50 mL Centrifuge Tube Screw Caps — HDPE, Black, Light-Protective | 300-3541-Z20 | 1000/Bag
These black High-Density Polyethylene screw caps are designed to close Caplugs® Evergreen 50 mL centrifuge tubes, providing the critical added benefit of visible-light protection for photosensitive analytes during storage, transport, and pre-analytical hold. Part number 300-3541-Z20 is the final color in the nine-color 300-3541 cap family, and it is the only cap in that range whose black HDPE absorbs visible light — every other color in the family delivers equivalent sealing performance but without light attenuation. Supplied non-sterile in 1000/Bag, these caps are rated for cryogenic storage to −80°C and autoclave sterilization at 121°C.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 300-3541-Z20 |
| Cap Type | Screw cap — threaded engagement |
| Material | High-Density Polyethylene (HDPE) |
| Color | Black |
| Light Protection | Yes — black HDPE absorbs visible light |
| Tube Compatibility | Caplugs® Evergreen 50 mL centrifuge tubes |
| Thread Note | Larger thread than 300-3532 and 300-3010 families — not interchangeable |
| Cryogenic Storage | Compatible to −80°C |
| Autoclave | 121°C / 15 psi |
| Sterility | Non-Sterile |
| Pack Size | 1000/Bag |
| BPA / Phthalates | BPA-free; no phthalate plasticizers |
| Country of Origin | USA (California) |
Applications
Black caps in the 300-3541 family serve every routine 50 mL centrifuge tube application while adding meaningful light protection wherever photosensitive analytes are involved:
- Photosensitive specimen storage: Bilirubin degrades within minutes under fluorescent light; black HDPE caps protect bilirubin, porphyrins, vitamins A and B2, and therapeutic drug monitoring (TDM) analytes in large-volume 50 mL tubes from light-induced degradation during refrigerated pre-analytical hold
- Therapeutic drug monitoring: Light-protected capping of 50 mL specimens containing photosensitive TDM analytes prevents analyte loss between collection and analysis
- Biorepository archiving: HDPE's −80°C cryo stability makes these caps suitable for long-term biobank storage of light-sensitive specimens, and the black color blocks incidental light exposure during freezer retrieval
- Clinical chemistry — large-volume serum and plasma: Light-protected capping during refrigerated storage prior to high-volume clinical chemistry runs
- Routine 50 mL tube capping: For non-light-sensitive specimens, these caps deliver the same HDPE thread engagement and sealing performance as every other color in the 300-3541 range
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers / serum / plasma | Excellent |
| Short-chain alcohols (brief contact) | Good |
| DMSO (≤10%) | Good |
| Storage at −20°C / −80°C | Suitable — HDPE cryo stability |
| Autoclave (121°C / 15 psi) | Compatible |
Quality & Procurement
Made in USA (California), these Caplugs® Evergreen caps are manufactured from BPA-free, phthalate-free HDPE resin. The 300-3541 series spans nine colors — Natural, Blue, Orange, Green, Lavender, Red, White, Yellow, and Black — all sharing an identical thread specification and cryogenic rating, so labs can adopt color-coding across specimen types without requalifying hardware. LabSupplies.com is an authorized Caplugs® Evergreen dealer shipping from USA inventory, with tiered volume pricing available for clinical laboratories, biorepositories, and institutional procurement programs.
Frequently Asked Questions
Why choose the black cap over other colors in the 300-3541 family?
Black is the only color in the nine-color 300-3541 range that absorbs visible light, making it the correct choice whenever a specimen contains photosensitive analytes — such as bilirubin, porphyrins, riboflavin (vitamin B2), vitamin A, or certain TDM compounds — that can degrade under ambient or fluorescent light. For specimens where light exposure is not a concern, any other color in the family provides equivalent sealing performance.
Are these caps compatible with centrifuge tubes from other manufacturers?
These caps are specified for Caplugs® Evergreen 50 mL centrifuge tubes. The 300-3541 thread is larger than those used by the 300-3532 and 300-3010 cap families and is not interchangeable with them. Confirm thread compatibility before use with tubes from other suppliers.
Can these caps be autoclaved, and are they suitable for −80°C freezer storage?
Yes to both. The HDPE material is rated for autoclave sterilization at 121°C / 15 psi and maintains its integrity at cryogenic temperatures down to −80°C, making these caps appropriate for both sterile-processing workflows and long-term biorepository archiving.
Are these caps supplied sterile?
No — they are supplied non-sterile in 1000/Bag packaging. Labs requiring sterile caps should autoclave them prior to use, which the HDPE material fully supports at standard autoclave conditions.