s oceans, improved our understanding of water’s interactions with Earth’s geologic materials, and given insight into the impact of human activities on waterbodies. It has also provided a clearer understanding of the limits of a waterbody’s ability to assimilate some level of pollution without harming the water system, its aquatic plants and animals, and humans who may use the water.
Background
Water is considered to be one of the basic substances supporting life and the natural environment, a primary component for industry, a consumer item for both humans and animals, and a vector for domestic and industrial pollution. Various directives provide a framework for the control of aquatic substances, the quality of bathing, surface, and drinking water and effluents.
Water analysis is crucial whenever a process requires water of a specific quality. Water used for sustaining life during specific production processes, and other basic living functions, requires specific and careful water analysis. Dangerous levels of microorganisms and mineral deposits can make a water source unfit, and only water analysis can afford the proper insight necessary to determine the relative safety of a source.
Due to the necessity of quality water, both in current processes and for future environmental quality, water analysis is a critically important scientific process. Water quality monitoring aims to minimise the concentration of harmful chemicals in drinking water, and many government agencies strive to ensure that certain standards are maintained to prevent various types of cancer. Moreover, humans are not the only ones threatened by poor water quality, as many ecosystems are sensitive to degraded waters.
Chemical identification
In the Nineteenth Century, before the rapid development of industry, it was estimated that in the environment around 300,000 chemical compounds were present. Recently, at the beginning of the Twenty-First Century, the number of chemical compounds present in the environment exceed 50,000,000. The vast majority of them are chemical compounds of anthropogenic origin.
About most of them we know a little, or only that they can be hazardous for humans. They are present in all parts of the environment, including different kinds of water, and have a huge impact on the environment and the quality of our lives. Their determination in very low concentration levels requires the application of new, more sensitive and accurate analytical methods and techniques.
Every day in hundreds of thousands of laboratories around the world, millions of analyses of different substances are carried out. Undoubtedly, the largest group of these samples are water samples. The development of new methods and improvement of existing ones are major tasks for analytical chemists.
Advances in analytical instrumentation, detection systems and separation techniques have, in many instances, provided analytical chemists the tools required to continually lower method detection limits. The ideal method for water analysis should meet the following requirements: determination of target analytes with limit of determination on 25% of maximum acceptable concentration; no sample pretreatment; short time spent on analysis; low cost of single analysis and method availability.
Substances present in various types of water may be classified as biological, chemical (both inorganic and organic), physical, and radiological impurities. Until 1975, only a small range of analytical parameters could be measured automatically. It was therefore necessary to develop and validate new methods to extend the scope of such parameters. The number of species determined in water has grown exponentially during the past 50 years. Very few have been studied, however, or have led to documented proof of their health effects.
Nearly half of the monitored parameters are being measured for operational reasons, e.g. iron, ammonium, pH, chloride, dissolved organic carbon, and for reasons of customer satisfaction, e.g. colour, taste, total hardness. Of the health-related substances, a number of metals and small groups of organic compounds and pesticides, in most countries, are being measured on a regular basis1. They include antimony, arsenic aluminum, chromium, magnesium, magnum, cadmium, copper, nickel, lead, mercury, and iron, as well as inorganic ions (ammonium, fluoride, nitrite, nitrate, and cyanide) and organic compounds (e.g. benzo(a)pyrene, trihalomethanes, chlorobenzenes, pesticides). Recently, inorganic oxyhalide disinfection byproducts such as bromate, chlorite, and chlorate have also begun to be measured.
Analytical methods
There are many methods of testing water, according to what substances are being tested for. Laboratory sample testing is often advised, but there are also home testing kits available. A wide range of analytical methods have been laid out by the US Environmental Protection Agency (US EPA) for testing of specific contaminants, which many laboratories and organisations must adhere to in the United States. The US EPA outlines various methods and their targeted application as part of the Safe Drinking Water Act, implemented in 1974 and amended in 1986 and 1996.
Organic substances are usually analysed by using gas and liquid chromatography methods. For the determination of metals and metalloids, spectroscopic methods such as atomic absorption spectrometry and inductively coupled plasma methods are used.
An important part of water analysis is determination of ions. The determination of common inorganic anions and cations was traditionally carried out using wet chemical methods such as gravimetry, titration, photometry, turbidimetry, and colorimetry. Many of these methods suffer from interferences and limited sensitivity, and they can be labour intensive and difficult to automate.
Although performance criteria – accuracy, precision, and limit of detection – can be specified for analytical methods, it is still difficult to obtain similar results in different laboratories. For example, there are more than 200 available methods to assay for sulphate and nitrate. Unfortunately, most of those methods are characterised by a lack of sensitivity or selectivity and they are difficult and cumbersome to use.
One of the prime analytical chemists of the Twentieth Century, Professor Harvey Diehl of Iowa State University, proposed that the Nobel Prize should be given to the scientist who developed a better method for sulphur analysis than gravimetry or nephelometry. An alternative, introduced in 1975, that has almost replaced most of the wet chemical methods used in water analysis is ion chromatography.
Ion chromatography
Ion chromatography methods meet these requirements and can be used for routine applications in environmental laboratories. Considering that several individual wet chemistry methods for common inorganic anions or cations could be replaced by one fast and reliable chromatographic separation, it is not surprising that ion chromatography has quickly become accepted worldwide by regulatory bodies to be used for the analysis of anions and cations in water and wastewater.
Ion chromatography can be considered to be a well established, mature technique for the analysis of anions and cations and many organisations, such as the ISO (International Organization for Standardization), US EPA, ASTM (American Society for Testing and Materials), and AOAC (Association of Official Analytical Chemists) base their standards or regulatory methods of analysis upon it. From 1992 to 2012, nine ion chromatography standards concerning ion determination in water and wastewater were published.
Elements occurring in ionic forms are believed to exhibit biological activity and toxicity towards living organisms. Bioinorganic speciation analysis in this area usually concerns elements that occur at different oxidation states. It consists of defining each element’s form and concentration. It is of vital importance when it comes to elements that demonstrate diversified toxic properties depending on their oxidation states, such as Cr(III)/Cr(VI), As(III)/As(V), Sb(III)/Sb(V). Nowadays, species analysis becomes more and more important.
Importance of sample preparation
Sampling and sample preparation are often a neglected area, which over the years has received much less attention than determination of analytes. In general, sample preparation methods are based on converting a real, complex matrix into a sample in a format that is suitable for analysis by a specific analytical technique. They have a common aim, which is as follows: • Removal of potential interferences from the sample, thus increasing the selectivity of the method • Increasing the concentration of the analyte(s) and, thus, the sensitivity of the determination • Converting the analyte into a more suitable form, if necessary • Providing a robust and reproducible method that is independent of variations in the sample matrix
In modern analytical chemistry, and particularly in trace analysis, sample preparation is usually more important than the determination method itself for the accuracy and reproducibility of the results. Adequate sample preparation is becoming more important because it allows full exploitation of all of the potential analytical methods. With the exception of traditional, classical sampling and sample preparation methods used in water analysis, new trends include the increased use of stir bar sorptive extraction, hollow fibre membrane microextraction, and passive samplers.
Purification treatments for water
Water treatment by disinfection processes is considered a major public health achievement of the Twentieth Century. Consequently, there has been a shift in the identification methods of water contaminants from microbiological to chemical7. In the 1970s, it was discovered that chlorination of drinking water produced carcinogens, such as trihalomethanes and haloacetic acids.
Since 1974, the presence of more than 500 disinfection byproducts has been determined in drinking water. Since that time, environmental regulatory agencies as well as drinking water treatment technologists have been carrying out extensive research for alternative disinfection methods that minimise the generation of byproducts with significant health risks.
Many drinking water utilities are replacing chlorine, as their primary disinfectant, with alternative disinfectants, such as ozone, chlorine dioxide, and chloramines, which reduce regulated trihalomethane and some organochlorine compound levels but, at the same time, often increase the level of other potentially toxic compounds, such as chlorite and chlorate, with bromate being another major consideration.
Hazard identification
The identification of new, possibly hazardous compounds in water has become an important task for water suppliers and analytical chemists. In an ideal situation, where standards for different intake routes of exposure are fully adjusted to each other, regular monitoring of these new compounds should only be necessary when they are carcinogens (genotoxic), or when the relative contribution of water to the total exposure or to the tolerable daily intake is high.
A procedure that can be followed to determine if a compound should be monitored regularly is: identify the compound in source water or tap water; determine possible health hazards; classify ‘priority substances’; establish the relative contribution of drinking water and other routes of exposure (if the compound is not genotoxic); determine the most cost effective way to reduce that exposure; and monitor regularly if exposure to drinking water should be reduced.
New technologies
New chromatography trends include the use of two dimensional chromatography, hydrophilic interaction chromatography (HILIC), and ultra-performance liquid chromatography (UPLC). Time-of-flight (TOF) MS is often used as the detector for gas chromatography because of its rapid acquisition capability. HILIC is a new liquid chromatography technique that provides improved separations and MS sensitivity for highly polar compounds.
Trends in detection include increased use of TOF and quadrupole Q-TOF-MS, as well as MS/MS mode. New analytical methods used in water analysis continue to push detection limits lower. Just a few years ago, microgram per litre detection limit was common. Today, it is unusual to see detection limits that are not at least low-nanogram per litre – or lower.
Despite common substances which are determined in water in daily routine analysis, there are several new emerging contaminants such as benzotriazoles, siloxanes, naphthenic acids, ethylene bromide, 1.4-dioxane, and nanomaterials. Other areas covered are perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), pharmaceuticals, hormones, endocrine disrupting compounds, sun creams, UV filters, disinfection byproducts, flame retardants, pesticide degradation products and new pesticides, algal toxins, perchlorate, methyl tery-butyl ether (MTBE) and microorganisms.
A trend in this ongoing research area is the study of the transformation of some of these compounds in drinking water and wastewater treatment.
Water analysis belongs to routine analyses which are carried out in many laboratories. In addition to commonly used conventional methods (so-called ‘wet methods’) more often in the analysis of water modern instrumental methods and techniques are used. The most important recent challenges related to the analysis of water include: new sample preparation methods; improving the speed and selectivity of the separation of analytes; lowering of limits of detection and limits of quantification; extending the scope of applications of methods and analytical techniques; development of new standard methods; extending the scope of the analysis of a new group of substances; and miniaturisation.
Published: 07th Mar 2013 in AWE International
