A Study on the Improvement of Methods for Determining Key Parameters in Iron-Chromium Electrolytes Using Inductively Coupled Plasma Mass Spectrometry
Release time:
2026-08-11
Abstract: This study aims to establish a precise and efficient technical system for the detection of key indicators. By systematically optimizing sample pretreatment procedures and inductively coupled plasma mass spectrometry (ICP-MS) detection conditions, a method for the simultaneous detection of multiple elements was developed using a mixed nitric-hydrochloric acid gradient digestion technique combined with the helium collision cell mode, and incorporating the matrix-matched internal standard method to correct for matrix effects. Experimental results demonstrate that this method effectively addresses interference from polyatomic ions and enables the simultaneous and precise determination of Fe, Cr, and various impurity elements. Its detection performance meets the high-precision and accuracy requirements for electrolyte quality control in industrial production.
As a core functional material in the electrochemical industry, the precise control of the main elements—Fe and Cr—as well as impurity elements such as Cu and Ni in iron-chromium electrolytes directly determines the performance stability and service life of electrochemical products. Traditional detection methods generally suffer from severe matrix interference, long detection cycles, and insufficient detection limits, making it difficult to meet the efficient quality control requirements of modern production. The stability and accuracy of existing detection systems urgently need to be improved. Accordingly, this study focuses on the targeted optimization and application of inductively coupled plasma mass spectrometry (ICP-MS) technology. Through systematic improvements to sample pretreatment procedures and instrument monitoring parameters, we have established a multi-element precision detection system fully adapted to the characteristics of the iron-chromium electrolyte matrix, thereby providing reliable technical support for quality control in related industrial production.
1 Materials and Methods
1.1Equipment and Reagents
Inductively Coupled Plasma Mass Spectrometer (NexION 5000), PerkinElmer, Inc., USA; Ultrapure Water System (UPT-II-20T), Chengdu Ultrapure Technology Co., Ltd.; Intelligent Graphite Digestion System (G8), Beijing Labtech Instruments Co., Ltd.; High-Speed Refrigerated Centrifuge (Centrifuge 5810R), Eppendorf AG, Germany; Pipettes (100–1000 μL), Prandl GmbH, Germany [1]. Iron (1000 μg/mL) and chromium (1000 μg/mL) standard stock solutions, National Analysis and Testing Center for Non-ferrous Metals and Electronic Materials; copper, nickel, silver, bismuth, gold, tin, and palladium standard stock solutions (1000 μg/mL), Tanmo Quality Inspection Technology Co., Ltd.; Nitric acid and hydrochloric acid (analytical grade), Sinopharm Chemical Reagents Co., Ltd.; hydrofluoric acid, Jingrui Electronic Materials Co., Ltd.; internal standard solutions of scandium (Sc), rhodium (Rh), and rhenium (Re) (100 μg/mL), Agilent Technologies, Inc., USA; experimental water was ultrapure water with a resistivity of ≥18.2 MΩ·cm [2].
1.2 Analytical Methods
1.2.1 Sample Preparation
Accurately transfer 5.0 mL of electrolyte sample into a PTFE digestion tube, add 8 mL of a nitric acid–hydrochloric acid mixture (V nitric acid : V hydrochloric acid = 3 : 1), and place the digestion tube in a graphite digestion system for gradient heating digestion. Set the digestion program as follows: 30 min of pre-digestion at 100 °C, 60 min of isothermal digestion at 150 °C, and heating to 180 °C to drive off the acid until the remaining volume of the digest is approximately 1 mL [3]. After the digestion tube has cooled to room temperature, transfer the contents to a 50 mL volumetric flask using ultrapure water, add 50 μL of the internal standard mixture (Sc, Rh, and Re, all at a mass concentration of 10 μg/mL), dilute to the mark with ultrapure water, and shake thoroughly before analysis. For the blank test, replace the electrolyte sample with 5.0 mL of ultrapure water and prepare the reagent blank solution following the same steps described above [4].
1.2.2 Optimization of Testing Conditions
Plasma conditions: RF power 1550 W; plasma gas flow rate 15 L/min; auxiliary gas flow rate 0.8 L/min; atomization gas flow rate 0.95 L/min; sampling depth 8 mm; peristaltic pump speed 30 r/min [5]. Mass spectrometry conditions: Collision reaction cell (CRC) mode was used, with helium as the collision gas at a flow rate of 4.5 mL/min; the detection mode was peak-hopping scan; the dwell time was 50 ms per isotope; three acquisitions were performed for each isotope; and interference-free isotopes were selected for detection (see Table 1).
Table 1: Selection of Target Element Isotopes and Internal Standards
1.3 Calibration Curve and Method Validation
The stock solutions of each element were serially diluted with 5% nitric acid to prepare a series of standard working solutions, with mass concentrations of Fe and Cr ranging from 0.1 to 100.0 μg/mL, and mass concentrations of Cu, Ni, Ag, Bi, Au, Sn, and Pd ranging from 0.001 to 1.000 μg/mL. Using the reagent blank solution as the matrix, prepare a matrix-matched standard solution to correct for matrix effects [6].
1.4 Method Performance Validation
Limit of Detection (LOD) and Limit of Quantification (LOQ): Perform 11 consecutive determinations on a reagent blank solution; calculate the limit of detection as 3 times the standard deviation (3σ) and the limit of quantification as 10 times the standard deviation (10σ) [7]. Precision: Spiked samples at three concentration levels—low, medium, and high—are selected, and each concentration is analyzed in six replicates to calculate the relative standard deviation (RSD) [8].
2 Results and Discussion
2.1 Optimization of Preprocessing Methods
To address the issues of the complex matrix of iron-chromium electrolytes and the interference caused by organic additives, this study compared various acid digestion systems and determined that a mixed nitric-hydrochloric acid system (V nitric acid : V hydrochloric acid = 3 : 1) is the optimal digestion system. This system rapidly breaks down the matrix, effectively preventing the formation of insoluble compounds from chromium while fully dissolving precious metal impurities. Building on this, the temperature and time parameters were further optimized, ultimately establishing a gradient heating digestion program. This program ensures complete sample digestion while minimizing the loss of target elements and ensuring that blank values meet detection requirements.
2.2 Optimization of Instrumental Conditions and Correction for Matrix Effects
2.2.1 Optimization of Collision Reaction Tank Parameters
High concentrations of Fe in iron-chromium electrolytes can easily cause interference from polyatomic ions; for example, 40Ar16O+ interferes with 56Fe+, while Cr faces interference from 40Ar12C+ on 52Cr+. The experiment compared the interference suppression effects of the gas-free mode, helium collision mode, and hydrogen reaction mode. The results showed that the helium collision mode can effectively remove polyatomic ion interference through the kinetic discrimination effect, reducing the proportion of interference signal intensity to below 3% in all cases. This suppression effect was significantly superior to that of the other two modes; therefore, the helium collision mode was selected for subsequent detection.
2.2.2 Effectiveness of the Internal Standard Method and Matrix-Matching Correction
To improve the accuracy of ICP-MS analysis results for iron and chromium electrolytes, this experiment compared the effects of three calibration methods—the external standard method, the internal standard method, and the matrix-matched internal standard method—on the results. Using the determination of Fe and Cu as examples, the external standard method was significantly affected by matrix effects, resulting in large deviations in recovery rates; the external standard method can partially correct for instrument signal drift, resulting in some improvement in recovery rates; whereas the matrix-matched internal standard method combines the dual advantages of matrix matching and internal standard correction, effectively compensating for errors caused by matrix effects and instrument fluctuations. Its recovery rates remained stable within the range of 95% to 105%, demonstrating the optimal correction performance. Therefore, the matrix-matched internal standard method was selected as the final calibration method for this experiment.
2.3 Method Performance Metrics
2.3.1 Linearity and Detection Limit
All target elements exhibited good linear relationships within the specified concentration ranges, with correlation coefficients (r) all greater than 0.9990; the limits of detection and quantification met the requirements for the analysis of iron-chromium electrolyte (see Table 2).
Table 2: Linear Regression Equations, Correlation Coefficients, Limits of Detection, and Limits of Quantification for Each Element
Table 2 lists the linear regression equations, correlation coefficients, limits of detection, and limits of quantification for each element. As shown in Table 2, the linear relationships for each element are excellent, and the limits of detection and limits of quantification meet the testing requirements.
2.3.2 Precision and Accuracy
At the three spiking levels (low, medium, and high), the recovery rates for each element ranged from 89.5% to 110.3%, with relative standard deviations (RSD) all below 5%, meeting the requirements of GB/T 27404—2008, “Laboratory Quality Control Specifications—Physicochemical Testing of Foods” (see Table 3).
Table 3: Precision and Accuracy of the Method (n=6)
As shown in Table 3, this method exhibits good recovery and precision and is suitable for the detection of target elements in iron-chromium electrolytes.
2.4 Application of the Method
Using the established improved method, 20 batches of iron-chromium electrolyte samples were analyzed. The results showed that the Fe content ranged from 45.2 to 58.7 g/L, the Cr content ranged from 8.3 to 12.6 g/L, and the concentrations of impurity elements such as Cu, Ni, and Ag were all below industry control standards. A comparison with the traditional atomic absorption spectroscopy (AAS) method was conducted using three selected samples: For Sample 1, the results obtained using this method were Fe 52.3 g/L and Cr 10.8 g/L, while the AAS results were Fe 53.1 g/L and Cr 11.0 g/L, with a relative deviation of 1.5%–1.8%; For Sample 2, the results obtained using this method were: Cu 0.042 mg/L, while the AAS results were 0.043 mg/L, with a relative deviation of 2.3%. The detection limit of this method is one order of magnitude lower, making it more suitable for the rapid and accurate detection of multiple elements in iron-chromium electrolytes.
3 Conclusion
This study successfully established an improved ICP-MS method for determining key parameters in iron-chromium electrolytes, in which the optimized mixed nitric-hydrochloric acid gradient digestion process enables complete digestion of samples without elemental loss. The helium collision cell mode effectively suppresses interference from polyatomic ions, while the matrix-matched internal standard method significantly reduces the impact of matrix effects. This method is not only simple to operate and highly efficient but also meets industrial testing standards in terms of linearity, precision, and accuracy. It enables the simultaneous and precise determination of both major constituents and impurity elements, providing a reliable technical tool for quality control of iron-chromium electrolytes.
References: Tianjin Chemical Industry; A Study on the Improvement of Methods for Determining Key Parameters in Iron-Chromium Electrolytes Using Inductively Coupled Plasma Mass Spectrometry; Zhu Yangyang, Li Xianrui
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