Analysis of Four Elements (Ca, Mg, Si, Sr) in Brine Using the Agilent 5100 ICP-OES

Significance of the Topic

The control of calcium, magnesium, silicon and strontium in sodium chloride brine is critical for the chloralkali industry. Impurities compromise membrane cell performance and product purity. Reliable trace-level analysis supports ion exchange efficiency, process optimization and cost savings in large-scale electrolysis operations.

Objectives and Study Overview

This application note evaluates the performance of the Agilent 5100 VDV ICP-OES for determining Ca, Mg, Si and Sr in brine at different purification stages. Three sample types were collected:

• Type A: incoming brine to the first ion exchange column
• Type B: incoming brine to the final purification column
• Type C: effluent from the final purification column

The goal was to assess method sensitivity, accuracy, repeatability, and purification efficiency across the treatment sequence.

Methodology and Sample Preparation

Brine samples (30 % NaCl) were diluted 1:2 with ultrapure water. Matrix effects were addressed using the method of standard additions due to the lack of high-purity NaCl for matrix-matched standards. Three replicates of each sample type were collected over three days. Standard additions covered concentration ranges appropriate for each element in each sample type.

Instrumentation Used

The Agilent 5100 VDV ICP-OES was employed in axial plasma viewing mode with a vertically oriented torch and solid-state RF generator (27 MHz). Key components and operating conditions:

• Seaspray glass concentric nebulizer with cyclonic spray chamber
• 1.8 mm i.d. injector torch
• RF power: 1.35 kW; plasma gas flow: 13.5 L/min; auxiliary gas: 1.1 L/min; nebulizer gas: 0.7 L/min
• Sample introduction by Agilent SPS 3 autosampler; two-tube pump configuration
• Read time: 10 s; replicates: 3; stabilization delay: 15 s; rinse: 40 s with 2 % HCl
• Selected wavelengths: Ca 396.847 nm; Mg 279.553 nm; Si 288.158 nm; Sr 407.771 nm

Main Results and Discussion

Calibration curves exhibited excellent linearity (correlation coefficients near 1.000) at low µg/L levels in diluted brine. Purification efficiencies on Day 1 showed:

• Ca reduced from ~1100 µg/L to ~6 µg/L
• Mg reduced from ~4.8 µg/L to ~0.9 µg/L
• Sr reduced from ~820 µg/L to ~3.8 µg/L

Spike recovery tests on sample C3 yielded recoveries within ±2 % for all elements. Repeatability over 50 measurements of spiked C2 showed RSD values below 6 %. Analysis throughput was 115 s per sample with 36 L argon consumption, demonstrating robust productivity.

Benefits and Practical Applications

The vertical torch design with SSRF ensures a stable plasma for high dissolved-solid matrices without an argon humidifier. Minimal sample preparation (2× dilution) and the standard addition approach overcome matrix challenges. The method supports routine process monitoring, early detection of ion-exchange breakthrough and quality control in chloralkali plants.

Future Trends and Opportunities

Advances in solid-state RF technology and enhanced detector sensitivity may further lower detection limits and increase throughput. Coupling ICP-OES data with real-time process analytics and AI-driven monitoring could enable predictive maintenance of purification systems. Expanded element panels could address emerging impurity concerns in evolving electrochemical industries.

Conclusion

The Agilent 5100 VDV ICP-OES delivers accurate, sensitive and repeatable analysis of trace Ca, Mg, Si and Sr in brine. Its robust plasma handles high salt loads with minimal maintenance. The method of standard additions ensures reliable quantification without complex sample pre-treatment, making it an effective tool for chloralkali process control.

Reference

Benefits of a vertically oriented torch—fast, accurate results, even for your toughest samples, Agilent publication, 5991-4854EN (2016).