The heavy metals mentioned in terms of environmental pollution mainly refer to metals or metals such as mercury, cadmium, lead, chromium, arsenic, and also general heavy metals with certain toxicity, such as copper, zinc, nickel, cobalt and tin. We discuss the hazards of heavy metals in terms of naturalness, toxicity, activity and persistence, biodegradability, bioaccumulation, and additive effects on organisms. Heavy metal detection method and application First, the hazardous characteristics of heavy metals The heavy metals mentioned in terms of environmental pollution mainly refer to metals or metals such as mercury, cadmium, lead, chromium, arsenic, and also general heavy metals with certain toxicity, such as copper, zinc, nickel, cobalt and tin. We discuss the hazards of heavy metals in terms of naturalness, toxicity, activity and persistence, biodegradability, bioaccumulation, and additive effects on organisms. (1) Naturalness: Humans who have lived in the natural environment for a long time have strong adaptability to natural materials. Some people analyzed the distribution of more than 60 common elements in the human body, and found that the majority of them in the human blood are very similar to their percentage in the earth's crust. However, humans are much less tolerant of synthetic chemicals. So distinguishing the natural or artificial properties of pollutants helps to estimate their degree of harm to humans. Heavy metals such as lead, cadmium, mercury, and arsenic are caused by the development of industrial activities, enriching in the human environment, entering the human body through the atmosphere, water, food, etc., accumulating in certain organs of the human body, causing chronic poisoning and harm. Human health. (2) Toxicity: The main factors determining the toxicity of pollutants are their physical properties, content and form. For example, chromium has two forms: divalent, trivalent, and hexavalent. Among them, hexavalent chromium is highly toxic, and trivalent chromium is one of the important elements of human metabolism. Generally, heavy metals in natural waters produce toxicity ranging from about 1 to 10 mg/L, while mercury, cadmium and the like produce toxicity ranging from 0.01 to 0.001 mg/L. (3) Time and space distribution: After the pollutants enter the environment, they are diluted and diffused with the flow of water and air, which may cause a wider range of pollution from the point source to the surface source, and the concentration and intensity distribution of the pollutants over time in different spatial locations. Change is different. (iv) Activity and persistence: Activity and durability indicate the degree of stability of the contaminant in the environment. Highly active pollutants are prone to chemical reactions in the environment or during processing, and the toxicity is reduced, but it is also possible to generate pollutants that are more toxic than the original, and constitute secondary pollution. For example, mercury can be converted into methylmercury and is highly toxic. Contrary to activity, persistence means that some pollutants can maintain their harmfulness for a long time. For example, heavy metals such as lead and cadmium are toxic and difficult to degrade in nature, and can cause bioaccumulation, which threatens human health and survival for a long time. (5) Biodegradability: Some pollutants can be absorbed, utilized and decomposed by organisms, and finally produce harmless stable substances. Most organic matter has the possibility of being biodegraded, and most heavy metals are not easily decomposed by organisms. Therefore, once heavy metal pollution occurs, it is more difficult and more harmful to treat. (6) Bioaccumulation: Bioaccumulation involves two aspects: First, pollutants accumulate in the environment through food chains and chemical physics. Second, the accumulation of pollutants in certain organs of the human body due to long-term intake. For example, cadmium can accumulate in organs and tissues such as the liver and kidney of the human body, causing damage to various organs and tissues. Another example is the watery disease incident in Japan from 1953 to 1961. Inorganic mercury is converted into methylmercury in seawater, and is accumulated by fish and shellfish. It is biomagnified by the food chain, and local residents are poisoned after eating. (7) Additiveness to the action of living organisms: A variety of pollutants exist simultaneously and interact with organisms. There are two types of effects of pollutants on organisms: one is synergistic, the pollutants are more harmful to the environment than the simple addition of pollutants; the other is antagonism, and the pollutants coexist. When the hazards weaken each other. Second, the quantitative detection technology of heavy metals Commonly accepted methods for analysis of heavy metals are: microspectral analysis (MS), ultraviolet spectrophotometry (UV), atomic absorption (AAS), atomic fluorescence (AFS), inductively coupled plasma (ICP), and X-ray fluorescence. (XRF), inductively coupled plasma mass spectrometry (ICP-MS). In addition to the above methods, microspectral technology introduces spectroscopy to detect, with higher precision and more accuracy! Some countries in Japan and the European Union use inductively coupled plasma mass spectrometry (ICP-MS) to analyze, but for domestic users, the cost of the instrument is high. Some also use X-ray fluorescence (XRF) analysis, the advantage is non-destructive testing, can directly analyze the finished product, but the detection accuracy and repeatability is not as good as the spectroscopy method. The latest popular detection method, the anodic dissolution method, has a fast detection speed and accurate numerical values, and can be used for environmental emergency detection such as on-site. (a) Atomic Absorption Spectrometry (AAS) Atomic absorption spectroscopy is a new instrumental analysis method established in the 1950s. It is complementary to atomic emission spectroscopy, which is mainly used for the qualitative analysis of inorganic elements, and has become the main means for quantitative analysis of inorganic compounds. The atomic absorption analysis process is as follows: 1. Make the sample into a solution (while making a blank); 2. Prepare a series of calibration solutions (standard samples) of known concentrations of the analytical elements; 3. Measure the corresponding values ​​of the blanks and the standards in turn. 4. Calculate the calibration curve according to the above corresponding values; 5. Measure the corresponding value of the unknown sample; 6. Determine the concentration value of the sample according to the calibration curve and the corresponding value of the unknown sample. Nowadays, due to the development of computer technology, chemometrics and the emergence of a variety of new components, the precision, accuracy and automation of atomic absorption spectrometers have been greatly improved. The atomic absorption spectrometer controlled by the microprocessor simplifies the operating procedure and saves analysis time. Gas chromatography-atomic absorption spectroscopy (GC-AAS) has been developed to further expand the application of atomic absorption spectroscopy. (2) UV-visible spectrophotometry (UV) The detection principle is: heavy metal and color developing agent - usually an organic compound, which can form a complex reaction in a heavy metal to form a colored molecular group, and the color depth of the solution is proportional to the concentration. Colorimetric detection at a specific wavelength. There are two kinds of spectrophotometric analysis, one is to use the substance itself to measure the absorption of ultraviolet and visible light; the other is to generate a colored compound, that is, "color development", and then measured. Although many inorganic ions are absorbed in the ultraviolet and visible regions, they are less useful for quantitative analysis because of their generally weaker strength. Photometric determination is carried out by adding a coloring agent to convert the substance to be tested into a compound having absorption in the ultraviolet and visible regions, which is currently the most widely used test method. The color developing agent is classified into an inorganic color developing agent and an organic color developing agent, and is used in an organic color developing agent. Most of the organic developers are themselves colored compounds, and the compounds formed by the reaction with metal ions are generally stable chelates. The selectivity and sensitivity of the color reaction are high. Some colored chelates are easily soluble in organic solvents and can be subjected to colorimetric detection after extraction and leaching. In recent years, a color development system that forms a multi-component complex has attracted attention. A multi-component complex refers to a complex formed from three or more components. The formation of a multi-component complex can improve the sensitivity of spectrophotometry and improve the analytical characteristics. The selection and use of chromogenic reagents in pretreatment extraction and detection of colorimetry are important research topics in spectrophotometry in recent years. (3) Atomic Fluorescence Method (AFS) Atomic fluorescence spectroscopy is a method for determining the content of an element to be tested by measuring the intensity of fluorescence emission generated by the atomic vapor of an element to be tested at a specific frequency. Although atomic fluorescence spectrometry is an emission spectroscopy method, it is closely related to atomic absorption spectroscopy, and has the advantages of both atomic emission and atomic absorption methods, and overcomes the shortcomings of the two methods. Atomic fluorescence spectroscopy has the characteristics of simple emission line, higher sensitivity than atomic absorption spectroscopy, and less linear interference. It can perform simultaneous determination of multiple elements. Atomic fluorescence spectrometer can be used to analyze 11 kinds of elements such as mercury, arsenic, antimony, antimony, selenium, antimony, lead, tin, antimony and cadmium zinc. Environmental monitoring, medicine, geology, agriculture, drinking water and other fields have been widely used. In the national standard, atomic fluorescence spectroscopy has been legally defined as the first method in the measurement standards for elements such as arsenic and mercury in food. After the gaseous free atom absorbs the characteristic wavelength radiation, the outer electron of the atom will transition from the ground state or the low energy state to the high energy state, and emit the same or different energy radiation as the original excitation wavelength, that is, atomic fluorescence. The emission intensity If of atomic fluorescence is proportional to the number N of ground states of the element in a unit volume in the atomizer. When the atomization efficiency and the fluorescence quantum efficiency are fixed, the atomic fluorescence intensity is proportional to the sample concentration. Atomic fluorescence spectrometers have been developed for simultaneous determination of multiple elements. They use multiple high-intensity hollow cathode lamps as light sources and inductively coupled plasma (ICP) with very high temperatures as atomizers to enable multiple elements. At the same time achieve atomization. The multi-element analysis system is centered on the ICP atomizer, and a plurality of detection units are installed around the hollow cathode lamps at right angles to each other, and the generated fluorescence is detected by a photomultiplier tube. After the photoelectrically converted electrical signal is amplified, it is processed by a computer to obtain the analysis result of each element. (4) Electrochemical method - anodic stripping voltammetry Electrochemical method is a fast-developing method in recent years. It relies on the classical polarographic method. On this basis, oscillographic polarography and anodic stripping voltammetry are derived. The detection limit of electrochemical method is low, the test sensitivity is high, and it is worthy of popularization and application. The fifth method in the method for determining lead in the national standard and the second method for measuring the chromium are all oscillopolarography. Anodic stripping voltammetry is an electrochemical analytical method that combines potentiostatic electroconcentration with voltammetric determination. This method can continuously measure a plurality of metal ions at a time, and has high sensitivity, and can measure metal ions of 10-7-10-9 mol/L. The instrument used in this method is relatively simple and easy to operate, and is a good means of trace analysis. China has issued a national standard for anodic stripping voltammetry for the determination of metallic impurities in chemical reagents. Anodic stripping voltammetry is measured in two steps. The first step is "electrolysis", that is, at a constant potential, the measured ions are electrolytically deposited and concentrated on the working electrode to form an amalgam with mercury on the electrode. For a given metal ion, if the stirring speed is constant and the pre-electrolysis time is fixed, then m = Kc, that is, the amount of metal in the electrowinning is proportional to the concentration of the metal to be measured. The second step is “dissolutionâ€, that is, after the end of enrichment, after a typical static period of 30s or 60s, a reverse voltage is applied to the working electrode, and the metal in the amalgam is reoxidized into an ion return solution by a negative positive scan. , an oxidation current is generated, and a voltage-current curve, that is, a volt-ampere curve, is recorded. The curve is peak-shaped, and the peak current is proportional to the measured concentration in the solution, which can be used as the basis for quantitative analysis. The peak potential can be used as the basis for qualitative analysis. Oscillopolarography is also known as "single-scan polarography". A new method of polarographic analysis. It is a polarographic method that is quickly added to the electrolysis voltage. Usually in the late stage of the growth of the mercury drop electrode, a zigzag pulse voltage is quickly added to the two poles of the electrolytic cell, and a polarogram is obtained in a few seconds. In order to quickly record the polarogram, the oscilloscope is usually used. The fluorescent screen of the tube is used as a display tool and is therefore called oscillopolarography. Its advantages: fast and sensitive. (5) X-ray fluorescence spectrometry (XRF) X-ray fluorescence spectroscopy is a method of qualitatively or quantitatively determining the components in a sample by varying the absorption of the x-rays by the sample as a function of the composition of the sample and how much. It has the characteristics of rapid analysis, simple sample preparation, wide range of analytical elements, simple spectral lines, less spectral interference, sample morphology diversity and non-destructive determination. It is not only used for the qualitative and quantitative analysis of constant elements, but also for the determination of trace elements. The detection limit is mostly 10-6. Combined with separation, enrichment and other means, up to 10-8. The range of elements measured includes all elements from the FU in the periodic table. Multi-channel analyzers can simultaneously measure the content of more than 20 elements in a matter of minutes. The x-ray fluorescence method can not only analyze the bulk sample, but also analyze the composition and film thickness of each layer of the multilayer coating. When the sample is irradiated by x-rays, high-energy particle beams, ultraviolet light, etc., since the high-energy particles or photons collide with the sample atoms, the electrons in the inner layer of the atom are ejected to form holes, and the atoms are in an excited state. The lifetime is very short. When the outer electrons move toward the inner layer, the excess energy is released in the form of x-rays, and new holes are generated in the outer layer of the teaching and new x-ray emission is generated, thus producing a series of Characteristic x-ray. Characteristic x-rays are inherent to various elements and are related to the atomic coefficients of the elements. Therefore, as long as the wavelength λ of the characteristic x-ray is measured, the element generating the wavelength can be found. You can do qualitative analysis. When the sample composition is uniform, the surface is smooth and flat, and the elements are not mutually excited, when x-rays (primary x-rays) are used to excite the original irradiation sample to produce characteristic x-rays (fluorescent x-rays) in the elements. If the element is the same as the experimental conditions, there is a linear relationship between the intensity of the fluorescent x-ray and the content of the analytical element. Quantitative analysis based on the intensity of the line (6) Inductively coupled plasma mass spectrometry (ICP-MS) The detection limit of ICP-MS is extremely impressive. The detection limit of the solution is mostly ppt level, and the actual detection limit cannot be better than the cleaning conditions in your laboratory. It must be pointed out that the ppt-level detection limit of ICP-MS is for a simple solution with a small amount of dissolved substances in the solution. If the detection limit of the concentration in the solid is involved, the ICP-MS has poor salt tolerance, ICP- The advantages of MS detection limits can be as much as 50 times worse. Some common light elements (such as S, Ca, Fe, K, Se) have serious interference in ICP-MS and will also deteriorate their detection limits. ICP-MS consists of three parts: an ion source ICP torch, an interface device, and a mass spectrometer as a detector. The ionization source used in ICP-MS is inductively coupled plasma (ICP). The main body is a torch consisting of a three-layer quartz sleeve. The upper end of the torch is wound with a load coil, and the three-layer tube carries the carrier gas from the inside to the outside. The auxiliary gas and the cooling gas are coupled by a high frequency power supply to generate a magnetic field perpendicular to the plane of the coil. If the argon gas is ionized by the high-frequency device, the argon ions and electrons collide with other argon atoms to generate more ions and electrons under the action of the electromagnetic field to form a eddy current. The powerful current generates high temperatures, which instantly cause argon to form a plasma torch with a temperature of up to 10,000k. The sample to be analyzed is typically introduced into the argon stream as an aerosol of aqueous solution and then into the central region of the argon plasma at atmospheric pressure excited by radio frequency energy. The high temperature of the plasma desolvates the sample, vaporizes dissociation and ionization. Part of the plasma enters the vacuum system through different pressure zones. In the vacuum system, positive ions are pulled out and separated according to their mass-to-charge ratio. At a temperature of about 10 mm above the load coil, the torch temperature is about 8000 K. At such a high temperature, the element having an ionization energy lower than 7 eV is completely ionized, and the ionization energy of the element having an ionization energy lower than 10.5 ev is greater than 20%. Since most of the important elements have ionization energies below 10.5 eV, they have high sensitivity. A few elements with higher ionization energy, such as C, O, Cl, and Br, can be detected, but the sensitivity is low. 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