💊 Residual solvents — GC
Determination of residual solvents (methanol, acetone, dichloromethane, toluene, etc.) in active substances and finished drugs by gas chromatography with headspace technique.
Overview
Residual solvents are volatile organic compounds remaining in active substances (API) and finished medicinal products after synthesis, purification, and crystallization processes. ICH Q3C classifies solvents into 3 classes: class 1 — solvents to be avoided (benzene, CCl₄ — carcinogenic), class 2 — limited (DCM ≤600 ppm, methanol ≤3000 ppm, toluene ≤890 ppm), class 3 — low toxicity (acetone, ethanol — ≤5000 ppm total).
The method involves gas chromatography analysis with headspace technique (HS-GC-FID or HS-GC-MS). Sample substance is dissolved in higher boiling point solvent (DMSO, DMF, water), thermostated in headspace vial, and vapors above solution are analyzed on GC column.
Method principle
Pharmaceutical substance sample is dissolved in DMSO or water in sealed headspace vial. After thermostatting (80°C, 30–60 min), volatile solvents transfer to gas phase (headspace). Gas phase sample is automatically collected by headspace sampler and injected into gas chromatograph. Separation on capillary column (DB-624 or WAX), FID detection. Identification based on retention times, quantitative determination using calibration curve (solvent standards in DMSO).
Applications
- Quality control of active substances (API) — batch release
- Testing of finished medicinal products
- Control of pharmaceutical raw materials (excipients, coating)
- Production process validation (drying, crystallization)
- Drug registration — CTD Module 3 documentation
Key parameters
| Parameter | Value |
|---|---|
| Class 1 solvents | Benzene (2 ppm), CCl₄ (4 ppm), 1,2-dichloroethane (5 ppm) |
| Class 2 solvents | DCM (600 ppm), MeOH (3000 ppm), toluene (890 ppm), ACN (410 ppm) |
| Class 3 solvents | Acetone, EtOH, MTBE, ethyl acetate — ≤5000 ppm total |
| Technique | Headspace GC-FID (or GC-MS) |
| Headspace temperature | 80°C / 30–60 min |
Standard
- Standard number
- European Pharmacopoeia 2.4.24, ICH Q3C(R8)
- Title (PL)
- Identyfikacja i kontrola rozpuszczalników resztkowych
- Title (EN)
- Identification and control of residual solvents
Step-by-step procedure
1. Sample preparation
Weigh 100–500 mg substance into 20 mL HS vial. Add 5 mL DMSO. Cap with crimp. Mix by vortex.
2. Standard preparation
Prepare solvent standards in DMSO at 50–200% ICH limit level.
3. Headspace thermostatting
Place vials in HS sampler. Thermostat 80°C / 45 min with shaking.
4. GC-FID analysis
Program: 40°C (5 min) → 10°C/min → 240°C (10 min). DB-624 column. FID detection.
5. Identification and calculations
Identify solvents by retention times. Calculate concentrations from calibration curve. Convert to ppm (µg/g).
6. Result evaluation
Compare with ICH Q3C limits. Class 1: <absolute limit. Class 2: <individual limit. Class 3: sum <5000 ppm.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Gas chromatograph GC-FID | Agilent 8890, Shimadzu GC-2030, Thermo TRACE 1310 | 150 000–300 000 PLN |
| Headspace sampler | Agilent 7697A, PerkinElmer TurboMatrix, Shimadzu HS-20 | 80 000–180 000 PLN |
| Capillary column DB-624 | Agilent DB-624, 30 m × 0.53 mm × 3 µm | 2 000–4 000 PLN |
| Headspace vials 20 mL | Glass vials with aluminum crimp cap + septum | 1–3 PLN/pc |
| Analytical balance | Mettler Toledo ME204 | 5 000–15 000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| DMSO (dimethyl sulfoxide) | 67-68-5 | Headspace grade, sample solvent (b.p. 189°C) |
| Class 2 solvent standards | — | Mix: DCM, MeOH, toluene, ACN, hexane, chloroform — certified CRM in DMSO |
| ICH class 1 standard | — | Benzene, CCl₄, 1,2-dichloroethane — low concentrations, CRM |
| Hydrogen (carrier gas) or helium | 1333-74-0 | Purity 5.0 (99.999%) |
Health and safety (OHS)
- Class 1 solvents (benzene, CCl₄) — carcinogenic! Work in fume hood with carbon filter.
- DMSO — penetrates skin and transports substances into organism. Gloves mandatory.
- Hydrogen as carrier gas — flammable, check installation tightness
- Headspace vials under pressure after thermostatting — caution when opening