Sulphite (Free) Test Kits
Titrimetric Kits
| Range | MDL | Method | Type | Kit Cat. No. | Refill |
|---|---|---|---|---|---|
| 2 - 20 ppm as SO3 | 2.0 ppm | Iodometric | Titrets | K-9602 | |
| 5 - 50 ppm as SO3 | 5.0 ppm | Iodometric | Titrets | K-9605 | |
| 10 - 100 ppm as SO3 | 10 ppm | Iodometric | Titrets | K-9610 | |
| 50 - 500 ppm as SO3 | 50 ppm | Iodometric | Titrets | K-9650 | |
| 10 - 100 ppm as SO2 | 10 ppm | Ripper (Sulphite in Wine) | Titrets | K-9610W* |
CHEMetrics offers test kits employing the well-known Iodometric and Ripper Methods to deliver sensitivity and accuracy within two minutes or less. The Iodometric Method is used for the water analysis kits. The Ripper Method is used for the Sulphite in White Wines test kit. Based on CHEMetrics patented Self-Filling Reagent Ampoule technology. Premixed. Premeasured. Precise. Each kit contains 30 tests (* except for Sulphite in Wine which contains 10 tests).
The Iodometric Method (Sulphite)
CHEMetrics free sulphite test kits employ the iodometric chemistry in which sulphite is titrated with iodide-iodate titrant in an acid solution using a starch indicator. Thiosulphate will titrate as sulphite. Sulphamic acid is added to the sample to prevent interference from nitrite. Results are expressed as ppm (mg/l) SO3.
CHEMetrics free sulphite kits can be used to measure thiosulphate. Multiply test results by 1.4 to convert from ppm sulphite (SO3) to ppm thiosulphate (S2O3). Please be aware that the sulphite kits cannot distinguish between thiosulphate and sulphite.
References:
ASTM D 1339-84, Sulphite Ion in Water, Test Method C.
APHA Standard Methods, 22nd ed., Method 4500-SO3 2- B - 2000.
USEPA Methods for Chemical Analysis of Water and Wastes, Method 377.1 (1983).
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Technical Data Sheet |
The Ripper Method (Sulphite in Wine)
CHEMetrics' sulphite in wine test kit is based on the Ripper method, which the wine industry has used for years as a standard for rapid sulphite analysis. Sulphite is titrated with an iodide-iodate solution, using a starch end point indicator. Phosphoric acid is used to adjust the pH of the sample. Results are quantified using direct-reading titration cells. The test determines free sulphite as ppm (mg/l) SO2.
Results for this test kit are acceptable for white wines (although they can have an error of up to 10 ppm). This test kit is not recommended for use with red wines or white wines containing ascorbic acid or tannin. These wines often give false high test results.
References:
ASTM D 1339-84, Sulphite Ion in Water, Test Method C.
APHA Standard Methods, 22nd ed., Method 4500-SO3 2- B -2000.
USEPA Methods for Chemical Analysis of Water and Wastes, Method 377.1 (1983).
Titrets Technology
CHEMetrics Sulphite test kits utilize Titrets® ampoules. Titrets ampoules use a reverse titration technique to measure analyte concentration levels (titrant volume inside the ampoule is fixed while the sample volume is varied). After snapping the ampoule tip, sample is drawn into the test ampoule in small doses until a color change signals the endpoint has been reached. The titration is stopped at the end point, and the liquid level in the ampoule corresponds to the concentration printed on a scale on the ampoule’s outer surface.
Applications
Sodium sulphite is the most common form of sulphite and is a strong reducing agent. Sodium or potasium sulphite are commonly used as an oxygen scavengers in low pressure boiler systems to inhibit corrosion. They are the preferred oxygen scavenger for many operators owing to the low cost of sulphite compounds. Sulphite levels in boiler water are measured to ensure application of correct dosage amounts and sufficient residual to prevent corrosion within the system. Frequent testing can keep costs low by preventing costly maintenance and wasted chemicals owing to overtreatment. Waste treatment plants that use sulphur dioxide to remove excess chlorine must monitor their effluents for sulphite.
Sulphites have been used for centuries to sanitise and preserve foods and beverages. They are used worldwide in the wine industry as antioxidant and antimicrobial agents and to stop fermentation to a set point. However, sulphites have been identified as causative agents in certain allergic reactions suffered by asthmatics. As a result, both the FDA and ATF in the USA, and EU food labelling legislation, have mandated that sulphites in foods and beverages, at levels of 10 ppm or higher, be identified on the label. Sulphite is measured to ensure production facilities operate within prescribed limits. The sulphite concentration in wine is measured at different points in the fermentation and/or packaging processes, to verify that levels are sufficient to prevent spoilage and yet low enough to maintain the quality of the wine. Sulphite tests can prevent wasting time and money on product that is not meeting the necessary requirements to ship.
What is Sulphite?
Sulphites are compounds that contain the sulphite ion or the sulphate (IV) (SO32-), sulphur dioxide, bisulphites and metabisulphites. The sulphite ion is the conjugate base - an acid donating a proton - to bisulphite. Sulphite is a strong reducing agent and readily oxidised by dissolved oxygen to sulphate. Sulphite ions are stable in the absence of oxygen unlike sulphurous acid which readily breaks down to sulphur dioxide and water. The sulphite ion is a resonance structure consisting of one sulphur atom bonded to one oxygen atom with a double bond (zero charge) and two oxygen atoms with a single bond (each carrying a -1 charge), with a total charge of -2 for the anion. If sulphite is discharged in effluents or from domestic wastewaters, it readily oxidises to form sulphate. Sulphite may be present in treated industrial wastewater but is not usually present in natural bodies of water such as surface waters for that reason. Sulphites occur naturally in some foods.