Analytical characteristics of ICP spectrometer

The plasma is generally a neutral gas composed of ions, electrons, central atoms and molecules, and its positive and negative charge densities are almost equal. Usually, it is composed of a high frequency generator, a plasma torch and an atomizer. The function of the high frequency generator is to generate a high frequency oscillating magnetic field that supplies plasma energy. The plasma torch consists of a three-layer concentric quartz glass tube (also made of other materials). A cooling gas Ar is introduced into the outer tube to prevent the plasma torch from burning out the quartz tube. The middle quartz tube outlet is made into a horn shape, and Ar is introduced to maintain the plasma. The inner quartz tube has an inner diameter of 1-2 mm, and the sample aerosol is introduced into the plasma from the inner tube by a carrier gas (generally Ar). The use of the monoatomic inert gas Ar lies in a compound which is stable in nature and does not form a hard dissociation with the sample, and its spectrum is simple.

After the plasma torch is formed, a carrier gas is introduced from the inner tube to form a passage in the axial direction of the plasma torch. Since the plasma flame is in a ring structure, it is advantageous for the sample aerosol supplied by the atomizer to be injected from the plasma center channel and to maintain the stability of the flame; the lower carrier gas flow rate (<1 L/min can penetrate) ICP, the sample stays in the central channel for 2~3ms, can be completely evaporated and atomized; the high temperature of the central channel of the ICP ring structure is higher than the temperature of any flame or arc spark, and is the optimal excitation temperature of atoms and ions. The analyte is indirectly heated in the central channel, which affects the ICP discharge properties. The ICP source is a light source with a small self-priming phenomenon and no electrode discharge and no electrode contamination. These features make the ICP source excellent. The analytical performance is in accordance with the requirements of an ideal analytical method. Therefore, the ICP emission spectrometer analysis has the following excellent analytical characteristics:

1) The ICP spectrometer analysis method is firstly an emission spectrum analysis method, which can be simultaneously determined by multiple elements. Whether it is multi-channel direct reading or single-channel scanning equipment, a large number of elements (30--50 or even more) can be simultaneously measured in the same sample solution. Up to 78 analytical elements have been reported in the literature, that is, all elements except argon, all elements present in nature, have been reported by ICP emission spectrometry. In practical applications, not all elements can be easily measured by ICP-AES. Some elements are more effective by other methods, although ICP spectrometry is still the most effective method for elemental analysis.

2) The linear analysis range is wide. The analyte is ionized and excited in a lower temperature intermediate channel, which eliminates the self-priming phenomenon of general emission spectroscopy due to the high ambient temperature. In a certain high concentration (the concentration of a typical element of several hundred μg / mL solution), the working curve can still maintain a straight line; while the low content (0.0Xμg / mL or less) can extend the working curve downward due to the low detection limit . Therefore, the linear range of the working curve can reach 5 to 6 orders of magnitude, and the mass concentration of the element to be tested is generally in a good linear relationship below 1000 μg/L. For ICP direct reading spectroscopy, primary, low and trace elements can be analyzed simultaneously.

3) The ICP spectrometer has high evaporation, atomization and excitation capabilities, and the interference level is relatively low. Due to the abnormally high temperature of the plasma source, chemical interference and matrix interference of the general analysis method can be avoided, and the interference level is relatively low compared with other spectral analysis methods. The temperature of the plasma flame is higher than that of a general chemical flame, and can atomize and excite elements that are difficult to be excited by a general chemical flame, so that it is advantageous for the measurement of difficult-to-excite elements. Further, it is difficult to form a refractory metal oxide in the Ar atmosphere, so that the effects of the matrix effect and the coexisting element become inconspicuous. The self-priming of the ICP source is very low, and the linear range of the calibration curve can be as much as 5-6 orders of magnitude. In most cases, the elemental concentration is simply linear with the measured signal. Therefore, manually prepared calibration solutions can be used in many cases. Under certain conditions, the difficulty of strictly matching the reference sample can be reduced, and the internal standard method can generally not be used. The ionization interference of the Ar-ICP source is small, and even if there is an easily ionized K or Na in the sample, the reference sample does not have a component matching K or Na. In the flame atomic absorption spectrometry, when analyzing Na, it is necessary to add a large amount of K to suppress the ionization interference of Na. Low interference levels and high analytical accuracy are among the most important advantages of ICP spectroscopy. It can measure both low-concentration components and high-concentration components at the same time. It is a very valuable analytical property to fully utilize the ICP spectrometer to analyze the simultaneous determination of multiple elements.

4) ICP spectrometer analysis can directly analyze samples in different states. The superiority of the analysis of the liquid sample is obvious. For the analysis of the solid sample, the required sample preparation is less, and only the sample is dissolved to prepare a solution of a certain concentration. By dissolving the solution into a solution and analyzing it, not only the structural interference and non-uniformity of the sample can be eliminated, but also the preparation of the standard sample is facilitated.

5) Most elements have good detection limits. The high temperature and ring structure of the ICP torch allows the analyte to be fully preheated, devitrified, atomized, ionized and excited in an intermediate channel of about 1-3 mm in diameter; causing most of the elements in the periodic table to be in aqueous solution. The detection limit is 0.1-00 ng/ml, and if it is expressed by mass, it is about 0.01-10 μg/g, which is similar to the classical spectroscopy. However, for refractory elements and non-metallic elements, ICP spectrometry has a better detection limit than classical spectroscopy.

6) There are many wavelengths to choose from. Each element has several wavelengths for measurement and sensitivity, so ICP. AES is suitable for the determination of ultra-micro components to constant components.

7) High precision of analysis. The analyte is carried into the intermediate channel by the carrier gas, which is equivalent to atomization, ionization and excitation in an electrostatic screen region. The change of the analyte composition does not affect the plasma energy change, ensuring a high Analyze precision. When the analyte concentration is greater than or equal to 100 times the detection limit, the relative standard deviation (RSD) of the assay is generally in the range of 1-3%. Under the same circumstances, the RSD of a general arc and spark source is about 5 to 10%. Therefore, ICP spectrometry is superior to classical arc and spark spectroscopy, so it can be used for precision analysis and analysis of high content components.

8) Large or simultaneous multi-element measurement capability. At the same time, multi-element analysis capability is a common feature of emission spectroscopy, which is unique to non-ICP emission methods. However, due to the serious influence of the sample composition on the classical spectroscopy, it is difficult to simultaneously quantify the various components in the sample, the matching of the reference sample, the selection of the reference element, and the fractionation effect and the pre-ignition effect. The line intensity - the change in the time distribution curve, cannot be performed in sequential multi-element analysis. ICP spectroscopy, because of its high stability with low interference and time distribution and a wide linear analysis range, makes it easy to perform simultaneous or sequential multi-element measurements. Simultaneous determination of multiple elements, such as multi-channel spectrometer can complete the analysis of 30-40 elements in just 30s, and only consume 0.5mL of test solution.

9) The limitations and disadvantages of the ICP spectrometer analysis method are that the equipment cost and operation cost are high, the sample generally needs to be converted into a solution in advance, and the sensitivity of some elements (such as ruthenium) is rather poor; the matrix effect still exists, the spectrum Interference is still unavoidable and argon consumption is large. The field of application of the ICP-AES method has been rapidly expanded. There are more measurable elements than any similar analysis method, and it is certain that there is no simultaneous analysis method that can match it.

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