Determination of Major and Minor Elements in HF-Digested Soil Samples using an Agilent 5110 ICP-OES

Significance of the Topic

Accurate elemental analysis of soil samples is essential for environmental assessment, agricultural management, and regulatory compliance. Silicate minerals in soils require hydrofluoric acid (HF) for complete dissolution. However, HF digests corrode standard glass or quartz sample introduction systems, necessitating neutralization steps that add complexity, risk contamination, and reduce throughput. An inert sample introduction system enables direct analysis of HF-digested samples, improving efficiency and data integrity.

Objectives and Study Overview

The study evaluates the performance of an Agilent inert sample introduction system coupled to the 5110 Vertical Dual View ICP-OES for multi-element determination in HF-digested soil samples. Key objectives include:

• Validating complete digestion and accurate quantitation of 11 major and minor elements in a NIST soil reference material following US EPA 3052 microwave-assisted HF digestion.
• Assessing detection limits, dynamic range, and long-term stability over continuous operation.
• Comparing recoveries from HF-based and aqua regia-only digests.
• Demonstrating interference correction using Agilent’s FACT software.

Methodology and Instrumentation

Soil samples (0.45 g) and NIST SRM 2710a were digested in a microwave system with 10 mL HNO₃, 3 mL HF, and 3 mL HCl under US EPA 3052 conditions, brought to 40 mL. Calibration standards matched the acid matrix. An Agilent 5110 VDV ICP-OES with SPS 4 autosampler was equipped with:

• OneNeb Series 2 inert nebulizer
• Inert double-pass spray chamber with removable baffle
• Easy-fit inert demountable VDV torch with alumina injector (1.8 mm i.d.)
• Inline nebulizer gas humidifier

Operating conditions included 1.2 kW RF power, 12 L/min plasma flow, axial and radial viewing modes, and online addition of Lu and Y internal standards. FACT spectral deconvolution corrected complex overlaps.

Key Results and Discussion

Recoveries for all 11 elements were within ±10% of certified values, confirming method accuracy. Method detection limits ranged from 0.44 to 11.2 µg/kg (MDL) and 0.12 to 3.01 mg/kg (LOQ). Long-term precision over 7 hours of continuous analysis showed RSDs below 3%. FACT correction effectively removed a Cu interference on P 177.434 nm. Recoveries in aqua regia-only digests were significantly lower for Cr, Mn, Ti, and V, highlighting the necessity of HF for total digestion. Spike recoveries in the SRM were within ±10%, validating method robustness.

Benefits and Practical Applications

Direct analysis of HF-digested soils without neutralization streamlines workflows, reduces contamination risk, and supports high-throughput operations. The inert introduction system tolerates high dissolved solids and organic solvents while delivering accurate multi-element data across a broad dynamic range (ppm to percent levels). This approach benefits environmental laboratories, agronomic research, and industrial quality control.

Future Trends and Opportunities

Expanding inert introduction technology to other challenging matrices (e.g., sediments, sludges), integrating automated digestion workflows, and adapting similar systems for MP-AES will enhance analytical flexibility. Ongoing improvements in real-time spectral correction and detector technology will further lower detection limits and simplify complex sample analyses.

Conclusion

The combination of HF digestion and Agilent’s inert sample introduction on the 5110 VDV ICP-OES delivers reliable, efficient multi-element analysis of silicate-rich soils. The method offers complete sample decomposition, excellent accuracy and precision, robust long-term stability, and a wide dynamic range, making it a valuable tool for diverse analytical laboratories.

References

1. US EPA Method 3052. Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices; U.S. Environmental Protection Agency.
2. López-García I., Arnau-Jerez I., Campillo N., Hernández-Córdoba M. Determination of Tin and Titanium in Soils, Sediments and Sludges Using ETAAS with Slurry Sample Introduction. Talanta. 62(2):413–419 (2004).
3. Lyu S., Wei X., Chen J., Wang C., Wang X., Pan D. Titanium as a Beneficial Element for Crop Production. Front. Plant Sci. 8:597 (2017).
4. Agilent Technologies. Real-time Spectral Correction of Complex Samples Using FACT Spectral Deconvolution Software; Publication 5991-4837EN.