Determination of Fluorine in Coal with the Sundy SDXNS100 Combustion Ion Chromatography (CIC) According to ISO 11724:2019

Application Notes: SD-XNS-100-001

Abstract

The SDXNS100 high-temperature combustion ion chromatography analyzer was used to determine the fluorine content in coal. The results demonstrated excellent accuracy and high precision, and the repeatability limit met the requirement of ISO 11724:2019. The method detection limit was 0.19 mg/kg and the relative standard deviation (RSD) of all test results was below 1%.

Introduction

ISO 11724:2019 specifies the method for the determination of total fluorine in coal, coke, and fly ash. In this method, the fluorine released by high-temperature combustion is determined by ion-selective electrode (ISE) or ion chromatography (IC). The SDXNS100 high-temperature combustion ion chromatography analyzer complies fully with the requirements of this standard. It combines the high-temperature combustion furnace and the ion chromatograph in a single unit controlled by one software platform, and automates sample injection, water vapor generation, collection of the absorption solution, and calculation of the test results. The basic configuration is shown in Figure 1.

Figure 1. Schematic of the SDXNS100 High-Temperature Combustion Ion Chromatography System

1 Experimental

1.1 Instrument

1.1.1 SDXNS100 High-Temperature Combustion Ion Chromatography Analyzer

Figure 2. SDXNS100 High-Temperature Combustion Ion Chromatography Analyzer

1.2 Reagents and Samples

1.2.1 Certified mixed anion standard solution, 1000 mg/L. 1.2.2 Anion standard intermediate solution, 100 mg/L: transfer 10 mL of the standard solution (Section 1.2.1) into a 100 mL volumetric flask, dilute to volume, and mix thoroughly. 1.2.3 Sodium hydroxide (NaOH), analytical reagent grade. 1.2.4 Absorption solution, 0.025 mol/kg sodium hydroxide: weigh 2 g of NaOH, dissolve it in 500 mL of Grade 3 water (Section 1.2.7), and dilute with water to a final mass of 2000 g. 1.2.5 Oxygen (O₂), 99.99%. 1.2.6 Quartz sand, particle size 30-60 μm. 1.2.7 Grade 3 water in accordance with ISO 3696. 1.2.8 Certified reference material (CRM) of coal. 1.2.9 Eluent, 13 mM KOH.

1.3 Experimental Procedure

1.3.1 Test procedure: weigh approximately 0.25 g of the sample and place it in a crucible. Cover the sample surface with a thin layer of quartz sand (Section 1.2.6). Enter the test method, sample mass, and sample sequence number in the instrument control software, and start the run. 1.3.2 Blank test: before sample analysis, perform a blank with no sample using the same procedure as for the sample test. Before use, ignite the crucible and quartz sand in a muffle furnace at 1000°C for 2 h. 1.3.3 Calibration curve: transfer 0.25 mL, 0.5 mL, 1 mL, 2 mL, and 5 mL of the standard intermediate solution (Section 1.2.2) into separate 100 mL volumetric flasks, dilute each to volume, and mix thoroughly. Analyze the solutions by ion chromatography to obtain concentrations of 0.25 mg/L, 0.5 mg/L, 1 mg/L, 2 mg/L, and 5 mg/L. Plot the calibration curve with concentration on the x-axis and peak area on the y-axis. 1.3.4 Combustion Furnace Operating Conditions Furnace temperature: 1200°C O₂ flow rate: 750 mL/min Water vapor flow rate: 1.0 mL/min Absorption solution: 0.025 mol/kg NaOH solution (Section 1.2.4). 1.3.5 Ion Chromatography Operating Conditions Column temperature: 35°C Analytical column: SH-AP-1, 4×250 mm Guard column: SH-GP-2, 4×50 mm Eluent concentration: 13 mM KOH Injection loop: 10 μL Suppressor: SHY-A-7; Detector: SHD-3.

2 Results and Discussion

Under the conditions specified in ISO 11724:2019, the analytical performance of the SDXNS100 for the determination of fluorine in coal was verified.

2.1 Calibration Curve

The parameters of the fluorine calibration curve are summarized in Table 1.

Table 1. Calibration Curve

2.2 Accuracy and Repeatability

To verify the accuracy of the method and the repeatability limit, three certified reference materials (CRMs) at low, medium, and high concentrations were analyzed. The results are presented in Table 2.

Table 2. Test Results of Fluorine Certified Reference Materials (Unit: mg/kg)

For all three concentration levels, the measured values were within the certified value ranges, and the repeatability limits complied with ISO 11724:2019.

2.3 Stability

To verify the stability of the method, GBW11122 was analyzed six times in succession. The results are summarized in Table 3.

Table 3. Stability (Unit: mg/kg)

  The results show that the range of six consecutive measurements was within the repeatability limit specified in ISO 11724:2019, with an RSD below 1%.

2.4 Method Detection Limit

To determine the method detection limit (MDL), seven consecutive system blanks were analyzed using the same procedure as for the sample test. The MDL was calculated using the formula shown below. The results are summarized in Table 4.

MDL = t_n-1,0.99 × S

Table 4. Method Detection Limit (Unit: mg/kg)

Based on the blank test results, the method detection limit was calculated to be 0.19 mg/kg.

3 Conclusion

The test results show that, under the conditions specified in ISO 11724:2019, the determination of fluorine in coal with the SDXNS100 high-temperature combustion ion chromatography analyzer yielded results within the certified value ranges. The repeatability limits met the requirements of the standard; the method detection limit was 0.19 mg/kg; and the relative standard deviations (RSDs) were below 1%.

4 Innovations and Technical Advantages

4.1 Fully Automated End-to-End Testing Without Manual Intervention

The high-temperature combustion ion chromatography method fully automates the determination of fluorine in coal. The operator only needs to load the sample and enter the sample information to start the test with a single click — no further manual intervention is required. The system can also combust the next sample while the current sample is being analyzed, enabling a continuous workflow and improving laboratory efficiency.

4.2 High-Throughput Fully Automated Analysis with 18-Position Batch Processing

Equipped with an automated quartz boat drive system and an 18-position autosampler, the system runs unattended around the clock, meeting the demanding requirements of high throughput and reliability for large sample batches.

4.3 Full-Process Traceability and Data Compliance

The fully automated workflow minimizes human intervention and eliminates operational errors, ensuring that analytical results are stable, reliable, and traceable. This provides solid support for quality system certification and data auditing.

4.4 Integrated Information Management with Seamless LIMS Connectivity

The system supports seamless integration with a laboratory information management system (LIMS), enabling automated acquisition, uploading, and centralized management of test data. This in turn supports the digital transformation and automation of the laboratory.

The applications of the SDXNS100 high-temperature combustion ion chromatography analyzer are not limited to coal. The instrument is also well suited to quality control of raw materials, intermediates, and finished products, and to compliance monitoring against relevant regulations and standards (e.g., ISO 20999:2026, RoHS, and WEEE). By adjusting the combustion temperature, combustion gas ratio, and absorption solution composition, the method can also be extended to the determination of halogens (F, Cl, Br, I) and sulfur (S) in fuels, lubricants, additives, and other petroleum products, as well as in polymers, flame retardants, textiles, specialty chemicals, catalysts, and waste materials, demonstrating excellent matrix tolerance and method versatility. For more information about the Sundy SDXNS100 High-Temperature Combustion Ion Chromatography Analyzer, please contact us by phone or email.