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Fourth, inductively coupled plasma mass spectrometry
Inductively coupled plasma mass spectrometry (ICP-MS) is the newly developed elemental analysis technique
The so-called "plasma" is translated from the English "plasma".
(1) Determination method
1.
(1) Reference substance stock solution: accurately measure appropriate amounts of lead, cadmium, arsenic, mercury, and copper single element standard solutions, and dilute with 10% nitric acid solution to make each 1ml containing 1ug, 1ug, 0.
(2) Series concentration mixed solution: accurately measure the appropriate amount of each reference substance stock solution, dilute it with 10% nitric acid solution to make 0, 1, 5, 10, 20 ng lead, arsenic, and 0, 0.
(3) Preparation of internal standard solution: Precisely absorb an appropriate amount of single element standard solutions of germanium (Ge), steel (In), and bismuth (Bi), and dilute with water to make a mixed solution containing 1 ug per 1 ml
2.
(1) Solid samples: Unless otherwise specified, weigh an appropriate amount of the sample (0.
(2) Liquid samples: According to the sample's matrix, organic content, and element content to be tested, different measurement methods can be selected, such as direct analysis, analysis after dilution or concentration, and analysis after digestion treatment
3.
(2) Matters needing attention
1.
(1) ICP-MS method sensitivity is very high, special attention must avoid contamination and interference due to the reagent blank, the water, introduced in the environment
(2) The interference in ICP-MS measurement can be roughly divided into two types: one is mass spectrometry interference, which mainly includes isobaric, polyatomic ions, double-charged ions, etc.
2.
3.
4.
I 75 As + = I m/z75-(75.
77/24.
23× I 40 Ar 37 Cl +).
.
.
(Equation 13-17)
In the formula, 75.
77 and 24.
23 are the abundance values of the two isotopes of Cl, 35 Cl and 37 Cl, respectively
.
5.
The "memory effect" of mercury The memory effect of mercury is related to the chemical properties of the analyte.
The high concentration of the analyte in the sample may affect the instrument system (such as the sample transmission pipeline, nebulizer, mist, etc.
).
Chemical chamber, plasma torch, etc.
) cause pollution
.
If the sample solution contains high concentration of Hg, it is particularly easy to cause the memory effect of the instrument system, increase the blank value, and cause analysis deviation
.
Generally, a large amount of water or 5% nitric acid solution can be used for continuous washing
.
Through a suitable preliminary screening method, the solution with too high mercury content is fully diluted before ICP-MS analysis is an important means to protect the instrument
.
6.
The extent to which the matrix effect interferes with the matrix effect depends on the absolute amount of the matrix rather than its relative ratio to the analysis element
.
The increase in total solids and total salinity in the sample solution may cause blockage of the sampling cone, resulting in a decrease in ions transmitted to the mass spectrometer, thereby reducing the analyte ion signal
.
The sampling system, mainly the atomizer, must be flushed frequently, and the sampling cone must also be cleaned after a period of use
.
7.
Traditional Chinese medicine injections are mostly clear solutions.
In theory, they can be directly analyzed by ICP-MS.
However, because many injections contain not only Chinese medicine extracts, but also a large amount of co-solvents, the total solid content is relatively high.
The need to adjust pH and adjust isotonicity sometimes contains a large amount of inorganic salts, so it needs to be fully diluted during the determination.
Whether it is necessary to carry out organic digestion and destruction should be investigated and determined by sample recovery test
.
Related links: Determination of lead, cadmium, arsenic, mercury, and copper residues in traditional Chinese medicine (4)