Hach 21055-69 DPD Free Chlorine Reagent Powder Pillows
Overview
The Hach 21055-69 is a pack of Hach DPD free chlorine reagent powder pillows, individually dosed chemical packets designed for use with Hach colorimeters and portable spectrophotometers to determine free chlorine concentration in the 0.02 to 2.00 mg/L Cl2 range. Each pillow contains a precisely measured, boric-acid-free DPD (N,N-diethyl-p-phenylenediamine) formulation that reacts with free chlorine to develop a pink colour proportional to concentration, giving water treatment operators a fast, repeatable field or laboratory test.
Backed by genuine manufacturer documentation, Seven Star LLC proudly supplies the Hach 21055-69 reagent pillows with full manufacturer traceability and batch documentation. Water treatment plants and municipal laboratories across Muscat, Sohar, and Salalah rely on Seven Star LLC to source genuine Hach reagents quickly, avoiding the inconsistent colour development and failed compliance results that come with expired or counterfeit reagent stock.
Measurement Principle
The Hach 21055-69 reagent works on the DPD colorimetric principle: when the powder pillow is added to a 10 mL water sample, free chlorine present in the sample oxidizes the DPD indicator, producing a pink colour whose intensity is directly proportional to the free chlorine concentration. A Hach colorimeter or spectrophotometer then measures the light absorbance of the developed colour at 530 nm on a spectrophotometer or 520 nm on a colorimeter and converts the reading into a chlorine concentration in mg/L, following the USEPA-accepted Method 8021 for drinking water reporting.
Because each pillow is factory-dosed with an exact quantity of reagent, the method eliminates the weighing and mixing errors associated with bulk liquid reagents, and the boric-acid-free formulation avoids the buffer interference issues that affect some legacy DPD chemistries. The practical consequence for plant chemists is a test that is fast to execute, consistent from sample to sample, and directly defensible for regulatory reporting without additional calibration steps beyond routine colorimeter verification.
Interferences and Sample Handling
Because free chlorine is a strong oxidant and is unstable in collected samples, Hach specifies that samples for the Hach 21055-69 test must be analysed immediately after collection and cannot be preserved for later analysis. The reaction itself is immediate: the pink Wurster dye forms as soon as the powder pillow dissolves, and the reading should be taken within 60 seconds of reagent addition. That short window is not a convenience detail but a control on accuracy, because monochloramine causes a gradual upward drift in the result. Read within one minute, 3 mg/L of monochloramine adds less than 0.1 mg/L to the indicated free chlorine value; allowed to stand, that bias grows.
The DPD chemistry responds to other oxidants as well, and a competent laboratory accounts for this. Bromine, chlorine dioxide, inorganic chloramines and ozone all give positive interference at every level, while organic chloramines and peroxides may interfere. Sample chemistry also matters: acidity above 150 mg/L as CaCO3 or alkalinity above 250 mg/L as CaCO3 can prevent full colour development or cause the colour to fade instantly, and both are corrected by adjusting the sample to pH 6 to 7 before testing. Hardness has no effect below 1000 mg/L as CaCO3. Oxidised manganese and hexavalent chromium require a potassium iodide and sodium arsenite pre-treatment with a blank subtraction. Seven Star LLC supplies the Hach 21055-69 alongside the standards and pre-treatment reagents needed to run these checks correctly in Oman and the GCC.
Engineering Design of the Hach 21055-69
The Hach 21055-69 is supplied as a pack of 100 individually sealed powder pillows, each containing a precisely measured 10 mL-sample dose of the DPD reagent blend. The foil pillow packaging protects the reagent from moisture and light degradation during storage and transport, preserving reagent activity through the stated shelf life so that results remain accurate even after extended storage in regional climate conditions.
The pillow format is designed for direct, tool-free use: the operator tears open the pillow and empties the contents directly into the sample cell, eliminating pipetting, dilution, or mixing equipment. This single-dose design also standardizes the test across multiple operators and shifts, since every pillow delivers an identical reagent quantity regardless of who performs the test, which is a meaningful quality-control advantage for utilities running continuous compliance monitoring programs.
Key Features
The Hach 21055-69 reagent combines regulatory-grade accuracy with field-ready simplicity, and the following features summarize why water utilities standardize on this chemistry:
- USEPA-accepted DPD method supports direct use in regulatory compliance reporting for drinking water analysis.
- Boric-acid-free formulation avoids buffer interference issues associated with some legacy chlorine reagent chemistries.
- Individually dosed powder pillows eliminate weighing, pipetting, and mixing errors in the field or laboratory.
- Foil packaging protects reagent activity from moisture and light across extended storage periods.
- Measurement range of 0.02 to 2.00 mg/L Cl2 covers typical drinking water and process water disinfection targets.
- Compatible with Hach colorimeters and portable spectrophotometers already deployed across most regional utility labs.
- Consistent single-dose format standardizes results across multiple operators and testing shifts.
- 100-pillow pack size supports high-frequency sampling programs without frequent reordering.
Industrial Applications
The Hach 21055-69 reagent is used throughout municipal water treatment plants, wastewater facilities, and industrial process water programs where free chlorine residual must be verified for disinfection efficacy and regulatory compliance. In Oman, the reagent is widely specified for RO desalination post-treatment disinfection verification, district cooling water treatment monitoring, and municipal drinking water distribution network sampling across urban and industrial zones.
Working closely with plant engineers in the region, Seven Star LLC distributes DPD reagent chemistry to utility laboratories and environmental consultants throughout the Sohar and Salalah economic zones, as well as to hospitality chains and hospital complexes across Muscat that maintain their own potable water and cooling tower chlorine monitoring programs. The reagent’s consistent, regulatory-defensible results make it a standard component of water quality testing kits across the GCC.
Technical Specifications
The table below summarizes the key parameters of the Hach 21055-69 DPD free chlorine reagent.
| Parameter | Specification |
|---|---|
| Model | Hach 21055-69 |
| Test Parameter | Free Chlorine (DPD) |
| Method | USEPA Method 8021 |
| Range | 0.02 to 2.00 mg/L Cl2 |
| Sample Volume | 10 mL |
| Format | Powder pillow, boric-acid-free |
| Pack Size | 100 pillows |
| Compatible Instruments | Hach colorimeters, portable spectrophotometers |
| Application | Drinking water, wastewater, process water testing |
| Measurement Wavelength | 530 nm (spectrophotometer) / 520 nm (colorimeter) |
| Equivalent Standard Method | Equivalent to USEPA and Standard Method 4500-Cl G for drinking water |
| Reaction / Read Time | Immediate colour development; read within 60 seconds of reagent addition |
| Sample Handling | Analyse immediately; samples cannot be preserved |
| Sensitivity | 0.02 mg/L Cl2 concentration change per 0.010 Abs change |
| Precision (95% CI) | 1.23–1.27 mg/L Cl2 on a 1.25 mg/L Cl2 standard (program 80) |
| Scope | Water, treated waters, estuary and seawater |
| Higher Concentrations | Above 2 mg/L Cl2, use Hach Method 10069 (high range) |
Request a Quote for Hach 21055-69 DPD Free Chlorine Reagent Powder Pillows
With fast quotation turnaround and technical support, Seven Star LLC supports formal RFQ submissions, confirms lead time at quotation, and can provide the full technical datasheet for the Hach 21055-69 reagent on request. Contact the Seven Star LLC instrumentation division for genuine Hach water quality reagents and application support across Muscat, Sohar, and Salalah.
Related Products
- Instruction Manual Hach DPD Free Chlorine Method 8021 Manual Download
Hach analyzers, sensors and reagents listed
The Hach products on this page fall into four groups:- Online analyzers: CL17sc colorimetric chlorine analyzer, TU5300sc and TU5400sc laser turbidimeters, BioTector B3500ul TOC analyzer, Polymetron 9245 sodium analyzer and Orbisphere 510 dissolved gas analyzer
- Controllers and digital sensors: SC4500 controller and the LDO 2 luminescent dissolved oxygen sensor
- Portable and laboratory instruments: 2100Q turbidimeter, HQ4200 multi-parameter meter and IntelliCAL probes such as the LBOD101
- Reagents: DPD free chlorine powder pillows and DEHA reagents for oxygen scavenger testing
Where Hach instruments are used
Hach instruments appear in drinking water plants, desalination, sewage treatment, cooling and boiler water circuits, and industrial effluent monitoring across the GCC. Operators use the portable meters and reagents for spot checks, and the sc analyzers and probes for continuous signals to the control system.Ordering Hach products: what we need
Hach identifies every item by a catalog number, for example LXV416.99.20001 for a sensor or 21055-69 for a reagent pack, and the same reagent may be written with or without the dash. Send that number and the quantity. For analyzers and controllers, add the parameter and range, sample conditions, power supply, outputs and communication option. For sensors, tell us the controller model they will connect to and the cable length. For reagents, name the instrument and method so pack size and range can be confirmed against Hach documentation.Browse Hach products by category: Liquid Analytical Accessories, Liquid Analysis Sensors, Portable Test & Measurement, Liquid Analytical Systems.
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