10 Difficulties of ICP-MS, have you falled into the trap?---Nanjing binglab

ICP-MS, as the “star equipment” of elemental analysis in the laboratory, can achieve very low detection limit, the standard deviation is only 2-4%, and the determination time of each element is only 10s, which is a great helper for experimenters. However, in the process of using ICP-MS, there will be many problems that cause headaches. Here we sorted out these problems, hoping to help you.

The full name of ICP-MS is Inductively Coupled Plasma Mass Spectrometer, which can be used for qualitative, semi-quantitative and quantitative analysis of one or more elements in material samples. It can determine 90% of the elements in the periodic table, especially good at analyzing metal elements. It, ICP-OES and AAS are three commonly used instruments for chemical element analysis. Among them, the detection limit of ICP-MS is low, and the standard deviation is 2- 4%, the determination time of each element is only 10s, which is very suitable for the 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. Using high-pressure microwave digestion system, MILLSTONE or CEM, etc.

2. Microwave digestion or acid leaching, depending on the sample and elements, for isotopic abundance, leaching is sufficient

3. Depending on the environmental sample, the water sample can be fixed with acid, and the soil is more difficult to do, and microwave digestion is also possible, and different speeds and methods are used according to the different elements.

   
   

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

1. If the parallelism of all element content measurements is not good, it means that there is a problem 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 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 use <20ppb

4. With 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 made by diluting it, and it is better to wash it with alkali

   
   

Ⅵ. Can ICP-MS be used for trace elements in blood samples? The result is always low Fe, the recovery rate of the internal standard Sc is low, and an internal standard cannot be fixed for the determination of elements. For example, 209 is used for Pb today. Internal standard, the quality control value is very good, but the quality control value of Pb done the next day 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 instability of the determination of Pb calibrated by the 209 internal standard, either the mass number of the instrument has drifted, or the hydrolysis of the Bi solution has caused instability.

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

3. I do serums and am still in the method building phase. The literature is made with 10% ammonia water 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 ICPMS is used 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, and 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 I used 6ml of 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 with ultrapure water, the solution became cloudy (other pollution can be excluded) and the solution increased with the added water Increased turbidity. 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.

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 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 inside 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 temperature of the ion source 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.