ICP: inductively coupled plasma. But sometimes people may also use the abbreviation ICP instead of ICP-OES and ICP-AES in spoken English. Icp-ms means mass spectrometry by ICP ionization, that is, there are other kinds of mass spectrometry, sometimes referred to as “ICP mass spectrometry”. So how are they different from AAS? How to choose an analysis method?
Conceptual distinction ：
First, the simple distinction between ICP-AES and ICP-OES. OES Optical Emission Spectrometry; Aes-atomic Emission Spectrometry both are inductively coupled plasma Emission Spectrometry, but they are called differently in different periods.It is more scientific and accurate to call ICP-OES because not only atomic but also ion lines are used in plasma emission spectroscopy. Note: Comparison of ICP-OES is made below.
Followed by ICP-OES and ICP-MS. For those who have a background in ICP-OES technology, ICP-MS is a plasma detector (ICP) with a mass spectrometer as the detector, while mass spectrographers think that ICP-MS is a mass spectrometer with an ICP as the source.
Finally, AAS and ICP-MS. AAS is atomic absorption spectrum, because it only uses monochromatic light irradiation in atomic spectrum, so it can only detect the content of one element, but the detection limit is relatively low and the reproducibility is good. ICP-OES is atomic emission spectrum, detection of multiple lines in the atomic spectrum, the detection limit is relatively low, and multi-channel can simultaneously detect a variety of atoms and ions. It’s convenient and reproducible. ICP-MS is ICP mass spectrometry, using mass spectrometry to detect isotope content to detect the content of elements, the detection limit is the lowest, the effect is the most ideal.
Performance difference ：
Application: AAS is used for the detection of known element content; ICP can be used for both known and unknown, and is suitable for multielement analysis. ICP-MS is generally used for standard measurements because it is more expensive and has the lowest detection limit.
1. Detection limit
The detection limit of ICP-MS is very impressive, most of the detection limit of its solution is PPT level (it must be remembered that the actual detection limit can not be better than the cleaning conditions of your laboratory), the detection limit of graphite furnace AAS is subPPB, and the detection limit of most elements of ICP-OES is 1-10ppb. Some elements can also be detected in clean samples with remarkable sub-PPB detection limits.
It must be pointed out that the PPT-level detection limit of ICP-MS is for simple solutions with few dissolved substances. If the detection limit of solid concentration is involved, the advantages of ICP-MS detection limit will be reduced by as much as 50 times due to the poor salt tolerance of ICP-MS. Some common light elements (such as S, Ca, Fe, K, Se) have serious interference in ICP-MS, which will also worsen its detection limit.
2.Interference
These three techniques present different types and complex interference problems, and for this reason, we discuss each technique separately. Interference of ICP-MS: mass spectrum interference, matrix acid interference, double charge ion interference, matrix effect, ionization interference, space charge effect. ICP-OES interference: spectral interference, matrix effect, ionization interference. GFAAS interference: spectral interference, background interference, gas phase interference, matrix effect.
3. Ease of use
In daily work, ICP-OES is the most mature in terms of automation and can be used by unskilled personnel.
The operation of ICP-MS has been complex until now. Although there have been great advances in computer control and intelligent software since 1993, it still needs to be fine-adjusted by technicians before routine analysis. The study of ICP-MS methods is also complex and time-consuming. The routine work of GFAAS is relatively easy, but the formulation of methods still requires considerable skill.
4. Total solid solubility TDS in the sample
In routine work, ICP-OES can analyze solutions of up to 10%TDS and even up to 30% salt solutions. ICP-MS can analyze 0.5% solution in a short period of time, but most analysts are happy to use solutions up to 0.2%TDS. When the original sample is solid, ICP-MS requires a higher dilution ratio than ICP-AES and GFAAS, so it is not surprising that its conversion to the detection limit in the original solid sample does not show a great advantage.
5. Linear dynamic range LDR
ICP-MS has LDR in excess of 105, and various methods can develop LDR up to 108. However, for ICP-MS: high matrix concentration can cause many problems, and the best solution to these problems is dilution. For this reason, the main area of application of ICP-MS is in trace/ultra-trace analysis.
The LDR of GFAAS is limited to 102 ~ 103, and a higher concentration can be analyzed if a subsensitive line is selected. ICP-OES has more than 105 LDR and strong salt resistance, which can be used for the determination of trace and major elements. The concentration of ICP-OES can be determined as high as percentage content. Therefore, ICP-OES plus ICP-MS or GFAAS can meet the needs of laboratory well.
6. Precision
The short-term precision of ICP-MS is generally 1 ~ 3% RSD, which is obtained by using multiple internal standard methods in routine work. Long-term (several hours) precision is less than 5%RSD. Good accuracy and precision can be obtained by using isotope dilution methods, but the cost of this method is too high for conventional analysis.
The short-term precision of ICP-OES is generally 0.3 to 2%RSD, and the long-term precision of several hours is less than 3%RSD. The short-term precision of GFAAS ranges from 0.5 to 5%RSD. The long-term precision depends not on time but on the number of graphite tubes used.
7. Sample analysis ability
ICP-MS has an amazing ability to analyze large numbers of samples for the determination of trace elements, typically in less than 5 minutes per sample, and in some cases in as little as 2 minutes. Our laboratory believes that the main advantage of ICP-MS is its analytical capability.
The analysis speed of ICP-OES depends on whether full-spectrum direct reading type or single-channel scanning type is used. The time required for each sample is 2 or 6 minutes. Full-spectrum direct reading type is faster, usually 2 minutes for each sample.The analysis speed of GFAAS is 3-4 minutes for each element in each sample, and it can work automatically at night to ensure the analysis ability of samples.
8.Unmanned control operation
The ICP-MS, ICP-OES, and GFAAS can operate unattended overnight due to their modern automated design and safety using inert gases.
9. Operating costs
The start-up cost of ICP-MS is higher than that of ICP-OES because some components of ICP-MS have a lifetime and need to be replaced, including turbo molecular pumps, sampling cones and intercepting cones, and detectors. For ICP-MS and ICP-OES, the life of the atomizer is the same as that of the torch.
If the lab has chosen ICP-OES in place of ICP-MS, it is best to have GFAAS in the lab. GFAAS shall calculate the cost of its graphite tubes. Among the above three technologies, the cost of Ar gas is a similar budget, and the Ar cost of ICP technology is much higher than that of GFAAS.
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