The short version: a 0.22 µm filter removes bacteria and particulate from liquid passing through it. It does not remove endotoxin, it does not make a home-mixed vial equivalent to a manufactured sterile one, and it cannot fix a vial that has already gone wrong. Filtering the water on its way in costs you nothing; filtering the mixed solution afterwards costs you some of the peptide.
There are two completely different things people mean by "filtering", they happen minutes apart, and only one of them has a downside. Worth separating them before deciding anything.
This is the sensible order, and it is the one that gets criticised least. You draw your bacteriostatic water through a 0.22 µm syringe filter and into the peptide vial. The water is filtered; the peptide never touches the membrane.
That matters, because the standard objection to filtering — that peptide sticks to the filter and you lose product — simply doesn't apply here. Nothing valuable passes through the membrane, so nothing valuable can be left behind on it.
Where it earns its place is a water bottle you have been drawing from for a while. Bacteriostatic water arrives sterile and the benzyl alcohol in it inhibits bacterial growth, so filtering a bottle you opened this morning adds close to nothing. A 30 ml bottle you have pierced twenty times over six weeks is a different proposition, and that is the case where a filter is doing real work.
Every filter has a hold-up volume — liquid that stays in the housing and membrane instead of going through. Draw 2 ml, and rather less than 2 ml may reach the vial. That changes your concentration, which changes what you draw on the syringe and what each dose costs. Read the volume that actually went in and log that number.
A filter adds junctions. Syringe to filter, filter to needle, needle to stopper — each one is another surface that has to stay clean, and another chance to touch something you shouldn't. Done unhurriedly on a wiped surface, it is a net gain. Done in a rush, it can quite easily be a net loss. That is a point about technique rather than an argument against filtering.
Pushing an already reconstituted vial through a filter is a different trade, because now the peptide is what's going through the membrane.
Peptides adsorb to filter surfaces. How much you lose depends on the membrane material, the surface area and how dilute the solution is — a dilute vial loses a larger proportion than a concentrated one, because the same amount of surface takes roughly the same amount of peptide from a smaller total. The result is a vial that is weaker than the number you calculated, by an amount you cannot see or measure at home.
If you are going to do it anyway, membrane material is the lever that matters:
A smaller filter for a small volume also helps, simply because there is less surface for the peptide to find.
Visible particulate, cloudiness, floating strands or anything settled at the bottom are information. Filtering removes the information and leaves the cause.
A vial that won't go clear has usually either not finished dissolving — in which case it needs more standing time and gentle rolling, not a filter — or it has been shaken, warmed, or is not what the label says. Pushing it through a membrane produces clear liquid that looks reassuring and tells you nothing. If a vial looks wrong, the thing to do is stop and check the instructions supplied with it, not launder it.
Most vials that look like they need filtering just need another few minutes. Mixing a vial properly — aim at the glass, let it stand, roll rather than shake — removes the reason to reach for a filter in the first place.
A common ask is which compounds "have to" be filtered and which don't, split by whether they are peptides. It's a reasonable instinct but it isn't how filtration works.
A filter has no idea what is passing through it. It responds to particle size, not chemical class. What decides whether filtration is appropriate is the state of the liquid, how sterile the water was, how many times the vial has been entered, and what the supplied instructions say — all of which are true regardless of whether the molecule is a peptide.
Chemical class does change one thing, and it's the loss side rather than the need side. NAD+, methylene blue, glutathione and 5-Amino-1MQ are not peptides, so they have no folded structure to lose and they don't behave like peptides on a membrane. Several of them also arrive already in solution, in which case there is no reconstitution step to add a filter to. That is a difference in what happens during filtering — not a rule about who must.
If the volume that reached the vial isn't the volume you planned, every dose calculation after it is slightly wrong. Peptide Wizard works out your concentration from what actually went in, tells you what to draw on the syringe, what each dose costs, and which vial runs out next. Free on iPhone and Android.
Filtering the water on its way into the vial avoids the main drawback of filtering afterwards, which is that peptide binds to the membrane and some of the product never comes out the other side. If the water goes through the filter and the peptide never touches it, there is nothing to lose. The one thing to watch is volume: every filter holds back a little liquid, so measure what actually reached the vial rather than what you drew up.
Bacteria and particulate larger than the pore size, which is why 0.22 um is described as sterilising grade. It does not remove endotoxin, which is bacterial debris far smaller than the pores, and it does not remove anything already dissolved. Filtered is not the same as sterile-manufactured, and a filter cannot undo contamination that has already happened.
It can, when the peptide itself passes through the membrane. Peptides adsorb to filter surfaces, and how much is lost depends on the material, the surface area and how dilute the solution is. Low-binding membranes such as PES and PVDF hold back less than nylon or cellulose acetate. Dilute solutions lose a larger proportion than concentrated ones, because the same amount of surface takes the same amount of peptide from a smaller total.
No. Cloudiness or visible particulate is information about the vial, and filtering removes the evidence rather than the cause. A solution that will not go clear has either not finished dissolving, has been handled roughly, or is not what it should be. Filtering it produces clear liquid and tells you nothing about what is in it.
The question doesn't split that way. NAD+, methylene blue, glutathione and 5-Amino-1MQ are not peptides and so they don't have a folded structure to lose, but filtration is decided by the state of the liquid in front of you and the instructions supplied with it, not by which chemical class the molecule belongs to. Some of these compounds arrive already in solution, in which case there is nothing to reconstitute and no filtering step to add.
That depends on things only you can see: whether the water was sterile to begin with, how many times the vial has been entered, and how carefully it was handled. Bacteriostatic water arrives sterile and contains a preservative, so filtering a freshly opened bottle adds very little. A bottle you have been drawing from for weeks is a different case. The instructions supplied with your own vial and water take precedence over any general guidance, including this page.