Agilent ICP-MS Journal (January 2020, Issue 79)

Importance of the topic

The reliability of ICP-MS and ICP-QQQ analyses depends heavily on resolving spectral interferences and maintaining robust hardware and software workflows. In complex matrices such as crude oil, geological, and environmental samples, polyatomic and doubly-charged overlaps can obscure low-level analytes like chloride, arsenic, and selenium. At the same time, aggressive acid matrices accelerate interface corrosion, increasing maintenance and downtime. Streamlined software interfaces further enhance throughput and data consistency across routine laboratories.

Aims and overview of the issue

• Develop an H₂ mass-shift MS/MS method on the Agilent 8900 ICP-QQQ to quantify chloride in crude oil down to sub-mg/kg levels.
• Implement half-mass measurement mode on Agilent 7800/7900 ICP-MS to correct doubly-charged interferences on Zn, As, and Se.
• Introduce nickel-plated, platinum-tipped sampling cones to extend cone lifetime and reduce cleaning in aggressive acid matrices.
• Enhance the ICP Go browser-based software interface (version 1.2) to simplify routine workflows and remote instrument monitoring.

Methodology and instrumentation

The chloride determination used the Agilent 8900 ICP-QQQ in MS/MS mass-shift mode. Q1 was set to m/z 35, H₂ cell gas (4.6 mL/min) converted Cl⁺ to ClH₂⁺ (m/z 37), and Q2 transmitted the shifted ion free of ¹⁶O¹⁸O¹H⁺ and ³⁴S¹H⁺ interferences. Crude oil samples (0.3–2.5 wt.% S) were diluted 1:5 or 1:10 in o-xylene with matrix modifiers, spiked with Sc and Y internal standards. Operating conditions included 1500 W RF power, –2 °C spray chamber, and a 1 mm injector.

Half-mass mode on Agilent 7800/7900 ICP-MS exploited a high-frequency, hyperbolic quadrupole to achieve <0.5 u peak widths. Doubly-charged ions such as ¹⁵⁵Gd²⁺ (m/z 77.5) and ¹⁴⁵Nd²⁺ (m/z 72.5) were measured at half masses; built-in correction equations subtracted their contributions from analyte masses (m/z 75 for As, m/z 78 for Se).

The nickel-plated sampling cones (Cu base with Ni or Ni+Pt tip) were evaluated by continuous analysis of 10% aqua regia over 1090 h. Cone surfaces were assessed for corrosion and ease of cleaning compared to standard Cu cones.

ICP Go software revision 1.2 runs on the MassHunter workstation under Windows 10. New features include batch editing, profile backup/restore, and real-time internal standard stability plots accessible from any networked device.

Used instrumentation

• Agilent 8900 Triple Quadrupole ICP-MS
• Agilent 7800 and 7900 Quadrupole ICP-MS
• Agilent SPS 4, ASX 520, I-AS autosamplers
• ICP Go Software v1.2 on MassHunter 4.5
• Ni-plated and Pt-tipped ICP-MS sampling cones

Main results and discussion

• Chloride calibration in o-xylene yielded a DL of 0.01 mg/kg, LOQ of 0.04 mg/kg, and BEC of 0.24 mg/kg. NIST 1634c SRM recoveries were 99–107% at dilution factors of 5 and 10.
• Half-mass mode reduced the BEC for As from 6.13 ppb to 0.08 ppb and for Se from 33.76 ppb to 0.04 ppb. Spiked recoveries of 1 ppb As/Se in a 1 ppm REE matrix were within 7% of target.
• Ni-plated cones lasted more than twice as long as standard Pt-tipped Cu cones in 10% aqua regia, with cleaning intervals reduced three-fold.
• ICP Go 1.2 introduced dynamic batch control and streamlined profile management, enhancing productivity in routine QA/QC operations.

Benefits and practical applications

• Enables reliable trace chloride analysis in petroleum and other complex organics without extensive sample cleanup.
• Automated doubly-charged interference correction improves accuracy for critical elements in geological and environmental samples.
• Extended cone lifetime and reduced maintenance lower operational costs in high-throughput acid applications.
• Simplified software interface and remote monitoring tools accelerate routine workflows in analytical laboratories.

Future trends and opportunities

• Integration of advanced reaction gases and cell chemistries to tackle emerging spectral overlaps.
• Development of AI-driven spectral deconvolution algorithms for real-time interference correction.
• Continued innovation in durable, corrosion-resistant consumables and greener solvent systems.
• Expansion of browser-based and cloud-enabled software platforms for global lab networks.

Conclusion

The highlighted methods and tools demonstrate significant improvements in analytical performance, from sub-mg/kg chloride detection in challenging matrices to sub-ppb As and Se quantification amid REE interferences. Consumable innovations extend instrument uptime, and user-centric software streamlines sample throughput. Together, these advances support more robust, accurate, and cost-effective ICP-MS workflows.

Reference

1. Nelson J., Poirier L., Lopez-Linares F. J. Anal. At. Spectrom. 2019, 34, 1433–1438.
2. ASTM D8110–17 Standard Test Method for Elemental Analysis of Distillate Products by ICP-MS, ASTM International, 2017.
3. Nakano K. Agilent publication 5991-6852EN.
4. Nelson J., Poirier L., Lopez-Linares F. Agilent publication 5994-1094EN.
5. NIST SRM 1634c Certificate of Analysis, NIST.