Filter tips versus standard tips

An aerosol barrier protects the pipette barrel. It does not recalibrate a poor fit. This overview is the order of deciding between filter tips and standard tips, then checking that the pipette and the tip still agree on a volume. Tip choice in the wider plastic set is also part of when to use plastic tubes, tips and plates. Bulk volumetric glass, which tips do not replace, is mapped in choosing laboratory glassware.

Two different jobs in one rack

A standard tip is a disposable nozzle. It sets the liquid contact surface and, if it seals on the cone, lets the pipette's piston do what it was adjusted to do. A filter tip adds a porous plug in the upper air path. The plug is there to catch aerosols and small droplets that would otherwise travel into the barrel, sit there, and come back out into a later sample. That path is how nucleic-acid contamination, organisms and radioisotopes become a pipette problem rather than a single-tube problem.

The plug is not a membrane you filter the sample through. Liquid is not supposed to reach it. If you overshoot, reverse-pipette too aggressively, or lay the pipette down so liquid runs back, you wet the filter. A wet plug wicks, restricts airflow, and can hand the contamination straight to the place you hoped to keep clean. Discard that tip. If liquid may have passed the plug, treat the barrel as potentially contaminated and clean it as the pipette maker describes.

Sterile is a separate printed claim. A filter does not create it. Nuclease-free and endotoxin-controlled are further separate claims. Buy the claim you need, and do not infer the others from the presence of a white plug.

Where the barrier earns its place

Use filter tips when the barrel must not carry the sample forward. Typical research cases are PCR and other nucleic-acid amplification, where a few copies in the barrel become a false band later; culture work, where you would rather not inoculate the next tube from the pipette; and radioisotope work, where contamination is also a safety problem. Your radiation rules and biosafety rules outrank this paragraph.

Use standard tips for routine aqueous transfers that do not seed a sensitive assay: filling a gel tank, aliquoting a fresh buffer, adding a robust reagent the method does not treat as a contamination source. Solvents are a materials question before they are a filter question. Many tips are polypropylene. Some organics swell or leach that plastic. If the chart says no, move the transfer to a glass pipette or another rated device. A filter tip is not a solvent strategy.

Accuracy still belongs to the pipette, the tip fit and the person. ISO 8655-1 sets terminology, general requirements and user recommendations for piston-operated volumetric apparatus. It is the document to mean when someone says the pipette "should be accurate". A tip brand the pipette was not checked with can sit outside the conditions of that check. When you change tip brand, include the new tip in the next balance check or service. NIST laboratory metrology is the public background for why a check weight matters more than a feeling that the pipette "usually works".

Order of work

Select the pipette whose nominal range puts your volume away from the extreme bottom of the dial, where relative error grows. Select the tip named for that pipette. Open the box so the cones you do not use stay covered. Seat the tip with the force the maker expects, once, straight on. A rocking seat leaks.

Pre-wet when the method or the pipette guide asks, by aspiring and discarding the liquid once, so the air inside the tip is humid and the first dispensed volume is not the odd one. Do this only if it does not compromise a sterile or a contamination-sensitive step. For tiny nucleic-acid volumes, follow the assay insert rather than a generic pre-wet habit that dips a contaminated tip back into a stock.

Watch the filter. If the liquid climbs toward it, you are moving too fast, the tip is too small a mistake, or the pipette is leaking. Stop. For viscous liquids, a standard air-displacement approach may be the wrong tool entirely. A positive-displacement device is the class to consider, and that is a different purchase from a finer filter.

Deliver against the wall or into the liquid as the method prefers, with a consistent rhythm. Change tips between samples when carry-over would matter. A filter is not a licence to reuse the tip across a plate.

When the control volume fails

Weigh a delivered water portion if your laboratory checks pipettes that way, at the temperature your procedure states, and compare it with the band your quality rule uses. This article does not invent that band. If the weight is low on filter tips and acceptable on the standard tips the pipette was serviced with, the filter brand or a wet plug is the suspect. Reseat. Try a fresh rack. If it is still low, stop using that combination until someone who maintains the pipette has seen it.

If both tip types miss, the pipette, the technique or the balance setup is the suspect. A new filter specification will not heal a drifted piston. If samples contaminate with filter tips in use, the filter is being overshot, the box is open to a dirty bench, or the contamination never travelled by aerosol. Look at gloves, caps and shared stocks. A no-template control in nucleic-acid work is the scientific branch: a positive blank means the run is not interpretable, whatever tip you meant to use.

Safety

Radioisotope tips are radioactive waste under your radiation licence, filter or not. Culture tips are biohazard waste under your biosafety rules. The WHO laboratory biosafety manual and the CDC BMBL are background, not a waste SOP printed here. Filter tips do not make a pathogenic sample safe to pipette on the open bench. Research technique only. Nothing here is a clinical pipetting instruction.

What to specify

Pipette model and volume range, filter or standard, sterile or nuclease-free or ordinary as separate words, the chemistry the tip must touch, and the quantity of racks. Say if the pipette's current check was performed with a named tip style, so a substitution is visible. Use the laboratory plasticware catalogue and the quote request. Volumetric flasks for the solutions you aliquot belong in volumetric glassware, on their own line.