Is There Any Bismuth in Soft‑Guard™ Septa? Technical Clarification for LC/GC/LC‑MS Workflows
Short answer: No. Bismuth is not used in the manufacturing of either the silicone rubber or the septa assembly in Soft‑Guard™ closures.
Why this matters to analytical scientists
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ICP‑MS / elemental workflows: Bismuth (Bi) is commonly monitored at trace levels. Any contribution from consumables can elevate blanks or bias recoveries. Knowing that Soft‑Guard™ septa do not contain bismuth reduces risk when setting method detection limits or running contamination‑sensitive sequences.
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LC‑MS(/MS) background control: Even without bismuth, septa composition and purity still affect chromatographic cleanliness. Soft‑Guard™ uses high‑purity silicone rubber with a cast PTFE face to minimize extractables that can produce ghost peaks or ion suppression in LC‑MS(/MS).
Soft‑Guard™ materials & performance at a glance
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Material system: High‑purity silicone rubber + cast PTFE facing designed for low extractables and reliable resealing after needle penetration.
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Needle compatibility and reseal: Soft‑Guard™ septa are engineered for consistent penetration force and resealing, helping prevent coring, missed injections, and evaporation during long queues.
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Format options: Available in 9‑425 screw and 11 mm snap formats and with different pre‑slit geometries (e.g., X/Y) to balance penetration vs. reseal for various autosamplers (e.g., Waters™ Alliance/ACQUITY).
When to consider AQR™ instead of standard Soft‑Guard™
For ultra‑trace LC‑MS(/MS) assays that demand the lowest possible extractables background, MicroSolv recommends the ultra‑pure, colorless AQR™ septa and caps. These retain Soft‑Guard™ mechanics while pushing purity for the tightest S/N and baseline requirements.
Practical guidance for method developers & QA/QC
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Document septa composition in your method files and procurement specs—explicitly noting no bismuth content for Soft‑Guard™—to streamline elemental cleanliness justifications.
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Run solvent and matrix blanks during validation to verify background is within acceptance criteria. If baseline targets are extremely stringent, evaluate AQR™ as a next‑step option.
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Match slit geometry to instrument: pre‑slit designs (X or Y) ease penetration but may slightly reduce reseal vs. single‑slit; choose per autosampler/sequence needs.
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Maintain consistent torque and handling of caps to prevent variable compression of septa and ensure sealing repeatability across trays. (General Soft‑Guard™ handling guidance)
Key takeaways
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No bismuth is used in Soft‑Guard™ septa or silicone rubber.
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Soft‑Guard™ is designed for low extractables, easy penetration, and reliable resealing, supporting clean LC/GC/LC‑MS operation.
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For ultra‑trace LC‑MS(/MS), upgrade to AQR™ (ultra‑pure, colorless) to push background even lower while retaining Soft‑Guard™ performance characteristics.
