Determination of ultratrace elements in liquid crystal

Significance of the Topic

Ultratrace determination of metal contaminants in liquid crystal formulations is critical to ensuring the performance and longevity of modern large‐screen display technologies. Even sub‐nanogram‐per-gram levels of impurities can affect electro‐optical properties and yield in semiconductor‐grade materials.

Objectives and Study Overview

This study evaluates the capability of the Thermo Scientific™ Element 2™ High Resolution ICP-MS system to quantify sub-ppt levels of multiple metal elements directly in a liquid crystal matrix. The primary goals are to:

• Demonstrate instrument sensitivity in an organic diluent (propylene glycol monomethyl ether, PGME)
• Identify and resolve matrix‐induced polyatomic interferences using variable mass resolution
• Establish detection limits and accurate quantification via standard addition

Methodology

Liquid crystal samples were diluted 1:20 (m/m) in high-purity PGME and spiked with 500 pg/g rhodium as an internal standard. A standard addition calibration spanning 5–1000 pg/g was performed directly in the matrix. Each element was scanned at low (LR), medium (MR, R≈4000) or high resolution (HR, R≈10000) to identify and suppress interferences without altering operating conditions between scans.

Applied Instrumentation

• Thermo Scientific Element 2 High Resolution ICP-MS
• PFA concentric nebulizer (50 µL/min) with self-aspiration and oxygen addition port
• PFA spray chamber and quartz torch
• 1 mm ID sapphire injector with Pt-tipped sampling and skimmer cones

Key Results and Discussion

Investigation of matrix effects revealed ten out of fifteen elements (Li, Mg, Al, K, Ca, Ti, Cr, Mn, Fe, Zn) suffered significant polyatomic overlaps in LR mode. Medium or high resolution scans successfully separated elemental peaks from interferences such as 40Ar16O+, 12C2+, 12C2H+, and others. For example, at mass 56, a MR scan (R = 4000) resolved 56Fe from 40Ar16O+ and 12C2 16O2.

Sensitivity in PGME exceeded 1×10^6 cps per ng/g In in LR, matching performance in dilute nitric acid. Signal stability over two minutes was better than 1% RSD. Detection limits in PGME ranged from 0.7 to 50 pg/g across the fifteen elements. Standard addition calibrations demonstrated reliable sub-ppt quantification for trace metals such as 52Cr in MR mode.

Benefits and Practical Applications

• Direct analysis of liquid crystal samples without extensive matrix removal or chemical modification
• Flexible resolution settings to eliminate spectral interferences for accurate quantification
• High sensitivity in organic solvents enabling low detection limits and robust signal stability
• Rapid turnaround with all elements measured within five minutes under constant conditions

Future Trends and Potential Applications

Advances in high‐resolution mass spectrometry and inert sample introduction techniques will expand ultratrace analysis to more complex organic and polymer matrices. Integration with automated dilution and high‐throughput workflows may support real‐time monitoring of contamination in semiconductor and display manufacturing. Further development of software algorithms for interference prediction could streamline resolution selection and data processing.

Conclusion

The Element 2 HR-ICP-MS combined with PGME dilution provides a fast, sensitive, and interference‐free method for quantifying sub-ng/g metal contaminants in liquid crystal samples. Variable mass resolution and low detector noise enable accurate multi‐element analysis without reoptimization, making this approach highly suitable for quality control in advanced display and semiconductor applications.