A, conductivity:
In ecology, conductivity is the ability of a solution to conduct current in a digital representation. The physical meaning of conductivity is the performance of a material's conductivity. The higher the conductivity, the stronger the conductivity, and vice versa. The unit is expressed in Siemens per meter (S/m).
Influencing factors:
1) Temperature: There is a large correlation between conductivity and temperature. In a temperature range, the conductivity can be approximated as being proportional to the temperature. In order to compare the conductivity of materials at different temperature conditions, a common reference temperature must be set.
2) Doping level: Increasing the doping level will result in high conductivity. The conductivity of an aqueous solution depends on the concentration of the solute salt it contains, or other chemical impurities that decompose into electrolytes. The conductivity of a water sample is an important indicator for measuring salt content, ion content, impurity content, etc. of water. The purer the water, the lower the conductivity (the higher the resistivity). The conductivity of water is often recorded as the conductance coefficient; the conductivity coefficient is the conductivity of water at a temperature of 25°C.
3) Anisotropy: Some materials have anisotropic conductivity and must be expressed in a 3 X 3 matrix (in mathematical terms, second-order tensors, which are usually symmetric)
Second, TDS:
Total dissolved solids (also known as Total dissolved solids), also known as the total amount of dissolved solids, is measured in milligrams per liter (mg/L), which indicates how many milligrams of dissolved solids are dissolved in one liter of water. The higher the TDS value, the more impurities the water contains. Total dissolved solids refer to the total amount of all solutes in water, including both inorganic and organic content. Generally, the available conductivity value can be used to understand the salt content in the solution. Under normal circumstances, the higher the conductivity, the higher the salt content and the higher the TDS. In inorganic substances, in addition to the dissolved ionic components, there may be molecular inorganic substances. Since the organic matter contained in the natural water and the inorganic substance in the form of molecules are generally not considered, the salt content is generally also referred to as total dissolved solids. However, TDS does not effectively reflect water quality in specific waters. For example, in electrolyzed water, since the amount of charged ions, such as HO-electrolyzed water, is significantly increased, the corresponding amount of electricity is abnormally increased. There is often a relationship between conductivity and conductivity. Sometimes TDS can also be used to represent conductivity. The relationship between the two: 1TDS=2μS
Where μS is the unit of conductivity.
National standard GB5749-2006 "Drinking water for drinking water," the total amount of soluble total solids (TDS) requirements: total dissolved solids ≤ 1000mg / L
Third, salinity:
The definition of salinity goes through several stages.
1) Kensen's salinity formula
At the beginning of this century, Knudsen et al. established the definition of salinity. The definition of salinity at that time was defined in 1000 g of seawater. When carbonates were all changed to oxides, bromine and iodine were replaced by chlorine, all Total amount of solid material contained after total oxidation of organic materials. The measurement method is to take a certain amount of seawater, add hydrochloric acid and chlorine water, evaporate to dryness, and then dry at a constant temperature of 380° C. and 480° C. for 48 hours, and finally weigh the weight of the remaining solid matter.
The salinity of seawater measured by the above-mentioned weighing method is very complicated. It takes a few days to measure a sample, and it is not suitable for marine surveys. Therefore, in practice, the chlorine degree of seawater is determined according to the composition of seawater. In order to calculate salinity indirectly, the relationship between chlorination and salinity (Konyson salinity formula) is as follows:
S‰=0.030+1.8050Cl‰
When Cinson's salinity formula was used, the use of a unified silver nitrate titration method and a commonly used ocean table showed great advantages in practical work, and it has been used for 70 years. However, it has also been found in long-term use that Kölnson's salinity formula is only an approximate relationship, and its representativeness is poor; the titration method is also inconvenient to operate on a ship. So people are looking for more accurate and faster methods.
2) The above relation between salinity and chlorination is redefined and established on the basis of the law of constant ratio of seawater composition. This is not strict. Moreover, the water samples taken at that time were mostly Baltic Sea surface water and it was difficult to represent the entire ocean water. The law. In fact, the constant value of 0.030 in the relation does not meet the actual situation of ocean salinity changes. According to the conductivity of seawater depends on the nature of its temperature and salinity, the salinity of seawater can be obtained by measuring its conductivity and temperature.
After 1950, the research and development of conductance salinometers simplified the determination of salinity, improved the precision, and was more accurate and convenient than the method of calculating salinity after the determination of chlorination. Therefore, UNESCO, the International Council for the Exploration of the Sea (ICES), the Scientific Committee on Marine Research (SCOR), and the International Association for the Study of Marine Physics (IAPSO) jointly initiated four meetings and met in May 1962. A joint group of seawater equations was established. At the second meeting in 1963, the group was renamed the Joint Panel of Marine Experts and Standards (JPOTS). After many discussions and studies, in order to maintain the unity of historical data, the salinity formula was changed to
S‰=1.80655Cl‰
RA Cox et al. accurately measured the chlorinity values ​​of 135 water samples (within a depth of 100 meters) collected from various oceans and sea areas, converted the salinity according to the above formula, and measured the conductance ratio R15. The polynomial of the relationship between S‰ and R15
S‰=-0.08996+28.2970R15+12.80832R215-10.67869R315+5.98624R415-1.32311R515
Where R15 is the ratio of seawater sample to standard conductivity of seawater at S=35.000 at a standard atmospheric pressure and at 15°C. In 1966, JPOTS recommended this polynomial for the definition of seawater salinity. In the same year, the “International Ocean Table†published by UNESCO and the British National Institute of Oceanography, the salinity data of which was converted into salinity using the above-mentioned measurement of conductivity.
3) Practical salinity scale Since the 1970s, more and more applications of on-site instruments such as the conductivity-temperature-depth instrument (CTD) have been applied. However, the international ocean watch (1966) does not include the following 10°C. Salinity data, resulting in less than 10 °C on-site measurement results, can not be unified. In addition, the standard seawater prepared from 1967 to 1969 was measured, and it was also found that the salinity measured by the conductance method was inconsistent with that obtained from the conversion of the chlorination degree, and the reliability of the standard seawater as a conductivity standard appeared. Therefore, JPOTS decided to use standard potassium chloride solution to calibrate standard seawater, and recommended the practical salinity scale of 1978.
Originally, absolute salinity (SA) was the ratio of solute mass and seawater mass in seawater, but it was not actually measured directly. Therefore, the practical salinity (S) of seawater defined in K15 was used to express the results of ocean observations.
S=a0+a1K1/215+a2K15+a3K3/215+a4K215+a5K5/215
A0=0.0080 a1=-0.1692
A2=25.3851 a3=14.0941
A4=-7.0261 a5=2.7081
Σai=35.0000 2≤S≤42
In the formula, K15 is the ratio of electrical conductivity and mass ratio of seawater sample to the conductivity of potassium chloride solution of 32.4356×10-3 at 15°C and a standard atmospheric pressure. When K15 is exactly 1, S is exactly equal to 35.
The practical salinity value is 1000 times the past salinity value. For example, in the past, the salinity value was 0.03512 (ie, 35.12 ‰) and the practical salinity value was 35.12.
From the definition of the practical salinity formula, it can be seen that the chlorine degree is regarded as an independent variable independent of the practical salinity.
The general standard for practical salinity is still standard seawater, and the latter is still marked with the value of K15 in addition to the chlorination value.
Therefore, it can be found from the description of the above article that conductivity, TDS, and salinity are not the same concept, but the three are closely related.
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