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.
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.
