21 mL Round-Bottom Screw-Cap Test Tubes — PS, Natural Tube / Green Cap, 16 × 150 mm (214-2099-G50)
These 21 mL polystyrene round-bottom test tubes ship unassembled with green screw caps in a 1000/Bag pack, sized at 16 × 150 mm for large-volume sample storage, reagent preparation, and extended mixing workflows. Supplied non-sterile, they are the largest round-bottom tube in the Caplugs® Evergreen catalog, offering maximum working volume at the 15–21 mL scale. The green screw cap provides a re-sealable, leak-resistant closure and serves as an instant rack-level color identifier — a convention widely associated with lithium heparin plasma in clinical color-coding systems.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 214-2099-G50 |
| Capacity | 21 mL |
| Dimensions | 16 × 150 mm |
| Geometry | Round Bottom |
| Material | Polystyrene (PS) |
| Tube Color | Natural (clear) |
| Cap Style | Screw Cap |
| Cap Color | Green |
| Assembly | Unassembled (tubes and caps packed separately) |
| Sterility | Non-Sterile |
| Pack Size | 1000/Bag |
| BPA / Phthalate / Latex | BPA-Free, Phthalate-Free, Latex-Free |
| Country of Origin | USA |
Applications
- Sample storage at refrigerator (4 °C) or freezer (−20 °C) conditions, with the green cap providing immediate visual cohort identification at rack level
- Specimen transport in tube carriers or secondary containment — the screw cap delivers a leak-resistant closure without additional film or parafilm
- Reflex and add-on testing: re-cap and refrigerate after an initial run without transferring to a secondary aliquot tube
- Bulk reagent and calibrator preparation, with the 21 mL volume accommodating multi-day storage between uses
- Water bath incubation up to 60 °C in standard 16 mm tube racks
- Manual inversion mixing protocols — the longest tube in the Caplugs® Evergreen round-bottom family maximizes headspace for thorough mixing
- Centrifugation in clinical centrifuges fitted with 16 mm rotor positions
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers and saline | Excellent |
| Dilute acids and bases (routine chemistry pH range) | Good |
| Water bath incubation ≤ 60 °C | Compatible |
| Ethanol > 70% / isopropanol | Not recommended |
| Acetone / chlorinated solvents | Not recommended |
| Aromatic solvents (toluene, xylene) | Not recommended |
| Autoclaving | Not compatible — PS is not autoclavable |
Quality & Procurement
Made in USA, these Caplugs® Evergreen tubes are manufactured from FDA-compliant, BPA-free, phthalate-free, latex-free polystyrene under ISO 9001 quality management controls. The natural (clear) tube wall provides sufficient optical clarity for visual inspection and direct spectrophotometric reading of aqueous samples. The unassembled pack format — tubes and caps supplied separately — lets staff apply caps at the point of sealing, reducing open-tube exposure time in high-throughput workflows. LabSupplies.com is an authorized dealer and ships from USA inventory, typically same business day for stocking items; tiered pricing is available for institutional, hospital, and grant-funded laboratories ordering ten or more bags.
Frequently Asked Questions
Are these tubes and caps supplied already assembled?
No — the 1000/Bag pack ships unassembled, with tubes and green screw caps packed separately. This lets laboratory staff cap each tube at the point of use, minimizing open-tube exposure during high-throughput processing.
Can these tubes be autoclaved or used with organic solvents?
Polystyrene is not autoclavable and is not resistant to alcohols above 70%, acetone, chlorinated solvents, or aromatic solvents. These tubes are intended for aqueous reagents, biological samples, and dilute acid/base applications in the routine chemistry pH range.
Why is the cap green, and does it match clinical color-coding conventions?
Green is widely associated with lithium heparin plasma tubes in phlebotomy color-coding systems. Choosing green-capped storage tubes for the corresponding sample class allows staff to identify the analyte category at a glance across an entire rack without reading individual labels.
Is a tubes-only option available if we already have caps on hand?
Yes — the Caplugs® Evergreen catalog includes a 21 mL round-bottom tube without a cap (part number 214-2097-010, 1000/Bag). Additional screw-cap color options for the same 21 mL tube format include blue, orange, lavender, red, and yellow variants within the 214-2099 series.