WCPS: Dramatically improved sample throughput using a new sample introduction technique with ICP-OES

Importance of the Topic

The determination of major, minor and trace elements in soils and plant tissues is critical for environmental monitoring, agricultural research and quality control in food and related industries. Enhancing productivity and reducing operational costs without sacrificing analytical performance are key challenges in modern laboratories using ICP-OES techniques.

Objectives and Study Overview

This work evaluates a novel flow-injection sample introduction accessory (SVS2) coupled to an Agilent 720 Series simultaneous ICP-OES. The goals are to:

• Double sample throughput by cutting cycle time from about 60 s to under 30 s
• Maintain accuracy and precision when analysing soil (NIST SRM 2710) and orchard leaf (NIST SRM 1571) reference materials
• Reduce reagent and argon gas consumption, as well as wear on torches and pump tubing

Instrumentation

The system comprises:

• Agilent 720 Series simultaneous ICP-OES with axially viewed plasma and custom CCD detector covering 167–785 nm
• SPS 3 autosampler
• SVS2 flow-injection sample introduction unit with triple-stacked 4-way valve, sample loop and positive-displacement pump
• CEM Mars 5 closed-vessel microwave-assisted digestion system following US EPA Method 3051A

Methodology

Sample preparation involved microwave digestion in HNO3 and HCl to extract elements from soil and leaf samples. Online internal standardization and ionization buffering used yttrium and CsNO3. The SVS2 cycle consists of:

• Loop loading of ~0.5 mL sample in under 5 s at up to 500 rpm
• Valve switching to inject sample into plasma without high-speed uptake directly into the torch
• No separate uptake or rinse delays; stabilization time under 10 s
• Continuous rinse flow during measurement to achieve ~4 orders of magnitude washout in under 5 s

Standard operating parameters included 1.3 kW RF power, 15 L/min plasma gas, 1.5 L/min auxiliary gas, a single-pass cyclonic spray chamber and SeaSpray nebulizer at 0.7 L/min.

Main Results and Discussion

The SVS2 approach reduced the sample-to-sample cycle from ~60 s to <30 s while preserving analytical accuracy. Key findings from NIST SRM analyses include recoveries generally between 90% and 110% for major and trace elements in soil, and 87% to 128% in leaf material. Signal washout was achieved in seconds with negligible carry-over. Plasma stability improved due to a constant flow path and minimized dead volume.

Benefits and Practical Applications

The combined system delivers:

• More than double the daily throughput (over 2,800 samples vs. ~1,440)
• Lower argon and reagent consumption
• Reduced wear on torches and pump tubing
• Enhanced laboratory responsiveness for environmental, agricultural and food testing

Future Trends and Potential Applications

Further developments may include integration of flow-injection introduction in high-throughput and automated environments, adaptation to a wider range of matrices (e.g., pharmaceuticals, clinical samples), and miniaturization of sample loops for micro-volume analyses. Advances in valve materials and pump designs could further reduce carry-over and cycle times.

Conclusion

The SVS2 flow-injection accessory paired with an Agilent 720 Series ICP-OES achieves significant gains in productivity and cost efficiency without compromising data quality. This innovation offers a robust solution for routine high-throughput elemental analysis in diverse laboratory settings.

References

• Calderon V. Varian Application Note 35. Rapid measurement of major, minor and trace levels in soils using the Varian 730-ES2
• Ryan A. Varian Application Note 33. Rapid measurement of major, minor and trace elements in plant and food material using the Varian 730-ES3
• US EPA Methods 3051A Microwave Assisted Acid Digestion of Sediments, Sludge and Oils Revision 1, January 1998
• Hoobin D., Russell G. Dramatically improved sample throughput using a new sample introduction technique with ICP-OES. Agilent Technologies Australia, January 2011