Dimethyl sulphoxide (DMSO, CAS 67 68 5) is a highly polar, aprotic solvent supplied in GC grade for residual solvent analysis and headspace gas chromatography. Its exceptional dissolving power for both polar and non-polar pharmaceutical matrices, thermal stability at GC oven temperatures, and low background interference make it the preferred diluent for ICH Q3C residual solvent testing and USP <467> headspace GC methods. Lab Chemicals supplies dimethyl sulphoxide DMSO to GC specification with Certificate of Analysis, SDS documentation, and pan-India delivery in amber glass bottles, HDPE containers, and bulk formats.
Dimethyl sulphoxide is an organosulfur compound the sulfoxide most widely used in analytical chemistry and pharmaceutical science. Its molecular structure places a sulfur atom doubly bonded to oxygen between two methyl groups, creating an amphiphilic character that allows DMSO to dissolve both aqueous and organic compounds. This dissolving versatility is the single most important property of dimethyl sulphoxide DMSO for pharmaceutical residual solvent analysis it can solubilise solid drug substances, semi-solid excipients, and polymeric materials in a single solution for headspace injection without requiring multiple extraction solvents.
Chemical formula: C₂H₆OS | Molecular weight: 78.13 g/mol | CAS: 67 68 5
Structure: a sulfur atom doubly bonded to oxygen (sulfoxide group) with two methyl groups (-CH₃) singly bonded to sulfur. This gives DMSO its distinctive slightly garlic-like odour, high polarity (dipole moment 3.96 D), and complete miscibility with water and most organic solvents. The formula C₂H₆OS distinguishes it from dimethyl sulfide (C₂H₆S) and dimethyl sulfone (C₂H₆O₂S) — different oxidation states of the same carbon-sulfur framework.
GC grade designation means dimethyl sulphoxide has been tested and verified against chromatographic performance parameters beyond standard laboratory grade:
DMSO is classified as an ICH Q3C Class 3 solvent (PDE 50 mg/day) the lowest toxicity class, meaning it is acceptable at higher levels than Class 1 or Class 2 solvents and is not typically a target analyte in most residual solvent methods. This makes it ideal as the sample diluent for testing other residual solvents without itself interfering as a regulated impurity in most drug product specifications.
Standard or LR grade DMSO may not meet GC specifications using lower-grade solvent in residual solvent headspace analysis risks false positives and elevated baselines that lead to non-compliance with USP <467> and EP 2.4.24 protocols.
Dimethyl sulphoxide DMSO is the standard diluent for ICH Q3C residual solvent analysis of pharmaceutical APIs and finished products. It dissolves most solid pharmaceutical matrices at concentrations suitable for headspace injection, releasing volatile Class 1, 2, and 3 residual solvents into the headspace vial for GC-FID or GC-MS detection. Its high boiling point (189°C) ensures it remains predominantly in the liquid phase during headspace equilibration at standard temperatures (80–120°C), contributing minimal background signal in the GC analytical window. It is compatible with USP <467> and EP 2.4.24 headspace methods and can be used alongside nn dimethyl formamide as a co-solvent for samples that are poorly soluble in DMSO alone — both are high-boiling polar aprotic solvents compatible with headspace equilibration conditions.
In pharmaceutical development, dimethyl sulphoxide is used as a solubilising agent for active ingredients during formulation screening particularly for BCS Class II and IV compounds with poor aqueous solubility. It is employed in bioavailability and stability studies, in-vitro and in-vivo drug delivery testing, and as a penetration enhancer in transdermal formulation research. In analytical workflows, it is also used alongside acetonitrile for HPLC in complementary methods DMSO for headspace GC and acetonitrile as the reversed-phase HPLC mobile phase solvent for the same compound set.
Dimethyl sulphoxide DMSO is used as a cryoprotectant in cell preservation protocols typically at 5–10% v/v in cell freezing media to protect cell membranes during slow-rate freezing and prevent ice crystal formation. It is used in PCR and DNA sequencing buffer systems to reduce secondary structure formation in GC-rich template sequences. It also dissolves lipophilic bioactive compounds and natural products for pharmacological testing where aqueous solubility is insufficient.
DMSO acts as a reaction medium in polymer synthesis, photochemistry, and organometallic catalysis. It is used as a carrier solvent in microelectronics and coating technologies, and supports sample dispersion in analytical surface science. Note: industrial grades are used for these applications GC grade is specified only for analytical and pharmaceutical use where documented purity is required.
DMSO melts at ~18.5°C and will solidify if stored below room temperature or in a cold laboratory. Always bring DMSO to room temperature (20–25°C) and confirm it is completely liquid before preparing sample solutions dissolved sample material will crystallise or precipitate if DMSO solidifies after preparation. For headspace GC, allow the DMSO sample solution to equilibrate in the sealed headspace vial at the programmed oven temperature for a minimum of 45–60 minutes before injection, as DMSO's high viscosity slows vapour–liquid equilibration compared to lower-boiling solvents. Programme your GC oven to ramp above 189°C at the end of the run to ensure complete elution of DMSO and prevent column contamination between injections.
Lab Chemicals has supplied GC-grade solvents, analytical reagents, and laboratory chemicals to pharmaceutical manufacturers, NABL-accredited testing laboratories, contract research organisations, and research institutions across India for over three decades. We supply dimethyl sulphoxide DMSO to GC specification with Certificate of Analysis confirming purity ≥99.9%, water content ≤0.05%, and non-volatile residue ≤0.001%, in amber glass bottles and bulk formats with pan-India delivery. Our technical team can advise on DMSO grade selection, headspace method development, and documentation requirements for ICH Q3C and USP <467> compliance.
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