Honeywell HPLC Grade Isopropyl Alcohol (IPA), 2-Propanol 99.9%, Isopropanol Solution is supplied under the Burdick & Jackson high-purity solvent line for reversed-phase and normal-phase liquid chromatography, sample preparation, and instrument wash applications. The product is identified by CAS 67-63-0 and EINECS 200-661-7; the 4 L amber-glass presentation, commonly ordered as AH323-4, is used in analytical laboratories where solvent purity must be matched to detector baseline requirements. Gas chromatographic assay release data typically report ≥99.9% 2-propanol. Water content is controlled by Karl Fischer titration, evaporation residue by gravimetric determination, and UV absorbance by spectrophotometry in 1 cm quartz cells against a water reference. These release controls distinguish the product from commodity or ACS-grade isopropanol, which may meet general laboratory purity limits but do not consistently address detector baseline stability, piston seal wear, or column contamination risk. The substance has a molecular weight of 60.10 g/mol, a density of approximately 0.786 g/cm³ at 20 °C, a boiling point of 82.5 °C at 101.3 kPa, a closed-cup flash point of 12 °C, and a vapour pressure of 4.4 kPa at 20 °C.

How Does the 99.9% Minimum Assay Affect UV Baseline Stability at 210 nm?

In reversed-phase gradient separations with photodiode-array detection, the solvent must remain optically transparent at the monitored wavelength. IPA has a UV cutoff near 205 nm; below this threshold, the solvent itself absorbs strongly and reduces the dynamic range available for analyte quantitation. Lot release documentation for the product addresses this through absorbance ceilings at 210 nm, 220 nm, 230 nm, and 260 nm. Typical acceptance limits are 1.00 AU at 210 nm, 0.50 AU at 220 nm, 0.20 AU at 230 nm, and 0.05 AU at 260 nm in a 1 cm cell. These limits do not guarantee that every detector system will be noise-free at 210 nm; detector lamp intensity, flow cell pathlength, and gradient mixing efficiency also contribute to baseline drift. For methods operating below 210 nm, the solvent absorbance profile should be checked against the specific detector and column because small lot-to-lot shifts in trace UV-absorbing impurities may be magnified by gradient compression. In practice, the ≥99.9% GC assay is less important for spectroscopic behaviour than the non-solvent impurity classes; concentration of aldehydes, ketones, and unsaturated oxygenated species at part-per-million levels is controlled by the UV absorbance release test. The lower UV transmittance of IPA relative to acetonitrile or methanol requires a higher reference photomultiplier gain or longer integration time when using UV detection at 210 nm to 220 nm. For electrospray ionisation LC-MS, the product may be used as an organic modifier, but dedicated LC-MS-grade solvents are separately controlled for metal ions and plasticizers; published data for this specific HPLC-grade IPA configuration is limited, and laboratories requiring trace metal values should request lot-specific certificates rather than infer equivalence.

The water and UV absorbance limits in the release matrix are not redundant. A solvent can pass a 99.9% GC assay while still failing a low-wavelength absorbance test because UV-active impurities at 0.01% or less may be sufficient to raise background absorbance. This is a key difference from bulk chemical purity grades. In gradient HPLC, the UV background is not constant across the solvent programme. When the IPA fraction increases from 5% to 95%, any solvent impurity is concentrated in the mobile-phase front, exposing downstream detector cells to transient absorbance excursions. The release test therefore uses fixed-wavelength measurements in a 1 cm cell as a surrogate for detector response. For critical impurity profiling, a blank gradient should be executed after each new lot, and the data system should be configured to compare blank baseline slope between the previous lot and the new lot. If the blank baseline slope at 210 nm changes by more than the method's integration threshold, the lot should not be used without verifying detector lamp age and flow cell cleanliness.

Normal-phase retention time reproducibility is sensitive to water in the mobile phase. At the product's water limit of ≤0.05%, silica and cyano columns equilibrate more predictably than with technical-grade isopropanol, which may contain several tenths of a percent of water. For example, a hexane/IPA gradient used for class separation of phospholipids or fat-soluble vitamins will shift retention times when water dissolved in IPA alters the activity of silica silanol sites. The Karl Fischer water value is therefore not merely a purity benchmark; it is part of the effective mobile-phase composition. Laboratories that replace fresh, tightly sealed bottles with partially used bottles that have been exposed to ambient humidity can exceed the water limit even if the original solvent met the certificate of analysis. A bottle opened at 60% relative humidity can absorb atmospheric water and gradually move retention times in normal-phase methods. For critical separations, the solvent system should be prepared fresh, and the IPA bottle should be blanketed with dry nitrogen if multiple acquisitions span days. In reversed-phase methods, the water content of an added organic modifier is less impactful, but the same headspace moisture uptake can influence gradient proportioning and biological sample reconstitution.

In high-pressure gradient pumps, the compressibility and viscosity of isopropanol differ from acetonitrile. IPA has a higher viscosity; at 20 °C, pure isopropanol is approximately 2.0 mPa·s, roughly double that of acetonitrile at 0.37 mPa·s. Isopropanol-water mixtures can generate higher backpressure than methanol-water or acetonitrile-water at the same flow rate and column temperature. The pressure rise is not a product defect but a physical property that must be accounted for when setting system upper-pressure limits. A method transferred from acetonitrile to IPA requires re-evaluation of the pump stroke volume, gradient proportioning valve timing, and seal wash flow. If the system is fitted with a 10 mm UV flow cell, the higher viscosity can also alter detector cell pressure; most analytical flow cells are rated for pressures of 6.9 bar to 10.3 bar, but backpressure from the column often provides a margin below the rated value. Users should monitor system pressure with a pressure transducer and set an alarm at 80% of the lowest-rated component.

When the Product Replaces Technical-Grade IPA in Sample Preparation and Instrument Wash Cycles

In sample preparation, technical-grade isopropanol may introduce nonvolatile residue, phthalates, or trace carbonyl impurities that concentrate during nitrogen blowdown or solid-phase extraction elution. The HPLC-grade product's evaporation residue specification of ≤5 mg/L is intended to reduce the mass of nonvolatile material that would otherwise be co-concentrated with analytes. In methods using large solvent volumes—such as liquid-liquid extraction of environmental samples with 100 mL or more of extractant per sample—the residue contribution becomes analytically significant when the final extract is reconstituted in 1 mL to 2 mL of mobile phase. A solvent with 5 mg/L residue can contribute up to 0.5 mg of nonvolatile contamination per 100 mL extraction volume if no further cleanup is applied. The assay of ≥99.9% reduces co-eluting impurity peaks in gas and liquid chromatograms, but it does not eliminate the need for matrix blanks, because sample-derived interferences remain.

For instrument wash cycles, the product is used in aqueous/organic seal wash and needle wash solutions. The low residue limit protects high-pressure pumping systems from deposits on check valves and pistons; however, IPA is a stronger solvent for some polymeric seals than methanol or acetonitrile. Seal compatibility should be verified against the pump manufacturer's chemical resistance tables before long-term exposure. The product should not be used as a sole wash solvent for buffers that crystallize in pure organic solvents; a water-miscible intermediate wash is required to prevent salt precipitation in the pump head.

For LC-MS, the product can be used in the sample preparation stage, but dedicated LC-MS-grade solvents are controlled for sodium and potassium at low parts-per-billion levels because metal adducts suppress ionisation. The HPLC-grade product is not excluded from LC-MS use, but its certificate of analysis may not include metal ion data. Therefore, if the mass spectrometer is configured for negative-mode or low-signal analyses, the laboratory should not assume equivalence between the HPLC-grade and LC-MS-grade product. This is a product-differentiation boundary rather than a quality failure. For gradient LC-MS where the spray-chamber temperature exceeds 300 °C, the lower water and residue values still reduce mobile-phase-generated background ions.

Storage Chemistry, Peroxide Limits, and Flammability Boundaries

The product remains flammable under normal ambient conditions, with a closed-cup flash point of 12 °C and a lower explosion limit of 2.0 vol% in air. Storage requires ventilated flammables cabinets, bonded grounding for bulk containers, and exclusion of ignition sources. The safety data sheet carries hazard classification for flammable liquid category 2, serious eye irritation category 2, and specific target organ toxicity single exposure category 3. Use is typically governed by local chemical hygiene plans and 29 CFR 1910.106 for US facilities or Directive 1999/92/EC for EU installations. These classifications are independent of chromatographic performance and must be incorporated into storage and handling systems.

Air exposure during bottle dispensing is not merely a flammability concern. Isopropanol can form organic peroxides on prolonged storage under oxygen and light, although at a slower rate than diethyl ether or tetrahydrofuran. Peroxide formation in secondary alcohols proceeds through free-radical autoxidation. After an induction period, alkyl hydroperoxides and hydrogen peroxide may accumulate; the induction period is shortened by UV light, transition metal ions, and oxygen partial pressure. A partially used 4 L bottle with a loose cap can develop measurable peroxide levels over months. Standard peroxide test strips with a detection limit of 0.5 mg/L are used for screening. Laboratories that retain partially used bottles for more than twelve months should implement peroxide screening; distillation or evaporation of aged material to dryness must be avoided because peroxide decomposition can be violent. The amber glass packaging reduces photochemical degradation, but it does not remove dissolved oxygen. For long-term stability, blanketing with nitrogen and storage in a certified flammable-liquid refrigerator or solvent cabinet is required by standard chemical hygiene practice.

The product is not a substitute for USP/NF-grade isopropanol in drug formulation, nor is it automatically equivalent to LC-MS-grade isopropanol. In regulated analytical methods, the user should verify that the certificate of analysis meets the specific pharmacopeial or compendial requirements for water, residue, UV absorbance, and assay. Method transfer from one production site to another should compare the lot release certificate against the method's established blank and baseline acceptance criteria, because solvent-related baseline artefacts may appear only in the gradient region where the proportion of IPA is highest. For methods requiring low peroxide background—such as derivatisation or oxidative-sensitive sample preparation—fresh lot inventory is preferable. Distillation of aged isopropanol for solvent purification should be performed with stirring and temperature monitoring; do not distil to a dry residue, and peroxide-negative verification should precede any thermal concentration step.