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[161.38.202.170]) by mx.google.com with UTF8SMTPS id 41be03b00d2f7-c76916baac1si13822824a12.70.2026.03.30.09.49.05 for (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 30 Mar 2026 09:49:05 -0700 (PDT) Received-SPF: pass (google.com: domain of bounce+91e48a.63af5d-tjphuhs=gmail.com@mg-d0.substack.com designates 161.38.202.170 as permitted sender) client-ip=161.38.202.170; Authentication-Results: mx.google.com; dkim=pass header.i=@mg-d0.substack.com header.s=mailo header.b=aiQoxEjO; dkim=pass header.i=@mailgun.org header.s=mg header.b=chF5lnVc; spf=pass (google.com: domain of bounce+91e48a.63af5d-tjphuhs=gmail.com@mg-d0.substack.com designates 161.38.202.170 as permitted sender) smtp.mailfrom="bounce+91e48a.63af5d-tjphuhs=gmail.com@mg-d0.substack.com"; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=substack.com DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg-d0.substack.com; q=dns/txt; s=mailo; t=1774889344; x=1774896544; h=List-Unsubscribe-Post: List-Unsubscribe: List-Post: List-Id: List-Archive: List-Owner: Reply-To: In-Reply-To: References: Sender: Sender: Date: Message-Id: To: To: From: From: Subject: Subject: Content-Type: Mime-Version: X-Feedback-Id; bh=AH240hzSHDVQlR+hW8YQLxi1QWUi7IPJQr59/MK9Fqs=; b=aiQoxEjOq4r1h+XlVjgJcMbdEpiIwcilRcvSP6kVJw0ADL/WEKgYLG3cvL+ywEcfAL859k4FDCCUBCP7mTu38wR8yKbFVy8K5ftFHOC/8GJ1K8Cl6MZcf9ElZD+Jl8hCFglFV9OdOnSLQaQOjUMlXh9ZSM3y9zLPVktxJgMbx7U= DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mailgun.org; q=dns/txt; s=mg; t=1774889344; x=1774896544; h=List-Unsubscribe-Post: List-Unsubscribe: List-Post: List-Id: List-Archive: List-Owner: Reply-To: In-Reply-To: References: Sender: Sender: Date: Message-Id: To: To: From: From: Subject: Subject: Content-Type: Mime-Version: X-Feedback-Id; bh=AH240hzSHDVQlR+hW8YQLxi1QWUi7IPJQr59/MK9Fqs=; b=chF5lnVcoaYRI3do4/f0a7+KO45J4zZmsakk2e9pNIrF45TXy2aYWSGhlHV83q2hWF0ZXDQ9Q6S0g2sgDn/QuO9qVgph/9aLEdZoMrdshVuIIEH6aN7aoqTe36KPkOJQufcwvQTsI6cXNVuRJEWwam6bYBb+AbGwFK8q/WKXLXA= X-Mailgun-Sid: WyJkZWU4NyIsInRqcGh1aHNAZ21haWwuY29tIiwiNjNhZjVkIl0= X-Feedback-Id: postmaster@mg-d0.substack.com:post:6148c7d8a45790427cda307f:mailgun Received: by 37f33708e84c4860334361637609e39dff35887f3892a1e76a445e56150f14f0 with HTTP id 69caa9803988ca445d627841; Mon, 30 Mar 2026 16:49:04 GMT X-Mailgun-Sending-Ip: 161.38.202.170 Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="b2aa63fe3c0332035a3550a6e528d83f2385ca953bd7a187f43ed1504eaf" Subject: Can You Filter Your Way Out of Failed Sterility? From: Derek from Peptide Price To: tjphuhs@gmail.com X-Mailgun-Tag: post X-Mailgun-Track-Clicks: false Message-Id: <20260330164822.3.b467a927a7fdb512@mg-d0.substack.com> Date: Mon, 30 Mar 2026 16:48:22 +0000 Feedback-Id: post-192631819:cat-post:pub-3365367:substack Sender: Derek from Peptide Price References: In-Reply-To: Reply-To: Derek from Peptide Price List-Owner: List-Url: List-Archive: List-Id: List-Post: List-Unsubscribe: List-Unsubscribe-Post: List-Unsubscribe=One-Click X-Mailgun-Variables: {"category": "post", "email_generated_at": "1774889344466", "is_freemail": "true", "post_audience": "everyone", "post_id": "192631819", "post_type": "newsletter", "pub_community_enabled": "true", "publication_id": "3365367", "subdomain": "derekpruski", "user_id": "273622398"} --b2aa63fe3c0332035a3550a6e528d83f2385ca953bd7a187f43ed1504eaf Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable View this post on the web at https://derekpruski.substack.com/p/can-you-fil= ter-your-way-out-of-failed Got a great question from a researcher recently that I think cuts to the he= art of why third-party sterility testing exists in the first place =E2=80= =94 and why filtration isn=E2=80=99t a workaround. The question: =E2=80=9CIf researching with product already in hand without USP 71 Sterili= ty Testing, would filtering it through a PES Hydrophilic Membrane 0.2=CE=BC= m Lab Filter remove any living microorganisms but not endotoxins? And would= the greater health risk be microorganisms vs endotoxins?=E2=80=9D This is a genuinely good question, and parts of it are technically correct.= But the conclusion it=E2=80=99s leading toward =E2=80=94 that filtration c= an substitute for proper sterility testing =E2=80=94 doesn=E2=80=99t hold u= p. Let=E2=80=99s break it down. What the question gets right 0.2=CE=BCm filtration can remove most living bacteria and fungi. And yes, e= ndotoxins are generally the bigger concern compared to living microorganism= s in most research scenarios. Both of those things are true. But here=E2=80=99s where it breaks down: even if a product would fail steri= lity testing, running it through a 0.2=CE=BCm filter does not mean it would= pass afterward. Why filtration isn=E2=80=99t a sterility guarantee USP 71 Sterility Testing has zero tolerance. Any microbial growth equals a = failure. Filtration reduces microbial load =E2=80=94 it doesn=E2=80=99t eli= minate it entirely, and it doesn=E2=80=99t come close to replicating what s= terility testing actually verifies. Here=E2=80=99s what can still get through or survive: Spore-forming bacteria like Bacillus species are highly resistant and can s= urvive filtration Biofilms and clumped bacteria can partially shield organisms from being cap= tured Mycoplasma ranges from 0.1=E2=80=930.3=CE=BCm and can pass through a 0.2=CE= =BCm filter Smaller viruses pass through entirely Any breach in filter integrity or technique error compromises the whole pro= cess And critically: none of this touches endotoxins at all. What 0.2=CE=BCm filtration actually removes Most bacteria (typically 0.5=E2=80=935=CE=BCm) Most fungi and yeasts (typically 2=E2=80=9310=CE=BCm+) Larger particles and debris Some larger viruses What it does not remove Endotoxins =E2=80=94 bacterial toxins that are only 10=E2=80=93100kDa in mo= lecular weight, orders of magnitude smaller than the filter pores Smaller viruses Mycoplasma Other bacterial toxins and pyrogens Chemical contaminants Bacterial spores that survive the process Why endotoxins are usually the bigger concern Living microorganisms require active multiplication to cause significant is= sues. A research subject=E2=80=99s immune response can often handle small a= mounts, and refrigerated storage slows growth considerably. Endotoxins operate differently. They don=E2=80=99t need to be alive to caus= e problems. They trigger immediate inflammatory responses, are potent at ve= ry small concentrations, and are significantly harder to remove once presen= t. Fever, inflammation, systemic reactions =E2=80=94 endotoxins are behind = all of it, and no amount of post-purchase filtration gets rid of them. The analogy that makes it click Think of a failed sterility product like the aftermath of a house party you= weren=E2=80=99t invited to host. You can remove most of the people =E2=80=94 but you=E2=80=99re still left w= ith all the garbage, spills, and damage they left behind, plus a few stragg= lers hiding in the closets. Filtration gets rid of some of the guests. It doesn=E2=80=99t clean the hou= se. The bottom line If a product was contaminated during manufacturing, filtering it afterward = leaves you with all the toxic byproducts the bacteria produced while multip= lying, potentially some resistant organisms that made it through, and still= no guarantee the product would pass sterility testing. There is no DIY workaround for proper manufacturing standards. This is exac= tly why USP 71 Sterility Testing exists =E2=80=94 and why it=E2=80=99s beco= me the benchmark worth paying attention to when evaluating vendors. All research discussed is for research use only. Not for human consumption. Unsubscribe https://substack.com/redirect/2/eyJlIjoiaHR0cHM6Ly9kZXJla3BydXN= raS5zdWJzdGFjay5jb20vYWN0aW9uL2Rpc2FibGVfZW1haWw_dG9rZW49ZXlKMWMyVnlYMmxrSW= pveU56TTJNakl6T1Rnc0luQnZjM1JmYVdRaU9qRTVNall6TVRneE9Td2lhV0YwSWpveE56YzBPR= Gc1TXpRMExDSmxlSEFpT2pFNE1EWTBNalV6TkRRc0ltbHpjeUk2SW5CMVlpMHpNelkxTXpZM0lp= d2ljM1ZpSWpvaVpHbHpZV0pzWlY5bGJXRnBiQ0o5Lm1DU250TlVJeDAweTItQkkzdjJZcDRtbmo= 4VlZXNXRJNHVHVWtMSzI3dE0iLCJwIjoxOTI2MzE4MTksInMiOjMzNjUzNjcsImYiOnRydWUsIn= UiOjI3MzYyMjM5OCwiaWF0IjoxNzc0ODg5MzQ0LCJleHAiOjIwOTA0NjUzNDQsImlzcyI6InB1Y= i0wIiwic3ViIjoibGluay1yZWRpcmVjdCJ9.DKiWB9YighCuDkdM-kwmkjg2KIb7riAP9UVnqTS= j11w? --b2aa63fe3c0332035a3550a6e528d83f2385ca953bd7a187f43ed1504eaf Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable Can You Filter Your Way = Out of Failed Sterility?3D""
Spoiler: No. Here’s why that matters.
͏     = ­͏     ­͏     ­͏  =   ­͏     ­͏     ­T= 7;     ­͏     ­͏     &= #173;͏     ­͏     ­͏   =   ­͏     ­͏     ­͏= ;     ­͏     ­͏     &#= 173;͏     ­͏     ­͏   &= #8199; ­͏     ­͏     ­͏=     ­͏     ­͏     = 73;͏     ­͏     ­͏   &#= 8199; ­͏     ­͏     ­͏ =     ­͏     ­͏     = 3;͏     ­͏     ­͏   = 199; ­͏     ­͏     ­͏ &= nbsp;   ­͏     ­͏     ­= ;͏     ­͏     ­͏   Q= 99; ­͏     ­͏     ­͏ &n= bsp;   ­͏     ­͏     ­= ͏     ­͏     ­͏   ̳= 9; ­͏     ­͏     ­͏ &nb= sp;   ­͏     ­͏     ­&= #847;     ­͏     ­͏    = ; ­͏     ­͏     ­͏ &nbs= p;   ­͏     ­͏     ­&#= 847;     ­͏     ­͏    = ­͏     ­͏     ­͏  = ;   ­͏     ­͏     ­= 47;     ­͏     ­͏     = ­͏     ­͏     ­͏  =   ­͏     ­͏     ­T= 7;     ­͏     ­͏     &= #173;͏     ­͏     ­͏   =   ­͏     ­͏     ­͏= ;     ­͏     ­͏     &#= 173;͏     ­͏     ­͏   &= #8199; ­͏     ­͏     ­͏=     ­͏     ­͏     = 73;͏     ­͏     ­͏   &#= 8199; ­͏     ­͏     ­͏ =     ­͏     ­͏     = 3;͏     ­͏     ­͏   = 199; ­͏     ­͏     ­͏ &= nbsp;   ­͏     ­͏     ­= ;͏     ­͏     ­͏   Q= 99; ­͏     ­͏     ­͏ &n= bsp;   ­͏     ­͏     ­= ͏     ­͏     ­͏   ̳= 9; ­͏     ­͏     ­͏ &nb= sp;   ­͏     ­͏     ­&= #847;     ­͏     ­͏    = ; ­͏     ­͏     ­͏ &nbs= p;   ­͏     ­͏     ­&#= 847;     ­͏     ­͏    = ­͏     ­͏     ­͏  = ;   ­͏     ­͏     ­= 47;     ­͏     ­͏     = ­͏     ­͏     ­͏  =   ­͏     ­͏     ­T= 7;     ­͏     ­͏     &= #173;͏     ­͏     ­͏   =   ­͏     ­͏     ­͏= ;     ­͏     ­͏     &#= 173;͏     ­͏     ­͏   &= #8199; ­͏     ­͏     ­͏=     ­͏     ­͏     = 73;͏     ­͏     ­͏   &#= 8199; ­͏     ­͏     ­͏ =     ­͏     ­͏     = 3;͏     ­͏     ­͏   = 199; ­͏     ­͏     ­͏ &= nbsp;   ­͏     ­͏     ­= ;͏     ­͏     ­͏   Q= 99; ­͏     ­͏     ­͏ &n= bsp;   ­͏     ­͏     ­= ͏     ­
Forwar= ded this email? Subscribe her= e for more
=

Can You Filter Your Way Out of Failed Sterility?<= /h1>

= Spoiler: No. Here’s why that matters.

 
Derek<= /div>
<= tr>
<= td height=3D"16" style=3D"font-size:0px;line-height:0;"> 
=
3D""
3D""
=3D""
READ IN APP<= img class=3D"icon text-icon" src=3D"https://substackcdn.com/image/fetch/$s_= !ET-_!,w_36,c_scale,f_png,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsu= bstack.com%2Ficon%2FLucideArrowUpRight%3Fv%3D4%26height%3D36%26fill%3Dnone%= 26stroke%3D%2523808080%26strokeWidth%3D2" width=3D"18" height=3D"18" style= =3D"min-width: 18px;min-height: 18px;border: none;vertical-align: middle;ma= rgin-right: 0;margin-left: 0;max-width: 18px" alt=3D"">
&nb= sp;

Got a gr= eat question from a researcher recently that I think cuts to the heart of w= hy third-party sterility testing exists in the first place — and why = filtration isn’t a workaround.

The question:

“If researching with product already in hand without USP = 71 Sterility Testing, would filtering it through a PES Hydrophilic Membrane= 0.2μm Lab Filter remove any living microorganisms but not endotoxins?= And would the greater health risk be microorganisms vs endotoxins?”<= /em>

This is a genuinely good question, and parts of it are= technically correct. But the conclusion it’s leading toward — = that filtration can substitute for proper sterility testing — doesn&#= 8217;t hold up. Let’s break it down.

=3D"bacteria.gif"

What the = question gets right

0.2μm filtration can remo= ve most living bacteria and fungi. And yes, endotoxins are generally the bi= gger concern compared to living microorganisms in most research scenarios. = Both of those things are true.

But here’s where it br= eaks down: even if a product would fail sterility testing, running it throu= gh a 0.2μm filter does not mean it would pass afterward.

Why filtration isn’t a sterility guarantee

USP 71 Sterility Testing has zero tolerance. Any microbial growth e= quals a failure. Filtration reduces microbial load — it doesn’t= eliminate it entirely, and it doesn’t come close to replicating what= sterility testing actually verifies.

Here’s what can= still get through or survive:

    <= li style=3D"margin: 8px 0 0 32px;mso-special-format: bullet;">

    Spore-forming bacteria lik= e Bacillus species are highly resistant and can survive filtration

    =

  • Biofilms and clumped bact= eria can partially shield organisms from being captured

  • Mycoplasma ranges from 0.1–0= =2E3μm and can pass through a 0.2= μm filter

  • Smaller viruses pass through entirely

    =

  • Any breach in filter= integrity or technique error compromises the whole process

And critically: none of this touches endotoxins at all.

What 0.2μm filtration actually removes

  • Most bacteria (typically 0.5–5μm)

  • Most fungi and yeasts (typically 2= 211;10μm+)

  • L= arger particles and debris

  • Some larger viruses

What it doe= s not remove

  • Endotoxins — bacterial toxin= s that are only 10–100kDa in molecular weight, orders of magnitude sm= aller than the filter pores

  • Smaller viruses

  • Mycoplasma

  • Other bacterial toxins and pyrogens

  • Chemical contaminants

  • Bacterial spores that survive the process

=

Why endotoxins are usually the bigger concern

Living microorganisms require active multiplication = to cause significant issues. A research subject’s immune response can= often handle small amounts, and refrigerated storage slows growth consider= ably.

Endotoxins operate differently. They don’t need= to be alive to cause problems. They trigger immediate inflammatory respons= es, are potent at very small concentrations, and are significantly harder t= o remove once present. Fever, inflammation, systemic reactions — endo= toxins are behind all of it, and no amount of post-purchase filtration gets= rid of them.

The analogy that makes it click

Think of a failed sterility product like the aftermath of= a house party you weren’t invited to host.

You can r= emove most of the people — but you’re still left with all the g= arbage, spills, and damage they left behind, plus a few stragglers hiding i= n the closets.

Filtration gets rid of some of the guests. I= t doesn’t clean the house.

The bottom line

If a product was contaminated during manufacturing, fi= ltering it afterward leaves you with all the toxic byproducts the bacteria = produced while multiplying, potentially some resistant organisms that made = it through, and still no guarantee the product would pass sterility testing= =2E

There is no DIY workaround for proper manufacturing stand= ards. This is exactly why USP 71 Sterility Testing exists — and why i= t’s become the benchmark worth paying attention to when evaluating ve= ndors.

All research discussed is for research use only. Not= for human consumption.

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© 2026 Derek Pruski
548 Market Street PM= B 72296, San Francisco, CA 94104
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