21 mL Round Bottom Test Tubes with Natural Screw Caps — PS, Sterile, 16 × 150 mm (222-2099-050)
These 21 mL polystyrene round-bottom test tubes ship sterile and unassembled — tubes and natural screw caps packaged separately within each 25/Bag unit for assembly immediately before use. At 16 × 150 mm, the round-bottom geometry concentrates cell pellets and precipitates at the tube base for efficient resuspension and aspiration after centrifugation, while the threaded natural screw cap delivers a leak-resistant closure for specimen containment during storage and transport. The optical clarity of polystyrene makes these tubes a standard choice for flow cytometry, immunofluorescence, and cell sorting workflows.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 222-2099-050 |
| Volume | 21 mL |
| Dimensions | 16 × 150 mm |
| Bottom Style | Round Bottom |
| Cap Style | Natural Screw Cap |
| Assembly | Unassembled |
| Material | Polystyrene (PS) |
| Color | Natural |
| Sterility | Sterile |
| Pack Size | 25/Bag |
| BPA / Phthalate Free | Yes |
| Country of Origin | USA |
Applications
- Flow cytometry and FACS analysis — round-bottom PS format is the standard tube geometry for most flow cytometer sample ports
- Immunofluorescence staining — polystyrene optical clarity supports visual and instrument-based inspection of fluorescent samples
- Cell sorting — round bottom concentrates sorted cell populations for downstream recovery
- Hematology sample preparation — 21 mL capacity accommodates larger-volume whole-blood and buffy-coat workflows
- Serological and agglutination assays — round-bottom geometry provides a defined endpoint for agglutination reading
- Specimen collection and general sample handling — threaded screw cap ensures secure containment during centrifugation, transport, and storage
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers / saline / PBS | Excellent |
| Dilute acids | Good |
| Dilute bases | Good |
| Methanol | Good — short-term contact |
| Isopropanol | Good — short-term contact |
| Acetonitrile | Good — short-term contact |
| Aromatic / chlorinated solvents | Not recommended |
| Autoclave / heat sterilization | Not recommended — PS is not autoclavable |
Quality & Procurement
Made in USA, these Caplugs® Evergreen test tubes are manufactured at ISO-certified facilities using virgin-grade, FDA-registered polystyrene resin that is BPA-free and phthalate-free. Lot-level quality controls ensure consistent tube geometry, wall thickness, and dimensional uniformity across every bag. LabSupplies.com is an authorized Caplugs® Evergreen dealer shipping from USA inventory, with tiered volume pricing available for clinical labs, research institutions, and biotech facilities operating under CAP, CLIA, or ISO 15189 accreditation.
Frequently Asked Questions
Are these tubes sterile when they arrive?
Yes — part number 222-2099-050 is supplied sterile. Tubes and caps are packaged separately within the sealed bag and should be assembled immediately before use to maintain sterility at the point of use.
Why are the tubes and caps packaged unassembled?
Shipping tubes and caps separately prevents cap deformation and ensures the threaded closure seats correctly when assembled fresh before use, maintaining a reliable leak-resistant seal.
Are polystyrene tubes suitable for centrifugation?
PS tubes are compatible with standard low- to moderate-speed centrifugation as used in cell pelleting and sample preparation. Confirm the g-force limits with your centrifuge rotor specifications; PS is generally not rated for high-speed ultracentrifugation applications.
Can these tubes be used with standard flow cytometers?
Round-bottom 12 × 75 mm tubes are the more common flow cytometry format, but many instruments and sample-handling racks also accommodate the 16 × 150 mm format. Verify that your cytometer's sample port or tube holder accepts 16 mm diameter tubes before ordering for automated workflows.