EDS
The Energy Dispersive System tells the specific element by analyzing the energy of electron-hole pairs. It consists of electron gun, detector, amplifier, and multi-channel analyser (MCA), as shown in Figure 1 [1].
Figure 1. The work flow of EDS accompanied by TEM [1]
EDS works based on the interaction between the electrons and the sample to provide characteristic x-ray and identify the element, as shown in Figure 1. The electrons with sufficient energy collide and eject an inner-shell electron, then an outer-shell electron fills the hole and releases the characteristic x-ray. Then the x-ray is captured by the detector, converted, amplified, and displayed on the screen [1].
EDS is applicable to both qualitative and quantitative analysis for the characteristic x-ray is specific to target material and related electron shells. By measuring the energy and wavelength, the Indium can be identified qualitatively. Additionally, the measured x-ray intensity is proportional to the number of Indium atoms, thus, by measuring the intensity, the amount and the purity of the Indium can be observed [1]. The input energy decides the resolution of EDS, ranging from 130eV to 5.9keV [1].
Figure2. EDS spectra of Indium deposited on glass [2]
The Indium EDS spectra reflects its characteristic x-rays of electron transitions from M to L (Lα) and from N to L (Lα), as shown in Figure X+1. To avoid overlapping between different elements, multiple peaks are used to identify. According to the relation between wavelength and accelerating voltage U,
where h is Plank’s constant, m is the electron mass, and e is electron charge, the wavelength of Lα transition is longer than that of Lβ transition, in accordance with the lowest energy rule. According to the intensity, Lα transition is the majority transition.
ICP
The structure of ICP-MS is shown in Fig. 2. Ions produced by the ion source are first transferred through the sampling interface. Then, the ions are converged into the mass spectrometer through the ion lens. The ions can be sorted by mass due to different atomic masses with the mass spectrometer. Finally, the sorted ions are detected by the detector.
Figure 3 ICP-MS Structure [3]
There are three working modes of ICP-MS which are collision cell technology (CCT), conventional XS-, and cool plasma mode. Each mode is suitable for different element detection. The target element, precision, and detection limit (DL) can be seen in Table 1.
Table 1. Detected elements, precision, and detection limit of each working mode [3]
The impurity contents were shown in Table 2 which accounted for < 1% in the indium sample.
Table 2. Impurity content in the indium (Unit: μg·g-1) [4]
GFAA
Figure 4. Schematic diagram of spectrophotometry
GFAA, which is designed for qualitative analysis and quantitative measurement of the indium composition, includes two parts, the dissolution of indium and spectrophotometry. Dissolution uses Fe3+ to react with In3+ in the In(NO3)3 solution and form the complex anion [InBr4]-, which generates an ion-associated complex with MIBK. Spectrophotometry measures the absorbance of light at specific wavelengths (325.6, 303.9). Figure 5. Indicates the schematic diagram of spectrophotometry. The characteristic spectral lines emitted by the indium hollow cathode lamp are selectively absorbed, which is proportional to the mass concentration of indium in a certain range.[5]
Figure 5. Flow chart of GFFA
The whole procedure is divided into three steps as shown in Figure 6. Digestion obtains the measurable In elements. In the Graphite furnace, indium ground state atomic vapour was formed after drying, ashing and atomisation. Ultimately, absorbance is analysed to obtain the concentration of indium in the calibration steps.[6]
GFFA has the advantages of strong selectivity and high sensitivity. With the addition of a matrix modifier (palladium nitrate-magnesium nitrate mixed solution), the relative standard deviation of the test method can reach less than 10%. As seen in Table 3, the more than 93% recovery rate presents a high measurement accuracy.
Table 4. Measuring range, precision, and accuracy of GFFA [7]
Figure.6 The relationship between the concentration and the absorbance
C: concentration of sample
x: concentration of sample on the calibration curve
y: concentration of standard solution on the calibration curve
s: concentration of standard solution
Reference
[1]NXC5015 Electron Diffraction.pd
[2]X, Lu. J, Li. M et al. Hierarchically ZnIn2S4 nanosheet-constructed microwire arrays: Template-free synthesis and excellent photocatalytic performances, Nanoscale, vol:10, January 2018, pp: 4735-4744
[3] Hitachi-hightech.com. 2021. Principle of ICP Mass Spectrometry (ICP-MS): Hitachi High-Tech GLOBAL. [online] Available at: <https://www.hitachi-hightech.com/global/products/science/tech/ana/icp/descriptions/icpms.html> [Accessed 20 May 2021].
[4] Qin, Z., 2009. Application of inductively coupled plasma mass spectrometry in the analysis of high purity indium impurities. [online] Available at: <https://kns.cnki.net/kcms/detail/detail.aspxdbcode=CMFD&dbname=CMFD2010&filename=2009241037.nh& v=rY0z4lj7mBNHztGtJtV3DML%25mmd2Bor7GDlHK4Um5vNFjZx3Vb61TPZcvb%25mmd2FfeQcSYLAzq> [Accessed 20 May 2021].
[5] Krawczyk-Coda, M., & Stanisz, E. (2018). Low cost adsorbents in ultrasound-assisted dispersive micro solid-phase extraction for simultaneous determination of indium and nickel by high-resolution continuum source graphite furnace atomic absorption spectrometry in soils and sediments. Analytical Methods, 10(23), 2681-2690.
[6] Ganure, K. A., Shinde, B. L., Mandle, U. M., Dhale, L. A., Tigote, R. M., & Lohar, K. S. (2021). Synthesis, structural and magnetic properties of Ni2+ and In3+ doped cobalt ferrite and application as catalyst for synthesis of Bis- (Indolyl) methane derivatives. Materials Today: Proceedings.
[7] Wang, Y., Dong, J., Luo, Y., Tang, J., Lu, H., Yu, J., ... & Chen, Z. (2017). Indium tin oxide coated two-mode fiber for enhanced SPR sensor in near-infrared region. IEEE Photonics Journal, 9(6), 1-9.