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Do you know the 10 most difficult aspects of ICP-MS?---Nanjing Binglab

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Do you know the 10 most difficult aspects of ICP-MS?---Nanjing Binglab

CEM microwave digestion vessels are specialized laboratory equipment used to prepare samples for analysis


ICP-MS is an inductively coupled plasma mass spectrometer that can be used for the qualitative, semi-quantitative and quantitative analysis of one or more elements in a material sample, and is capable of determining 90% of the elements in the periodic table.


Especially good at the analysis of metal elements. He, ICP-OES and AAS are three commonly used instruments for chemical element analysis. Among them, the detection limit of ICP-MS is low, the standard deviation is 2-4%, the measurement time of each element is only 10s, which is very suitable for simultaneous determination and analysis of multiple elements.


The following summarizes the common problems in the use of ICP-MS, hoping to serve as a reference:

Ⅰ. For environmental samples, what are the faster pretreatment methods for ICP-MS detection?

1, adopt high-pressure microwave digestion system, MILESTONE or CEM, etc.;


2. Microwave digestion or acid leaching, depending on the sample and elements, if it is used for isotope abundance, leaching is enough;


3. It depends on the environmental sample. Water samples can be fixed with acid. Soil is more difficult to do, and microwave digestion is also possible. Different speeds and methods are used according to the different elements.


Ⅱ. When using ICP-IES to measure the metal content in the soil. Use a microwave digestion instrument for pretreatment. Air-dry the soil first, then grind it into powder, and then sieve it. After weighing about 0.2g, there is no solid after digestion, but the test results of the two parallel samples are very poor, What is the reason for the relative deviation reaching 200%?

1. If the parallelism of all element content measurements is not good, it means that there has problems in the sample preparation or digestion process. If it is an individual element, such as iron, it may be caused by pollution;

2. It is possible that the sample is not uniform;

3. The microwave digestion process is likely to cause poor parallelism.


Ⅲ. ICP-MS is not effective in measuring food samples. How can it be applied well? When measuring arsenic, lead, selenium, copper, selenium, etc. in food samples, do they interfere with each other?

1. Arsenic\Selenium should use CCT (or DRC);

2. How is your standard curve (r-value)? If the content of Cu in the sample is relatively high, you can consider Cu65 measurement, As should consider the interference of ArCl75, apply CCT (or DRC), and Se is easy to escape during the sample digestion process;

3. As75 should pay attention to the interference of ArCl, if the CL is very high, it is difficult to use mathematical correction method;

4. Se82 has low sensitivity, As75 has interference, and 7500a has no collision reaction cell. These two elements are not easy to measure. It is better to use atomic fluorescence to measure these two elements, and other elements should be fine;

5. For sample processing, use a microwave digester, nitric acid plus hydrogen peroxide, and digest under high pressure. Se and As should be injected into ICP-AES or AFS with a hydride generator, and ICP-MS is not suitable.


Ⅳ. Is there any good way to clean the system when ICP-MS is doing Hg?

1. Add some gold (Au) compounds to the cleaning solution, Au and Hg are easy to combine to form a complex;

2. The general concentration is 10ppm, so that the residue of Hg can be better cleaned;

3. Do not use ICP-MS as mercury with high concentration, mercury is easy to volatilize, generally it is better to operate <20ppb;

4. Use 0.1% mercaptoethanol;

5. Alkaline solution is an empirical solution, and the effect is better.


Ⅴ. How effective is ICP-MS in measuring Hg? What is the detection range?

1. The range of Hg measured by ICP-MS can be as low as ppt level, but the sample treatment and medium are very important, otherwise the deviation will be large, and the memory effect will be large; Hg measurement is very troublesome, mainly for memory, and it is effective to wash with alkaline solution;

2. Generally speaking, it is better to make about 10ppb or less, because the memory effect is very large, and it takes a long time to clean after finishing. It can be done with dilute, and it is better to wash with alkali.


Ⅵ. Can ICP-MS be used for trace elements in blood samples? The result of Fe is always low, the recovery rate of the internal standard Sc is low, and an internal standard cannot be fixedly selected for the determination of elements. For example, 209 is used as the internal standard of Pb today, and the quality control value is very good, but the next day The quality control value for Pb is much lower. what reason?

1. The blood sample focuses on the digestion process. Generally, the influence of the matrix is not too great. If Fe is made with a cold flame, the ionization of Sc itself is not good, and the signal is not very stable. As for the unstable determination of 209 internal standard calibration Pb, or the mass number of the instrument has drifted, or the hydrolysis of the Bi solution causes instability.

2. The blood sample is directly diluted for measurement, the organic matter is not digested, and the viscosity is relatively high, which leads to serious memory effect in the sampling pipeline and poor measurement effect; HNO3 should be used to block and dissolve the sample to digest organic matter, so that the dilution factor can be reduced and the test effect is good;

3. The literature is made with 10% ammonia and EDTA, adding 0.01% TritonX-100, adding 1.5% n-butanol to the diluent will be better for As and Se;

4. No precipitation with 1% nitric acid, but poor day-to-day precision for many elements.


Ⅶ. How to deal with samples when using ICPMS to measure heavy metals in seawater? Including sample dilution, mass number selection, etc.

1. Acidification, over-membrane. Note that nitric acid and utensils must be clean. It is recommended to use redistilled nitric acid. Generally, ten-fold dilutions are used;

2. You are measuring heavy metals, whether it is ORS, DRC, or CCT, the effect is not too great. The effect of the reaction cell is better for mass numbers below 85. cd111 will be interfered by oxides such as MOZr, you can edit the correction equation, Pb application 206+207+208, Hg 202;


Ⅷ. When used 6ml nitric acid to pre-treat PP plastic in a microwave digester, the digestion solution was very clear, but when it was transferred into a volumetric flask and added ultrapure water, the solution became turbid (other pollution can be excluded). With the addition of water Increasing solution turbidity increases. The acidity of the final solution is about 6%. What is the reason? How to solve it?

1. It may be that some substances have different solubility under different acidity after digestion. You can add a certain amount of water first, and then filter, the filtrate should no longer be turbid, pay attention to wash the filter paper several times and then make it to volume;

2. It turns out that when digesting biological samples, if the digestion is not complete, turbidity will appear when adding water. You can try to increase the amount of acid to see if it is not completely digested;


Ⅸ. Recently, ICP is used as ore sample, and the linearity measured by the standard addition method is not bad, but the working curve measured by the internal standard method is not very good. And many quantitative analyzes use the internal standard method. Are there many using the standard addition method?

1. The standard addition method can well overcome the problem of matrix matching. The matrix of the ore sample is more complicated, so it is better to use the standard addition method. For samples with a simple background, the internal standard method is simpler;

2. If you use the internal standard method, you must first ensure that your sample matrix does not contain the element you choose as the internal standard;

3. I personally think that the internal standard method is the first choice, and the standard addition method is used if the matrix cannot be overcome. Too much trouble, if there are too many samples, there will be no way;


Ⅹ. Organic mass spectrometers prohibit inorganic things from entering, because inorganic salts are not volatile and will contaminate the mass spectrometer. So how does inorganic mass spectrometry overcome this problem?

1. The sample processing of inorganic mass spectrometry is generally digested, and there are very few organic residues, which will be completely decomposed after ICP;

2. Inorganic mass spectrometers enter very few ions into the instrument and are quickly pumped out by the vacuum system. Of course, if the sample with high matrix is used for a long time, the interior of the instrument will still be polluted. At this time, it is necessary to clean the quadrupole and ion lens;

3. The ability of all mass spectrometers to tolerate salt is limited. The ion source temperature of organic mass spectrometry and inorganic mass spectrometry is different. The ion source temperature of organic mass spectrometry is low, and inorganic salts cannot be decomposed, so the deposition phenomenon will be very serious. The high-temperature source of inorganic mass spectrometry can dissociate most inorganic compounds, but some oxides will still be deposited near the cone, so the interface needs to be cleaned frequently.


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