Trace Elemental Analysis

Elemental analysis is an analysis method to study the characteristic spectral lines absorbed or released by the middle and outer electrons of the measured element atoms when they transition from the ground state to the excited state, which refers to the selection of different analysis and test methods according to the different characteristics of the sample for analysis and testing, so as to obtain the type and content of the elements in the sample, realize the determination of the type and content of elements in the sample, and meet the requirements of customers for element detection.

1. Detection of popular elements

Selenium, carbon, deuterium in water, silicon, stainless steel N, iron, chlorine, coal, alloying elements

2. The element analysis and detection method

1. Atomic absorption spectrometry (AAS): The atomic absorption spectroscopy elemental analysis method is an analysis method based on the absorption intensity of the corresponding atomic resonance radiation lines of the outer layer of the gaseous ground state atom to the ultraviolet light and visible light range to quantify the content of the measured element, which is a method for measuring the absorption of optical radiation by specific gaseous atoms. It has a wide range of applications in geology, metallurgy, machinery, chemical industry, agriculture, food, light industry, biomedicine, environmental protection, material science and other fields. This method is mainly suitable for the analysis of trace and trace components in samples.

2. Spectrophotometry (SP): one is to use the substance itself to measure the absorption of ultraviolet and visible light; The other is to generate colored compounds, i.e. “chromogenic”, which are then determined. Although many inorganic ions are absorbed in the ultraviolet and visible regions, they are generally weaker and less directly used for quantitative analysis. Adding a color developer to convert the substance to be measured into a compound that absorbs in the ultraviolet and visible regions for photometric determination, which is currently a widely used test method.

3. Atomic fluorescence spectroscopy (AFS): an emission spectroscopy method, but it is closely related to atomic absorption spectroscopy, which combines the advantages of atomic emission and atomic absorption analysis methods, and overcomes the shortcomings of the two methods. Atomic fluorescence spectroscopy has the characteristics of simple emission line, higher sensitivity than atomic absorption spectroscopy, wide linear range, less interference, and can be measured simultaneously by multiple elements. Atomic fluorescence spectrometer can be used to analyze 11 elements such as mercury, arsenic, antimony, bismuth, selenium, tellurium, lead, tin, germanium, cadmium and zinc. It has been widely used in environmental monitoring, medicine, geology, agriculture, drinking water and other fields. In the national standard, the atomic fluorescence spectroscopy has been legalized as the first method in the determination standards of arsenic, mercury and other elements in food.

4. Electrochemical method: (anode dissolution voltammetry) The polarographic method of observing or recording the polarographic curve using a cathode ray oscilloscope (see polarographic method and voltammetry). There are two types of this method: linear conjugation oscilloscope polarography and AC oscilloscope polarography method. The former is called single-scan polarography and the latter is called oscillopolography , also known as Helovsky-Forriit;

5. X-ray fluorescence spectroscopy analysis (XRF): It is a method of qualitatively or quantitatively determining the composition of a sample by using the absorption of X-rays by the sample with the change of the composition in the sample and its changes. It has the characteristics of rapid analysis, simple sample preparation, wide range of analyzable elements, simple spectral lines, less spectral interference, sample morphological diversity and non-destructive during measurement. It is not only used for qualitative and quantitative analysis of macroelements, but also for the determination of trace elements, and its detection limit can reach 10-6. Combined with separation, enrichment and other means, up to 10-8. The range of elements measured includes all elements from F-U in the periodic table.

6. Cost control inductively coupled plasma mass spectrometry (ICP-MS): It is the same as the ICP used in atomic emission spectrometer, the main body of which is a torch tube composed of a three-layer quartz casing, the upper end of the torch is wrapped around the load coil, the three-layer tube is passed through the carrier gas, auxiliary gas and cooling gas from the inside to the outside, and the load coil is coupled with a high-frequency power supply to generate a magnetic field perpendicular to the coil plane. If argon is ionized by a high-frequency device, argon ions and electrons will collide with other argon atoms under the action of electromagnetic field to produce more ions and electrons, forming eddy currents. The powerful current generates high temperature, which instantly causes argon to form plasma torches with a temperature of up to 10,000 K. Evaporation, decomposition, excitation and ionization of the sample brought into the plasma torch by the carrier gas is carried out, and the auxiliary gas is used to maintain the plasma in an amount of about 1 L/min. The cooling gas is introduced into the outer pipe in the tangential direction, creating a spiral air flow that cools the inner wall of the outer tube at the load coil with a cooling air flow of 10-15 L/min.

7. Trace analysis, including the determination of the total concentration of trace elements in the sample, and the use of probe technology to determine the distribution of trace elements in the sample or on the surface of the sample, trace analysis has two schemes: one is to separate the main components from the sample, let the trace components remain in the solution; The other is to separate the trace components and leave the main components in solution. In order to improve the separation and enrichment effect, masking techniques are usually applied.

3. The principle of element detection

Elemental analysis is an analysis method to study the characteristic spectral lines absorbed or released by the middle and outer electrons of the measured element atoms when they transition from the ground state to the excited state, and the elemental composition, chemical bonds, atomic content and relative concentration of the sample to be measured can be understood through the analysis of the characteristic spectral lines. Elemental analysis is an indispensable part of component analysis for the preliminary elemental analysis of unconventional components in the sample, auxiliary and corroborative chromatographic analysis.

FTIR: is a tool for characterizing unknowns as a quick and easy tool.

Energy spectrometer: a simple and fast tool for elemental characterization and quantification.

Low-temperature plasma emission spectrometer: an effective tool for elemental quantification.

X-ray fluorescence: fast and accurate analysis of complex compositions and elements in materials.

X-ray diffraction: P method for identifying the composition and structure of substances.

Ion chromatography: Determination of various anions and cations, ion chromatography is a common method for the analysis of anions.