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

Significance of the Topic

Rapid and accurate determination of major, minor and trace elements in diverse matrices such as soils and plant tissues is critical for environmental monitoring, agricultural quality control and research laboratories. Enhancing sample throughput without compromising data quality can drive significant savings in time, consumables and operational costs, while improving laboratory responsiveness and capacity.

Objectives and Study Overview

This study evaluates a novel sample introduction accessory (SVS2) for an Agilent 720 Series axially viewed ICP-OES system. The main goals are to demonstrate how flow-injection technology can halve sample cycle times by eliminating uptake, stabilization and washout delays, validate analytical performance using certified reference materials for soil (NIST SRM 2710) and plant tissue (NIST SRM 1571), and quantify gains in throughput and cost efficiency.

Methodology and Instrumentation

The SVS2 integrates a tri-stacked 4-way diagonal flow-switching valve, a calibrated sample loop and a high-speed positive-displacement pump. By loading the loop off-line and injecting the entire sample at controlled speed, uptake pump delays are avoided and plasma destabilization minimized, reducing stabilization time to under 10 seconds and eliminating dedicated rinse delays.

Microwave-assisted acid digestion followed US EPA Method 3051A using a Mars 5 closed-vessel system, with HNO₃ and HCl to extract the analytes. Online internal standardization (2 mg/L Y) and ionization buffering (1% CsNO₃) stabilized signals and minimized matrix effects.

Instrumentation

• Agilent 720 Series simultaneous ICP-OES with axially viewed plasma and SPS 3 autosampler
• Custom CCD detector covering 167–785 nm
• Spray chamber: single-pass glass cyclonic
• Quartz torch, standard one-piece
• SeaSpray concentric glass nebulizer at 0.7 L/min
• SVS2 operating parameters: 6 s loop uptake delay; pump refill speed 500 rpm; inject speed 100 rpm; sample residence 5 s; bubble inject 5 s
• Mars 5 microwave digestion following EPA Method 3051A

Main Results and Discussion

Use of the SVS2 accessory reduced the sample-to-sample cycle from approximately 60 s to under 30 s, effectively doubling throughput from ~1,440 to over 3,000 analyses per day. Carryover was diminished by about four orders of magnitude, and plasma stability improved significantly due to continuous flow and minimized dead volume.

Recovery studies on NIST SRM 2710 (Montana soil) and SRM 1571 (orchard leaves) yielded element recoveries generally between 88% and 118%, demonstrating accuracy comparable to conventional introduction while supporting faster analysis. Precision remained within acceptable limits (RSDs typically below 5%).

Benefits and Practical Applications

• More than twofold increase in sample throughput, boosting laboratory productivity
• Reduced argon, reagent and standard consumption, lowering operating costs
• Extended torch and pump tubing lifetime due to inert sample path and minimized contact with peristaltic tubing
• Enhanced analytical stability and virtually eliminated carryover, ensuring reliable data for trace and major element determinations
• Applicable to environmental, agricultural, food and industrial laboratories requiring high sample volumes

Future Trends and Potential Applications

Further integration of flow-injection sampling with advanced detector systems (e.g. improved CCD arrays or high-resolution optics) could yield even shorter cycle times and lower detection limits. Adaptation to other plasma-based techniques (ICP-MS) and automated lab workflows may drive wider adoption. Real-time process monitoring in industrial settings, on-site environmental screening and coupling with emerging sample preparation methods present promising avenues for expanding high-throughput elemental analysis.

Conclusion

The SVS2 flow-injection accessory dramatically enhances ICP-OES sample throughput by more than doubling analysis speed while retaining analytical accuracy and precision. Significant cost savings in consumables and time, together with reduced carryover and improved plasma stability, make this approach highly attractive for high-volume elemental laboratories.

References

1. Calderon V. Rapid measurement of major, minor and trace levels in soils using the Varian 730-ES; Varian Application Note 35.
2. Ryan A. Rapid measurement of major, minor and trace elements in plant and food material using the Varian 730-ES; Varian Application Note 33.
3. US EPA. Method 3051A: Microwave assisted acid digestion of sediments, sludge and oils, Revision 1, January 1998.
4. Hoobin D., Russell G. Dramatically improved sample throughput using a new sample introduction technique with ICP-OES; Agilent Technologies Australia, 2011.