Rapid Analysis of High-Matrix Environmental Samples Using the Agilent 7500cx ICP-MS

Importance of the Topic

The determination of trace elements in environmental samples is critical for regulatory compliance, pollution monitoring, and public health protection. Traditional multi-mode ICP-MS methods require complex optimization and multiple cell conditions, limiting throughput and increasing operational complexity. The Agilent 7500cx equipped with an Octopole Reaction System (ORS) operating in a single helium collision mode addresses these challenges by simplifying interference removal and dramatically improving sample throughput.

Objectives and Study Overview

This study evaluates the capability of the Agilent 7500cx ICP-MS in helium mode to:

• Analyze a complete suite of environmental elements, including mercury and major matrix constituents, in a single analysis mode.
• Eliminate or minimize polyatomic matrix interferences without multiple cell gas exchanges.
• Achieve high throughput (less than 2.5 minutes per sample) across a 12-hour, 300-sample sequence while maintaining accuracy and precision.

Methodology

The analytical protocol involved:

• An initial calibration with blank and standards at 1, 10, 50 and 100 ppb (1 ppb for Hg).
• A sequence of 22 repeated blocks, each containing:
  
  • Certified reference water (NIST 1640).
  • USEPA Interference Check Solution (ICS-A) and a modified spike version (ICS-AB) at 20 ppb.
  • Two high total dissolved solids mineral water samples.
  • Continuing calibration blank (CCB) and continuing calibration verification (CCV) samples after each block.
• No mode switching or recalibration was performed during the 12-hour run.

Instrumentation Used

This evaluation employed a standard Agilent 7500cx ICP-MS with:

• Glass concentric nebulizer (MicroMist) and quartz 2.5 mm torch.
• Nickel sample and skimmer cones.
• ORS operated exclusively in helium collision mode at 5.0 mL/min.
• Plasma conditions: 1550 W RF power, 0.80 L/min carrier gas, 0.23 L/min makeup gas, and 8.5 mm sampling depth.
• Integration time of 0.1–0.3 seconds per isotope, one point each.

Main Results and Discussion

Interference Removal and Sensitivity:

• Helium mode reduced background equivalent concentrations (BECs) and detection limits (IDLs) for key isotopes by an order of magnitude compared to no-gas mode, effectively removing Ar-, Ca-, S- and Cl-based polyatomic overlaps.
• Sub-ppt IDLs achieved for most elements despite minor signal losses from ion–gas collisions.

Calibration Stability and Precision:

• Fifty ppb CCV measurements over 25 replicates remained within ±10% of target, with no calibration failures.
• ICS-AB spike recoveries (20 ppb, 1 ppb Hg) across 44 replicates ranged from 97 to 104%, with RSDs below 5%.
• NIST 1640 certified water analyses (n=44) yielded recoveries of 92–99% for major and trace elements, RSDs typically under 5%.

Throughput and Run-to-Run Times:

• Single helium mode eliminated cell evacuation and repressurization steps required by multi-mode CRC systems.
• Pre-emptive and intelligent rinse functions reduced idle time between samples.
• Measured run-to-run time averaged 2.46 minutes per sample over 300 analyses.

Benefits and Practical Applications

The universal helium mode offers:

• Consistent removal of polyatomic interferences without prior knowledge of sample matrix.
• Simplified tuning and method development by avoiding multiple cell gases.
• High productivity suitable for contract environmental and industrial laboratories requiring rapid turnaround.
• Reliable quantification of mercury, major and trace elements in high-matrix matrices with minimal carryover.

Future Trends and Applications

Advances in collision cell design and software are expected to further reduce analysis times and improve sensitivity. Potential developments include:

• Integration of real-time interference monitoring and adaptive collision gas control.
• Expanded use of helium-only modes for food, clinical and geochemical analyses.
• Further miniaturization and automation of sample introduction to support high-throughput screening and on-site environmental monitoring.

Conclusion

The Agilent 7500cx ICP-MS operating exclusively in helium ORS mode delivers rapid, interference-free multi-element analysis for high-matrix environmental samples. By combining robust interference removal with pre-emptive rinse and stable calibration, the system achieves routine sample throughput under 2.5 minutes, maintaining excellent accuracy and precision over extended sequences.

References

• Wilbur S. Rapid Analysis of High-Matrix Environmental Samples Using the Agilent 7500cx ICP-MS, Application Note 5989-7297EN, Agilent Technologies, 2007.
• Agilent Application Note 5989-6663EN, Performance Characteristics of the Agilent 7500cx ICP-MS.