On-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry for the analysis of organic acids

Principles, developments and applications of on-line coupling of extraction with chromatography

On-line coupling of extraction and chromatographic separation allows the whole analysis to be performed in a closed system. On-line systems are particularly useful when the analytes are labile, the amount of sample is limited, or very high sensitivity is required. Many on-line systems have been developed both for liquid and for solid samples. This review discusses the different instruments that have been constructed and the factors that need to be considered in the coupling. Selected illustrative applications are described to illustrate the potential of the on-line systems.

Development of a supercritical fluid extraction-gas chromatography-mass spectrometry method for the identification of highly polar compounds in secondary organic aerosols formed from biogenic hydrocarbons in smog chamber experiments

A new one-step method for the analysis of highly polar components of secondary organic aerosols (SOA) has been developed. This method should lead to a better understanding of SOA formation and evolution since it enables the compounds responsible for SOA formation to be identified. Since it is based on supercritical fluid extraction coupled to gas chromatography-mass spectrometry, it minimizes the analysis time and significantly enhances sensitivity, which makes it suitable for trace-level compounds, which are constituents of SOA. One of the key features of this method is the in situ derivatisation step: an online silylation allowing the measurement of highly polar, polyfunctional compounds, which is a prerequisite for the elucidation of chemical mechanisms. This paper presents the development of this analytical method and highlights its ability to address this major atmospheric issue through the analysis of SOA formed from the ozonolysis of a biogenic hydrocarbon (sabinene). Ozonolysis of sabinene was performed in a 6 m3 Teflon chamber. The aerosol components were derivatised in situ. More than thirty products, such as sabinaketone, sabinic acid and other multifunctional compounds including dicarboxylic acids and oxoacids, were measured. Nine of them were identified and quantified. The sensitivity and the linearity (0.91<R<0.98) of the method were both good and detection limits ranged from 1.2 to 6.4 ng for the investigated compounds.

Characterization of organic compounds in aerosol particles from a coniferous forest by GC-MS

Atmospheric aerosol particles were collected in a Finnish Scots pine forest as part of a European Union project. Sampling was done in March-April 2003 with a high-volume sampler. Dynamic ultrasonic-assisted solvent extraction and gas chromatography-mass spectrometry (GC-MS) were applied to the analysis of aerosol samples for analytes such as n-alkanes, polycyclic aromatic hydrocarbons (PAH), oxidized polycyclic aromatic hydrocarbons (oxy-PAHs), sesquiterpenes (SQT) and oxidized sesquiterpenes (oxy-SQT). The highest concentrations were found for the n-alkanes, which were present in a wide range (C11-C32) indicating both biogenic and anthropogenic sources. PAH compounds were found in every sample while oxy-PAH compounds were present in low concentrations in a few samples. A few oxidized monoterpenes, most notably (-)-verbenone and pinonaldehyde, were found in several samples in concentrations clearly exceeding the PAH concentrations. The effect of temperature could be seen in most samples, where the concentrations of n-alkanes declined with decreasing temperatures. Particle formation events were accompanied by higher concentrations of heavy n-alkanes, verbenone and pinonaldehyde.

Purification of pharmaceutical excipients with supercritical fluid extraction

Supercritical fluid extraction (SFE), with carbon dioxide as the solvent, was tested for its ability to remove common reactive impurities from several pharmaceutical excipient powders including starch, microcrystalline cellulose (MCC), hydroxypropylcellulose (HPC), polyethylene oxide (PEO), and polyvinylpyrrolidone (PVP). Extraction of the small molecule impurities, formic acid and formaldehyde, was conducted using SFE methods under conditions that did not result in visible physical changes to polymeric excipient powders. It could be shown that spiked, largely surface-bound, impurities could be removed effectively; however, SFE could only remove embedded impurities in the excipient particles after significant exposure times due to slow diffusion of the impurities to the particle surfaces. Attempts at hydrogen peroxide extraction were hindered by its low solubility in CO2, thereby effectively precluding SFE for removal of hydrogen peroxide from excipients. This work suggests that SFE will only be commercially useful for removal of low molecular weight impurities in polymeric excipients when migration of the impurities to the particle surfaces is sufficiently rapid for extraction to be completed in a reasonable time frame.

Identification of organic compounds in atmospheric aerosol particles by on-line supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry

Atmospheric particles were collected with a high-volume sampling system at an urban site in Helsinki (Finland). The samples were analysed by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry (SFE-LC-GC-MS). The aerosol sample was first extracted by SFE. The extract was then transferred to a liquid chromatograph where it was fractionated into four fractions according to polarity. Each fraction from the liquid chromatograph was transferred to a gas chromatograph by large-volume injection, where final separation was carried out. The first LC fraction (280 microl) contained nonpolar compounds, such as n-alkanes, hopanes and steranes. The second fraction (840 microl) included polycyclic aromatic hydrocarbons (PAHs) and alkyl-PAHs, while the third and fourth fractions (840 microl each) contained more polar compounds, such as n-alkan-2-ones, n-alkanals, oxy-PAHs and quinones.

On-line coupled liquid chromatography-gas chromatography

On-line coupled liquid chromatography-gas chromatography (LC-GC) is a powerful technique that combines the best features of LC and GC and is ideal for the analysis of complex samples. This review describes the unique features of on-line coupled LC-GC. The different interfaces and evaporation techniques are presented, along with their advantages and disadvantages. Guidelines are given for selecting a suitable LC-GC technique and representative applications are noted.

Dynamic microwave-assisted extraction coupled on-line with solid-phase extraction and large-volume injection gas chromatography: determination of organophosphate esters in air samples

An on-line method was developed for the extraction, cleanup, and analysis of airborne organophosphate esters collected on glass fiber filters. The extraction and cleanup step was performed by conducting the dynamic microwave-assisted extraction (DMAE) coupled to solid-phase extraction (SPE). This system was further connected to include large-volume injection gas chromatography. The Injection interface was a programmable temperature vaporizer. The system performance test was investigated using spiked glass fiber filters. The DMAE-SPE recovery of the organophosphate esters was found to be greater than 97%. The repeatability of the uncorrected peak areas and the retention times was determined to be 4.2-8.0 and 0.03% relative standard deviation, respectively, and limits of detection were in the range 61-186.2 pg/m3. The method was tested in a newly restored office, in which several of the targeted organophosphate esters were detected. The total sampling and analysis time was less than 1.5 h.

Capillary electrophoretic separation of dicarboxylic acids in atmospheric aerosol particles

2,3-Pyrazinedicarboxylic acid (PZDA), 2,6-pyridinedicarboxylic acid (PDA) and 2,3-pyridinedicarboxylic acid (QUIN) solutions were studied as background electrolytes (BGEs) in the capillary electrophoretic analysis of dicarboxylic acids in aerosol particles with indirect UV detection. The BGEs were selected on the basis of similarity in structure with the analytes so that mobilities would be compatible. Optimised pH values for PZDA, PDA and QUIN solutions were 10.6, 11.0 and 10.2, respectively. Myristyltrimethylammonium hydroxide and myristyltrimethylammonium bromide were added to reverse the electroosmotic flow in the solutions in the direction of anode to enable fast anion detection. Separation was obtained for nine dicarboxylic acids (C2-C10) differing in the number of CH2 groups in their skeleton. The electrophoretic mobilities were determined to lie in the range 3.0 x 10(-4)-7.0 x 10(-4) cm2 V(-1) s(-1). The relative standard deviations (RSDs) for the absolute migration times of the analytes were mostly less than 0.5% (n=6) in PZDA solution. In PDA solution the within-day and day-to-day RSD values for migration were less than 1% and between 2 and 4%, respectively. Peak heights and areas mostly deviated between 1 and 15% in both PZDA and PDA solutions. Detection limits ranged between 1 and 5 mg/l. Methods were applied to the analysis of dicarboxylic acids isolated from aerosol particles.

Semi-rotating cryogenic modulator for comprehensive two-dimensional gas chromatography

A laboratory-made cryogenic modulator for comprehensive two-dimensional gas chromatography (GCxGC) was constructed and evaluated. Analytes were trapped with carbon dioxide and desorbed with heated GC oven air. The GCxGC system included a non-polar first-dimension column and a semi-polar second-dimension column connected to a flame ionisation detector. A laboratory-written Matlab-based program was used for the data analysis. Peak widths at half height for n-alkanes, obtained with use of new modulator, were at narrowest 60 ms.