Determination of Polar Solvents by Static Headspace Extraction – Gas Chromatography (SHE-GC)

Abstract

ABSTRACT The term “headspace” is defined as the vapor that forms above or around a liquid or solid sample in a closed container. Usually, the vapor is above the liquid or solid at the top of the container, hence the term headspace. Headspace sampling is a method for separating volatile materials that may be extracted from a more solid sample matrix and then analyzed using gas chromatography. Headspace extraction refers to the collection and analysis of the vapor phase in the container. The Static Headspace Extraction – Gas Chromatography (SHE-GC) technique has been used since the early days of Gas Chromatography (GC). In this procedure, the two phases in the sample vial are under static conditions, and sample transfer is conducted after they have reached equilibrium. The fundamentals of headspace analysis will be discussed along with modes and types of available headspace systems. The blood breath partition ratio assumes that 2100 mL of breath contains the same amount of alcohol as 1 mL of blood. It was used for over forty years ago by the National Safety Council\u27s Committee for Tests on Intoxication. After reviewing blood-breath correlation data, the partition ratio was assigned a value of 2100, and that value has been used for calibration of breath testing instruments. Vapor phase calibration (VPC) is used to determine the partition coefficient of ethanol in water at 37 oC. Using static HS-GC with a pressure balanced headspace sampling system, peak responses obtained by varying the solvents and headspace sampler parameters were compared and investigated. The following organic solvents were used as analytes: (1) methanol; (2) ethanol; (3) acetone; (4) acetonitrile; (5) methylene chloride; (6) tetrahydrofuran; and (7) pyridine. Peak responses obtained for the following solvents and solvent mixtures as diluents were compared: (1) water; (2) a 1:1 mixture of water and dimethyl sulfoxide (DMSO); and (3) DMSO. Also, peak responses from the above diluents with and without the electrolytes (salting out) were compared. Peak responses obtained by varying the following individual headspace sampler parameters were investigated: (1) oven thermostat time; (2) sample volume in the headspace vial; and (3) injection time. The resulting peak area responses for the varied headspace sampler parameters with different solvents and solvent mixtures were plotted for comparison and investigation. Ionic liquids (IL) are salts in which the ions are poorly coordinated, resulting in liquid state forms at oC or at room temperature (RTILs). At least one of the ions has a delocalized charge, and one component is organic, thus preventing a crystal lattice formation. ILs are largely composed of ions and short-lived ion pairs. Due to ILs’ unique properties (such as higher boiling points with high thermal stability), these compounds can be used as the stationary phase for capillary GC columns. A rapid and highly sensitive method has been developed for the determination of the high boiling class 2 solvents 2-ethoxyethanol, 2-methoxyethanol, ethylene glycol, formamide, N-methylpyrrolidone, and sulfolane using static HS-GC with an IL:1-butyl 3-methylimidazolium tetrafluoroborate (Bmim BF4) as diluent