Hach COD Pre-digested Reagent Vials for 20-Minute Digestion

Overview

Hach TNTplus COD reagent vials are pre-formulated, sealed, single-use digestion tubes engineered for rapid, standardized chemical oxygen demand (COD) analysis in accordance with the dichromate oxidation method (APHA Standard Method 5220C, ISO 6060, and EPA Method 410.4). These vials employ a micro-reflux digestion principle under strongly acidic (H₂SO₄) and high-temperature conditions, where potassium dichromate (K₂Cr₂O₇) serves as the primary oxidant. The extent of oxidation is quantified spectrophotometrically by measuring the reduction of Cr(VI) to Cr(III) at 600 nm or 420 nm—directly proportional to the oxygen demand of organic and inorganic reducible substances in the sample. Designed for compatibility with Hach DRB200 digital block digesters and Hach portable or benchtop spectrophotometers (e.g., DR850, DR900, DR1010, DR1900, DR2700, DR2800, DR3900, DR5000, DR6000), this system delivers traceable, reproducible results within a total analytical cycle time of less than 60 minutes—including digestion, cooling, and photometric measurement.

Key Features

• 20-minute digestion protocol: Optimized thermal profile in the DRB200 digester enables complete oxidation in precisely 20 minutes at 150 °C—reducing turnaround time without compromising method validity.
• Pre-measured, factory-sealed reagents: Each 16-mm-diameter glass vial contains exact quantities of K₂Cr₂O₇, H₂SO₄, Ag₂SO₄ (catalyst), and HgSO₄ (chloride interference suppressant), eliminating manual preparation errors and exposure risks.
• Multi-range coverage: Available in four calibrated ranges—TNTplus 820 (0–15 mg/L), 821 (0–150 mg/L), 822 (0–1,500 mg/L), and 823 (0–15,000 mg/L)—ensuring optimal signal-to-noise ratio across municipal, industrial, and wastewater applications.
• Enhanced safety architecture: Hermetically sealed vials prevent acid fume release, splashing, and cross-contamination; integrated pressure-relief design mitigates over-pressurization during heating.
• Traceable calibration & QC: Each production lot undergoes rigorous validation against NIST-traceable COD standards; certificate of analysis (CoA) includes batch-specific blank values, recovery data, and uncertainty estimates.
• GLP-compliant workflow integration: Compatible with Hach’s DataCapture™ software and instrument audit trails meeting FDA 21 CFR Part 11 requirements for electronic records and signatures.

Sample Compatibility & Compliance

The TNTplus COD system is validated for use with raw influent, secondary effluent, sludge supernatant, and treated drinking water sources. It accommodates chloride concentrations up to 2,000 mg/L (with HgSO₄ compensation) and exhibits minimal interference from nitrate, phosphate, and common metal ions when operated per Hach Method 8000 series protocols. All reagent vials comply with ISO 9001-certified manufacturing processes and conform to EU REACH Annex XIV restrictions on hazardous substances. Method performance meets the precision criteria of ISO 5667-3 (±5% RSD for repeatability, ±10% RSD for reproducibility) and supports regulatory reporting under US EPA NPDES permits and China’s GB 11914–89 standard.

Software & Data Management

When paired with Hach spectrophotometers, the TNTplus system leverages embedded method libraries (e.g., “COD TNTplus 821”) that auto-apply wavelength selection, calibration curves, and unit conversions. Data export supports CSV, PDF, and LIMS-ready XML formats. Hach’s LogR software enables full chain-of-custody documentation—including user ID, timestamp, instrument serial number, vial lot number, and raw absorbance values—with configurable retention policies aligned with GLP/GMP archival mandates. Optional cloud synchronization via Hach Connect ensures secure, role-based access control and automated backup across distributed laboratory networks.

Applications

• Wastewater treatment plant (WWTP) process control: real-time monitoring of influent/effluent COD to optimize aeration basin loading and sludge retention time.
• Industrial pretreatment compliance: verification of discharge limits for food processing, pharmaceutical, textile, and electroplating facilities.
• Environmental monitoring programs: field-deployable analysis for river basin management and pollution source tracking.
• Research laboratories: method development, inter-laboratory comparison studies, and validation of alternative oxidation techniques.
• Educational settings: standardized teaching kits for environmental chemistry curricula emphasizing metrological rigor and safety-first practice.

FAQ

Are TNTplus COD vials compatible with non-Hach digesters or spectrophotometers?
Yes—provided the digester achieves and maintains 150 °C ± 2 °C for 20 minutes with uniform block temperature distribution, and the spectrophotometer offers stable photometric measurement at 600 nm with ≤0.005 AU noise specification.
How should used vials be disposed of after digestion?
Spent vials contain hexavalent chromium residues and concentrated sulfuric acid; they must be treated as hazardous waste per local regulations (e.g., US EPA D002/D007 codes) and disposed of through licensed chemical waste contractors.
Can these reagents be used for chlorinated solvent-containing samples?
No—samples containing chlorinated hydrocarbons (e.g., chloroform, carbon tetrachloride) may yield falsely elevated COD due to incomplete oxidation; such matrices require method modification or alternative TOC analysis.
What is the shelf life of unopened TNTplus vials?
24 months from date of manufacture when stored at 10–30 °C, protected from direct sunlight and moisture; vials exhibit no measurable degradation in oxidant concentration or blank stability within this period.
Is method validation documentation available for regulatory submissions?
Yes—Hach provides comprehensive validation packages including ICH Q2(R2)-aligned accuracy, precision, specificity, linearity, and robustness data upon request for QA/QC departments and accreditation bodies (e.g., ISO/IEC 17025).