ICP-AES and ICP-MS, AAS method comparison - Database & Sql Blog Articles
With the popularity of ICP-AES, many laboratories are faced with the purchase of an additional ICP-AES, or stay in the original choice of using AAS. Now a new technology ICP-MS has emerged. Although the price is higher, ICP-MS has the advantages of ICP-AES and lower detection limit than graphite furnace atomic absorption (GF-AAS). So how do you judge the applicability based on the analysis task?
ICP-MS is a plasma with a mass spectrometer as a detector. The injection sections and plasma of ICP-AES and ICP-MS are very similar. ICP-AES measures optical spectra (120 nm - 800 nm) and ICP-MS measures ion mass spectrometry, providing information on the atomic mass per atom (amu) in the range of 3-250 amu. Isotope measurements can also be performed. In particular, its detection limit is extremely impressive. The detection limit of the solution is mostly ppt grade, the detection limit of graphite furnace AAS is sub-ppb grade, and the detection limit of most elements of ICP-AES is 1- 10ppb, some elements can also get the detection limit of sub-ppb level. However, due to the poor salt tolerance of ICP-MS, the detection limit of ICP-MS will actually be worse, 50 times larger. Some light elements (such as S, Ca, Fe, K, Se) have serious interference in ICP-MS, and the actual detection limit is also poor. The table below lists the comparison of the detection limits for these methods:
Table 3 Comparison of detection limits of ICP-MS, ICP-AES and AAS methods (ug/L)
The analytical performance of this centralized analysis technique can be compared from the following aspects:
1. Easy to use:
In daily work, ICP-AES is the most mature in terms of automation, and can be used by unskilled personnel to apply the methods developed by ICP-AES experts. The operation of ICP-MS is still complicated until now. Although there have been great advances in computer control and intelligent software in recent years, it is still necessary to make precise adjustments by technicians before routine analysis. ICP-MS method research is also Very complicated and time consuming work. Although the routine work of GF-AAS is relatively easy, the method of formulation still requires quite skilled techniques.
2. Analyze the total solid dissolved amount (TDS) in the test solution:
In routine work, ICP-AES can analyze solutions of 10% TDS, even up to 30% salt solution. In a short period of time, ICP-MS can analyze a 0.5% solution, but in most cases a solution of no more than 0.2% TDS is preferred. When the original sample is solid, ICP-MS requires a higher dilution factor than ICP-AES, GP-AAS, and the detection limit converted to the original solid sample shows no significant advantage.
3. Linear dynamic range (LDR):
ICP-MS has an LDR of more than 105, and various methods allow its LDR to proceed to 108. But no matter what, for ICP-MS: high matrix concentration can cause problems in the analysis, and the best solution to these problems is dilution. Therefore, the main area of ​​ICP-MS applications is in trace/ultra-trace analysis.
The LDR of GF-AAS is limited to 102-103. For example, a sub-sensitive line can be used for higher concentration analysis.
ICP-AES has an LDR of 105 or more and is resistant to salt. It can be used for the determination of trace amounts and major elements. The concentration of ICP-AES can be measured up to a percentage. Therefore, ICO-AES can meet the needs of the laboratory. The need for routine analysis of trace elements.
4. Precision:
The short-term precision of ICP-MS is generally 1-3% RSD, which is obtained by routine application of multi-internal standard method.
The short-term precision of ICP-AES is generally 0.3-1% RSD, and the long-term precision of several hours is less than 3% RSD.
The short-term precision of GF-AAS is 0.5-5% RSD. The long-term precision factor is not the time and the number of times the graphite tube is used.
5. Sample analysis ability:
The analytical capabilities of ICP-MS and ICP-AES are reflected in the simultaneous determination of multiple elements.
The speed of analysis of ICP-AES depends on whether it is a full-spectrum direct-reading type or a single-channel scanning type. The time required for each sample is 2 or 6 minutes. The full-spectrum direct reading type is faster, and a sample is usually measured in 2 minutes.
The analysis speed of GF-AAS takes 3-4 minutes for each element in each sample, and it can be operated automatically by no one to ensure its ability to analyze the sample.
6. Operating costs:
ICP-MS runs at a higher cost than ICP-AES because some components of ICP-MS, such as molecular turbo pumps, sampling cones and interceptors, and detectors have a long life and need to be replaced.
ICP-AES is mainly the consumption of nebulizers and torches. Like ICP-MS, its service life is the same.
GF-AAS is mainly the service life of graphite tubes and their costs.
All three technologies use Ar gas, and the consumption is a considerable cost. The Ar cost of ICP technology is much higher than that of GF-AAS.
It can be seen that these technologies complement each other. No single technology can satisfy all the analysis requirements, as long as one technology is slightly better than the other. The following table is a simple comparison of the analytical performance of the three technologies AAS, ICO-AES, and ICP-MS:
Table 4 Simple comparison of ICP-MS, ICP-AES and AAS analysis performance
According to the concentration of the element to be tested in the analysis solution, if each sample is measured for 1-3 elements, the element concentration is sub- or lower than ppb. If the measured element requirements can be satisfied, GF-AAS is the most. Suitable; if 5-20 elements per sample, the content is sub-ppm to %, ICP-AES is the most suitable; if each sample needs to measure more than 4 elements, the sub-ppb content, and the number of samples It is also quite large, and ICP-MS is more suitable.
It can be seen that ICP-AES is an ideal analytical method and a routine analytical tool that should be configured in the laboratory. If the laboratory chooses ICP-AES instead of ICP-MS, then the laboratory is best equipped with GF-AAS. This configuration meets the needs of general laboratories for primary, secondary, and trace component analysis.
The biggest difficulty that ICP-AES can have in metallurgical analysis applications is how to solve the spectral interference problem. This is also a research topic that needs to be continuously solved in the development of ICP analysis technology.
The matrix effect of the IVP-AES method can be applied to the internal standard method to solve the matrix effect caused by, for example, the spray chamber effect and the viscosity difference between the sample and the standard solution; the background background can be corrected by offline background, and the dynamic background correction is applied. Improving accuracy is also very effective. The biggest interference of the IVP-AES method is spectral line interference, and the number of spectral lines is large and the spectral line interference is also difficult to solve. There are more than 50,000 ICP-AES lines recorded, and the spectral line interference between the elements and the spectral line interference of the matrix are also serious. Therefore, the analysis of certain samples such as steel and metallurgical products must use high-resolution ICP-AES instruments to separate the lines that may interfere. Spectral lines or bands of various molecular particles (such as OH) also interfere with certain low levels of measured elements, affecting the actual detection limits in their sample analysis. Therefore, the instrument of the CCD array detector is used to obtain the spectral line and the adjacent background information accurately and quickly, and the measurement spectrum and the background are synchronously measured, so that the off-peak method can be measured while avoiding the spectral line interference, or The MSF method or the IEC method deducts interference. Selecting the appropriate analytical conditions for each element or adding an ionization retarder (such as an excess of Group I elements) can reduce the effects of easily ionized elements.
summary:
The ICP-AES analysis technique is the most mature in daily work, and can be performed by unskilled personnel using analytical methods developed by ICP-AES technicians. In routine work, ICP-AES can analyze 10% TDS solutions, even up to 30% salt solution. ICP-AES has a linear range of LDR of 106 or more and is highly resistant to salt. It can simultaneously measure trace amounts and major elements. ICP-AES can simultaneously directly measure the concentration of 0.001-60%. ICP-AES plus ICP-MS, or GF-AAS can meet the analytical needs of the laboratory. For the analysis of 5-20 elements for each sample, the content is in the sub-ppm to %, and ICP-AES is most suitable. Thanks to modern automation design and the safety of inert gas, ICP-AES and GF-AAS can be left unattended overnight. Therefore, ICP instruments will become the basic configuration of metallurgical analysis laboratories, and their analytical techniques play an increasingly important role in metallurgical analysis.
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