Physical interference and elimination in ICP spectrometer analysis

Plasma spectroscopy (ICP-OES) has been widely used in laboratories in recent years, and there are more and more researches on plasma analysis methods, and more and more interference with plasma spectroscopy. This article briefly introduces ICP. Object interference in spectrometer analysis.

The interference effect caused by the difference in physical properties of the solution is called physical interference, also known as physical interference, which is mainly caused by the difference in solution viscosity, surface tension and density caused by the analysis of the sample. Mainly manifested as acid effect and salt effect.

1, acid effect

In the ICP spectrometer technology, the sample solution is mainly atomized into an aerosol using a pneumatic atomizer. The atomization injection amount of the pneumatic atomizer and the size of the aerosol particles are related to the physical properties of the sample solution, the standard solution and The sample solution requires the addition of a quantity of mineral acid during the preparation to prevent hydrolysis and precipitation of the analyte. Since the physical properties of various inorganic acids such as viscosity and density are different, the so-called "acid effect" is caused when the amount of addition is different, that is, the difference in acidity value and acid type of the solution will affect the intensity of the line. The acid effect is expressed as the ratio of the intensity of the line in the presence of acid to the intensity of the line in the absence of acid. The mechanism of the acid effect is mainly generated during the injection atomization process. As the acidity increases, the line intensity decreases significantly. The inorganic acid increases the viscosity of the sample, and lowers the rate of increase, resulting in a decrease in the analytical signal. A large number of studies have shown that various elements decrease in signal intensity with increasing acid concentration, and there is an irregular signal change between elements. The concentration of nitric acid and sulfuric acid increased, and the atomic and ion signals of magnesium, calcium, zinc, iron and manganese decreased significantly. When the concentration of nitric acid reached 2 mol/L, the relative signal intensity decreased to 0.7-0.8. . Phosphoric acid has an inhibitory effect on the emission intensity of atomic and ion lines of strontium, magnesium, manganese, iron, copper, zinc, etc., and the signal value decreases as the acid concentration increases. Experiments show that the influence of acid matrix on the analysis signals of manganese and copper indicates that the inhibition rate of 5% to 20% hydrochloric acid is 8% to 10%; the inhibition rate of 5% to 10% is 10% to 13%; 0.5% to 2%. The sulfuric acid inhibition rate is as high as 40%.

The acid effect is mainly attributed to the change of the physical properties of the solution, that is, the increase of the viscosity, which leads to the decrease of the atomizer lifting amount and the reduction of the atomization efficiency. The existence of the peristaltic pump overcomes the influence of the viscosity on the lifting amount.

(2) Salt effect

The physical properties such as the viscosity of the solution increase as the salt content of the solution increases, thereby affecting the injection volume, atomization efficiency, and aerosol transmission rate of the solution and ultimately affecting the intensity of the line. Some data show that with the increase of salt content in the solution and the change of physical properties, the lifting amount of the solution, that is, the intensity of the line gradually decreases, and the effect is very obvious. Forced injection with a peristaltic pump can reduce the fluctuation of the amount of solution lift, but the effect of salt content on the efficiency of the sample and the intensity of the line cannot be eliminated.

Elimination of physical interference

(1) Standard addition method

Changes in the concentration of coexisting elements in a complex sample often cause changes in the background level. The line spectrum and band spectra of the coexisting components and various forms of stray light cause the background signal to move. The standard addition method is a method that can correct the interference and matrix effects without prior knowledge of the spectrum of the sample matrix. The disadvantage of the conventional extrapolation standard addition method is that the background equivalent concentration BEC of ICP is high and unstable.

(2) Matrix matching method

The matrix matching method is a method in which a standard solution used to establish a working curve is matched with a main component concentration and an acid concentration of an analysis sample solution. Because the principal components are similar, the non-spectral interference to the analytical elements is similar. The non-spectral interference of the matrix or principal component can be deducted by the matching method, which is more common in ICP-^ES analysis.

(3) Elimination of acid effect interference

Research to overcome the acid matrix effect has focused on changing the acid-producing factors, such as improving the atomizer and optimizing the spray chamber. Increase the degassing system and the plasma operating parameters of the enhanced state, such as increasing the radio frequency (rf) power.

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