Liquid-Liquid Extraction of Aromatics from Hydrocarbon Mixtures in Capillaries (original) (raw)
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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, 2003
The benzene, toluene, ethylbenzene and xylenes system (BTEX) in clean water is studied to verify the performance of capillary extraction as an extraction-preconcentration technique well hyphenated with GC. The approach uses pieces of coated capillaries usually 5−30 cm long, trimmed from customary high-resolution GC columns but carrying glass press-fits at their ends. The preparation of these 'capillary extractors' is explained, and their performance is discussed providing guidelines for use. Injection by capillary extraction is such that (i) band broadening in time is null, and (ii) band broadening in space cannot be higher than the extractor length. Speed, cleanliness and operative simplicity of the capillary extraction approach are remarkable, pros and cons are complementary to those of solid phase microextraction (SPME) or stir bar sorptive extraction (SBSE). Capillary extraction-capillary GC analysis of aqueous BTEX samples, in a clean water matrix, allows low part-per-billion detection limits, and does not require heated injectors or cryofocusing devices.
Analytica Chimica Acta, 1981
Current advances in the technology of capillary columns for gas chromatography permit extension of the range of polycyclic aromatic compounds which may be eluted. High-performance liquid chromatography (h.p_l.c.) in the non-aqueous, reversed-phase mode shows promise forseparation of even larger molecules: an inquiry into the feasibility of capillary h.p.1.c. in this area has resulted in elution of polycyclic compounds containing up to eleven aromatic rings. The detrimental health effects caused by polycyclic aromatic compounds (PAC) that are generated in various combustion processes are wellestablished. Certain of these substances are known to be mutagenic and carcinogenic. While various analytical procedures have been developed in numerous labortories for their determination, chromatographic separations play a prominent role in this field [ 11. Mixtures of PAC isolated from various products of combustion (e.g., soot, coal tar, or smoke condensates) are frequently very complex, and the same is true for materials derived from petroleum or coal. When highefficiency gas chromatographic columns are employed, it is not unusual to observe 1OW200 compounds in such mixtures [2-41 in the range of 2-ring to 6-ring PAC structures. Capillary gas chromatography (g-c.) and high-performance liquid chromatography (h.p.1.c.) have been developed over the years as successful methods for PAC separation. Both methods hold advantages and disadvantages of their own. As has been established in previous studies [2-41, relatively short thin-film glass capillary columns (yielding typically 30 OOO-80 000 theoretical plates for such separations) can clute PAC containing up to six rings within the usual temperature range of modem g.c. The typical
Journal of Separation Science, 2012
A sensitive method for the extraction and determination of polycyclic aromatic hydrocarbons (PAHs) using alcoholic-assisted dispersive liquid-liquid microextraction (AA-DLLME) and HPLC was developed. The extraction procedure was based on alcoholic solvents for both extraction and dispersive solvents. The effective parameters (type and volume of extraction and dispersive solvents, amount of salt and stirring time) on the extraction recovery were studied and optimized utilizing factorial design (FD) and central composite design (CCD). The best recovery was achieved by FD using 2-ethyl-1-hexanol as the extraction solvent and methanol as the dispersive solvent. The results showed that volume of dispersive solvent and stirring time had no effect on the recovery of PAHs. The optimized conditions were 145 mL of 2-ethyl-1-hexanol as the extraction solvent and 4.2% w/v of salt (NaCl) in sample solution. The enrichment factors of PAHs were in the range of 310-325 with limits of detection of 0.002-0.8 ng/mL. The linearity was 0.01-800 ng/mL for different PAHs. The relative standard deviation (RSD) for intra-and inter-day of extraction of PAHs were in the range of 1.7-7.0 and 5.6-7.3, respectively, for five measurements. The method was also successfully applied for the determination of PAHs in environmental water samples.
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.
Sample extraction plays a key role in modern analytical methodology, which affects the accuracy and precision of the final results. However, traditional sample extraction procedures, based on conventional liquidliquid extraction (LLE) is often time-consuming, laborintensive, and environmentally unfriendly due to the utilization of large amounts of potentially toxic organic solvents. Solid phase extraction (SPE) utilizes much less solvent and is less time-consuming than LLE, but requires column conditioning and is relatively expensive [1,2]. In the past few years, the promising objectives of green chemistry caused many research efforts focusing on the development of efficient, miniaturized and environmentally friendly extraction methods such as liquid-phase micro-extraction (LPME) [3-5], and solid-phase micro-extraction (SPME) [6-8]. SPME is a solvent-free extraction technique which unifies extraction and pre-concentration in a single step. However, SPME fiber is expensive, fragile and has a limited lifetime, also sample carry-over can be a great problem in this method [9]. LPME approaches are much more cost-effective and can be divided into two broad categories: membrane-protected solvent and exposed solvent. The protected LPME modes include hollowfiber-protected 2-phase micro-extraction, hollow-fiberprotected 3-phase micro-extraction, and electro-Article history:
Liquid-phase microextraction of polycyclic aromatic hydrocarbons: A review
Reviews in Analytical Chemistry, 2020
Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds comprised of two or more fused benzene rings, which arise from the incomplete combustion of organic materials. These compounds have been of concern as carcinogens and mutagens for the past 50-60 years. Lately, they are also receiving attention as endocrine-disrupting chemicals. Therefore, proper analytical methods are required for sampling and analyzing these compounds. In response to problems associated with the conventional methods like solid-phase extraction (SPE) and liquid-liquid extraction (LLE), many studies have focused on the miniaturization of different sample preparation techniques. In this regard, the use of different types of liquid phase microextraction (LPME) techniques has increased significantly during the recent few decades. LPME techniques are advantageous because they use single-step sample preparation and have shown a greater sensitivity, selectivity, and efficiency than the conventio...
Separation of Aromatics using Benign Solvents
Separation of aromatics from aliphatics is challenging because of the close range of their boiling points and the formation of several combinations of azeotropes. Until now, no feasible separation process is available for aromatic concentrations below 20 wt%. In this work, we have investigated the possibility of using selected Deep Eutectic Solvents (DESs) for the liquid-liquid extraction of aromatics. DESs have emerged as green solvents that may offer several industrial alternatives. The DESs used in this work were synthesized from ammonium salt with ethylene glycol, lactic acid and sulfolane as Hydrogen Bond Donor (HBD). Equilibrium data for the ternary system consisting of ethylbenzene and n-octane with all DESs were measured at 25°C and atmospheric pressure. The results showed comparable distribution ratio and selectivity with commercial solvents. The absence of the HBD in the hydrocarbon layer, means the reduction of the number of separation stages. In addition, the Non-Random Two Liquid (NRTL) model was successfully used to correlate the experimental tie-lines and to calculate the phase compositions of the ternary systems.
Journal of Chromatography A, 2011
A methacrylate-based monolithic capillary column has been evaluated for the preconcentration of polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. For this purpose, the monolyte was in situ synthesized in a 6 cm × 0.32 mm id fused-silica capillary. The microextraction unit was fitted to a micro-HPLC pump to pass 10 mL of sample. The isolated pollutants were eluted by means of 10 L of methanol, the organic phase being directly collected in a specific interface that can be fitted to the injection port of the gas chromatograph without modification. The interface allows the on-line thermal desorption of the PAHs, avoiding the dilution and providing enough sensitivity to reach the legal limits established for these pollutants in the matrices selected. The limits of detection achieved for 10 mL of water ranged between 2.8 ng/L (indeno(1,2,3-cd)pyrene) and 11.5 ng/L (acenaphthene) with acceptable precision (between 4.5 and 18.2% RSD). The method was applied to the determination of the selected PAHs in tap, river waters and sewage, being fluoranthene and pyrene detected in all of them at concentrations lower than the legal limits established for these compounds in the matrices assayed.
Selective Aromatics extraction from hydrocarbon mixtures
This work is aimed at the study of liquid-liquid equilibrium of systems of industrial interest, particularly the purification of oil and gas in the oil refining industry. We present experimental results on the solubility of aromatics in the liquid-liquid equilibrium obtained by gas -liquid chromatography at different temperatures. We used a mixture of solvents to improve the characteristics of selectivity and aromatics extraction. The solvent is a binary mixture of N-methyl 2-pyrrolidone (NMP) and diethylene glycol (DEG). The results presented are for two mixtures consisting of 90% NMP + 10% DEG, and 70% NMP +30% DEG. Heptane was used as hydrocarbon solvent and toluene as aromatic compound. Furthermore, we applied the equation of state NRTL (Non Random Two Liquids) and UNIQUAC (Universal Quasi Chemical) for coexistence curves and the critical point.