Approaches for on-line coupling of extraction and chromatography

This review provides an overview of the approaches available in order to perform on-line coupling of various extraction techniques with liquid and gas chromatography, for the analysis of semivolatile and nonvolatile analytes in liquid and solid samples. The main focus is on the instrumental set-up of these techniques. Selected real applications are described by way of illustration. The extraction methods suitable for on-line coupling covered in this review are: liquid-liquid extraction, solid-phase extraction, membrane-based techniques, pressurised liquid extraction, supercritical fluid extraction, and microwave- and sonication-assisted extractions. The following systems are not covered in this review: on-line coupled solid-phase extraction-liquid chromatography, purge-and-trap-GC, and membrane extraction with a sorbent interface-GC.Abbreviations DMAE Dynamic microwave-assisted extraction - DSAE Dynamic sonication-assisted extraction - FIA Flow injection analysis - FID Flame ionisation detection - GC Gas chromatography - HGAAS Hydride generation atomic absorption spectroscopy - IC Ion chromatography - IPLC Ion pair liquid chromatography - LC Column liquid chromatography - LLE Liquid-liquid extraction - LVI Large-volume injection - MAE Microwave-assisted extraction - MESI Membrane extraction with a sorbent interface - MMLLE Microporous membrane liquid-liquid extraction - MS Mass spectrometry - NP Normal-phase - OTT Open-tubular trapping - OTTTD Open-tubular trapping with thermal desorption - PAH Polycyclic aromatic hydrocarbon - PHWE Pressurised hot water extraction - PCB Polychlorinated biphenyl - PLE Pressurised liquid extraction - PTV Programmed-temperature vaporizer - RP Reversed-phase - RSD Relative standard deviation - SAE Sonication-assisted extraction - SFE Supercritical fluid extraction - SIM Selective ion monitoring - SLM Supported liquid membrane - SPE Solid-phase extraction - SPE-TD Solid-phase extraction-thermal desorption - SVE Solvent vapour exit - TD Thermal desorption     

Applications of coupled LC-GC: A review

Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review.     

Resolution of enantiomers and isotopic compositions by selective complexation gas chromatography on metal complexes

Summary The high selectivity of complexation gas chromatography has been employed for enantiomer resolution and isotope separation. Thus, a chiral olefin, 3-methylcyclopentene, has been resolved analytically on optically active dicarbonyl-rhodium(I)-3-trifluoroacetyl-1R-camphorate in squalane. The deuterated ethylenes C₂H_4–nD_n have been separated on the same rhodium(I)-containing stationary phase. The chiral aliphatic oxiranes epoxypropane andtrans-2,3-epoxybutane have been resolved on optically active nickel(II)-bis-3-trifluoroacetyl-1R-camphorate in squalane.     

Investigation of interaction of olefin-bonded transition metal complexes by gas chromatography. Diphenylphosphine complexes with CoCl2 and CoBr2

Summary Packings consisting of diphenylphosphine complexes with CoCl₂ and CoBr₂, chemically bonded to the silica surface, were synthesized and their retention parameters determined. The packings are capable of specifically interacting with electron-donating compounds by forming -complexes. The interaction is considerably stronger in the case of CoBr₂-containing packing than in the case of CoCl₂-containing packing.     

Analysis of turkish lignite tar by coupled LC/GC,GC/MS,and capillary SFC

This work describes the analysis of a pyrolysis product of a lignite sample obtained from the Turkish Goynuk reserve. The aliphatic, aromatic and polar compounds present in the tar are separated and identified by various chromatographic techniques: Capillary gas chromatography/mass spectrometry (GC/MS), on-line high performance microbore liquid chromatography/capillary gas chromatography (LC/GC) and capillary supercritical fluid chromatography (SFC). The suitability of each technique for this particular application is discussed, and semi-quantitative results are presented for the major components detected.     

Investigation of the interaction of olefin-bonded transition metal complexes by gas chromatography. II. Phosphine complexes of Cu(II)

Summary Packings consisting of chemically bonded diphenylphosphine complexes with CuCl₂ and CuBr₂ were synthesized and their retention parameters determined. The packings investigated are capable of specific interactions with electron-donating compounds and are characterized by particularly high selectivity in relation to cis and trans isomers allowing their complete separation.Part 1: see ref. [1]     

Electrodialytic sample treatment coupled on-line with high-performance liquid chromatography

Summary An electrodialytic sample treatment method coupled on-line with high-performance liquid chromatography (EDIST-HPLC) is discussed in this paper. The performance of EDIST as a function of the donor-phase (sample solution) flow rate, the voltage applied over the electrodialysis block, and the time of dialysis has been studied using the basic drug ephedrine as a model compound. Enrichment of the analyte by a factor of 10–20 was possible. The determination of human plasma spiked with ephedrine is briefly discussed.     

Reversed-phase liquid chromatography coupled on-line with capillary gas chromatography use of an anion-exchange membrane to remove an ion-pair reagent from the eluent

Summary In order to enable the coupling of reversed-phase liquid chromatography (RPLC) with capillary gas chromatography (GC), the performance of an anion-exchange micromembrane device has been studied to remove the ion-pair reagent methanesulphonic acid from an acetonitrile/water LC eluent. The regenerant in the membrane was tetrabutylammonium hydroxide dissolved in acetonitrile/water, which effects an anion-exchange of methanesulphonate ions for regenerant hydroxide ions. The efficiency of the exchange process was found to be 99.9%. This enabled the direct introduction of the LC eluent, free of ions and with the proper acetonitrile/water ratio, into the GC. The applicability of the on-line LC-micromembrane-GC system has been illustrated for the potential drug eltoprazine, which is quantitatively recovered with a coefficient of variation for standard solutions of 3% at the 150 g/ml analyte level.     

Retention behaviour of metal complexes with 5-sulphoquinoline-8-ol in reversed-phase ion-pair liquid chromatography

Summary The reversed-phase ion-pair liquid chromatographic behaviour of several metal complexes with 5-sulphoquinoline-8-ol (HQS) on an octadecyl-modified silica column was investigated by using a fluorescence detector. The aluminum complex gave two peaks on the chromatograms when eluents containing phosphate buffer were used. The effects of the pH of the eluent, HQS concentration, the nature of anions in the eluent, and the column temperature on the retention behaviour of the aluminum complex are discussed on the basis of the equilibria and the kinetics of the complexation of the aluminum ion with HQS and anions in the eluent. The equilibrium constant for the interconversion reaction between the two Al(III)-HQS species which correspond to the two peaks observed and the second stepwise formation constant for the Zn(II)-HQS complex were evaluated from the HPLC data obtained.     

Coupling miniaturized liquid chromatography to capillary gas chromatography (micro-LC-CGC): Possibilities of reversed phase LC

Retention gaps with different polarity treatments were evaluated for reversed phase solvents. Aminopropyl- and cyanopropyl-deactivated retention gaps showed the best results for methanol-water mixtures. A reversed phase packed fused silica capillary LC column is connected on-line with a capillary gas chromatography column. The combination was used for the analysis of diazepam in urine. Volume overloading on packed fused silica columns without loss of too much efficiency was demonstrated for propranolol.     

Automated on-line microdialysis sampling coupled with high-performance liquid chromatography for simultaneous determination of malondialdehyde and ofloxacin in whole blood

We have developed a system that couples an on-line microdialysis (MD) system with flow injection high-performance liquid chromatography (HPLC)-fluorescence detection for simultaneous measurement of the concentrations of malondialdehyde (MDA) and ofloxacin (OFL) in whole blood samples. The sample matrix was first cleaned with an MD system using an MD probe. A continuously flowing dialysate stream was derivatized on-line and auto-injected into a separation column. MDA and OFL were separated through a reverse-phase C18 column (250 mm × 4.6 mm) at a flow rate of 0.8 mL min⁻¹ and then detected using a fluorescence detector (excitation: 532 nm; emission: 553 nm); the system's components were connected on-line using a valve control. Validation experiments demonstrated good linearity, precision, accuracy, and recovery. The precisions for the determinations of MDA and OFL, measured in terms of relative standard deviations, were 6.5% and 4.6%, respectively, for intra-day assays and 7.5% and 8.7%, respectively, for inter-day assays. The average recoveries of MDA and OFL spiked in plasma were each close to 100%. The use of this on-line MD-HPLC system permitted continuous monitoring of MDA and OFL in OFL-treated whole blood subjected to UV-A irradiation. Based on our results, the UV-A irradiation markedly increased the level of MDA in the OFL-treated whole blood.     

Metal ion capillary zone electrophoresis with direct UV detection: Separation of metal cyanide complexes

Mixtures of cyanide complexes of iron(III), copper(I), iron(II), nickel(II), chromium(III), mercury(II), palladium(II), silver(I), cadmium(II), zinc(II), cobalt(II), and cobalt(III) have been separated by capillary zone electrophoresis using a fused silica capillary and 20 mM phosphate buffers containing 1–2 mM sodium cyanide. The complexes were detected by direct UV absorpticn at 214 nm; detection limits are in the mid ppb range for all metals except cadmium and zinc. The different detectability of various metal cyanide complexes enables the application of the method to the analysis of complex matrices such as cyanide plating bath solutions.     

Automated on-line gas chromatographic injection of samples completely liquified by pressure

Summary A modified on-line liquid injection technique with rotary valves for gas chromatography has been developed. Applications for the on-line analysis of 2-methylpropene, cyclohexene and 1-butene are described. All samples were loaded under pressure. The results obtained show excellent reproducibility with less than 0.1% relative standard deviation (r.s.d.; n=6) for the peak areas measured. The method is particularly advantageous for samples containing both gas and liquid ccomponents at one bar.     

Separtation of metal tetrakis(p-tolyl)porphine complexes by reversed-phase high-performance liquid chromatography

Summary The feasibility of reversed-phase high-performance liquid chromatography for the separation of several metal complexes ofmeso-tetrakis(p-tolyl)porphine (TTP) is described. A combination of an octadecyl-bonded stationary phase with a non-aqueous polar mobile phase, such as an acetone-acetonitrile mixture, has proved effective for the separation. Thus, the TTP complexes of Mg, VO, Ni, Cu, Zn, and Pd and also TTP free acid were successfully separated in about 10min on a Li-Chrosorb RP-18 column (7m, 250×4mm i.d.) with a 7030 (vol/vol) mixture of acetone and acetonitrile at a flow-rate of 1 mlmin^–1.     

Column liquid chromatography coupled on-line with mass spectrometry using post-column phosphate suppression

The coupling of column liquid chromatography on-line with mass spectrometry using post-column phosphate suppression is described. A membrane suppressor is used to remove the non-volatile phosphate ions from the mobile phase after the chromatographic separation prior to introduction into the mass spectrometer. Using post-column phosphate suppression by a membrane device phosphate concentrations up to 10 mM phosphate, at a mobile phase flow rate of 0.1 ml/min, could be removed for more than 99% without any decay of the sensitivity of the MS detection. Using a new antidepressant tetracyclic basic compound, ORG 4428, and some structure related compounds as model compounds electron impact as well as chemical ionisation spectra of all compounds could be obtained. The set-up could be used for several weeks running, using a phosphate containing mobile phase, without any loss of performance.     

Simultaneous determination of some food additives in soft drinks and other liquid foods by flow injection on-line dialysis coupled to high performance liquid chromatography

Flow injection on-line dialysis was developed for sample pretreatment prior to the simultaneous determination of some food additives by high performance liquid chromatography (FID-HPLC). A liquid sample or mixed standard solution (900 μL) was injected into a donor stream (5%, w/v, sucrose) of FID system and was pushed further through a dialysis cell, while an acceptor solution (0.025 mol L⁻¹ phosphate buffer, pH 3.75) was held in the opposite side of the dialysis membrane. The dialysate was then flowed to an injection loop of the HPLC valve, where it was further injected into the HPLC system and analyzed under isocratic reverse-phase HPLC conditions and UV detection (230 nm). The order of elution of five food additives was acesulfame-K, saccharin, caffeine, benzoic acid and sorbic acid, respectively, with the analysis time of 14 min. On-line dialysis and HPLC analysis could be performed in parallel, providing sample throughput of 4.3 h⁻¹. Dialysis efficiencies of five food additives were in ranges of 5-11%. Linear calibration graphs were in ranges of 10-100 mg L⁻¹ for acesulfame-K and saccharin, 10-250 mg L⁻¹ for benzoic acid and 10-500 mg L⁻¹ for caffeine and sorbic acid. Good precisions (RSD < 5%) for all the additives were obtained. The proposed system was applied to soft drink and other liquid food samples. Acceptable percentage recoveries could be obtained by appropriate dilution of the sample before injecting into the system. The developed system has advantages of high degrees of automation for sample pretreatment, i.e., on-line sample separation and dilution and low consumption of chemicals and materials.     

Polynuclear metal complexes of ligands containing phenolic units

The coordination properties of a selected series of acyclic and macrocyclic ligands containing one or more phenolic groups are explored. The formation of polynuclear metal complexes was only considered highlighting the key role played by the phenoxide oxygen atom in binding two metal centres in a bridge disposition. This arrangement allows two metal ions to stay close each other and consequently these dinuclear centres are able to mimic many biological sites, especially those where the two metals can cooperate to form an active centre. Catalytic properties of these polynuclear complexes, when studied, have been reported. Also some of the numerous heterodinuclear metal complexes that have been synthesized are here reviewed, included several crystal structures.     

Stereoisomeric flavour compounds XXXVIII: Direct chirospecific analysis of γ-lactones using on-line coupled LC-GC with a chiral separation column

Summary Chiral -lactones from the raw flavour extract of strawberries and commercially available fruit-containing products are stereoanalyzed directly by on-line coupling of liquid chromatography (LC) to gas chromatography (GC) and enantiomer separation with 2,6-di-O-pentyl-3-O-acetyl--cyclodextrin as the chiral stationary phase.     

A continuous two-phase reaction system coupled on-line with capillary chromatography for the determination of polar solutes in water

Gas chromatographic procedures are described for the determination of carboxylic acids and chlorinated anilines in water samples. Propionic acid and 2,6-difluorobenzoic acid in aqueous solution have been simultaneously alkylated and extracted by means of a continuous two-phase reaction system, and then quantitated by on-line coupled capillary gas chromatography; tetrahexyl-ammonium hydrogen sulfate was used as phase transfer catalyst and pentafluorobenzyl bromide as reagent. A factorial design approach was used to optimize on-line derivatization of aqueous propionic acid with regard to pH and concentration of phase transfer catalyst. Alkylation and extraction, under optimized conditions, followed by quantitation of the pentafluorobenzyl ester by flame ionization detection furnished a linear calibration for concentrations between 0.1 and 10 μg/ml. The relative standard deviation was 9–15 %. The continuous two-phase reaction system was also used to determine (chlorinated) anilines present in water at concentrations of 0.1–1 μg/ml; pentafluorobenzoyl chloride was used as reagent and analysis was performed by capillary gas chromatography with flame ionization or electron capture detection. The on-line acylation of p-chloroaniline was optimized with regard to pH, reagent concentration, and reaction time. The on-line reaction system worked satisfactorily for both applications, although excess reagent caused some problems with the chromatography.