Lacmoid: Properties, Applications & Lab Uses

Lacmoid is a synthetic azine dye widely employed in research laboratories as a pH indicator and biological staining reagent, valued for its distinct color transition and versatile solubility in aqueous and organic media.

Common Name

Lacmoid (also known as Resorcin Blue)

Chemical Class

Synthetic azine (phenazine-type) dye

pH Indicator Range

Approximately pH 4.4 (red) to pH 6.4 (blue); color transition from red/pink to blue/violet

Solubility

Soluble in ethanol and dilute alkali; sparingly soluble in water

Primary Applications

pH indication, biological staining, analytical chemistry

Aladdin SKU

L404617

Source

TCI (L0079)

Chemical Identity and Physical Properties

Lacmoid, also commonly referred to as Resorcin Blue, is a synthetic dye belonging to the azine (phenazine-type) class of organic colorants. It is prepared by the oxidation of resorcinol (benzene-1,3-diol) in the presence of nitrous acid or similar oxidizing agents, yielding a dark blue to black solid powder.

Key physical and chemical properties include:

• Appearance: Dark blue-black crystalline powder
• Solubility: Readily soluble in ethanol and dilute alkaline solutions; sparingly soluble in cold water; more soluble in hot water
• Melting Point: Reported in the range of approximately 100–110 °C (exact value subject to verification)
• Molecular Formula: C₁₂H₉NO₄ (approximate; subject to verification against primary literature)
• CAS Number: 6371-61-5 (subject to verification)

The dye exhibits strong visible-light absorption, with the dominant chromophore responsible for its deep color arising from the extended conjugated aromatic system within its phenazine-type backbone.

Function as a pH Indicator

One of the primary uses of Lacmoid in analytical and research laboratories is as an acid-base (pH) indicator. It undergoes a well-defined color transition across a moderately acidic pH range, making it suitable for titrations and colorimetric assessments in this region.

Indicator Transition:

• Acidic conditions (below ~pH 4.4): Red to pink coloration
• Transition interval (~pH 4.4–6.4): Mixed intermediate hues
• Basic/neutral conditions (above ~pH 6.4): Blue to violet coloration

Lacmoid is typically prepared as a stock solution dissolved in 70% ethanol (approximately 0.2% w/v) for use in titrations. This ethanolic solution is stable when stored in a sealed amber glass bottle away from direct light and heat.

Compared to litmus (a natural dye of related appearance), Lacmoid is a defined synthetic compound with more reproducible lot-to-lot color characteristics, making it preferable in standardized analytical protocols.

Biological Staining and Analytical Applications

Beyond its role as a pH indicator, Lacmoid has been employed in biological staining protocols and specialty analytical applications:

Biological Staining

Lacmoid has been used as a histological and cytological stain for examining various biological specimens. Its affinity for certain cellular components under defined pH conditions allows for contrast staining in light microscopy. Specific tissues or organelles may show selective uptake depending on preparation conditions.

Staining of Aphids and Small Invertebrates

A notable specialized application of Lacmoid is the clearing and staining of aphids and other small soft-bodied arthropods for taxonomic and morphological studies. Specimens are treated with Lacmoid solution to render internal structures visible under a dissecting or compound microscope, facilitating identification of diagnostic anatomical features.

Analytical Chemistry

Lacmoid has been explored as a complexometric or colorimetric reagent for the detection of certain metal ions and other analytes in solution, leveraging the dye's ability to form colored complexes under defined conditions. Researchers should consult primary literature for specific protocols and sensitivity data.

Preparation, Storage, and Safety

Preparation of Working Solution:

1. Weigh out the required amount of Lacmoid powder (e.g., 0.2 g per 100 mL final volume).
2. Dissolve in a small volume of absolute ethanol with gentle warming if necessary.
3. Dilute to final volume with 70% aqueous ethanol.
4. Filter through a 0.45 µm membrane filter if a particle-free solution is required.
5. Transfer to an amber glass bottle, label with date and concentration, and store at room temperature (15–25 °C) away from light.

Storage Conditions: Store the solid reagent in a tightly sealed container at room temperature, protected from light and moisture. Shelf life under appropriate conditions is typically 2–3 years, though verification at time of use is recommended.

Safety Considerations: Lacmoid is a synthetic organic dye; standard laboratory precautions apply. Avoid inhalation of dust and contact with skin and eyes. Use in a well-ventilated area or fume hood when handling powder. Consult the Safety Data Sheet (SDS) provided by Aladdin Scientific (SKU L404617) for complete hazard information, first-aid measures, and disposal guidance before use.

Disposal: Dispose of Lacmoid solutions and contaminated materials in accordance with local institutional and regulatory guidelines for organic dye waste.

Ordering Lacmoid from Aladdin Scientific

Aladdin Scientific supplies Lacmoid (SKU: L404617) sourced from TCI (TCI catalogue reference L0079), ensuring traceability to a trusted synthetic reagent manufacturer. This product is suitable for research-grade applications including pH indication, biological staining, and analytical chemistry.

Key ordering information:

• SKU: L404617
• Source: TCI (L0079)
• Grade: Research reagent (confirm purity specification on product page or certificate of analysis)
• Available Quantities: Please refer to the current Aladdin Scientific product listing for available pack sizes and pricing

For bulk quantities, custom packaging, or technical support, contact Aladdin Scientific's customer service team. Certificates of Analysis (CoA) and Safety Data Sheets (SDS) are available upon request or via the product page.

Frequently asked questions

What is Lacmoid used for in the laboratory?

Lacmoid is primarily used as an acid-base pH indicator, with a color transition from red (acidic) to blue (basic) across approximately pH 4.4–6.4. It is also employed as a biological stain for histological specimens and small arthropods, and has applications in analytical colorimetry for detecting certain metal ions.

How do I prepare a Lacmoid indicator solution?

A standard working solution is prepared by dissolving approximately 0.2 g of Lacmoid in 100 mL of 70% aqueous ethanol with gentle stirring or mild warming. The resulting solution should be filtered if clarity is required and stored in a sealed amber glass bottle away from light at room temperature.

How does Lacmoid compare to litmus as a pH indicator?

Both Lacmoid and litmus display red-to-blue color transitions in the acidic-to-basic pH range and share a similar visual appearance. However, Lacmoid is a defined synthetic compound, offering more consistent lot-to-lot performance and reproducibility compared to litmus, which is a natural product mixture derived from lichens and may vary between batches.

What solvent should I use to dissolve Lacmoid?

Lacmoid dissolves well in ethanol (including 70% aqueous ethanol) and in dilute alkaline aqueous solutions. It has limited solubility in pure cold water. For most laboratory applications, a 70% ethanol solution is the recommended solvent system.

Where can I purchase Lacmoid for research use?

Lacmoid is available from Aladdin Scientific under SKU L404617, sourced from TCI (L0079). It can be ordered directly through the Aladdin Scientific website. Certificates of Analysis and Safety Data Sheets are available with each lot.

References

1. Sigma-Aldrich / Merck product documentation for Lacmoid (Resorcin Blue). General chemical and indicator properties.
2. TCI Chemicals product catalogue entry L0079 – Lacmoid. Physical property data and application notes.
3. Vogel, A.I. Vogel's Textbook of Quantitative Chemical Analysis. Longman Scientific & Technical. (General reference for acid-base indicators including Lacmoid transition pH range.)
4. Stary, J. The Solvent Extraction of Metal Chelates. Pergamon Press. (Reference for use of dyes including azine-type compounds in metal ion colorimetry.)

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.