Inductively coupled plasma mass spectrometry, known as "ICP-MS technique", can identify multiple elements in samples at the same time. It is widely used in the monitoring of drinking water samples, water source water samples and surface water samples at present, and it is included in the "Standard Test Method of Domestic Applied Water". This paper mainly discusses the working principle of inductively coupled plasma mass spectrometry, the basic constitution of the instrument, the general operation steps and precautions, and lists some of its applications in domestic projects.

1. Basic principle of the instrument

Inductively coupled plasma mass spectrometry is mainly used for simultaneous identification of multiple elements in samples. Its instrument consists of two parts, ICP and MS. ICP is a high temperature ion source with a temperature of 8000K, and MS is a quadrupole fast scanning mass spectrometer. The sample in the instrument will undergo evaporation, dissociation, atomization, ionization and other processes in the channel under the action of high temperature ion source. The ionized ions then proceed through the sample cone interface and ion transport system to a high vacuum quadrupole fast scanning mass spectrometer, where all ions are separated and measured by high speed sequential scanning. The specific process is as follows: After the sample is injected into the sample cone, the sample is atomized with argon (or other carrier gas) in the atomizer. After atomization, the sample enters the central area of plasma with high temperature (about 10000K), in which desolvation, steam dissociation and ionization occur. Finally, the sample continues to advance in the form of ions into the mass spectrometer for detection, and finally the qualitative and quantitative analysis results are obtained.

2. Basic composition and common models of the instrument

The basic composition of ICP-MS instrument can be divided into inductively coupled plasma generator part, electromagnetic separation part, detector, vacuum device and sampling cone. The inductively coupled plasma generator includes atomization system and plasma central region, which is composed of high frequency power amplifier tube, coil, concentric quartz tube, atomizer and carrier air source. Electromagnetic separation separation parts, there are many types, such as quadrupole (4 mass filters), single focus, double focus, ion trap, etc. Among them, four-stage bar is the most common, with simple structure, good effect and relatively low cost. A few devices use eight-stage bar as analyser in order to improve spatial resolution. A detector that converts ionic signals into electrical signals. The vacuum device is used to maintain the vacuum state of the detector and the electromagnetic separation part, so that the ions can get as large a free path as possible to facilitate the passage of the separator to the detection device. The sampling cones are generally made of metallic materials. Platinum and nickel cones are common. Platinum cones are relatively expensive but have good corrosion resistance. It can make the ions produced by the plasma generator enter the electromagnetic separator and reduce the electromagnetic interference of the plasma tail flame. The detector is used to convert ion signals into electrical signals.

3. Domestic monitoring project application

3.1 Application of ICP-MS6880 in water quality monitoring

When using ICP-MS method to detect water quality, the main target is trace elements such as zinc and silver in the water. At the same time, the correlation rate is analyzed systematically, and the correlation coefficient is always controlled at 0.9995. In addition, for the accuracy of detection results, the detection range of ICP-MS technique should be controlled within 0.01~4.12μg/L, and the correlation recovery rate should be controlled. This method has the characteristics of less interference, rapid detection speed, accurate and reliable results when used to detect drinking water. At present, up to 31 elements can be analyzed by ICP-MS analysis method (Standard Test Method of Water for Domestic Application), which can be used to monitor drinking water samples, water source water samples and surface water samples. However, there are some problems in the discussion of Standard Test Method for Domestic Water Application, such as the lack of pre-treatment provisions for various samples, the sample analysis process and instrument analysis conditions are not fully described. Moreover, the reference indexes of precision and accuracy of water quality samples provided in this method are also inconsistent with most current surface water samples analysis. In addition, some examples of practical application in recent years are given. Wang Junping et al. determined the contents of Cd, Cr, Pb, Zn, Cu and Ni6 elements in drinking water by ICP-MS method after acidifying the collected water samples with nitric acid and filtering them with filter membrane. Min Guangquan et al. used ICP-MS to systematically analyze and understand trace elements such as Li, Zn and Ag in water. The correlation coefficient was controlled within 0.9995, the detection limit was controlled between 0.01 and 4.12μg/L, and the standard recovery rate was well controlled.

3.2 Application of ICP-MS6880 in soil monitoring

In addition to the detection of elements in water, ICP-MS can also effectively detect chemical elements in soil, so it plays an important role in the field of soil pollution monitoring. When ICP-MS is used to detect the soil, the sample must be dissolved first. The specific method is to add a specific concentration of nitric acid and hydrofluoric acid mixture (the composition of the mixture can be adjusted according to the detected elements) to the sample in a low temperature and low pressure environment, and then use the instrument for detection. With Sc45, In115 and Tl2O4 as the basic elements, ICP-MS was used to measure the metal elements in rice soil and detect the standard substances, which made the test results consistent with the standard requirements. Wang Sina et al. used the mixture of nitric acid, hydrofluoric acid and sulfuric acid for pre-treatment, acid removal and constant volume, ICP-MS detection, optimization of instrument parameters, selection of appropriate isotopes and internal standard elements to eliminate interference, and compared with the national first-class standard elements, it has the advantages of high accuracy, wide linearity and low detection limit.

3.3 Use with other technologies

As mentioned above, ICP-MS is widely used, but there are still some deficiencies in its use. In order to improve these deficiencies, ICP-MS is combined with other technologies. For example, combined with chromatographic technology, combined with laser ablation technology and so on. Among them, it is widely used in combination with high performance liquid chromatography, which has the advantages of efficient separation and detection of similar components (such as the four interferences described above), and can be used in the analysis of material morphology. It is often used in the research of improving column separation effect, multistage combined use, reducing detection limits and other directions.

4. Prospects

Since the emergence of ICP-MS technology in the 1990s, it has been developed for nearly 30 years. Due to the advantages of high efficiency and fast use, and the ability to detect a variety of trace and trace substances at the same time, ICP-MS technology has gradually attracted people's attention. Many advanced technologies such as chromatographic co-use and laser ablation co-use have been developed successively. By 2020, it has also attracted much attention and is a hot research field for researchers. I believe that there will be better research results and application in the future, and it will play a better role.

5. Conclusion

Inductively coupled plasma mass spectrometry is mainly used for simultaneous identification of multiple elements in samples. Its instrument consists of two parts, ICP and MS. ICP is a high temperature ion source with a temperature of 8000K, and MS is a quadrupole fast scanning mass spectrometer. Under the action of high temperature ion source, the samples in the instrument will undergo evaporation, dissociation, atomization, ionization and other processes in the channel, and finally enter the high vacuum quadrupole fast scanning mass spectrometer, where all ions are separated and measured by high-speed sequential scanning. This method is widely used at home and abroad, and a large number of scholars have studied it.