Performance Characteristics of the Agilent High Matrix Sample Introduction (HMI) Accessory for the 7500 Series ICP-MS

Significance of the Topic

The analysis of trace elements in samples with high dissolved solids content poses challenges for conventional ICP-MS due to matrix suppression, interferences, and instrument instability. The Agilent High Matrix Introduction (HMI) accessory aims to address these limitations by enabling direct analysis of samples with up to 1% total dissolved solids without dilution, improving robustness, sensitivity, and reliability.

Objectives and Study Overview

This study evaluates the performance of the Agilent 7500 ORS ICP-MS equipped with the HMI accessory. Key goals include assessing plasma robustness via CeO+/Ce+ ratios, matrix suppression effects, signal stability, and interference reduction in high-matrix samples compared to standard ICP-MS operation.

Methodology

The HMI system introduces an online aerosol dilution approach by reducing nebulizer gas flow and adding a dilution gas line between the spray chamber and torch injector. This lowers the sample aerosol load while maintaining carrier gas flow, generating a hotter, more robust plasma. Performance was tested using undiluted seawater standards, zinc matrix ramps, extended sample sequences, and molybdenum interference on cadmium.

Used Instrumentation

• Agilent 7500 ORS ICP-MS
• High Matrix Introduction (HMI) accessory with modified torch assembly
• Digital 27 MHz RF generator
• Wide-diameter (2.5 mm) torch injector and reduced-flow nebulizer

Main Results and Discussion

• Plasma robustness improved to CeO+/Ce+ ratios of 0.2% (HMI) versus 1%–2% in standard mode.
• Matrix suppression in undiluted seawater was nearly eliminated, with signal recoveries close to 100% even for elements with high ionization potentials.
• Zinc matrix up to 10,000 ppm caused less than 20% signal loss across the mass range without internal standards, and no mass-dependent suppression.
• Internal standards remained stable (<±10% variation) over 150 consecutive samples of high-matrix solutions.
• Lower oxide levels reduced molybdenum oxide interference on cadmium, enabling accurate measurement of 1 ppb Cd in matrices with up to 5 ppm Mo.

Benefits and Practical Applications

The HMI accessory eliminates the need for conventional sample dilution, reducing preparation time, contamination risks, and waste volume. Its enhanced robustness and simplified internal standardization make it suitable for a wide range of high-matrix analyses, including:

• High-purity metals and RoHS compliance testing
• Undiluted seawater and high-TDS groundwater
• Soil digests and landfill leachate (TCLP)
• Food and pharmaceutical matrices
• Geological samples and HPLC-ICP-MS with saline buffers

Future Trends and Potential Applications

Advances may include integration of automated aerosol dilution control, expansion of HMI technology to other ICP-MS platforms, and real-time process monitoring in industrial and environmental settings. Further research could explore nanoparticle characterization and coupling with advanced separation techniques.

Conclusion

The Agilent HMI accessory significantly enhances the robustness and accuracy of ICP-MS for high-matrix samples by coupling aerosol dilution with optimized plasma conditions. It streamlines workflows, minimizes maintenance, and broadens the applicability of ICP-MS to challenging sample types without compromising sensitivity.