Our diluent chemistry guide covers what goes into a solution. This page covers what the solution touches on the way in and out — filters, vials, and syringe materials — and why that choice isn't just a matter of convenience.
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Get my free report + free book →A 0.22-micron pore size is the standard threshold for what's called sterilizing-grade filtration, and it's chosen because most bacteria fall in the 0.5-to-5-micron range — large enough to be reliably trapped by a filter that size. It's important to be precise about what that does and doesn't mean: a 0.22-micron filter removes bacteria, but it does not remove viruses, which are substantially smaller, and it does not remove anything dissolved in the solution — salts, small molecules, and the peptide itself all pass straight through, because filtration by pore size only stops particles, not dissolved compounds. "Filtered" is not a synonym for "purified" in the sense of removing unwanted dissolved substances; it specifically addresses one category of contamination risk.
Sterile filters aren't interchangeable just because they share a pore size. Polyethersulfone, commonly abbreviated PES, is widely used for protein and peptide solutions specifically because it binds less protein than alternatives like nylon or cellulose acetate — a filter that grabs onto some of the peptide itself as the solution passes through effectively reduces the concentration of what you actually end up with. For a protein or peptide solution, that low-binding property is usually the more relevant spec than pore size alone.
Our diluent chemistry guide covers DMSO, acetonitrile, and DMF as diluents used when water alone isn't enough to dissolve certain sequences. Those solvents are chemically aggressive by design, and that has a practical side effect: some lower-grade plastics aren't fully inert to them. Polypropylene is generally considered robust against DMSO exposure and is a common choice for that reason, but even polypropylene isn't immune from every risk — concentrated (neat) DMSO, elevated temperature, or extended contact time can extract trace compounds out of some plastic formulations and into the solution, particularly with less-controlled plastic sourcing. That doesn't mean plastic is unsafe by default; it means material compatibility is a real variable with these particular solvents, not a detail unique to laboratory settings, and it's part of why the specific diluent and container combination your pharmacy uses reflects their own material testing, not a universal rule.
For the diluent side of this picture, see diluent chemistry. For what can go wrong over time regardless of container, see degradation science.
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