With the increasing use of ion chromatography, many samples cannot be analyzed by ion chromatography using the traditional methods of sampling, dilution, and direct injection after filtration. For a large number of samples of complex matrices, ion chromatography can be performed using a suitable method and then analyzed by ion chromatography after pretreatment. This can solve the problem of contamination of the ion chromatographic column by the complex matrix of the sample on the one hand, and can also greatly increase the complexity of the sample on the other hand. The matrix sample determines the results and accuracy and improves the sensitivity of the analytical method. The analytical sample pretreatment methods and characteristics of ion chromatographic analysis are summarized below:
With regard to the sample pretreatment method, with the improvement of the user level of domestic ion chromatography, there have been a large number of related pretreatment methods for ion chromatography. These methods have the following characteristics:
(1) For most of the sample preparation, domestic materials are used. The cost of pretreatment is very low, and it is more suitable for China's national conditions and can be widely used in China;
(2) Most of the sample pretreatment methods use off-line methods and do not require expensive on-line equipment; however, relatively speaking, the sample processing time is longer and the amount of sample required is also more;
(3) Compared with some sample pretreatment methods that have emerged in the world, most of the sample preparations that have occurred in the country are from the grass-roots units and are highly practical; however, there are relatively few theoretical discussions. Therefore, many domestic sample pretreatment methods can be further discussed theoretically on the one hand, and on the other hand can be adapted to the preprocessing of on-line samples by including both domestic and foreign instruments.
The principles followed in ion chromatographic sample pretreatment (1) The content of the components to be tested after the sample treatment shall not be lower than the detection limit of the detector;
(2) The separation of the components in the sample must meet the chromatographic quantitative requirements;
(3) The sample can not contain mechanical impurities and fine particles, so as not to block the column;
(4) As far as possible to avoid the chemical changes of the components to be tested, to prevent and reduce the loss of the components to be measured;
(5) The stoichiometry of the components to be tested must be clear and the reaction must be thorough;
(6) Avoid and reduce the introduction of irrelevant ions and compounds, prevent the components to be tested from being contaminated and increase the difficulty of separation.
1. Membrane treatment method 1.1. Filter Membrane or Sand Core Treatment Membrane filtration Membrane filtration is the most common method for pretreatment of aqueous samples by ion chromatography. In general, if the sample contains a particulate sample, it can be directly filtered by filtration through a 0.45 or 0.22 μm microporous membrane. Since the general filter cannot withstand high pressure, the filter can only be used for off-line sample processing. Sometimes online sample processing is required, or the method is used in the instrument pipeline. A sand core filter must be used. However, the membrane filtration method can only remove particulate insoluble substances. For extremely small particles or organic macromolecular soluble compounds and metal water-soluble ions, it can enter the column to interfere with sample determination and contaminate the column.
1.2. The electrodialysis treatment method in China is characterized by the use of electrodialysis. Compared with other membrane treatment methods, electrodialysis treatment has a certain degree of selectivity, so it can not only effectively remove particulate matter and organic pollutants, but also Remove heavy metal ion contaminants. It is one of the most effective methods for handling complex matrix samples.
1.3. The determination of trace ions in strong acid and alkali by electrolytic neutralization method is a difficult problem to be solved by ion chromatography. The application of electrolytic neutralization method solves the problem. This method utilizes hydrogen ion or hydroxide ion generated by water electrolysis to neutralize high-concentration acid or alkali, and is an ideal method for reducing high concentration of acid base.
1.4. Ultrafiltration and nanofiltration ultrafiltration is one of the most widely used membrane technologies, and it is also the most highly developed membrane species in China. It is mainly used to process biochemical samples containing macromolecules. The use of membranes is primarily one-time use to avoid sample cross-contamination. The nanofiltration membrane is interposed between the reverse osmosis membrane and the ultrafiltration membrane, and the separation layer on the membrane surface may have a nanoscale microporous structure. Nanofiltration membranes are mainly used to remove about one nanometer-sized lysosomes, and their retained molecular weight is generally 100-2000.
Nanofiltration membranes have removal rates only for specific solutes. At present, the understanding of the mechanism, characteristics, etc. of nanofiltration is not sufficient. In the field of analytical testing, it is mainly used to remove alkanes, odors, color, pesticides, synthetic detergents, soluble organics, etc. in aqueous solutions.
2. Chemical reaction matrix elimination method Chemical reaction matrix elimination method is based on the chemical nature of the interference matrix and the component to be measured in the sample. Using the characteristics of the chemical reaction and the stoichiometric relationship, the interference matrix is ​​separated from the component to be measured through chemical reaction. Common chemical reactions include redox, complexation, precipitation, and ion exchange. The method is used to clarify the chemical state and the existing form of the matrix, and attention should be paid to avoiding the generation of new interference components while eliminating the interference of the original matrix.
The main advantage of this method is that it is simple, flexible, and does not require special equipment; the disadvantage is that it is easy to bring in impurities of chemical reagents, the operation is time consuming, and the problems to be solved have limitations; the scope of application is that the chemical composition of the matrix is ​​relatively clear and has a fixed stoichiometry Reaction to the relationship of the sample.
3. Solid-phase extraction solid-phase extraction is the most widely used method for pretreatment of ion chromatography samples in China. The pollutants in different solutions can be processed by various means such as reversed phase, ion exchange, and chelating resins. Extraction methods can also use conventional solid-phase extraction and solid-phase microextraction, but solid-phase microextraction generally uses the reverse process of sample concentration and removal of matrix interference on liquid chromatography, so solid-phase microextraction It is more convenient for use in ion chromatography, and a solid-phase microextraction column can be used multiple times.
3.1. Reversed-Phase and Adsorption Solid-Phase Extraction For reversed-phase or adsorptive stationary phases, there can be many types. From the size of the stationary phase, it can be divided into conventional adsorption resin, solid phase microextraction can also be used, the difference is the processing sample The amount is different; the stationary phase can also be silica gel or polymer, but it should be noted that for high pH samples, the polymer type of stationary phase should be used.
3.2. Ion exchange resin method Different types of ion exchange resins can effectively remove different targeted contaminants. For example, cation exchange resins can remove metal ion contamination, and specific forms of anion exchange resins can remove high levels of anions, such as silver type Anion exchange resins can remove excess chloride or other halide anions, while quinoid anion exchange resins can remove excess sulfate ions. In some cases, some organics can also be removed by ion exchange resins, while ion exchange resins can be used in combination with adsorbed or reversed-phase resins to remove both organic and ionic compounds. The following table shows the use of ion exchange resin method for stationary phase extraction in China in recent years.
3.3. The chelating resin chelating resin method can be used for the concentration and enrichment of trace transition metals and lanthanide metal ions in complex matrices. The selectivity of the method is good, and the use of an appropriate eluent can remove metal ion interferences online. The functional groups of the currently used chelating resins are mostly weak acids (COOH) and weak bases (NH), so the pH value of the eluent has a great influence on its binding ability. Sample pretreatment of ion chromatography involves a variety of different principles And types, which involve a variety of different types of physical and chemical methods, including filtration, precipitation, adsorption, electrochemical and chemical reactions, and more and more sample preparation methods are used by ion chromatography by selecting the appropriate sample before The treatment can effectively broaden the application range of ion chromatography.
In addition, sample preparation directly affects the speed, sensitivity, and precision of ion chromatography. Therefore, the actual sample should be determined according to the nature of the sample, the test requirements and the instrument to select the appropriate sample preparation method, so as to achieve the purpose of rapid and accurate analysis.
With regard to the sample pretreatment method, with the improvement of the user level of domestic ion chromatography, there have been a large number of related pretreatment methods for ion chromatography. These methods have the following characteristics:
(1) For most of the sample preparation, domestic materials are used. The cost of pretreatment is very low, and it is more suitable for China's national conditions and can be widely used in China;
(2) Most of the sample pretreatment methods use off-line methods and do not require expensive on-line equipment; however, relatively speaking, the sample processing time is longer and the amount of sample required is also more;
(3) Compared with some sample pretreatment methods that have emerged in the world, most of the sample preparations that have occurred in the country are from the grass-roots units and are highly practical; however, there are relatively few theoretical discussions. Therefore, many domestic sample pretreatment methods can be further discussed theoretically on the one hand, and on the other hand can be adapted to the preprocessing of on-line samples by including both domestic and foreign instruments.
The principles followed in ion chromatographic sample pretreatment (1) The content of the components to be tested after the sample treatment shall not be lower than the detection limit of the detector;
(2) The separation of the components in the sample must meet the chromatographic quantitative requirements;
(3) The sample can not contain mechanical impurities and fine particles, so as not to block the column;
(4) As far as possible to avoid the chemical changes of the components to be tested, to prevent and reduce the loss of the components to be measured;
(5) The stoichiometry of the components to be tested must be clear and the reaction must be thorough;
(6) Avoid and reduce the introduction of irrelevant ions and compounds, prevent the components to be tested from being contaminated and increase the difficulty of separation.
1. Membrane treatment method 1.1. Filter Membrane or Sand Core Treatment Membrane filtration Membrane filtration is the most common method for pretreatment of aqueous samples by ion chromatography. In general, if the sample contains a particulate sample, it can be directly filtered by filtration through a 0.45 or 0.22 μm microporous membrane. Since the general filter cannot withstand high pressure, the filter can only be used for off-line sample processing. Sometimes online sample processing is required, or the method is used in the instrument pipeline. A sand core filter must be used. However, the membrane filtration method can only remove particulate insoluble substances. For extremely small particles or organic macromolecular soluble compounds and metal water-soluble ions, it can enter the column to interfere with sample determination and contaminate the column.
1.2. The electrodialysis treatment method in China is characterized by the use of electrodialysis. Compared with other membrane treatment methods, electrodialysis treatment has a certain degree of selectivity, so it can not only effectively remove particulate matter and organic pollutants, but also Remove heavy metal ion contaminants. It is one of the most effective methods for handling complex matrix samples.
1.3. The determination of trace ions in strong acid and alkali by electrolytic neutralization method is a difficult problem to be solved by ion chromatography. The application of electrolytic neutralization method solves the problem. This method utilizes hydrogen ion or hydroxide ion generated by water electrolysis to neutralize high-concentration acid or alkali, and is an ideal method for reducing high concentration of acid base.
1.4. Ultrafiltration and nanofiltration ultrafiltration is one of the most widely used membrane technologies, and it is also the most highly developed membrane species in China. It is mainly used to process biochemical samples containing macromolecules. The use of membranes is primarily one-time use to avoid sample cross-contamination. The nanofiltration membrane is interposed between the reverse osmosis membrane and the ultrafiltration membrane, and the separation layer on the membrane surface may have a nanoscale microporous structure. Nanofiltration membranes are mainly used to remove about one nanometer-sized lysosomes, and their retained molecular weight is generally 100-2000.
Nanofiltration membranes have removal rates only for specific solutes. At present, the understanding of the mechanism, characteristics, etc. of nanofiltration is not sufficient. In the field of analytical testing, it is mainly used to remove alkanes, odors, color, pesticides, synthetic detergents, soluble organics, etc. in aqueous solutions.
2. Chemical reaction matrix elimination method Chemical reaction matrix elimination method is based on the chemical nature of the interference matrix and the component to be measured in the sample. Using the characteristics of the chemical reaction and the stoichiometric relationship, the interference matrix is ​​separated from the component to be measured through chemical reaction. Common chemical reactions include redox, complexation, precipitation, and ion exchange. The method is used to clarify the chemical state and the existing form of the matrix, and attention should be paid to avoiding the generation of new interference components while eliminating the interference of the original matrix.
The main advantage of this method is that it is simple, flexible, and does not require special equipment; the disadvantage is that it is easy to bring in impurities of chemical reagents, the operation is time consuming, and the problems to be solved have limitations; the scope of application is that the chemical composition of the matrix is ​​relatively clear and has a fixed stoichiometry Reaction to the relationship of the sample.
3. Solid-phase extraction solid-phase extraction is the most widely used method for pretreatment of ion chromatography samples in China. The pollutants in different solutions can be processed by various means such as reversed phase, ion exchange, and chelating resins. Extraction methods can also use conventional solid-phase extraction and solid-phase microextraction, but solid-phase microextraction generally uses the reverse process of sample concentration and removal of matrix interference on liquid chromatography, so solid-phase microextraction It is more convenient for use in ion chromatography, and a solid-phase microextraction column can be used multiple times.
3.1. Reversed-Phase and Adsorption Solid-Phase Extraction For reversed-phase or adsorptive stationary phases, there can be many types. From the size of the stationary phase, it can be divided into conventional adsorption resin, solid phase microextraction can also be used, the difference is the processing sample The amount is different; the stationary phase can also be silica gel or polymer, but it should be noted that for high pH samples, the polymer type of stationary phase should be used.
3.2. Ion exchange resin method Different types of ion exchange resins can effectively remove different targeted contaminants. For example, cation exchange resins can remove metal ion contamination, and specific forms of anion exchange resins can remove high levels of anions, such as silver type Anion exchange resins can remove excess chloride or other halide anions, while quinoid anion exchange resins can remove excess sulfate ions. In some cases, some organics can also be removed by ion exchange resins, while ion exchange resins can be used in combination with adsorbed or reversed-phase resins to remove both organic and ionic compounds. The following table shows the use of ion exchange resin method for stationary phase extraction in China in recent years.
3.3. The chelating resin chelating resin method can be used for the concentration and enrichment of trace transition metals and lanthanide metal ions in complex matrices. The selectivity of the method is good, and the use of an appropriate eluent can remove metal ion interferences online. The functional groups of the currently used chelating resins are mostly weak acids (COOH) and weak bases (NH), so the pH value of the eluent has a great influence on its binding ability. Sample pretreatment of ion chromatography involves a variety of different principles And types, which involve a variety of different types of physical and chemical methods, including filtration, precipitation, adsorption, electrochemical and chemical reactions, and more and more sample preparation methods are used by ion chromatography by selecting the appropriate sample before The treatment can effectively broaden the application range of ion chromatography.
In addition, sample preparation directly affects the speed, sensitivity, and precision of ion chromatography. Therefore, the actual sample should be determined according to the nature of the sample, the test requirements and the instrument to select the appropriate sample preparation method, so as to achieve the purpose of rapid and accurate analysis.
Car Bags,Roof Bag,Car Garbage Bag,Car Storage Bag
Ningbo Yonghai Auto Products Co., Ltd. , https://www.nbyonghai-manufacturer.com