Determination of water pollutants using photometric analysis

Significance of the topic

Water quality monitoring is a critical global challenge driven by population growth, industrial activity and regulatory requirements. Reliable, high-throughput determination of inorganic pollutants (ammonium, chloride, nitrate/nitrite, orthophosphate, silicate and sulfate) is essential for compliance with directives such as the EU Water Framework Directive and for protecting drinking, surface, ground and industrial waters. Automated photometric discrete analyzers provide a standardized, reproducible approach to measure these key ions with minimized operator error, effective traceability and compliance with international standards such as ISO 15923-1.

Objectives and study overview

This application note demonstrates compliance of Thermo Scientific Gallery, Gallery Plus and Aquakem discrete analyzers with ISO 15923-1 for automated photometric determination of seven common water analytes. The study evaluated reagent composition, calibration strategies, method detection limits (MDLs), linear ranges, precision (within-run and between-run), automation features and sample throughput using Thermo Scientific system reagents and validated instrument applications.

Methodology

The analytical approach follows ISO 15923-1 guidance for discrete photometric analysis. Key methodological points include:

• Analytes: ammonium (as N), chloride, total oxidized nitrogen (TON: nitrate + nitrite), nitrite (as N), orthophosphate (as P), silicate, and sulfate.
• Reagents: ready-to-use, bar-coded Thermo Scientific system reagents formulated to be ISO-compliant; reagents provided in 4 × 20 mL vials for traceability and inventory control.
• Calibration: zero calibration mandated by ISO; calibrations implemented with linear or second-order (polynomial) fits depending on analyte and range; example calibration graphs provided for each analyte.
• Blanking and matrix compensation: blank measurement performed after dispensing sample and pre-chromogenic reagents to account for sample color; software supports compensating solutions and standard addition to address matrix effects.
• Operating conditions: reagent/sample volumes adapted for low-range methods (e.g., 120 µL sample, 120 µL maximum single reagent addition); photometric reads at wavelengths between 340 and 880 nm; typical reaction temperature 37 °C.
• QC and automation: automated quality control (QC) scheduling (e.g., control standard every ≤20 samples), reagent lot tracing, automatic dilution for out-of-range samples, and automated result calculation by instrument software.

Used instrumentation

• Thermo Scientific Gallery discrete analyzer
• Thermo Scientific Gallery Plus discrete analyzer
• Thermo Scientific Aquakem discrete analyzer

These analyzers support automated discrete photometry, optional electrochemical unit (Gallery) for pH and conductivity, random access, onboard dilution and multiple calibration models.

Main results and discussion

The study results demonstrate that the analyzed systems meet or exceed ISO 15923-1 detection requirements and provide robust analytical performance across relevant concentration ranges. Key findings include:

• Method detection limits (theoretical MDLs) for low-range methods meet ISO thresholds (examples: ammonia low — 0.5 µg/L as N; nitrite — 0.4 µg/L as N; phosphate low — 0.4 µg/L as P; silica — 0.01 mg/L; chloride low — 0.035 mg/L).
• Linearity: broad method linear ranges suitable for environmental and process waters (e.g., ammonia low up to 1000 µg/L; chloride up to 1000 mg/L; nitrite up to 2500 µg/L as N; sulfate up to 500 mg/L depending on range).
• Precision: within-run and between-run variability were low across matrices (tap, pond, lake, well water) and concentrations. Coefficients of variation (CV%) were generally below ~5% for most tested conditions, with particularly strong repeatability at higher concentrations.
• Blanking and matrix handling: blank subtraction procedures and software features (compensating solutions and standard addition) reduce bias from sample color and matrix effects, enhancing result reliability.
• Throughput: the analyzers produce a full set of seven ISO-required tests for a single sample in approximately 18 minutes; batch operations and efficient washing permit high sample throughput (e.g., 100 sulfate tests in ~25 minutes).

Discussion points emphasize that the combination of ISO-compliant reagents, automated QC, bar-coded reagent traceability and flexible software calibration supports both regulatory compliance and routine laboratory efficiency. Low reagent volumes and automation also reduce operator error and waste.

Practical benefits and applications

• Regulatory compliance: validated workflows aligned to ISO 15923-1 support environmental and public-health monitoring programs.
• Operational efficiency: automation of calibration, QC, dilutions and blank corrections reduces hands-on time and accelerates turnaround.
• Traceability and QA: bar-coded reagents and integrated software trace reagent lots and calibration history to results, strengthening auditability.
• Versatility: analyzers can measure additional parameters (alkalinity, total hardness, pH, conductivity, fluoride, metals in selected chemistries) expanding utility across water testing labs.
• Environmental footprint: small sample and reagent volumes reduce chemical consumption and laboratory waste.

Future trends and potential uses

• Integration with laboratory information management systems (LIMS) and cloud-based data platforms for centralized compliance reporting and trend analysis.
• Expanded on-board chemistries and multi-parameter panels to address emerging contaminants and routine inorganic suites in a single platform.
• Improved matrix correction algorithms and adaptive calibration strategies (e.g., automated standard addition routines) to further reduce sample-specific biases.
• Miniaturization and field-deployable discrete photometric systems for near real-time monitoring in remote locations.
• Enhanced sustainability: development of greener reagent formulations and recyclable consumable formats.

Conclusion

The Thermo Scientific Gallery, Gallery Plus and Aquakem discrete analyzers, together with ISO-compliant system reagents, deliver accurate, precise and traceable photometric determinations of key inorganic water pollutants. The platforms meet ISO 15923-1 detection and procedural requirements, offer flexible calibration and QC automation, and provide high throughput with low reagent consumption. These capabilities make them suitable for regulatory monitoring, municipal and industrial water testing, and research applications where standardized, reproducible ion analysis is required.

References

1. International Organization for Standardization. Ammonium, Chloride, Nitrate, Nitrite, Orthophosphate, Silicate. ISO 15923-1.
2. ISO & Water: Global Solutions to Global Challenges. International Organization for Standardization; January 2012.
3. European Environment Agency. Water overview and policy context. European Environment Agency publications.