Wool Processing Sulfite Test Strips

SKU: 33817-S

$29.25USD or lower Each

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Test wool for residual sulfites used in anti-felting and oxidative treatments. Indigo® sulfite test strips detect free sulfite for quality control in wool processing and textile labs.

Sulfite-based treatments play an important role in modern wool processing. When wool is oxidized, its disulfide bonds become more reactive, allowing nucleophilic agents such as sulfite to modify the keratin structure. This chemistry supports anti-felting, shrink-resistance, and enhanced dye uptake. Indigo® sulfite test strips provide a fast, inexpensive way to detect free sulfite on processed wool, helping manufacturers verify treatment effectiveness and maintain consistent product quality.

We've been selling sulfite test strips since 2007. Buy fully documented Indigo® sulfite test strips,100 strips/vial with a guaranteed 3 year shelf life (dated back from expiration date "yyyy.mm.dd").
Details Specs Docs Reviews
Details

How to Test Wool for Sulfite Residues

  • Prepare a rinse extract: Cut a small sample (1–2 g) of treated wool.
    Immerse in 20–30 mL of warm distilled water (40–50 °C improves extraction).
    Agitate gently for 2-3 minutes.
  • Prepare the test strip: Wet the sulfite pad with distilled or deionized water.
  • Test the extract: Dip the wetted pad quickly into the wool extract OR
    Touch the wetted pad to the surface of the wool while still damp.
  • Read the color change: Compare the pad to the color chart. Detection range: 10-500 ppm free sulfite.
  • Interpretation: Positive color = residual sulfite present on fiber or in process bath.
    Lower color = treatment exhaustion or insufficient nucleophilic reaction.
    No color = little or no free sulfite remaining.

Educational Value of Testing Sulfites in Wool Processing

Concept Description Activity Learning Link
Keratin Disulfide Bonds Wool fibers contain S-S crosslinks that determine strength, elasticity, and felting behavior. Observe how sulfite reacts differently depending on oxidation pretreatment. Protein chemistry, disulfide bond cleavage.
Nucleophilic Attack by Sulfite Sulfite ions act as nucleophiles that can modify oxidized protein structures. Compare sulfite presence before and after anti-felting treatment. Nucleophilic substitution, textile finishing chemistry.
Quality Control in Wool Processing Testing ensures consistent shrink-resistance and treatment uniformity. Measure residual sulfite across batches or different processing conditions. Industrial chemistry, process validation.
Analytical Detection Limits Strips measure free sulfite from 10-500 ppm, suitable for QA screening. Prepare wool extracts and record concentration comparisons. Analytical method selection, colorimetric analysis.

For those interested in the chemistry of how these strips work, please refer to this pdf which explains the theory of how free sulfite is detected.

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Specifications

Indigo® sulfite test strips indicate the presence of sulfite ion in increments of 10, 50, 100, 250, and 500ppm after 15 seconds.

  • The number of strips (100) vial is approximate.
  • These strips have a guaranteed shelf of 3 years from date of manufacture (indicated by expiration date)
    Vial must be kept tightly sealed & kept at typical room temperatures.
  • Vial has a built in desiccant and strips can, in principle, last much longer.
    For more information, see: Test Strip Expiration Dates; Good Today, Dead Tomorrow?
  • Strips test for: sulfite, bisulfite and metabisulfite
Documentation

A Certificate of Conformance is available on request after shipment.
Indigo® sulfite test strips are made in USA & calibrated with NIST standards.

Test Strip Documentation
Stability Statement Certificate of Analysis SDS
Indigo Sulfite Test Strips 0-500ppm Stability Statement Indigo Sulfite Test Strips 0-500ppm Certificate of Analysis Indigo Sulfite Test Strips 0-500ppm SDS
Reviews (2)
2023-10-27

Test strips worked as described, including the red wine citric acid method. I first did some comparisons using sulfites in water. Dipping the strips and the citric acid method gave the same result, albeit a little lower than expected. Solution was mixed to 100 ppm and both strips showed about 75. Used a similar technique on red wine, although dipping does not work. Wine with no sulfites showed zero. Added and got similar readings to the water results. Thanks for the great product and the citric acid trick.

2021-01-22

Great place for a hard to find product. Excellent price! Quick shipping.

— Quality Control
— Indigo:

Thanks for letting us know. This might interest you since you are in quality control: Can 10ppm of Sulfite & Quat Really Mean Zero?

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