Isopropyl Alcohol (CAS 67-63-0): The Grade Landscape
Isopropyl alcohol, also called isopropanol or IPA, is a secondary alcohol with the formula C3H8O, CAS number 67-63-0, molar mass 60.10 g/mol, boiling point 82.6 °C, density 0.786 g/cm³ at 20 °C and complete miscibility with water. Its closed-cup flash point of 12 °C makes it a flammable liquid, and its combination of high polarity, moderate evaporation rate and low residue has made it the default solvent for cleaning, disinfection and formulation work. There is no single "best" grade: the four grades in commercial supply differ in water content, non-volatile residue, acidity and trace metals, and the correct choice is the one whose limits match the process.
Industrial and Technical Grades
Industrial grade is typically 99.0% minimum assay with water up to about 1.0% and non-volatile residue in the tens of parts per million. It is used in paints, coatings, printing inks, adhesives and general degreasing, where a small water and residue load does not affect the finished product. Technical grade tightens the same parameters, normally 99.5% minimum with water at or below 0.5% and residue below about 20 ppm, and is the grade specified for precision cleaning of optical parts, electronics assemblies before conformal coating, and laboratory solvents where trace residue would leave films or interfere with analysis.
Pharmaceutical and Electronic Grades
Pharmaceutical grade is produced to the isopropyl alcohol monographs of the USP and the European Pharmacopoeia, which control assay, water, acidity, non-volatile residue, and in some cases absorbance and benzene limits. It is the grade used in disinfectants, medical wipes, hand sanitiser bases and as a process solvent in pharmaceutical manufacture. Electronic grade is the tightest specification: 99.9% and above, water often at or below 0.1%, and metals and particles controlled for semiconductor and display processes, where a single residue monolayer can destroy yield. It is supplied in dedicated stainless steel or fluoropolymer-lined packaging to avoid contamination from the container itself.
Grade Comparison and Selection
| Grade | Assay | Water | Non-volatile residue | Typical use |
|---|---|---|---|---|
| Industrial | ≥ 99.0% | ≤ 1.0% | Coatings, inks, degreasing | |
| Technical | ≥ 99.5% | ≤ 0.5% | ≤ 20 ppm | Precision cleaning, laboratory |
| Pharmaceutical (USP / EP) | Per monograph | Per monograph | Per monograph | Disinfection, medical, process solvent |
| Electronic | ≥ 99.9% | ≤ 0.1% | Metals and particles controlled | Semiconductor, optics, displays |
Volumes and packaging follow the same logic. Industrial and technical grades move in 160 kg drums, 1,000 L intermediate bulk containers and road tankers. Pharmaceutical grade is supplied in drums with a documented chain of custody. Electronic grade is drummed in smaller lots under a cleanliness protocol. Price rises with each step because of distillation and drying energy and because low-residue packaging adds cost.
Storage, Safety and Transport Classification
IPA is a Class 3 flammable liquid, UN 1219, packing group II, with a flash point of 12 °C and a flammable range of roughly 2–12% by volume in air. Storage areas need bonding and grounding of drums and transfer equipment, a vapour-tight headspace, and separation from oxidisers such as peroxides and nitrates. Stainless steel, carbon steel with a suitable coating and high-density polyethylene are all acceptable materials of construction; ordinary gaskets and adhesives must be checked for solvent compatibility. Because IPA absorbs atmospheric moisture, an opened drum will slowly fall below its graded assay, so containers should stay closed and be used on a first-in, first-out rotation.
Frequently Asked Questions
Q: Which type of isopropyl alcohol is best?
A: The one matching your process limits. Industrial grade for coatings and general degreasing, technical grade for precision cleaning, USP or EP pharmaceutical grade for medical and process uses, and electronic grade of 99.9% or higher for semiconductor and optical work.
Q: What is the difference between industrial grade and technical grade IPA?
A: Both are produced by similar distillation, but technical grade holds water at or below about 0.5% and non-volatile residue below about 20 ppm, while industrial grade allows up to about 1.0% water and higher residue. That difference decides whether a film or residue is left behind.
Q: Can 99% IPA be used in place of electronic grade?
A: No. Electronic grade controls water at or below about 0.1% as well as metals and particles. A 99% product carries far more water and trace metals and can leave residue on wafers, optics and display surfaces.
Q: Is isopropyl alcohol the same as rubbing alcohol?
A: Rubbing alcohol is a consumer preparation, usually 60–70% IPA in water with additives. It is not a substitute for a 99%+ industrial or technical grade in cleaning or formulation work, because the water and additive load is uncontrolled.
Q: How is isopropyl alcohol classified for transport?
A: As UN 1219, Class 3 flammable liquid, packing group II. Drums and tanks require bonding and grounding, and storage must be separated from oxidising agents.
Q: Does IPA absorb water from the air?
A: Yes. It is fully miscible with water and hygroscopic in an open container, so an opened drum gradually falls below its graded assay. Keep containers closed and rotate stock first-in, first-out.
