{"product_id":"caplugs-300-3541-z20-hdpe-screw-cap-50ml-centrifuge-tube-black","title":"50 mL Centrifuge Tubes, Screw Caps, HDPE, Black — 300-3541-Z20 | 1000\/Bag | Caplugs® Evergreen","description":"\u003ch2\u003e50 mL Centrifuge Tube Screw Caps — HDPE, Black, Light-Protective | 300-3541-Z20 | 1000\/Bag\u003c\/h2\u003e\n\u003cp\u003eThese 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.\u003c\/p\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003ctable\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eSpecification\u003c\/th\u003e\n\u003cth\u003eValue\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003ePart Number (MPN)\u003c\/td\u003e\n\u003ctd\u003e300-3541-Z20\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCap Type\u003c\/td\u003e\n\u003ctd\u003eScrew cap — threaded engagement\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMaterial\u003c\/td\u003e\n\u003ctd\u003eHigh-Density Polyethylene (HDPE)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eColor\u003c\/td\u003e\n\u003ctd\u003eBlack\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eLight Protection\u003c\/td\u003e\n\u003ctd\u003eYes — black HDPE absorbs visible light\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eTube Compatibility\u003c\/td\u003e\n\u003ctd\u003eCaplugs® Evergreen 50 mL centrifuge tubes\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eThread Note\u003c\/td\u003e\n\u003ctd\u003eLarger thread than 300-3532 and 300-3010 families — not interchangeable\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCryogenic Storage\u003c\/td\u003e\n\u003ctd\u003eCompatible to −80°C\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAutoclave\u003c\/td\u003e\n\u003ctd\u003e121°C \/ 15 psi\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSterility\u003c\/td\u003e\n\u003ctd\u003eNon-Sterile\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePack Size\u003c\/td\u003e\n\u003ctd\u003e1000\/Bag\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBPA \/ Phthalates\u003c\/td\u003e\n\u003ctd\u003eBPA-free; no phthalate plasticizers\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCountry of Origin\u003c\/td\u003e\n\u003ctd\u003eUSA (California)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch2\u003eApplications\u003c\/h2\u003e\n\u003cp\u003eBlack caps in the 300-3541 family serve every routine 50 mL centrifuge tube application while adding meaningful light protection wherever photosensitive analytes are involved:\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePhotosensitive specimen storage:\u003c\/strong\u003e 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\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eTherapeutic drug monitoring:\u003c\/strong\u003e Light-protected capping of 50 mL specimens containing photosensitive TDM analytes prevents analyte loss between collection and analysis\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBiorepository archiving:\u003c\/strong\u003e 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\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eClinical chemistry — large-volume serum and plasma:\u003c\/strong\u003e Light-protected capping during refrigerated storage prior to high-volume clinical chemistry runs\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eRoutine 50 mL tube capping:\u003c\/strong\u003e 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\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eChemical Resistance\u003c\/h2\u003e\n\u003ctable\u003e\n\u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eReagent \/ Condition\u003c\/th\u003e\n\u003cth\u003eCompatibility\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eAqueous buffers \/ serum \/ plasma\u003c\/td\u003e\n\u003ctd\u003eExcellent\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eShort-chain alcohols (brief contact)\u003c\/td\u003e\n\u003ctd\u003eGood\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eDMSO (≤10%)\u003c\/td\u003e\n\u003ctd\u003eGood\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eStorage at −20°C \/ −80°C\u003c\/td\u003e\n\u003ctd\u003eSuitable — HDPE cryo stability\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eAutoclave (121°C \/ 15 psi)\u003c\/td\u003e\n\u003ctd\u003eCompatible\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch2\u003eQuality \u0026amp; Procurement\u003c\/h2\u003e\n\u003cp\u003eMade 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.\u003c\/p\u003e\n\n\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eWhy choose the black cap over other colors in the 300-3541 family?\u003c\/strong\u003e\u003cbr\u003eBlack 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.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eAre these caps compatible with centrifuge tubes from other manufacturers?\u003c\/strong\u003e\u003cbr\u003eThese 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.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCan these caps be autoclaved, and are they suitable for −80°C freezer storage?\u003c\/strong\u003e\u003cbr\u003eYes 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.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eAre these caps supplied sterile?\u003c\/strong\u003e\u003cbr\u003eNo — 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.\u003c\/p\u003e\n\n\u003cscript type=\"application\/ld+json\"\u003e{\"@context\":\"https:\/\/schema.org\/\",\"@type\":\"Product\",\"name\":\"50 mL Centrifuge Tube Screw Caps, HDPE, Black, Light-Protective — 1000\/Bag\",\"sku\":\"300-3541-Z20\",\"mpn\":\"300-3541-Z20\",\"brand\":{\"@type\":\"Brand\",\"name\":\"Caplugs® Evergreen\"},\"material\":\"High-Density Polyethylene (HDPE)\",\"color\":\"Black\",\"offers\":{\"@type\":\"Offer\",\"priceCurrency\":\"USD\",\"price\":\"115.50\",\"availability\":\"https:\/\/schema.org\/InStock\"}}\u003c\/script\u003e\n\u003cscript type=\"application\/ld+json\"\u003e{\"@context\":\"https:\/\/schema.org\/\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"Why choose the black cap over other colors in the 300-3541 family?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"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. 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