Proposal

Abstract

This project develops and validates a solution-mode inductively coupled plasma mass spectrometry (ICP-MS) method to quantify the trace metals in bottled and West Campus tap waters. The research tests the hypothesis that measurable elemental differences exist between bottled and municipal water sources due to distinct treatment processes, infrastructure, and source chemistry. The analytical method will focus on optimizing helium kinetic-energy discrimination (He-KED) to reduce polyatomic interferences and improve low-ppb detection limits. Oxides and doubly charged ratios will be monitored as well (CeO⁺/Ce⁺ < 3%, Ba²⁺/Ba⁺ < 3%). Quality control will include calibration verification, matrix spikes, duplicates, blanks, and determination of method detection limits (MDLs) and limits of quantification (LOQs). Expected outcomes include a validated method capable of quantifying As, Pb, Cd, Cr, Cu, Zn, Mn, Fe, Al, Ba, Sr, and Se with precision under 10% relative standard deviation and recoveries expected between 85–115%, which accounts for minor over-recovery due to matrix effects. The results will support comparison of metal profiles between consumer bottled water and West Campus tap water to evaluate potential health or infrastructure-related differences.

Research Hypothesis:
Trace metal concentrations in bottled and West Campus tap water differ due to variations in water treatment, storage, and distribution systems, leading to distinct elemental signatures that can be quantified using ICP-MS.

Objectives:

• Develop a He-KED solution ICP-MS method for accurate quantification of trace metals at sub-ppb to low-ppb levels.

• Optimize RF power, nebulizer gas flow, and He cell gas rate to minimize matrix interferences (e.g., ArCl⁺ on ⁷⁵As, ArO⁺ on ⁵⁶Fe, ArC⁺ for Cr).

• Establish linear calibration curves for each analyte (optimally, r² ≥ 0.999).

• Determine method detection limits and limits of quantification, precision, and accuracy using: laboratory blanks, spiked samples, and certified reference materials.

• Evaluate inter-sample reproducibility (using internal standard–normalized counts) and internal standard recoveries (Sc, Ge, Rh, In, Tb).

• Generate comparative metal profiles for bottled and tap water to support environmental and public-health assessments.

Target Analytes:
As, Pb, Cd, Cr, Cu, Zn, Mn, Fe, Al, Ba, Sr, Se (major and trace metals of regulatory or geochemical significance).

Monitoring metals in drinking water is essential for several reasons: assessing human exposure, infrastructure corrosion, and treatment efficiency. Tap water in older urban areas may accumulate Pb, Cu, or Zn from pipes, while bottled water often reflects different geological and treatment conditions. Existing literature reports variation in elemental content up to 3× between sources (WHO 2023; USEPA 2022).
Developing a robust ICP-MS method with He-KED is important because interference-free detection of toxic metals like As and Pb requires discrimination against chloride- and oxide-based polyatomics common in drinking-water matrices. The method must achieve ±10% accuracy and precision and detect metals at or below the EPA’s maximum contaminant levels, which are 10 µg/L for As and 15 µg/L for Pb (USEPA 2022) to be useful for environmental monitoring. Preliminary literature indicates municipal tap waters in Texas occasionally exceed secondary contaminant limits for Fe and Mn—supporting the need for accurate local measurements.

Previous ICP-MS studies on drinking and bottled waters demonstrate the necessity of collision/reaction cell technology to reduce spectral interferences (Al-Masri et al., 2021; Li et al., 2020). Studies comparing bottled and tap waters in Spain and Japan used He KED mode to effectively suppress ArCl⁺ (m/z 75) and ArO⁺ (m/z 56), achieving <5% signal overlap for As and Fe.
Research by Smedley and Kinniburgh (2017) emphasized that natural variation in Sr and Ba correlates with groundwater source lithology, while elevated Pb and Cu in tap water generally show plumbing corrosion. The EPA Method 200.8 remains the standard for trace metals but requires matrix-specific optimization (e.g., optimizing cell gas for low-TDS samples). Recent advances focus on improved internal standard selection and time-resolved quality control tracking to manage instrumental drift. Analytical challenges expected include:

• Polyatomic interferences (ArCl⁺, ArO⁺, ArC⁺), mitigated by He-KED mode.

• Matrix effects from dissolved solids in mineral waters mitigated by sample dilution and internal standards.

• Memory effects for certain elements (Pb)

  This method builds on those approaches to tailor ICP-MS performance for low-ionic-strength water samples representing both bottled and municipal drinking sources.

Materials and Methods

Sample set:

• Tap Water: Three West Campus buildings (morning first-draw and post-flush samples).

• Bottled Water: Five brands (Ozarka, Fiji water, Rising Star, SmartWater, LIFE WTR

• Quality assurance samples: trip blank, method blank, laboratory reagent blank (LRB), laboratory fortified blank (LFB), matrix spike/matrix spike duplicate (MS/MSD), and continuing calibration check (CCV).

Sample Preparation:
Samples acidified to pH <2 with ultrapure trace metal grade HNO₃. Stored at 20 °C until analysis. Bottled samples degassed if carbonated.

Instrument and Settings:

Instrument and Settings (Agilent 8900)

Analyses were performed using an Agilent 8900 triple quadrupole ICP-MS (ICP-QQQ) housed in the Jackson School of Geosciences ICP-MS laboratory at the University of Texas at Austin. The instrument is equipped with a 27 MHz solid-state RF generator, a Peltier-cooled Scott double-pass spray chamber, a MicroMist concentric nebulizer, and an octopole collision/reaction cell (ORS⁴). The triple-quadrupole configuration (Q1–ORS–Q2) enables enhanced control of spectral interferences through mass-filtered collision/reaction chemistry, improving selectivity and accuracy for trace-metal determinations in complex or chloride-bearing water matrices.

Helium collision mode (He-KED) was used for most analytes to attenuate polyatomic interferences through kinetic energy discrimination, while Q1 mass filtering restricted the ion population entering the cell to the target m/z, minimizing formation of new reaction-cell species.

Operating Parameters

The instrument was tuned daily using a multi-element tuning solution containing Li, Y, Ce, and Tl (1 µg/L each in 2% HNO₃). The following operating conditions provided optimal sensitivity, stability, and interference suppression:

• Instrument: Agilent 8900 ICP-QQQ

• RF Power: 1550 W

• Sampling Depth: 8.0 mm

• Sample Uptake Rate: 0.30 mL/min

• Nebulizer Gas Flow: 1.05 L/min

• Makeup Gas Flow: 0.10 L/min

• He Cell Gas Flow: 4.5 mL/min

• Auxiliary Gas Flow: 0.8 L/min

• Plasma Gas Flow: 15 L/min

• Dwell Time per Isotope: 10 ms

• Integration Time per Isotope: 0.3 s

Tuning acceptance criteria required CeO⁺/Ce⁺ < 3% and Ba²⁺/Ba⁺ < 3%, confirming low oxide and doubly charged ion formation. Sensitivity was verified by achieving signal intensities exceeding 50,000 cps for ⁷Li⁺, ⁸⁹Y⁺, and ²⁰⁵Tl⁺ in standard mode.

Internal Standards and Sample Introduction

Internal standards (Sc, Ge, Rh, In, Tb) were introduced online via a mixing tee and monitored continuously to correct for instrumental drift, matrix effects, and nebulization variability. Samples were aspirated using a peristaltic pump fitted with acid-washed Tygon tubing. A 2% ultrapure HNO₃ rinse was applied between samples to minimize memory effects, particularly for Pb and Ba.

Calibration and Quality Control:

Calibration was performed using a six-point multi-element external calibration curve spanning 0.2-20 µg/L, prepared from NIST-traceable single-element standards (High-Purity Standards, Charleston SC). Calibration blank and verification standards were prepared in 2% ultrapure HNO₃ to match the sample matrix.

Each analyte’s calibration curve was generated by plotting counts per second (cps) versus concentration, yielding correlation coefficients r² ≥ 0.95. Linear regression was verified with residual plots and back-calculated recoveries within ±10% of expected values.

• Initial Calibration Verification: Measured immediately after calibration using a second-source standard; recoveries required to be within 90–110%.

• Continuing Calibration Verification (CCV): Conducted every ten samples and after blanks to confirm calibration stability. Acceptable deviation = ±10%.

• Laboratory Reagent Blank (LRB): Monitored for background contamination; analyte signals were required to remain below the method detection limit (MDL).

• Laboratory Fortified Blank (LFB): Spiked at 10 µg/L to assess overall method accuracy; recoveries between 85–115% were required.

• Matrix Spike / Matrix Spike Duplicate (MS/MSD): Used to evaluate matrix-specific recovery and precision in representative samples; relative percent difference (RPD) ≤ 10%.

• Method Detection Limit (MDL) and Limit of Quantitation (LOQ): Determined from seven replicate low-level spikes using the Student-t approach (n = 7, 99% confidence).

• Internal Standard Recovery Monitoring: Internal standards (Sc, Ge, Rh, In, Tb) were introduced online and tracked throughout all runs. Acceptable recovery range = 70–130% of nominal signal intensity.

Possible Outcomes

If successful, the method will provide a validated and interference-free ICP-MS protocol for quantifying trace metals in clean water matrices. Anticipated benefits include:

• Establishing defensible data on metal variability between bottled and municipal sources.

• Demonstrating He-KED efficiency for eliminating polyatomic interferences in low-TDS matrices.

• Producing calibration and quality control data suitable for environmental reporting standards.

• Identifying whether local tap water shows elevated Cu, Pb, or Fe consistent with corrosion or distribution-system leaching.

Ultimately, the method could serve as a template for student or municipal laboratories evaluating drinking-water quality at low cost and high reproducibility.

Timeframe and Budget

3 weeks total

Week 1: Sampling and Preparation

• Samples will be collected and preserved
• 3 West Campus tap sites will be collected (first draw + flushed) and 5 bottled water brands.
• Filter (0.45 µm) and acidify to pH < 2 with ultrapure nitric acid (HNO₃). Label, store at 4 °C. Prepare blanks (pure water) and spike solutions.

Week 2: Optimize ICP-MS

• Tune plasma and optimize He-KED parameters using a tuning solution (Li, Y, Ce, Tl).
• Establish calibration (6-point curve, 0.2-20 μg/L)
• Conduct method detection limit and limit of quantitation
• Run preliminary quality control (blanks, laboratory fortified blank, continuing calibration verification)

Week 3: Final runs and Validation

• Run bottled and tap samples, duplicates, spike recoveries.
• Evaluate accuracy (85–115 %) and precision (≤10 % RSD).
• Evaluate CeO⁺/Ce⁺ and Ba²⁺/Ba⁺ ratios for final tuning validation

3 week duration, which involves about 9 hours of instrument time along with prep and analysis.

Budget Calculation

Estimated instrument time: ~9 hours

Total cost: $760

This number of analyses keeps this project feasible and sufficient to show reproducibility and accuracy. Approximately 58% of total analyses are devoted to quality control. This proportion ensures compliance with EPA 200.8 QC frequency (approximately 1 QC per 3–4 analytical runs)  This timeline allows for sampling logistics, instrument tuning, and data verification.