CALDUR® Sulfite – Colorimetric
Sulfite determination in water by color card (0.5-20 mg/l SO₃²-)
Private customers can also find our range in our partner store Ampha-Analyse.
Reagent for CALDUR® Sulfite – Colorimetric:
See also:
CALDUR® Sulfite Test Set – Colorimetric
What is Sulfite measured for?
Sulfite (SO₃²-) is used in water treatment as an oxygen binding agent to prevent corrosion
in steam boilers, heating systems and closed cooling systems. As a reducing agent
, Sulfite reacts with dissolved oxygen and thus protects pipelines and system components from
oxygen corrosion.
The optimum Sulfite concentration in boiler water is 20-30 mg/l SO₃²-.
Regular monitoring is essential, as values that are too low do not provide sufficient corrosion protection
, while concentrations that are too high are uneconomical and promote the formation of sulfate.
Sulfite is also used as a preservative and antioxidant in the food industry.
Monitoring the concentration of sulfite is therefore of great importance in various industrial sectors.
How does the test set work?
The CALDUR® Sulfite Test Set – Colorimetric is based on the proven thiobenzoic acid method.
After adding two reagents to the water sample, a
characteristic color develops within 3 minutes, the intensity of which is proportional to the Sulfite concentration.
The measured value is determined by direct color comparison with a supplied 6-level color chart.
Optionally, the sample can also be evaluated photometrically with the WINLAB Data Line photometer.
Advantages of the CALDUR® test set
- Quick analysis in just 3 minutes
Ideal for regular checks in boiler systems – immediate results on site
- Wide measuring range from 0.5 to 20 mg/l SO₃²-
Covers the entire practical range for boiler water and industrial applications
- 150 determinations per set – economical in continuous use
Cost-efficient for daily checks in power plants, heating systems and industrial operations
- Can be used colorimetrically and optionally photometrically
Flexible for simple on-site tests or precise laboratory analyses with photometer
- Easy handling without special equipment
No additional technology required – ideal for quick routine checks
- Robust, waterproof plastic housing with hinged lid
Safe transportation and protection of reagents – durable and reliable even under harsh conditions
Areas of application
Carrying out the measurement:
- Fill water sample into test tube up to the 10 ml mark
- Add reagent A and mix well by swirling carefully
- Add reagent B and mix again
- Wait exactly 3 minutes (observe the waiting time!)
- Evaluation by color comparison with color chart or photometric measurement
💡 Tip for best results
For best results, the water sample should be clear and free of suspended solids.
If the water is cloudy, pre-filtration with a filter paper (e.g. Whatman No. 1) is recommended.
The measurement should be carried out as soon as possible after sampling, as Sulfite oxidizes in the air.
⚠️ Important notes
- Bring reagents to room temperature before use
- Observe waiting time of 3 minutes exactly for precise measurement results
- Protect sample from air (Sulfite oxidizes quickly)
- Avoid direct sunlight during the measurement
- Rinse test tubes thoroughly with distilled water after use
- For boiler water: Allow the sample to cool down or use a sample cooler
Measuring range
| Measuring level | Description |
|---|---|
| 0.5 mg/l | Very low concentration (light yellow) |
| 1.0 mg/l | Low concentration (yellow) |
| 2.5 mg/l | Increased concentration (yellow-orange) |
| 5.0 mg/l | Average concentration (orange) |
| 10 mg/l | High concentration (orange-brown) |
| 20 mg/l | Very high concentration (brown) |
If the color lies between two fields, you can form the mean value
(e.g. between 5.0 and 10 mg/l = approx. 7-8 mg/l).
Number of possible determinations
You can carry out 150 measurements with one CALDUR® Sulfite test kit.
This refers to the quantity of reagents contained.
Measuring accuracy and reproducibility
Readability: ± 1 color level
Reproducibility: Very good if the application instructions are followed
Interferences: Turbidity and coloration of the sample can influence the result (filter the sample if necessary). High concentrations of sulphide can interfere with the measurement.
What to do if measured values are out of range?
Measured value > 20 mg/l
| Dilution | Procedure | Calculation of the measured value |
|---|---|---|
| 1:1 | 5 ml sample + 5 ml distilled water | Measured value × 2 |
| 1:4 | 2 ml sample + 8 ml distilled water | Measured value × 5 |
| 1:9 | 1 ml sample + 9 ml distilled water | Measured value × 10 |
Measured value < 0.5 mg/l
The measured value is below the detection limit. This indicates that the Sulfite concentration is very low. For boiler water, this means insufficient corrosion protection – the addition of sulphite should be increased.
Specifications at a glance
| Property | Value |
|---|---|
| Parameters | Sulfite (SO₃²-) |
| Item number | 31-072530 |
| Method | Colorimetric |
| Measuring principle | Color comparison with 6-stage color chart (thiobenzoic acid method) |
| Measuring range | 0.5 to 20 mg/l SO₃²- |
| Color scale | 6 measuring levels (0.5 / 1.0 / 2.5 / 5.0 / 10 / 20 mg/l) |
| Analysis time | 3 minutes |
| Number of determinations | 150 |
| Packaging | Hinged lid box |
| Packaging size | 103 x 91 x 36 mm |
| weight | approx. 150 g |
Scope of delivery
| Component | Component description |
|---|---|
| 2 reagent bottles | Reagent A and B with detailed labeling |
| 1 test tube | With 10 ml scale |
| 1 color chart | With 6 measuring levels for precise color comparison |
| Operating instructions | Detailed in DE/EN |
| Safety data sheets | For all reagents |
| Packaging | Robust hinged lid box (103 x 91 x 36 mm) |
Reagent details
| Reagent | Volume | Shelf life | Notes |
|---|---|---|---|
| Reagent A (Sulfite) | 30 ml | 36 months (36M) | Shake before use, store in a cool, dark place |
| Reagent B (Sulfite) | 10 ml | 36 months (36M) | Shake before use |
Shelf life: The shelf life starts from the date of manufacture (printed on the bottle).
After opening, the reagents should be used within 18 months.
Store the test kit in a dry, cool place (10-25°C) and away from direct sunlight.
Additional information
| Packaging | Hinged lid box, Refill pack |
|---|---|
| Product category | Test kit |
Flyer
Operating instructions
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