Isopropanol, also called isopropyl alcohol or IPA, is one of the most widely used cleaning solvents in industry because it combines three properties that rarely appear together: it dissolves oils, greases and flux residues, it evaporates quickly without leaving a film, and it is available at high purity for very little cost. This article explains the chemistry behind that performance, the concentrations that suit different jobs, and the practical rules that keep electronics, optics and hard surfaces clean without damaging either the part or the operator.
Isopropanol is a secondary alcohol with the molecular formula C3H8O and the CAS registry number 67-63-0. It is also known as 2-propanol or isopropyl alcohol. In its pure form it is a colourless, transparent liquid with an odour that sits between ethanol and acetone, it is fully miscible with water, and it mixes freely with alcohols, ethers, benzene and chlorinated solvents. Its boiling point is about 82.5 degrees Celsius and its closed-cup flash point is about 12 degrees Celsius, so it dries fast and is a genuine flammable liquid rather than a borderline one.
Commercial material is sold in a small number of grades, and choosing the right one matters more than most buyers expect:
Technical grade, usually 99% or lower purity: general degreasing, tool and equipment cleaning, workshop use.
Pharmaceutical and cosmetic grades: materials with controlled residue and trace-metal limits for regulated production.
Electronic grade: filtered, low-water, low-particle material for circuit boards, connectors and optical parts.
Diluted ready-to-use solutions: typically 70% IPA by volume with water, for surface disinfection.
Why IPA Cleans So Effectively
Isopropanol sits at a useful point on the polarity scale. The hydroxyl group gives it enough polarity to break the films left by salts, fingerprints and ionic flux residues, while the two-carbon alkyl chain gives it enough non-polar character to dissolve light oils, mould release agents and resin-based soils. Because its surface tension is low, it wets metal, glass and most plastics readily and penetrates under the contamination instead of floating on top of it.
Evaporation behaviour is equally important in production work. IPA leaves almost no residue when it dries, which is why it can be used on parts that must not be re-cleaned or re-dried by hand. The water content of the dilution is not a defect in this context: in a 70% solution, the water slows evaporation enough to hold liquid contact on the surface for a useful time, which is exactly what disinfection and soil lifting need.
Working Concentrations and What They Suit
The correct concentration depends on the task, not on the assumption that stronger is always better.
| Concentration | Typical use | Notes |
|---|---|---|
| 99% and above | Electronics, connectors, optics, water-sensitive assemblies | Fastest drying, lowest residue; highly flammable |
| 91% | Electronic assemblies, general precision cleaning | Slightly slower flash-off, easier wetting on some surfaces |
| 70% by volume | Hard-surface and instrument disinfection | Water content lengthens contact time; standard clinical dilution |
| 60-90% by volume | General disinfectant range | Effective against many bacteria and enveloped viruses |
| Blends with other solvents | Specialist flux removal and stencil cleaning | Formulated to lift heavy ionic and resin soils |
Electronics, Optics and Precision Components
In electronics manufacture, high-purity IPA is the default cleaning medium for printed circuit boards after soldering, for connector contacts, for optical windows and lenses, and for metal parts that must be free of oil before assembly. It removes activated and rosin flux, solder paste residues, oils, and handling marks. The working method matters as much as the solvent: apply the liquid to a lint-free wipe rather than flooding the board, work from the cleanest area outward, and allow the part to dry fully in a ventilated space before power is applied.
Two precautions prevent most damage. First, never clean equipment while it is powered or live, because IPA is flammable and conductive residues plus solvent can create both fire and electrical risk. Second, check compatibility before use: polycarbonate, polystyrene, some acrylic parts and certain printed coatings and adhesives can be attacked, stress-crazed or dulled by prolonged contact, so test an inconspicuous area first.
Surface Disinfection and Clinical Practice
Solutions between 60% and 90% IPA destroy a broad range of bacteria and many viruses on hard, non-porous surfaces and are widely used for instrument wipes, work surfaces and equipment housings. A 70% by volume solution is the usual choice, because the added water slows evaporation and keeps the alcohol in contact with the surface long enough to act.
Two limits should be understood. IPA is not a sterilant: it does not reliably kill bacterial spores and it should not be used as a replacement for validated sterilisation or for hand hygiene in regulated environments. It also works only on clean surfaces, because organic soil protects microorganisms, so disinfection must follow cleaning rather than replace it. Never mix IPA with hypochlorite bleach, hydrogen peroxide or other oxidizing cleaners, since the reaction can release heat and hazardous vapours.
Safety, Storage and Disposal
Isopropanol is flammable with a flash point near 12 degrees Celsius, and its vapour is heavier than air, so it can travel to a distant ignition source along the floor. Use it in a well-ventilated area, keep containers closed, bond and earth metal containers when decanting bulk quantities, and keep it away from flames, hot surfaces and static-generating processes.
For personal protection, wear chemical-resistant gloves and safety goggles. Repeated skin contact defats the skin and can cause cracking and dermatitis, so contaminated gloves should be changed rather than reused, and enclosed spaces should never be entered where vapour may accumulate. Store the product in a cool, dry, ventilated area in tightly closed containers of approved material, away from oxidizers, and dispose of waste solvent through a licensed route in line with local regulations.
Frequently Asked Questions
Q: Can isopropanol be used for cleaning?
Yes. IPA is one of the most common industrial cleaning solvents and is used on electronics, metal parts, optical components, instruments and hard surfaces.
Q: What concentration of IPA is best for disinfection?
Solutions of 60 to 90 percent are effective, and 70 percent by volume is most often recommended because the water slows evaporation and extends contact time.
Q: Is IPA safe on plastic parts?
It is safe on many engineering plastics but can attack polycarbonate, polystyrene and some acrylics or printed coatings, so compatibility should be tested on a hidden area first.
Q: What are the CAS number and formula of isopropanol?
Isopropanol has the CAS registry number 67-63-0 and the molecular formula C3H8O, and it is also known as 2-propanol.
Q: Is isopropanol flammable?
Yes. Its flash point is about 12 degrees Celsius, so it must be kept away from ignition sources and stored only in closed, approved containers.
Q: Can isopropanol be mixed with bleach?
No. Mixing IPA with hypochlorite bleach or other oxidizers can generate heat and hazardous vapours, so the two should never be combined.
Q: Does IPA leave residue on cleaned parts?
High-purity IPA evaporates almost completely and leaves practically no residue, which is why it is preferred for parts that cannot be rinsed or dried afterwards.