Isopropyl Alcohol Pharmacopoeia Comparison
Combined and comparative analysis of the USP, European Pharmacopoeia and British Pharmacopoeia monographs for Isopropyl Alcohol / Propan-2-ol.
1. Overview
The three uploaded monographs do not represent three completely independent pharmacopoeial standards. The BP 2025 text is based on Ph. Eur. monograph 0970, so the BP and European Pharmacopoeia requirements are essentially aligned. The most meaningful technical comparison is therefore USP versus Ph. Eur./BP.
2. Overall Comparative Specification
| Test / Parameter | USP | Ph. Eur. 11.0 | BP 2025 | Comparative Assessment |
|---|---|---|---|---|
| Official name | Isopropyl Alcohol | Isopropyl Alcohol / Propan-2-ol | Isopropyl Alcohol / Propan-2-ol | Same substance |
| Formula | C₃H₈O | C₃H₈O | C₃H₈O | Same |
| Molecular mass | 60.10 | 60.1 | 60.1 | Same |
| CAS | 67-63-0 | 67-63-0 | 67-63-0 | Same |
| Definition | NLT 99.0% isopropyl alcohol | Propan-2-ol | Propan-2-ol | USP includes quantitative content requirement |
| Appearance | No separate appearance requirement shown | Clear, colourless liquid | Clear, colourless liquid | Ph. Eur./BP include appearance control |
| Solubility | Not stated in uploaded monograph | Miscible with water and ethanol (96%) | Same | Ph. Eur./BP |
| IR identification | Required | Required | Required | Common requirement |
| GC retention-time identification | Required | Not used | Not used | USP-specific |
| Refractive index as identification | No | Yes | Yes | Ph. Eur./BP |
| Chemical colour reaction | No | Alternative identification route | Alternative identification route | Ph. Eur./BP |
| Methanol limit as identification | Required | No | No | USP-specific |
| Specific / relative density | 0.783–0.787 | 0.785–0.789 | 0.785–0.789 | Mathematical overlap: 0.785–0.787 |
| Refractive index | 1.376–1.378 at 20°C | 1.376–1.379 | 1.376–1.379 | USP range is narrower |
| Water | NMT 0.5% | NMT 0.5% | NMT 0.5% | Aligned |
| UV absorbance | 230–310 nm limits | Same limits | Same limits | Aligned |
| Peroxides | No separate test shown | No colour develops | No colour develops | Ph. Eur./BP-specific |
| Benzene | No separate numerical benzene limit shown | NMT 2 ppm | NMT 2 ppm | Important Ph. Eur./BP control |
| Nonvolatile residue / substances | 2.5 mg from 50 mL; stated as 0.005% | NMT 20 ppm | NMT 20 ppm | Ph. Eur./BP give lower stated residue limit |
| Quantitative assay | GC, NLT 99.0% | No separate assay shown | No separate assay shown | USP-specific |
| Storage | Tight container; avoid excessive heat; protect from light | Protected from light | Protected from light | USP wording is more detailed |
3. Identification Comparison
USP
USP uses three identification components:
- Identification A: infrared spectroscopy.
- Identification B: retention time of the major sample peak corresponds to the 2-propanol peak in the GC system.
- Identification C: compliance with the methanol limit.
The USP monograph explicitly states that the methanol test must be performed in addition to Identifications A and B.
Ph. Eur. / BP
Ph. Eur. and BP provide two identification routes:
- First identification: refractive index + infrared spectroscopy.
- Second identification: relative density + refractive index + chemical colour reaction.
The chemical reaction produces a bright reddish-violet ring at the interface, followed by violet colour in the sulfuric-acid layer.
4. Assay
USP provides a quantitative GC assay and requires:
The result is calculated from the isopropyl alcohol peak response relative to the total of all sample peak responses.
The uploaded Ph. Eur. and BP monographs do not show a separate quantitative assay procedure or numerical IPA assay limit. Their control strategy relies more on identification, physical properties, chromatographic impurity testing and other purity tests.
5. Volatile Impurities and Related Substances
USP impurity limits
| Impurity | USP Limit |
|---|---|
| Methanol | NMT 0.02% v/v |
| Ethyl ether | NMT 0.1% v/v |
| Acetone | NMT 0.1% v/v |
| Diisopropyl ether | NMT 0.1% v/v |
| 1-Propanol | NMT 0.1% v/v |
| 2-Butanol | NMT 0.1% v/v |
| Individual unspecified impurity | NMT 0.1% v/v |
| Total impurities | NMT 1.0% v/v |
Ph. Eur. / BP impurity controls
Ph. Eur. and BP use a different GC method and explicitly control:
- Benzene: NMT 2 ppm.
- Total impurities apart from 2-butanol: complies with the prescribed area comparison corresponding to 0.3%.
The Ph. Eur./BP impurity list includes acetone, benzene, diisopropyl ether, diethyl ether, methanol and 1-propanol.
6. GC Method Comparison
| Parameter | USP | Ph. Eur./BP |
|---|---|---|
| Technique | GC-FID | GC-FID |
| Column length | 60 m | 30 m |
| Internal diameter | 0.25 mm | 0.32 mm |
| Film | 1.4 µm, phase G43 | 1.8 µm cyanopropyl(3)phenyl(3)methyl(94)polysiloxane |
| Injection volume | 1 µL | 1 µL |
| Split ratio | 50:1 | 1:5 |
| Carrier gas | Helium | Helium |
| Flow | 2.3 mL/min | Linear velocity 35 cm/s |
| Initial oven temperature | 35°C | 40°C |
| Final oven temperature | 100°C | 240°C |
| Injector temperature | 150°C | 280°C |
| Detector temperature | 200°C | 280°C |
| Key system suitability | Resolution NLT 1.5 between acetone and IPA | Resolution NLT 10 between propanol and 2-butanol |
| Run / programmed time | 26 min | 42 min programmed temperature sequence |
7. Common and Supporting Quality Tests
UV absorbance — aligned across all three
| Wavelength | USP | Ph. Eur. | BP |
|---|---|---|---|
| 230 nm | NMT 0.30 | NMT 0.30 | NMT 0.30 |
| 250 nm | NMT 0.10 | NMT 0.10 | NMT 0.10 |
| 270 nm | NMT 0.03 | NMT 0.03 | NMT 0.03 |
| 290 nm | NMT 0.02 | NMT 0.02 | NMT 0.02 |
| 310 nm | NMT 0.01 | NMT 0.01 | NMT 0.01 |
All three also require a steadily descending spectrum with no observable peaks or shoulders.
Water
All three: NMT 0.5%, determined on a 5.0 g sample.
Acidity / alkalinity
USP: 50 mL IPA + 100 mL carbon dioxide-free water; NMT 0.70 mL of 0.020 N sodium hydroxide.
Ph. Eur./BP: gently boil 25 mL for 5 minutes, add 25 mL carbon dioxide-free water, cool under protection from atmospheric carbon dioxide; NMT 0.6 mL of 0.01 M sodium hydroxide to the endpoint.
Nonvolatile residue / substances
USP: 50 mL sample, NMT 2.5 mg residue, stated as 0.005%.
Ph. Eur./BP: 100 g sample, maximum 2 mg residue = 20 ppm.
Peroxides
Ph. Eur./BP include a peroxide test using potassium iodide and starch reagent. After standing protected from light for 30 minutes, no colour develops.
8. Proposed Multi-Compendial Working Specification
This table is a proposed internal composite specification derived from the uploaded monographs. It is not itself an official pharmacopoeial monograph.
| Test | Proposed Requirement | Basis |
|---|---|---|
| Description | Clear, colourless liquid | Ph. Eur./BP |
| Solubility | Miscible with water and ethanol (96%) | Ph. Eur./BP |
| Identification — IR | Conforms to reference standard | All three |
| Identification — GC | Main peak retention time corresponds to 2-propanol | USP |
| Refractive index | 1.376–1.378 | Narrower USP range also lies inside Ph. Eur./BP range |
| Density | 0.785–0.787 may be considered as mathematical overlap only | USP + Ph. Eur./BP; method equivalence should be confirmed |
| Assay | NLT 99.0% | USP |
| Water | NMT 0.5% | All three |
| UV at 230 nm | NMT 0.30 | All three |
| UV at 250 nm | NMT 0.10 | All three |
| UV at 270 nm | NMT 0.03 | All three |
| UV at 290 nm | NMT 0.02 | All three |
| UV at 310 nm | NMT 0.01 | All three |
| Methanol | NMT 0.02% v/v | USP |
| Ethyl ether | NMT 0.1% v/v under USP method | USP |
| Acetone | NMT 0.1% v/v | USP |
| Diisopropyl ether | NMT 0.1% v/v | USP |
| 1-Propanol | NMT 0.1% v/v | USP |
| 2-Butanol | NMT 0.1% v/v | USP |
| Any unspecified impurity | NMT 0.1% v/v under USP method | USP |
| Total impurities | NMT 1.0% v/v under USP method | USP |
| Benzene | NMT 2 ppm by Ph. Eur./BP method | Ph. Eur./BP |
| Ph. Eur./BP related-substances total | Complies with prescribed comparison corresponding to 0.3% | Ph. Eur./BP |
| Peroxides | No colour develops | Ph. Eur./BP |
| Nonvolatile substances | NMT 20 ppm by Ph. Eur./BP procedure | Ph. Eur./BP |
| Acidity / alkalinity | Perform applicable compendial method(s) until equivalence is established | Procedures differ |
| Storage | Tight container, protected from light and excessive heat | Combined wording |
9. Final Conclusion
The BP 2025 and Ph. Eur. monographs are substantially aligned, while USP uses a distinct control strategy. For a manufacturer seeking multi-compendial coverage, the most important combined controls from the uploaded documents are:
- USP assay: NLT 99.0%.
- USP individual volatile-impurity limits.
- Ph. Eur./BP benzene: NMT 2 ppm.
- Ph. Eur./BP peroxide test.
- Water: NMT 0.5%.
- Common UV absorbance profile from 230–310 nm.
- Ph. Eur./BP nonvolatile substances: NMT 20 ppm.
Source Documents Reviewed
- USP-NF — Isopropyl Alcohol monograph, official as of 01-Dec-2023 in the uploaded copy.
- European Pharmacopoeia 11.0 — Isopropyl Alcohol, monograph 0970, uploaded copy.
- British Pharmacopoeia 2025 — Isopropyl Alcohol, Ph. Eur. monograph 0970, Ph. Eur. 11.6 update, uploaded copy.
This comparative page summarizes and organizes the uploaded monograph requirements. The proposed combined specification is an internal analytical interpretation and should be reviewed under the applicable quality system before regulatory or release use.
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