Water chemistry analyses are carried out to identify and quantify the chemical components and properties of water samples. The type and sensitivity of the analysis depends on the purpose of the analysis and the anticipated use of the water.
Chemical water analysis is carried out on water used in industrial processes, on waste-water stream, on rivers and stream, on rainfall and on the sea. In all cases the results of the analysis provides information that can be used to make decisions or to provide re-assurance that conditions are as expected.
The analytical parameters selected are chosen to be appropriate for the decision making process or to establish acceptable normality.
Water chemistry analysis is often the groundwork of studies of
water quality
Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...
,
pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
,
hydrology
Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...
and
geothermal waters.
Analytical methods routinely used can detect and measure all the natural elements and their inorganic compounds and a very wide range of organic chemical species using methods such as
gas chromatography and
mass spectrometry. In water treatment plants producing drinking water and in some industrial processes using products with distinctive taste and odours, specialised
organoleptic
Organoleptic properties are the aspects of food, water or other substances that create an individual experience via the senses—including taste, sight, smell, and touch.
USDA uses
In traditional U.S. Department of Agriculture meat and poul ...
methods may be used to detect smells at very low concentrations.
Types of water
Environmental water
Samples of water from the natural environment are routinely taken and analysed as part of a pre-determined monitoring programme by regulatory authorities to ensure that waters remain
unpolluted, or if polluted, that the levels of pollution are not increasing or are falling in line with an agreed remediation plan. An example of such a scheme is the
harmonised monitoring scheme operated on all the major river systems in the UK. The parameters analysed will be highly dependent on nature of the local environment and/or the polluting sources in the area. In many cases the parameters will reflect the national and local
water quality standards determined by law or other regulations. Typical parameters for ensuring that unpolluted surface waters remain within acceptable chemical standards include
pH, major
cations and
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s including
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
,
nitrate,
nitrite,
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
,
conductivity
Conductivity may refer to:
*Electrical conductivity, a measure of a material's ability to conduct an electric current
**Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution
** Ionic conductivity (solid state), ele ...
,
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...
,
chemical oxygen demand
In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution whic ...
(COD) and
biochemical oxygen demand
Biochemical oxygen demand (BOD) is the amount of dissolved oxygen (DO) needed (i.e. demanded) by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period. ...
(BOD).
Drinking water supplies
Surface or ground water abstracted for the supply of drinking water must be capable of meeting rigorous
chemical standards following treatment. This requires a detailed knowledge of the water entering the treatment plant. In addition to the normal suite of environmental chemical parameters, other parameters such as
hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
,
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...
,
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
and in some cases a real-time organic profile of the incoming water as in the
River Dee regulation scheme.
Industrial process water
In industrial process, the control of the quality of process water can be critical to the quality of the end product. Water is often used as a carrier of reagents and the loss of reagent to product must be continuously monitored to ensure that correct replacement rate. Parameters measured relate specifically to the process in use and to any of the expected contaminants that may arise as by-products. This may include unwanted organic chemicals appearing in an inorganic chemical process through contamination with oils and greases from machinery. Monitoring the quality of the waste water discharged from industrial premises is a key factor in controlling and minimising pollution of the environment. In this application monitoring schemes analyse for all possible contaminants arising within the process and in addition contaminants that may have particularly adverse impacts on the environment such as
cyanide
Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms.
In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
and many organic species such as
pesticides. In then nuclear industry analysis focuses on specific isotopes or elements of interest. Where the nuclear industry makes waste water discharges to rivers which have drinking water abstraction on them, radio-isotopes which could potentially be harmful or those with long
half-lives such as
tritium
Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of ...
will form part of the routine monitoring suite.
Methodology
To ensure consistency and repeatability, the methods use in the chemical analysis of water samples are often agreed and published at a national or state level. By convention these are often referred to as "Blue book"s.
Certain analyses are performed in-field (e.g. pH, specific conductance) while others involve sampling and laboratory testing.
The methods defined in the relevant standards can be broadly classified as:
* ''Conventional wet chemistry'' including the
Winkler method for
dissolved oxygen
Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...
,
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
,
filtration for solids, acidification, neutralisation,
titration
Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant'' ...
etc. Colourimetric methods such as
MBAS assay which indicates
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
ic
surfactants in water and on site
comparator
In electronics, a comparator is a device that compares two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals V_+ and V_- and one binary digital output V_\text. The output is ideally
: ...
methods to determine
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
and
chloramine
Chloramines refer to derivatives of ammonia and organic amines wherein one or more N-H bonds have been replaced by N-Cl bonds. Two classes of compounds are considered: inorganic chloramines and organic chloramines.
Inorganic chloramines
Inorgan ...
s.
Nephelometer
A nephelometer or aerosol photometer is an instrument for measuring the concentration of suspended particulates in a liquid or gas colloid. A nephelometer measures suspended particulates by employing a light beam (source beam) and a light dete ...
s are used to measure solids concentrations as turbidity. These methods are generally robust and well tried and inexpensive, giving a reasonable degree of accuracy at modest sensitivity.
*''Electro chemistry'' including
pH,
conductivity
Conductivity may refer to:
*Electrical conductivity, a measure of a material's ability to conduct an electric current
**Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution
** Ionic conductivity (solid state), ele ...
and dissolved oxygen using oxygen electrode. These methods yield accurate and precise results using electronic equipment capable of feeding results directly into a laboratory data management system
*
Spectrophotometry
Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as sp ...
is used particularly for metallic elements in solution producing results with very high sensitivity, but which may require some sample preparation prior to analysis and may also need specialised sampling methods to avoid sample deterioration in transit.
*
Chromatography
In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system ( ...
is used for many organic species which are volatile or which can yield a characteristic volatile component of after initial chemical processing.
*
Ion chromatography
Ion chromatography (or ion-exchange chromatography) separates ions and polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including large proteins, small nucleotides, and amino acid ...
is a sensitive and stable technique that can measure
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...
,
ammonium NH
4 and many other low molecular weight ions using
ion exchange
Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
technology.
*
Gas chromatography can be used to determine
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
,
cyanide
Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms.
In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
, oxygen, nitrogen and many other volatile components at reasonable sensitivities.
*
Mass spectrometry is used where very high sensitivity is required and is sometimes used as a back-end process after
gas liquid chromatography
Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, ...
for detecting trace organic chemicals.
Depending on the components, different methods are applied to determine the quantities or ratios of the components. While some methods can be performed with standard laboratory equipment, others require advanced devices, such as
inductively coupled plasma mass spectrometry
Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry that uses an inductively coupled plasma to ionize the sample. It atomizes the sample and creates atomic and small polyatomic ions, which are then detected. It is ...
(ICP-MS).
Research
Many aspects of academic research and industrial research such as in pharmaceuticals, health products, and many others relies on accurate water analysis to identify substances of potential use, to refine those substances and to ensure that when they are manufactured for sale that the chemical composition remains consistent. The analytical methods used in these area can be very complex and may be specific to the process or area of research being conducted and may involve the use of bespoke analytical equipment.
Forensic analysis
In environmental management, water analysis is frequently deployed when pollution is suspected to identify the pollutant in order to take remedial action. The analysis can often enable the polluter to be identified. Such forensic work can examine the ratios of various components and can "type" samples of oils or other mixed organic contaminants to directly link the pollutant with the source.
In drinking water supplies the cause of unacceptable quality can similarly be determined by carefully targeted chemical analysis of samples taken throughout the distribution system.
In manufacturing, off-spec products may be directly tied back to unexpected changes in wet processing stages and analytical chemistry can identify which stages may be at fault and for what reason.
References
See also
*
Analytical chemistry
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...
*
Drinking water quality standards
Drinking water quality standards describes the quality parameters set for drinking water. Despite the truth that every human on this planet needs drinking water to survive and that water may contain many harmful constituents, there are no univers ...
*
Analytical quality control Analytical quality control, commonly shortened to AQC, refers to all those processes and procedures designed to ensure that the results of laboratory analysis
Analysis ( : analyses) is the process of breaking a complex topic or substance in ...
{{Water
Analytical chemistry
Geochemistry
Analysis
Analysis ( : analyses) is the process of breaking a complex topic or substance into smaller parts in order to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Aristotle (3 ...