WTW NH500/800 Ion-Selective Electrode (ISE) Series
| Brand | WTW |
|---|---|
| Origin | Germany |
| Type | Portable |
| Measurement Mode | Single-Parameter |
| Electrode Architecture | 500-Series (Half-Cell, Requires Separate Reference Electrode) / 800-Series (Integrated Reference Electrode, Composite Design) |
| Compatible Ions | NH₄⁺, Pb²⁺, Br⁻, Cd²⁺, Ca²⁺, Cl⁻, CN⁻, F⁻, I⁻, K⁺, Cu²⁺, Na⁺, NO₃⁻, Ag⁺, S²⁻ |
| Concentration Range (Typical) | 10⁻⁸–10⁻¹ mol/L (e.g., Cu²⁺) to saturation (e.g., F⁻) |
| Connector Options | BNC or DIN |
| Compliance | Designed for ASTM D6919, ISO 10304-2, USP <781>, and GLP/GMP-relevant measurement traceability |
Overview
The WTW NH500/800 Ion-Selective Electrode (ISE) Series comprises a comprehensive portfolio of potentiometric sensors engineered for precise, direct measurement of specific ionic species in aqueous solutions. Based on the Nernstian principle—where electrode potential varies logarithmically with the activity of the target ion—these electrodes deliver robust, interference-resistant quantification across environmental, industrial, pharmaceutical, and academic laboratories. The series is structured into two complementary architectures: the 500-series half-cells, which require external reference electrodes (e.g., WTW R 503/P or R 503/D) and are optimized for high-precision applications demanding modular configuration; and the 800-series composite electrodes, integrating a stable internal reference system within a single probe body—enabling rapid deployment, reduced calibration drift, and reliable analysis of low-volume samples (≥1 mL). Manufactured in Germany to stringent ISO 9001-certified quality standards, each electrode employs ion-selective membranes formulated for long-term stability, minimal leaching, and reproducible slope response (typically 54–59 mV/decade at 25 °C).
Key Features
- Modular Electrode Architecture: 500-series electrodes support flexible integration with WTW pH/ISE meters (e.g., Multi 3630 IDS, inoLab® pH/ION) and third-party systems via standardized BNC or DIN connectors; 800-series units eliminate cable management complexity with built-in reference junctions and factory-matched membrane-electrolyte pairing.
- Broad Ion Coverage: Certified performance for 15 analytes—including environmentally critical ions (NH₄⁺, NO₃⁻, F⁻, CN⁻), heavy metals (Pb²⁺, Cd²⁺, Cu²⁺, Ag⁺), alkali/alkaline earth cations (K⁺, Na⁺, Ca²⁺), halides (Cl⁻, Br⁻, I⁻), and redox-active species (S²⁻)—with documented selectivity coefficients (log Kij) per IUPAC guidelines.
- Field-Ready Portability: Lightweight, ruggedized housings (IP67-rated for splash resistance), 1-meter shielded cables, and optional replaceable sensor heads (e.g., CA 800/AT, K 800/AT, NO 800/AT) extend service life and reduce total cost of ownership.
- Calibration & Drift Management: Supports multi-point calibration (2–5 points) with certified standard solutions (ES-series); integrated temperature compensation (NTC 30 kΩ) ensures accurate activity-to-concentration conversion per IUPAC recommendations.
Sample Compatibility & Compliance
WTW ISEs operate effectively in complex matrices including wastewater, drinking water, soil extracts, fermentation broths, and pharmaceutical buffers—provided appropriate ionic strength adjustment (via TISAB, ISA/FK, MZ/NH₃/CN, or ISA/Ca) is applied to minimize activity coefficient variation. Electrodes meet requirements for routine compliance testing under EPA Method 300.0 (anions), ASTM D6919 (fluoride), ISO 10304-2 (multi-ion chromatography validation), and USP (potentiometric assay). For regulated environments, data integrity is supported through instrument-level audit trails (when paired with WTW IDS-capable meters), electronic signature capability, and alignment with FDA 21 CFR Part 11 principles for electronic records.
Software & Data Management
When used with WTW’s inoLab® or MultiLine® platforms, ISE measurements integrate seamlessly into the LabX®-compatible software ecosystem. Real-time slope monitoring, automatic calibration verification, and GLP-compliant report generation (including electrode ID, calibration date, temperature, and uncertainty estimates) are enabled. Raw mV data export (CSV/Excel) supports secondary analysis in MATLAB®, Python (SciPy), or LIMS interfaces. Firmware updates maintain alignment with evolving metrological best practices, including ISO/IEC 17025:2017 clause 7.7 on measurement traceability.
Applications
- Environmental monitoring: Ammonium and nitrate profiling in surface water and wastewater treatment plants (EN ISO 14911, DIN 38405-15).
- Food & beverage QA/QC: Sodium and potassium quantification in dairy products and beverages per AOAC 972.21.
- Pharmaceutical manufacturing: Chloride and fluoride content verification in active pharmaceutical ingredients (APIs) per EP 2.2.39.
- Industrial process control: Lead and cadmium screening in electroplating baths and semiconductor rinse waters.
- Academic research: Ion transport studies in membrane bioreactors and corrosion inhibition assays.
FAQ
What is the difference between 500-series and 800-series ISEs?
The 500-series are half-cells requiring an external reference electrode and salt bridge electrolyte, offering maximum configurability for research-grade setups. The 800-series integrate the reference system internally, simplifying field use and improving response time for routine analysis.
Do I need to purchase reference electrodes separately for 500-series ISEs?
Yes—models such as R 503/P (US-style plug) or R 503/D (banana plug) must be selected based on your meter interface; both require periodic replenishment of bridge electrolyte (ELY/BR/503).
How often should I calibrate an ISE?
Daily calibration is recommended for regulatory work; for non-critical applications, calibration before each analytical batch—with verification using a mid-range standard—is sufficient. Slope degradation >5% from theoretical indicates membrane replacement or cleaning.
Can I measure sulfide (S²⁻) and silver (Ag⁺) with the same electrode?
Yes—the Ag/S 500 and Ag/S 800 electrodes utilize a dual-mode silver sulfide membrane; however, separate conditioning, ISA selection (ISA/FK for Ag⁺; specialized reducing buffer for S²⁻), and fresh standard preparation are mandatory per application.
Are WTW ISEs compatible with non-WTW meters?
All 500/800-series electrodes feature industry-standard BNC or DIN connectors and output conventional mV signals compliant with ASTM D1129, enabling interoperability with most benchtop or portable pH/ISE meters supporting high-impedance input (>10¹² Ω).
