| Measurement Principle | Confirm whether the instrument uses a validated colorimetric, molybdenum-blue, ion-selective, or other analytical method suitable for the sample matrix. | Colorimetric phosphate testing commonly relies on phosphomolybdate chemistry and a defined reaction time. | Method principle, reagents, wavelength, reaction time, and interferences should be clearly documented. | 10% |
| Applicable Standard Methods | Check whether the supplier can support the method required by the end user, laboratory, or regulatory authority. | Relevant references may include ISO 6878 for water quality phosphate determination and EPA Methods 365.1 or 365.3, where applicable. | Supplier provides a method statement, validation data, and clear instructions for adapting the method to the instrument. | 12% |
| Measuring Range | Compare the stated low and high ranges with the expected phosphate concentration in drinking water, wastewater, process water, or laboratory samples. | Many photometric instruments offer selectable low- and high-range programs rather than one universal range. | The target concentration should fall near the middle of the selected range; samples outside the range should support dilution or a different program. | 10% |
| Limit of Detection and Resolution | Request detection-limit calculations, blank results, resolution, and representative raw data instead of relying only on marketing specifications. | Detection capability depends on optical design, reagent chemistry, sample volume, blank correction, and measurement procedure. | Detection limit and resolution are demonstrated using the same matrix and procedure required by the purchaser. | 12% |
| Accuracy and Precision | Review recovery tests, repeatability data, calibration results, and uncertainty information at low, medium, and high concentrations. | Performance should be assessed with certified reference materials, independently prepared standards, or matrix-matched quality-control samples. | Supplier provides replicate-test data and acceptance criteria agreed in advance; do not judge performance from a single test result. | 15% |
| Interference Control | Evaluate the effect of turbidity, color, suspended solids, silica, arsenate, iron, detergents, and other matrix components. | Colorimetric phosphate methods can be affected by sample color, turbidity, reaction conditions, and chemically similar species. | Interference limits and pretreatment procedures are stated in the manual and confirmed through matrix testing. | 10% |
| Calibration and Quality Control | Check calibration frequency, standard traceability, blank correction, automatic checks, and storage requirements for reagents. | Calibration should use standards with known concentration and documented preparation or traceability. | Instrument supports routine blanking, calibration verification, quality-control records, and clear out-of-control actions. | 10% |
| Reagent System | Assess reagent shelf life, lot consistency, packaging, hazardous-material information, preparation steps, and local availability. | Phosphate colorimetric tests commonly require an acidic reagent system and a molybdate-based or equivalent chemistry. | Reagents have labeled batch numbers, expiry dates, safety information, and documented storage conditions. | 8% |
| Environmental and Mechanical Suitability | Review operating temperature, humidity, ingress protection, vibration tolerance, portability, and power requirements. | Environmental specifications must be matched to the intended laboratory, plant, field, or online installation. | Supplier provides test conditions and confirms performance under the purchaser's actual operating environment. | 6% |
| Data Handling and Connectivity | Verify display units, result storage, export formats, time and date records, audit trails, USB, Ethernet, or other interfaces. | Data functions should support the user's laboratory information, reporting, and traceability requirements. | Results can be exported without manual transcription, with user access control or audit functions where required. | 5% |
| Documentation and Compliance | Request user manuals, calibration procedures, electrical safety documents, declarations, inspection records, and validation protocols. | Applicable conformity requirements depend on destination market, voltage, installation type, and intended use. | Technical documents are complete, consistent, available in English, and matched to the quoted model and configuration. | 7% |
| Factory Quality System | Assess production controls, incoming inspection, final testing, calibration management, corrective actions, and change control. | ISO 9001 certification can indicate a documented quality-management system, but it does not by itself prove analytical performance. | Supplier provides a valid certificate, scope, recent quality records, and model-specific final-test documentation. | 8% |
| After-Sales Service | Evaluate commissioning, training, spare parts, repair capability, response time, warranty terms, and remote technical support. | Service quality is especially important for analyzers requiring optical alignment, reagent maintenance, or periodic calibration. | Written service-level commitments, troubleshooting procedures, spare-parts availability, and clear warranty exclusions are provided. | 7% |
| Sample Evaluation and Factory Acceptance Test | Require testing with representative samples or blinded standards before bulk purchase or project acceptance. | Acceptance testing should compare repeatability, recovery, bias, response time, and operational stability against agreed criteria. | Purchase decision is based on documented test results rather than catalog specifications alone. | 15% |