Analysis of flue gas desulfurization wastewaters with the Agilent 7700x/7800 ICP-MS

Significance of the Topic

Flue gas desulfurization (FGD) wastewater analysis is critical to ensure regulatory compliance as updated US EPA effluent guidelines require accurate monitoring of toxic trace metals in high total dissolved solids matrices.

Objectives and Study Overview

This study aimed to develop, validate, and demonstrate a robust ICP-MS method using the Agilent 7700x (and 7800) equipped with high matrix introduction (HMI), Octopole Reaction System (ORS) in collision mode, and optional ISIS-DS discrete sampling to quantify trace elements at low ppb levels in variable, high-solids FGD wastewater.

Methodology and Instrumentation

• Sample Preparation: Samples were acidified to pH <2 and digested by nitric and hydrochloric acid per EPA 1638 to recover total analytes.
• Instrumentation: Agilent 7700x ICP-MS with Micromist nebulizer, HMI aerosol dilution (medium), ORS in helium collision mode for most analytes (H2 mode for Se), ISIS-DS accessory, and MassHunter software for auto-optimization.
• Quality Control: Determination of instrument detection limits (0.02–0.94 ppb), method detection limits via replicate spikes, calibration across low to high ranges, synthetic high-TDS FGD matrix blanks and spikes to assess matrix interferences, and routine CCV/CCB, LCS, MS/MSD in sequences of 10 samples.

Main Results and Discussion

• Detection Limits: IDLs ranged from 0.02–0.94 ppb; MDLs well below regulatory limits.
• Interference Removal: ORS-He mode effectively eliminated polyatomic interferences across complex matrices; H2 mode addressed Se overlaps.
• Matrix Performance: HMI maintained plasma stability in samples with >1% TDS; ISIS-DS minimized carryover in long sequences.
• Quality Metrics: Calibration verification recoveries within 85-115%; internal standard recoveries between 60-125%; spike recoveries within ±30%; RPDs <20% for all elements except occasional late-sequence Ag issues likely due to chloride effects.

Benefits and Practical Applications

This method offers a straightforward, reproducible workflow for routine monitoring of FGD wastewaters in environmental laboratories and power plant effluent testing. By combining robust plasma conditions, collision technology, and discrete sampling, laboratories can achieve reliable trace metal quantification in samples previously considered too challenging.

Future Trends and Applications

• Integration of automated sample handling to increase throughput.
• Extension to other high-matrix industrial waste streams such as mining and metallurgical effluents.
• Exploration of alternative collision/reaction gases and advanced plasma stabilization techniques.
• Application to emerging analytes and isotopic speciation studies in complex matrices.

Conclusion

The validated Agilent ICP-MS method provides robust, accurate, and reliable analysis of trace metals in FGD wastewater, overcoming high-matrix challenges and meeting stringent EPA guidelines. This approach enables routine environmental compliance monitoring with performance comparable to simpler sample types.

References

• US EPA. Technical Support Document for the Preliminary 2010 Effluent Guidelines Program Plan, 40 CFR Part 423.10.
• Agilent Technologies. 5990-8114EN. Analysis of FGD Wastewaters with the Agilent 7700x/7800 ICP-MS. June 2015.