Isopropyl Alcohol 99% ACS Reagent Grade is a high-purity aliphatic secondary alcohol with CAS registry number 67-63-0, molecular formula C₃H₈O, and molecular weight 60.10 g/mol. The product is supplied without denaturants and is controlled against the 2-propanol monograph in the American Chemical Society Committee on Analytical Reagents specifications. At 20 °C the typical density is 0.785–0.787 g/cm³, the refractive index n_D²⁰ is 1.3772, and the boiling point at 101.3 kPa is 82.5 °C. The closed-cup flash point is 11.7 °C, which classifies the material as a highly flammable liquid under the Globally Harmonized System. The vapour pressure at 20 °C is approximately 4.4 kPa, producing flammable vapour-air mixtures at ambient temperature. Common pack sizes include 500 mL, 1 L, 2.5 L, 4 L amber glass, and 20 L high-density polyethylene containers; larger 200 L steel drums are used for production-scale laboratory dispensing. Certificate-of-analysis traceability is maintained by batch number, with retest intervals commonly assigned at 24 months from date of manufacture.

Specification Limits, Test Methods, and Certificate-of-Analysis Traceability

The ACS reagent monograph imposes tighter purity limits than industrial solvent specifications. Assay, water, residue, ionic impurities, and ultraviolet absorbance are controlled to reduce interference in analytical workflows. The table below lists representative monograph limits and the corresponding test techniques used during certificate-of-analysis generation. These limits are not equivalent to pharmacopoeial or food-grade criteria, because the ACS grade is optimised for laboratory reagent use rather than for drug-product or topical formulation compliance.

What Limits Ultraviolet Suitability in ACS Reagent Isopropanol?

Ultraviolet cut-off and absorbance at short wavelength are limiting parameters for solvent-based spectroscopy and high-performance liquid chromatography. The ACS monograph for 2-propanol specifies absorbance limits measured against water in a 1 cm cell: maximum 0.10 at 220 nm, maximum 0.05 at 230 nm, and maximum 0.01 at 250 nm. These values are batch-tested by UV-visible spectrophotometry using air-saturated samples. Because the lower UV cut-off of pure isopropanol is approximately 205 nm, the reagent grade is generally suitable for detection wavelengths at or above 220 nm. For reversed-phase HPLC methods requiring baseline stability below 210 nm, a dedicated HPLC or LC-MS grade with lower specified absorbance is used. Published batch-specific data for this ACS grade below 210 nm is limited and should be verified against the certificate of analysis for the particular lot.

In sample preparation, the material functions as a general organic solvent for extraction, dilution, and glassware rinsing where low non-volatile residue is required. The residue after evaporation specification of ≤0.001% ensures that a 100 mL evaporation leaves no more than 1 mg of total non-volatile material, which is relevant in gravimetric analysis and trace-metal workflows. Water content is controlled to ≤0.2% by Karl Fischer coulometric titration; this limit prevents excessive hydrolysis in moisture-sensitive sample preparation and maintains consistent solvent strength in normal-phase chromatography. For gas chromatography, the assay is determined by capillary GC-FID using a bonded polyethylene glycol column with split injection; the resulting chromatographic purity of ≥99.5% limits the total unidentified organic impurity envelope. The titratable acid and base specifications, expressed as ≤0.0001 meq/g and ≤0.0002 meq/g respectively, restrict ionic contamination that can alter extraction equilibrium of acid-labile analytes.

When 99% ACS Reagent Isopropanol Replaces 70% Aqueous Isopropanol in Cleaning

Disinfection and surface cleaning are influenced by water content. A 99% solution has slower microbicidal action than 70% v/v isopropanol because water accelerates protein denaturation and reduces evaporation rate; this is a well-documented formulation principle in pharmaceutical compounding, but published efficacy data for this specific ACS grade under EN 1276 or EN 13624 are not applicable unless a validated end-use dilution is prepared. The reagent grade is therefore not supplied as a ready-to-use disinfectant. When diluted to 70% v/v with purified water, the resulting nonsterile solution should be prepared in a controlled environment and used within a defined holding period because the ACS product contains no preservative. In electronic cleaning, 99% concentration is preferred for rapid drying and for dissolving non-polar flux residues on polyimide or FR-4 substrates; however, the open-cup evaporation rate at ambient humidity depends on air velocity and film thickness. The absence of surfactants and denaturants differentiates this product from technical wiping alcohols and rubbing alcohol preparations.

Azeotropic behaviour governs the water-removal limits of isopropanol. The binary isopropanol-water azeotrope at 101.3 kPa boils at approximately 87.7 °C and contains approximately 12.3 wt% water. Because the ACS water limit is far below the azeotropic composition, the material is produced by dehydration, typically with molecular sieve drying or azeotropic distillation. Once the container is opened, the hygroscopic nature of the alcohol can raise water content above specification under high relative humidity; headspace moisture ingress is minimized by resealing with inert gas purge. Production-scale dispensing through 200 L drum pumps with PTFE diaphragms and 0.2 µm vent filters reduces particulate introduction, but it does not compensate for repeated opening under ambient laboratory air. Batch-to-batch variation in water content is usually small because the certificate of analysis is based on the actual production lot; incoming QC often repeats density, water, and residue after evaporation before release to analytical method development.

Oxidative Stability and Storage Boundaries Are Defined by Flammability and Headspace Control

Isopropanol is considered stable under normal storage conditions, but it is a flammable liquid and should be stored in a segregated flammable-solvent cabinet meeting NFPA 30 or EN 14470-1. The autoignition temperature is approximately 399 °C; vapour can travel to an ignition source. Avoid contact with strong oxidizers, aluminum trichloride, acid anhydrides, and acid chlorides; exothermic reactions may occur with concentrated nitric acid or hydrogen peroxide. Storage temperature is typically maintained below 30 °C and away from direct sunlight. Peroxide formation is not a primary degradation pathway for isopropanol under standard laboratory storage, but headspace oxygen in partially filled containers can support slow oxidation to acetone under prolonged exposure to light or heat. The acetone content is controlled in the ACS monograph as carbonyl compounds, usually expressed as ≤0.002% as acetone. Opened containers should be tested for water and residue if used in a method sensitive to solvent purity.

For high-sensitivity LC-MS and gradient HPLC, the ACS reagent grade is generally suitable when the analytical target does not require certified low background at nanogram-per-litre levels. However, a dedicated LC-MS grade is preferred where plasticizer leachables from the packaging, trace alkali metals, or unspecified non-volatile residue interfere with ionisation reproducibility. Published data for this specific ACS grade in electrospray ionisation suppression is limited; method developers therefore perform a solvent blank gradient before committing a batch to quantitative multiple-reaction-monitoring assays. The material is not suitable for use as a mobile phase after the bottle has been open for extended periods unless water content and UV absorbance are re-verified.