Determination of chloride and sulfate in saturated lithium hydroxide solution

Significance of the Topic

Lithium hydroxide plays a vital role as a feedstock in lithium-ion battery manufacturing and in various industrial processes such as electroplating, pigment production, and cleaning formulations. Accurate quantification of trace chloride and sulfate impurities in saturated lithium hydroxide solutions ensures product quality, supports battery performance, and aids recycling and supplier quality control.

Objectives and Overview of the Study

This work aims to develop and demonstrate a robust method for determining chloride and sulfate in saturated lithium hydroxide solutions. The approach uses reagent-free ion chromatography (RFIC) with a high-capacity anion-exchange column to achieve fast, sensitive, and reliable analysis suitable for industrial and research laboratories.

Methodology

Sample Preparation

• Saturate aqueous solution by dissolving lithium hydroxide monohydrate overnight
• Perform a 10x dilution of the saturated solution with deionized water
• Clean up the diluted sample using an OnGuard II H cartridge to remove matrix interferences

Chromatographic Conditions

• Eluent: 4.5 mM potassium carbonate and 2.0 mM potassium bicarbonate generated electrolytically
• Flow rate: 0.25 mL/min; injection volume: 5 µL (full loop)
• Column temperature: 30 °C; run time: 12 min
• Detection: suppressed conductivity with an AERS 500 carbonate suppressor in recycle mode at 9 mA

Calibration and Detection Limits

• Six-point calibration from 0.02 to 10 mg/L for both chloride and sulfate
• Method detection limits (MDLs) in saturated lithium hydroxide: 0.09 mg/L for chloride and 0.13 mg/L for sulfate

Instrumentation

The analysis was conducted on a Thermo Scientific Dionex ICS-5000+ RFIC system configured with:

• SP/DP Pump module and high-pressure degasser
• EG Eluent Generator module (EGC 500 K2CO3) with EPM 500 pH modifier and carbonate mixer
• DC Detector/Chromatography module with suppressed conductivity cell (AERS 500)
• IonPac AG29-Fast-4µm guard column (2×30 mm) and IonPac AS29-Fast-4µm analytical column (2×150 mm)
• AS-AP Autosampler with 250 µL syringe and 5 µL injection loop

Main Results and Discussion

Chloride and sulfate were resolved in less than 12 minutes with retention times of approximately 3.4 min and 8.1 min, respectively. Calibration curves exhibited excellent linearity (r2 = 0.9992 for chloride and 0.9999 for sulfate). Analysis of the saturated lithium hydroxide sample yielded 1.1 mg/L chloride and 3.2 mg/L sulfate. Precision was confirmed with RSD values ranging from 1 % to 6 %, and spike recoveries ranged from 91 % to 102 %, demonstrating both accuracy and reproducibility.

Benefits and Practical Applications

The presented RFIC method offers rapid throughput, low detection limits, and robust performance in challenging high-pH, high-ionic-strength matrices. It is well suited for quality control in battery material production, recycling facilities, and supplier compliance testing.

Future Trends and Applications

Emerging developments include coupling RFIC with mass spectrometry for enhanced selectivity, miniaturized and portable IC systems for field analysis, and further automation of sample preparation. The method may be extended to other lithium salts and related high-pH process streams.

Conclusion

A sensitive, precise, and accurate RFIC method using a Dionex IonPac AS29-Fast-4µm column was established for chloride and sulfate analysis in saturated lithium hydroxide solutions. The approach meets stringent industrial requirements and supports critical quality assurance needs in battery and chemical industries.

References

1. National Center for Biotechnology Information, PubChem Compound Summary for Lithium Hydroxide.
2. Qi Li et al., Review Article progress in electrolytes for rechargeable Li-based batteries and beyond, Green Energy & Environment, 2016, 1(1): 18–42.
3. Thermo Scientific Application Note 001967: Determination of Inorganic Anions in Saturated Lithium Carbonate Solution, 2023.
4. Thermo Scientific Dionex ICS-5000+ Ion Chromatography System Operator’s Manual.
5. Thermo Scientific Dionex IonPac AS29-Fast-4µm Anion-Exchange Column Product Information.
6. Thermo Scientific Dionex OnGuard II H Cartridges Product Information.
7. Thermo Scientific Dionex Eluent Generator Cartridges Product Manual.
8. Thermo Scientific Dionex AERS 500 Carbonate Suppressor Product Information.
9. Thermo Scientific Application Update 72331: In-Line Sample Preparation for Anion Determination in Sodium Hydroxide, 2017.