Performance of the Agilent 7900 ICP-MS with UHMI for High Salt Matrix Analysis

Significance of the Topic

ICP-MS is the method of choice for trace elemental analysis, but high total dissolved solids lead to signal drift, ionization suppression, space‐charge effects and polyatomic interferences. Extending matrix tolerance to percent‐level salt concentrations is essential for accurate analysis of environmental brines, hypersaline lakes, food salts, clinical fluids and industrial samples.

Objectives and Study Overview

This work evaluates the performance of the Agilent 7900 ICP-MS equipped with an Ultra High Matrix Introduction (UHMI) option and a fourth‐generation Octopole Reaction System (ORS4). The aim was to measure up to 25% NaCl solutions directly, with a single aqueous calibration, and to assess stability, accuracy, precision and detection limits without prior dilution or matrix removal.

Methodology and Instrumentation

Reagents: Reagent-grade NaCl was dissolved in deionized water containing 0.5% HNO3 and 0.6% HCl to prepare matrices from 0 to 25% w/w. Calibration standards were simple aqueous solutions. A mixed internal standard was added on-line. UHMI-100 (~100× aerosol dilution) and ORS4 cell gas in helium and optional hydrogen modes were employed. Key operating conditions included 1600 W RF power, extended sampling depth (10 mm), reduced carrier gas flow (~0.3 L/min), and a secondary argon dilution gas (~0.6 L/min) introduced between spray chamber and torch. Automated autotune optimized lens voltages.

Main Results and Discussion

• Internal standard signals dropped on transition to 25% NaCl but remained stable over four hours, indicating minimal cone fouling and no mass bias.
• Spike recoveries for majors and trace elements including As, Cd, Hg and Pb ranged from 83 to 118% with RSDs below 6% when calibrated against nonmatrix standards.
• Method detection limits in 25% NaCl remained in the sub-µg/L range for most trace analytes despite high dilution.
• Interfered elements (V, Cr, Ni, Cu) showed accurate quantification up to 25% NaCl, demonstrating efficient polyatomic removal in ORS4.
• Analysis of commercial sea and rock salt samples revealed element concentration patterns consistent with geographic origin.

Benefits and Practical Applications

• Direct measurement eliminates labor‐intensive dilution or cleanup, reducing contamination risk and improving throughput.
• Enables routine monitoring of hypersaline environments, food salts, clinical fluids, fish transport waters and oilfield brines.
• Presents an alternative to ICP-OES with lower detection limits and broader elemental coverage.

Future Trends and Opportunities

• Further optimization of reaction cell chemistries to suppress residual interferences and reduce detection limits.
• Extension of UHMI to other challenging matrices such as high‐organic or high‐viscosity samples.
• Integration with high‐resolution ICP-MS and advanced data automation for real‐time monitoring.
• Development of field‐deployable UHMI sampling modules for remote environmental analysis.

Conclusion

The Agilent 7900 ICP-MS with UHMI and ORS4 offers robust direct analysis of samples up to 25% TDS. It overcomes conventional ICP-MS limitations, delivering stable signals, accurate quantification and low detection limits while simplifying the workflow for high‐matrix elemental analysis.

Instrumentation

• Agilent 7900 ICP-MS with UHMI-100 option for up to 100× aerosol dilution
• Fourth‐generation ORS4 collision/reaction cell in helium and hydrogen modes
• Quartz spray chamber chilled at 2 °C and quartz torch with 2.5 mm injector
• Automated autotune and peristaltic pump sample introduction

Reference

1. D Beauchemin J W McLaren S S Berman Spectrochim Acta Part B 42 467–490 1987
2. J W McLaren D Beauchemin T V Voet Can J Spectrosc 30 29A–32A 1985
3. I Rodushkin T Ruth D Klockare J Anal At Spectrom 13 159–166 1998
4. P F Kehr J S Jones D A Fritz D E Harrington W R Bramstedt At Spectrosc 6 128–133 1985
5. W Li F Pan S You Q He D Kang Y Xu Spectrochim Acta Part B 42 853–858 1987
6. L Ebdon A Fisher H Handley P Jones J Anal At Spectrom 8 979–981 1993
7. L Halicz I Gavrieli E Dorfman J Anal At Spectrom 11 811–814 1996
8. F A M Silva C L P Da Silveira N Miekekey I L Kuechler Anal Sci 20 1295–1299 2004
9. T Shih W Chen Y Sun J Chromatogr A 1218 2342–2348 2011
10. A S Buchanan P Hannaker Anal Chem 56 1379–1382 1984
11. S Kagaya S Miwa K Tohda Anal Sci 23 1021–1024 2007