21 mL Round-Bottom Test Tubes with Yellow Screw Caps — PS, 16 × 150 mm, 1000/Bag (214-2099-Y50)
These 21 mL polystyrene round-bottom test tubes ship with matching yellow screw caps, unassembled, in a 1000/Bag pack — making them the largest round-bottom tube in the Caplugs® Evergreen catalog and well suited to bulk reagent preparation, extended inversion mixing, and large-volume culture or reaction workflows. The 16 × 150 mm format fits standard 16 mm tube racks, and the yellow screw cap provides a leak-resistant re-closure for sample storage, transport, and reflex testing without the need for aliquot transfer. Bearing part number 214-2099-Y50, these tubes are supplied non-sterile and are produced from BPA-free, phthalate-free, FDA-compliant polystyrene in a USA facility.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 214-2099-Y50 |
| Capacity | 21 mL |
| Dimensions | 16 × 150 mm |
| Geometry | Round bottom |
| Material | Polystyrene (PS) |
| Tube Color | Natural (clear) |
| Cap Style | Screw cap |
| Cap Color | Yellow |
| Assembly | Unassembled (tubes and caps supplied separately) |
| Sterility | Non-Sterile |
| Pack Size | 1000/Bag |
| BPA / Phthalate / Latex | BPA-Free, Phthalate-Free, Latex-Free |
| Country of Origin | USA |
Applications
- Sample storage and transport: The yellow screw cap creates a leak-resistant seal for refrigerated (4 °C) or frozen (−20 °C) storage and secondary-containment transport; the color provides immediate rack-level visual identification of specimen cohort, time point, or analyte panel.
- Reflex and add-on testing: Re-cap and refrigerate after an initial run without transferring to a secondary tube, preserving sample integrity for downstream analysis.
- Bulk reagent and calibrator preparation: The 21 mL working volume — the largest in the Caplugs® Evergreen round-bottom family — accommodates multi-day reagent storage with the cap maintaining concentration between uses.
- Water bath incubation: Polystyrene maintains dimensional stability during 37 °C water bath protocols; loosen the cap if gas generation is expected.
- Inversion mixing: The full 21 mL tube length maximizes headspace for thorough manual inversion mixing of suspensions, reagents, or blood-collection equivalents.
- Clinical centrifugation: Round-bottom geometry is compatible with standard clinical centrifuge rotors sized for the 16 × 150 mm format.
- Color-coded multi-arm study protocols: Yellow cap aligns with hepatitis panel workflows, SST/gold-top tube correspondence conventions, and research protocols where yellow designates a specific patient group or analyte class.
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers and saline | Excellent |
| Dilute acids and bases (routine chemistry pH range) | Good |
| Water bath incubation up to 60 °C | Compatible |
| Ethanol > 70% / isopropanol | Not recommended |
| Acetone | Not recommended |
| Chlorinated or aromatic solvents | Not recommended |
| Autoclaving | Not recommended (PS not autoclavable) |
Quality & Procurement
Made in USA under ISO 9001 quality management controls, these Caplugs® Evergreen tubes are molded from FDA-compliant polystyrene resin that is certified BPA-free, phthalate-free, and latex-free. The unassembled pack format lets laboratory staff apply caps at the point of sealing, minimizing open-tube exposure time in high-throughput workflows. LabSupplies.com is an authorized Caplugs® Evergreen dealer and ships from USA inventory — typically same business day for stocking items — with volume pricing available for institutional, hospital, and grant-funded procurement. If yellow is not the required identifier, the same 21 mL round-bottom tube is available with blue, orange, green, lavender, and red screw caps; a caps-free tubes-only option is also available for labs that source caps separately.
Frequently Asked Questions
Are these test tubes sterile?
No — they are supplied non-sterile, which is appropriate for the vast majority of reagent preparation, sample storage, and general chemistry workflows. If your application requires sterility, contact us to discuss alternative configurations.
Why are the tubes and caps shipped unassembled?
The unassembled pack format allows technicians to apply caps at the actual point of sealing rather than before sample addition, reducing the window during which open tubes are exposed to the bench environment. It also simplifies high-throughput loading onto tube racks and automated filling lines.
Is polystyrene suitable for use with organic solvents or for autoclaving?
Polystyrene provides excellent clarity and compatibility with aqueous buffers and dilute reagents, but it is not resistant to acetone, high-concentration alcohols, or chlorinated and aromatic solvents, and it should not be autoclaved. For workflows requiring solvent resistance or steam sterilization, polypropylene tubes would be the appropriate material choice.
What is the significance of the yellow cap color?
Yellow is conventionally associated with hepatitis panel specimens and SST/gold-top collection tube correspondence in many clinical laboratory color-coding systems. In research settings, yellow is frequently assigned to a designated patient cohort, study time point, or analyte panel, giving teams an immediate visual identifier at the rack level without consulting a label or manifest.