CN112305149B - Method for estimating water solubility inorganic carbon concentration - Google Patents
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Abstract
A method for estimating the concentration of water soluble inorganic carbon relates to a method for estimating the concentration of water soluble inorganic carbon, and aims to solve the technical problems of high precision of a test instrument, expensive materials and complex water sample pretreatment process of the existing method for measuring the concentration of water soluble inorganic carbon (DIC). The method comprises the following steps: collecting a water sample at a sampling point of a water body, placing the water sample in a vehicle-mounted refrigerator, conveying the water sample to a laboratory, refrigerating the water sample in a dark place for storage, and measuring the total alkalinity of the water body within 24 hours of conveying the water sample to the laboratory by using a neutralization titration method; the water alkalinity was substituted into formula DIC =0.2 × Alk +2.6 and the water soluble inorganic carbon concentration was estimated. The method is simple, the ratio of the calculated DIC value to the actually measured DIC value is 0.98, and the correlation precision is good. Can be used in the field of water quality monitoring and environmental evaluation.
Description
Technical Field
The invention relates to a method for estimating the concentration of soluble inorganic carbon in a water body, belonging to the field of evaluation of water environment of inland water bodies such as lakes, reservoirs, rivers and the like.
Background
Soluble nonpolar Carbon DIC (Dissolved Inorganic Carbon) is CO in ocean and inland water bodies 2 Important parameters of the system are related to the exchange and flow process of carbon among the atmospheric space, the water space, the biosphere and the rock space. In recent years, the CO in the atmosphere has been a cause of 2 、CH 4 The problem of the greenhouse effect caused by substances and the like has become a hot problem of international social attention. Scientists predict the CO in the atmosphere by the middle of this century 2 The concentration is increased by 1 time than that before industrialization, the global warming is intensified, a series of changes such as glacier melting, sea level rising, city inundation and the like are caused, and deep changes are generated on the global ecosystem and the human living environmentFar away. However, CO in the atmosphere 2 Has close relation with DIC in water body, and DIC is various inorganic carbonates CO in water body 3 -2 (aq), bicarbonate HCO 3 - (aq), carbonic acid H 2 CO 3 (aq) and CO 2 The sum of the gas concentrations. DIC equilibrium in natural water is influenced by many factors such as atmospheric pressure, headspace and atmospheric partial pressure, solution temperature, solution pH and various solute concentrations such as electrolyte concentration, and has important significance in influencing the pH of natural water, thereby determining that the water is discharged CO 2 (carbon source) is also absorbing CO 2 (carbon sink). In addition, it affects the migration and degradation of environmental pollutants through conversion with soluble organic carbon (DOC). Therefore, understand DIC components in water and study CO 2 The transfer and accommodation of water and air and the carbon circulation mechanism become important contents in the advanced field of international ocean and inland water body science research. Therefore, the method has important significance for accurately, quickly and conveniently measuring the DIC content in the water body.
Currently, the DIC determination methods generally adopted at home and abroad are as follows: gravimetric methods, gas chromatography, infrared absorption methods, alkalinity calculation methods, total organic carbon analyzers and other analysis methods, the gravimetric methods are the earliest and the complex operation has been replaced due to limited precision. Although the gas chromatography has higher precision, the requirements on materials and conditions of an experimental device are strict, and the correction calculation is complex and is not widely applied. The infrared absorption method has high precision and good stability, but has high price, complex transposition and inconvenient operation, and is improved after improvement. The alkalinity calculation method is a common method for measuring DIC in water, but firstly, the total alkalinity and carbonate alkalinity of the water are measured, the concentration of the DIC is calculated by utilizing a difference value and a thermodynamic principle, more parameters are needed, and the calculation process is complex. DIC obtained by total organic carbon analyzer method is similar to infrared absorption method in intermediate analysis process. It has been found in long-term practice and research that these methods have not been fully adaptable to the needs of scientific work such as rapid monitoring at a new time. Therefore, the development of a new, convenient and efficient method for measuring the DIC concentration in water has become an urgent need of scientific researchers.
Disclosure of Invention
The invention aims to solve the technical problems of high precision of a testing instrument, expensive materials and complex pretreatment process of a water sample of the conventional method for testing the concentration of the soluble inorganic carbon (DIC) in the water body, and provides a method for estimating the concentration of the soluble inorganic carbon in the water body.
The method for estimating the water body solubility inorganic carbon concentration comprises the following steps:
1. collecting a water sample in a 0.5-1 m surface layer of the water body at a sampling point of the water body by using a water sampler, placing the water sample in a vehicle-mounted refrigerator, conveying the water sample to a laboratory for cold storage and preservation in a dark place, and measuring the total alkalinity of the water body by using a neutralization titration method within 24 hours after conveying the water sample to the laboratory;
2. substituting the alkalinity of the water body into the following formula to estimate the water body solubility inorganic carbon concentration;
DIC＝0.2×Alk+2.6；
wherein DIC represents water soluble inorganic carbon concentration;
alk represents water alkalinity.
Further, the water body in the step one is a lake, a reservoir or a river;
furthermore, the water quantity of the water sample in the step one is 2-3L;
furthermore, the method for determining the total alkalinity of the water body by using a neutralization titration method in the step one comprises the following steps: filtering a water sample by using a filter with the aperture of 0.45 mu m, adding hydrochloric acid to adjust the pH of the water sample to 3-4, boiling, and removing CO 2 (ii) a And adding an indicator, and titrating excessive hydrochloric acid by using standard alkali to obtain the alkalinity of the water body. The method is stable, reliable, cheap and easy to operate.
Further, the indicator is bromocresol green or methyl red;
according to the invention, the DIC concentration is estimated through the total alkalinity of the water body, namely, the dissolved inorganic carbon concentration value of the water body can be obtained through calculation only by measuring the total alkalinity of the water body. The method is simple, the ratio of the calculated DIC value to the actually measured DIC value is 0.98, the correlation precision is good, and the reliability is high. Can be used in the field of water quality monitoring and environmental evaluation.
Drawings
FIG. 1 is a distribution diagram of 310 lake, reservoir and river samples nationwide in example 1;
FIG. 2 is a graph showing the correlation analysis between the correlation line of the estimated water solubility inorganic carbon concentration of the water body estimated in example 1 and the measured values of DIC;
FIG. 3 is a graph showing the correlation between the concentration of inorganic carbon in water solubility estimated in example 2 and the observed value of DIC.
Detailed Description
The following examples are used to demonstrate the beneficial effects of the present invention:
example 1: the method for estimating the water body solubility inorganic carbon concentration of the embodiment is carried out according to the following steps:
1. in 2018, 206 lakes, reservoirs and rivers which are distributed nationwide are sampled, a sampling point distribution diagram is shown in figure 1, each water body is provided with 2-4 sampling points, the total number of the sampling points is 687, a water sampler is used for collecting 2L water samples in 0.5-1 m of the surface layer of the water body, the water samples are placed in a vehicle-mounted refrigerator and conveyed to a laboratory for dark cold storage, the total alkalinity of the water body is measured within 24h conveyed to the laboratory by a neutralization titration method, and the specific neutralization titration method is used for measuring the total alkalinity of the water body and comprises the following steps: filtering water sample with a filter of 0.45 μm, adding excessive hydrochloric acid to adjust pH to 3.5, boiling to remove CO 2 Adding a methyl red indicator, titrating excessive hydrochloric acid by using standard alkali, and then obtaining the total alkalinity of the water sample, wherein the total alkalinity is expressed by Alk;
2. substituting the alkalinity of the water body into the following formula to estimate the water body solubility inorganic carbon concentration;
DIC＝0.2×Alk+2.6；
wherein DIC represents water soluble inorganic carbon concentration;
alk represents the alkalinity of the water body;
and obtaining the estimated water body solubility inorganic carbon concentration of each water body, and drawing a relation curve of the water body solubility inorganic carbon concentration changing along with the alkalinity of the water body into a graph 2.
Each water sample in example 1 was subjected to determination of dissolved inorganic matter concentration (DIC) using total carbon analyzer by the following procedure: filtering water sample with 0.45 μm glass fiber membrane produced by Seanda Industrials, china, storing at low temperature, taking ultrapure water as reference water sample, adopting low temperature reaction tube (150 deg.C), acidifying the water sample passing through the reaction tube to decompose inorganic carbonate into carbon dioxide, and sequentially introducing the generated carbon dioxide into non-dispersive infrared detector. The detection limit of the method is 0.3mg/L. The assay was repeated three times for each water sample and the mean was recorded and calculated as the actual measure of the soluble inorganic carbon (DIC) concentration at that point and also plotted in figure 2.
Correlation analysis of the relationship line between the estimated water solubility inorganic carbon concentration of the water body estimated in example 1 and the measured value of DIC was performed using Microsoft Excel 2017 software, and it can be seen that the measured value data points are uniformly distributed on both sides of the DIC =0.2 × Alk +2.6 line, and R is 2 =0.96, n =687, p < 0.001. It is noted that the correlation accuracy between the estimated value and the actually measured value is better, and the DIC calculated by the method of this embodiment has higher reliability.
Example 2: the method for estimating the water body solubility inorganic carbon concentration of the embodiment is carried out according to the following steps:
1. in 2019, 104 lakes, reservoirs and rivers which are distributed nationwide are sampled, each water body is provided with 2-4 sampling points, the total number of the 344 sampling points is sampled, a water sampler is used for collecting 2L water samples in 0.5-1 m of the surface layer of the water body, the water samples are placed in a vehicle-mounted refrigerator and conveyed to a laboratory for dark cold storage, the total alkalinity of the water body is measured within 24 hours of conveying to the laboratory by using a neutralization titration method, and the specific neutralization titration method is used for measuring the total alkalinity of the water body and comprises the following steps: filtering water sample with 0.45 μm, adding excessive hydrochloric acid to adjust pH to 3.8, boiling to remove CO 2 Adding a bromocresol green indicator, titrating excessive hydrochloric acid by using standard alkali, and then obtaining the total alkalinity of the water sample, wherein the total alkalinity is expressed by Alk;
2. substituting the alkalinity of the water body into the following formula to estimate the water body solubility inorganic carbon concentration;
DIC＝0.2×Alk+2.6；
wherein DIC represents water soluble inorganic carbon concentration;
alk represents the alkalinity of the water body;
and obtaining the estimated water solubility inorganic carbon concentration of each water body.
Each water sample in example 2 was subjected to determination of dissolved inorganic matter concentration (DIC) using total carbon analyzer by the following steps: filtering water sample with 0.45 μm glass fiber membrane, filtering, storing at low temperature, taking ultrapure water as reference water sample, adopting low temperature reaction tube (150 deg.C), acidifying the water sample passing through the reaction tube to decompose inorganic carbonate into carbon dioxide, and sequentially introducing the generated carbon dioxide into non-dispersive infrared detector. The detection limit of the method is 0.3mg/L. Repeatedly measuring each water sample for three times, recording and calculating an average value as an actual measured value of the concentration of the soluble inorganic carbon (DIC) at the point;
the correlation analysis of the estimated water solubility inorganic carbon concentration of the water body estimated according to the example 2 and the measured value of DIC was performed by using Microsoft Excel 2017 software, and the measured DIC was used as a horizontal scale and the calculated DIC according to the example 2 as a vertical scale to obtain a graph 3, from which it can be seen that the measured value data points are uniformly distributed on both sides of the line y =0.91x +5.51, and R is a vertical scale 2 And the result shows that the Mean Absolute Percent Error (MAPE) is only 30.24%, the ratio of the DIC value calculated according to the method to the actually measured DIC value is 0.98, the correlation precision is good, and the DIC calculated according to the method has high reliability.
Claims (3)
1. A method for estimating the concentration of water soluble inorganic carbon is characterized by comprising the following steps:
1. collecting a water sample in a range of 0.5-1m on the surface layer of the water body at a sampling point of the water body by using a water sampler, placing the water sample in a vehicle-mounted refrigerator, conveying the water sample to a laboratory for cold storage in a dark place, and measuring the total alkalinity of the water body by using a neutralization titration method within 24 hours after conveying the water sample to the laboratory; the water body is a lake, a reservoir or a river; the method for measuring the total alkalinity of the water body by using a neutralization titration method comprises the following steps: filtering a water sample by using a filter with the pore diameter of 0.45 mu m, adding hydrochloric acid to adjust the pH of the water sample to 3 to 4, boiling, and removing CO 2 (ii) a Adding an indicator, and titrating excessive hydrochloric acid by using standard alkali to obtain the alkalinity of the water body;
2. substituting the alkalinity of the water body into the following formula to estimate the water body solubility inorganic carbon concentration;
DIC = 0.2×Alk + 2.6；
wherein DIC represents water soluble inorganic carbon concentration;
alk represents water alkalinity.
2. The method for estimating the concentration of the inorganic carbon soluble in the water body according to claim 1, wherein the water sample in the step one is water in an amount of 2 to 3L.
3. The method of claim 1, wherein the indicator is bromocresol green or methyl red.
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