Guidelines for capillary extraction–capillary gas chromatography: preparation of extractors and analysis of aromatic compounds in water (original) (raw)
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Journal of Chromatography A, 2012
This study proposes a new optimization approach for the simultaneous determination of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene isomers (BTEX) from water samples using the solid-phase microextraction technique followed by gas chromatography-mass spectrometry (GC-MS) separation and detection. The objective of the study was to achieve compromise extraction conditions, suitable for all semi-volatile and volatile compounds, under which the amount extracted is maximized for all analytes. This was achieved by careful optimization of the fiber coating, salting-out effect, extraction time and temperature and extraction mode (headspace or direct immersion). With the optimized fiber coating -PDMS/DVB 65 m -the other selected factors were optimized using a response surface methodology through central composite designs. As expected, the optimized results for each class of analytes varied significantly, probably due to the differences in their volatility and the equilibrium constants for the analyte/fiber coating. In order to overcome this issue, a new optimization approach was proposed based on a combination of extraction modes and extraction temperatures in a single extraction procedure. The final optimized procedure was: 48 min of extraction in direct immersion mode with the sample maintained at 80 • C followed by a further 32 min of headspace extraction with the sample temperature kept at 10 • C. The proposed procedure was compared with conventional methods based on the use of a single extraction mode and temperature (80 min of headspace extraction at 60 • C or 80 min of direct immersion extraction at 50 • C). The newly proposed method was shown to be more attractive as it extracted higher amounts of both semi-volatile and volatile compounds in a single extraction procedure compared to the conventional approaches. The optimized method was validated and excellent results were obtained.
Microchimica Acta, 2013
We have developed a modified method for the extraction and preconcentration of benzene, toluene, ethylbenzene and xylenes (BTEX) in aqueous samples. It based on dispersive liquid-liquid microextraction along with solidification of floating organic microdrops. The dispersion of microvolumes of an extracting solvent into the aqueous occurs without dispersive solvent. Various parameters have been optimized. BTEX were quantified via GC with FID detection. Under optimized conditions, the preconcentration factors range from 301 to 514, extraction efficiencies from 60 to 103 %, repeatabilities from 2.2 to 4.1 %, and intermediate precisions from 3.5 to 7.0 %. The relative recovery for each analyte in water samples at three spiking levels is >85.6 %, with a relative standard deviation of <7.4 %. Keywords BTEX . Modified dispersive liquid-liquid microextraction . Solidification of floating organic micro drop . Water samples Electronic supplementary material The online version of this article (
Chromatographia, 2006
Benzene, toluene, ethylbenzene and o-, m-, and p-xylenes (BTEX), were extracted from aqueous samples by capillary extraction (CEx), a manual form of in-tube microextraction inherently compatible with capillary GC, and analyzed by HRGC analysis in order to quantify the post-extraction losses of these volatile organic compounds. Accuracy of the VOC determination by CEx-HRGC is dependent on these losses. The used active extraction devices were fused silica open-tubular capillaries of 0.25 mm i.d., with lengths in the range of 3-15 cm, coated with a 0.25 lm film of PTE-5 (5% phenyl methylpolysiloxane) stationary phase. The losses decreased remarkably when the extractor lengths were increased. In particular, the losses were modest or negligible for capillary extractors of usual length, though the losses increased with rising solute volatility and 'lag time' (the length of time required to connect in-line the laden capillary extractors with the HRGC column). BTEX losses between 2% (benzene) and 0.5% (o-xylene) resulted from CEx conducted under very usual conditions, independently from sample concentration. The short-term precision of the CE-HRGC experiments, expressed as relative standard deviation, was 0.8-4.9% (n = 5).
Journal of Chromatography A, 2002
Headspace solvent microextraction (HSM) is a novel method of sample preparation for chromatographic analysis. It involves exposing a microdrop of high-boiling point organic solvent extruded from the needle tip of a gas chromatographic syringe to the headspace above a sample. Volatile organic compounds are extracted and concentrated in the microdrop. Next, the microdrop is retracted into the microsyringe and injected directly into the chromatograph. HSM has a number of advantages, including renewable drop (no sample carryover), low cost, simplicity and ease of use, short time of analysis, high sensitivity and low detection limits, good precision, minimal solvent use, and no need for instrument modification. This paper presents analytical characteristics of HSM as applied to the determination of benzene, toluene, ethylbenzene and xylenes in water.
Liquid-Liquid Extraction of Aromatics from Hydrocarbon Mixtures in Capillaries
Brazilian Journal of Chemical Engineering, 2018
An aromatics extraction study was conducted in capillaries of internal diameters in the range of 0.8 mm to 2 mm. The systems chosen for study were 'n-heptane + toluene + propylene carbonate', 'n-heptane + toluene + furfural' and 'synthetic naphtha reformate + (propylene carbonate + tetraethylene glycol)'. The aim of the work was to evaluate the feasibility of conducting aromatic separation in micro-capillaries and evaluate maximum efficiency. The results showed efficiencies ranging from 46.3 % to 97.3 %, depending upon the combination of the flow velocity, residence time and channel diameter. The effect of individual parameters on extraction efficiency was also isolated from the various combinations. Efficiency increased from 68 to 83 % as flow velocity increased from 0.11 to 0.96 cm/s, while residence time and channel diameter were fixed at 0.78 min and 2 mm, respectively. The samples collected from the capillary quickly separated into clear liquid layers , indicating short settling times.
Journal of Separation Science, 2010
A needle trap (NT) device filled with Carbopack X as a sorbent material is evaluated for the static headspace analysis of benzene, toluene, ethylbenzene, and xylene (BTEX) compounds in aqueous samples. Injection parameters used with the NT device (e.g. volume of carrier gas and time to open the split valve) are evaluated to determine the mechanism involved during the desorption and transferring of the target compounds into the GC column. Furthermore, different parameters affecting the adsorption capacity of the sorbent are studied (e.g. sampling time and temperature, headspace/sample volume ratio, salting-out, and stirring). The evaluation of the method with aqueous samples shows that repeatability and recoveries with the NT device are equivalent to those obtained using solid-phase microextraction with a carboxen/PDMS (CAR/PDMS) coating. LODs obtained with flame ionization detection are in the range of 10-25 mg/L, and in the range of hundredths of mg/L with MS detection. The method developed is satisfactorily applied to the analysis of aqueous samples obtained from wastewater treatment plants.
Journal of Chromatography A, 2017
Water-insoluble -cyclodextrin polymer was synthesized by chemical cross-linking using epichlorohydrin (EPI) as a cross-linker agent. The produced water-insoluble polymer was used as a sorbent for the micro-solid phase extraction (-SPE) of benzene, toluene, ethylbenzene and xylenes (BTEX) from water samples. The-SPE device consisted of a sealed tea bag envelope containing 15 mg of sorbent. For the evaluation of the extraction efficiency, parameters such as extraction and desorption time, desorption solvent and salt concentration were investigated. At an extraction time of 30 min in the course of the extraction process, analytes were extracted from a 10 mL aqueous sample solution. The analytes were desorbed by ultrasonication in 200 L of acetonitrile for 20 min. Analysis of the analytes was done by a gas chromatography-flame ionization detector (GC-FID) system. The enrichment factor (EF) was found to be in the range 23.0-45.4 (EF max = 50.0). The method provided linearity ranges of between 0.5 and 500.0 ng/mL (depending on the analytes), with good coefficients of determination (r 2) ranging between 0.997 and 0.999 under optimized conditions. Detection limits for BTEX were in the range of between 0.15 and 0.60 ng/mL, while corresponding recoveries were in the range of 46.0-90.0%. The relative standard deviation of the method for the analytes at 100.0 ng/mL concentration level ranged from 5.5 to 11.2% (n = 5). The proposed method was concluded to be a cost effective and environmentally-friendly extraction technique with ease of operation and minimal usage of organic solvent.