Determination of water pollutants using photometric analysis

Significance of the topic

Clean, safe water is a critical global resource under increasing anthropogenic pressure. Regulatory frameworks such as the EU Water Framework Directive require robust, repeatable and comparable methods for monitoring inorganic pollutants in ground, surface, potable and waste waters. Automated photometric discrete analysis provides a practical route to meet regulatory needs by enabling standardized determinations of key ionic contaminants with high throughput and traceability.

Goals and overview of the study

This application note evaluates Thermo Scientific Gallery, Gallery Plus and Aquakem discrete analyzers and their system reagents for compliance with ISO 15923-1. The work documents reagent composition, calibration strategies, limits of detection, precision and throughput for the ISO-specified analytes: ammonium, chloride, nitrate/nitrite (TON), nitrite, orthophosphate, silicate and sulfate. The intent is to demonstrate that the automated procedures meet or exceed the ISO performance requirements while offering operational benefits for routine water analysis laboratories.

Methodology

Reagents and calibration

All tests used Thermo Scientific bar-coded, ready-to-use system reagents formulated to match ISO 15923-1 compositions. Calibration employed zero calibration solutions and either linear or second-order (polynomial) fits as appropriate. Where needed, sample blanking steps were applied following ISO Annex A to compensate for sample color. Calibration ranges covered both low and high method ranges with automated dilution for out-of-range samples.

Sample handling and assay conditions

Discrete analyzer applications used small sample volumes (e.g., 120 µL for low-range methods) and reagent additions limited to 120 µL per addition. Incubations and readings were performed at 37 °C with spectrophotometric measurement across 340–880 nm depending on the assay. Automated workflows included pre-programmed methods, optional standard addition to address matrix effects, and quality control routines.

Used instrumentation

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

The Gallery platform includes an electrochemical module for pH and conductivity; all systems are integrated with reagent lot tracing and automated QC features in the control software.

Main results and discussion

Detection capability and linearity

Calculated theoretical method detection limits (MDLs) met or exceeded ISO 15923-1 low-application requirements. Representative low-range detection capabilities included: ammonium (≤0.05 mg/L as N requirement; methods reported theoretical MDLs of 0.5–1.6 µg/L as N), nitrite (~0.01 mg/L as N requirement; MDLs in low µg/L), phosphate (≤0.01 mg/L as P requirement; MDLs down to 0.4 µg/L P), silica (≤0.05 mg/L requirement; MDL ~0.01 mg/L), chloride, sulfate and TON methods with suitable MDLs and extended linear ranges up to several hundred mg/L depending on the analyte.

Precision and accuracy indicators

Within-run, between-run and total precision data across natural and spiked waters showed low standard deviations and coefficients of variation typically below 5% for most matrices and concentrations; precision was especially strong at higher concentration levels. These results indicate robust repeatability and inter-run consistency appropriate for routine monitoring.

Automation, blanking and matrix handling

The analyzers automate blank subtraction, calibration management, reagent traceability and QC scheduling (e.g., control standard every ≤20 samples). Software supports compensating solutions (true sample blanks) and standard-addition approaches to address matrix effects. Blanking eliminates the need for separate correction factors for colored samples in most cases.

Throughput and operational notes

Typical throughput examples: all seven ISO-required tests from a single sample in ~18 minutes; 100 sulfate determinations in ~25 minutes. Low-ammonia assays are advised to be run in batches due to reagent volatility. The systems permit random-access analysis with multiple washing steps and automated dilutions for high-concentration samples.

Benefits and practical applications

• Regulatory compliance: methods and reagents conform to ISO 15923-1 enabling standardized reporting.
• Operational efficiency: bar-coded reagents, automation and software QC reduce hands-on time and human error.
• Analytical performance: sensitive MDLs, broad linear ranges and good precision suitable for environmental monitoring and industrial water QA/QC.
• Flexibility: support for additional parameters (alkalinity, hardness, pH, conductivity, some metals and enzymatic nitrate options) extends utility beyond the seven ISO assays.
• Environmental and cost benefits: low sample and reagent volumes reduce waste and running costs.

Future trends and opportunities

Future directions for discrete photometric water analysis include tighter integration with laboratory information management systems (LIMS) for end-to-end traceability, expanded assay portfolios for emerging contaminants, further miniaturization to reduce reagent use, and enhanced matrix-correction algorithms (automated standard addition workflows). Coupling discrete analyzers with remote sampling and real-time data reporting could extend continuous monitoring capabilities for distributed water networks and rapid regulatory response.

Conclusion

The evaluated Thermo Scientific discrete analyzer platforms and their system reagents comply with ISO 15923-1 requirements and exhibit suitable sensitivity, precision and throughput for routine determination of key ionic water pollutants. Automated calibration, QC, blanking and reagent traceability improve data quality and laboratory efficiency, making these systems appropriate for environmental and industrial water monitoring programs.

References

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