Direct coupling of capillary liquid chromatography with conventional high-performance liquid chromatography (original) (raw)
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Journal of Chromatography A, 2002
The retention of aromatic hydrocarbons with polar groups has been correlated as log k versus log k for reversed-phase 1 2 high-performance liquid chromatography systems with different binary aqueous mobile phases containing methanol, acetonitrile or tetrahydrofuran as modifiers. Distinct changes in separation selectivity have been observed between tetrahydrofuran and acetonitrile or methanol systems. Methanol and acetonitrile systems show lower diversity of separation selectivity. The changes in retention and selectivity of aromatic hydrocarbons with various polar groups between any two chromatographic systems with binary aqueous eluents (tetrahydrofuran vs. acetonitrile, tetrahydrofuran vs. methanol and methanol vs. acetonitrile) have been interpreted in terms of molecular interactions of the solute with especially one component of the stationary phase region, i.e. extracted modifier, and stationary phase ordering. The ordering of the stationary phase region caused by modifier type influences the chromatographic selectivity of solutes with different molecular shape.
Chromatographia, 1992
l(ey Words ~pillary gas chromatography A,,ua'hme glass capillary columns i~'~aline solution treatment t'~ hydrocarbons Sununary cla-lime glass-capillary columns treated with 1M sodihydroxide at 40-60 ~ for two days were employed for ,,e gas chromatographic separation of low-boiling hydroarbons. A 70.5 m x 97 um I.D. column oroduced 780,000 930,000 theoretical ulates for early-eluting components. se of " 9 -^. steam-doped carrier gas improved peak shape and ~ u, tnn efficiency. The system was successfully applied to Separation of complex mixtures. l~troduction ~W'boiling hydrocarbons or permanent gases have been t'~raraonly analyzed on packed columns by gas chroma-st~aphy (GC) because capillary columns with similar st UOnary phases do not retain such compounds very i~r?rlgly under the usual operating conditions. Strategies ~ Solving such drawbacks of capillary columns include r%. eular sieve or porous polymers have recently been ae available.
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.
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.
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
Talanta, 2010
A new procedure for optimizing PAHs separation in very complex mixtures by reverse phase high performance (RPLC) is proposed. It is based on changing gradually the experimental conditions all along the chromatographic procedure as a function of the physical properties of the compounds eluted. The temperature and speed flow gradients allowed obtaining the optimum resolution in large chromatographic determinations where PAHs with very different medium polarizability have to be separated. Whereas optimization procedures of RPLC methodologies had always been accomplished regardless of the physico-chemical properties of the target analytes, we found that resolution is highly dependant on the physico-chemical properties of the target analytes. Based on resolution criterion, optimization process for a 16 EPA PAHs mixture was performed on three sets of difficult-to-separate PAHs pairs: acenaphthene-fluorene (for the optimization procedure in the first part of the chromatogram where light PAHs elute), benzo[g,h,i]perylene-dibenzo[a,h]anthracene and benzo[g,h,i]perylene-indeno[1,2,3cd]pyrene (for the optimization procedure of the second part of the chromatogram where the heavier PAHs elute). Two-level full factorial designs were applied to detect interactions among variables to be optimized: speed flow, temperature of column oven and mobile-phase gradient in the two parts of the studied chromatogram. Experimental data were fitted by multivariate nonlinear regression models and optimum values of speed flow and temperature were obtained through mathematical analysis of the constructed models. An HPLC system equipped with a reversed phase 5 m C18, 250 mm × 4.6 mm column (with acetonitrile/water mobile phase), a column oven, a binary pump, a photodiode array detector (PDA), and a fluorimetric detector were used in this work. Optimum resolution was achieved operating at 1.0 mL/min in the first part of the chromatogram (until 45 min) and 0.5 mL/min in the second one (from 45 min to the end) and by applying programmed temperature gradient (15 • C until 30 min and progressively increasing temperature until reaching 40 • C at 45 min).
Capillary Electrochromatography: Analysis of Polycyclic Aromatic Hydrocarbons
Analytical Chemistry, 1995
Electrochromatography is utilized to separate a mixture of 16 different polycyclic aromatic hydrocarbons (PAHs). Fused-silica capillary columns ranging in size from 50 to 150 pm i.d. were packed (20-40-cm sections) with 3-pm octadecylsilica particles. A potential of 15-30 kV is applied across the 30-50-cm total length capillary column to generate electroosmotic flow that carries the PAHs through the stationary phase. An intracavity-doubled argon ion laser operating at 257 nm is used to detect the PAHs by laser-induced fluorescence. Efficiencies up to 400 000 theoretical platedm are obtained when detection is performed within the column packing and up to 150000 theoretical plates/m when detection is performed following a frit (used to hold the packing). The reproducibility of the peak retention times is better than 2% (RSD). The limits of detection for individual PAHs range between lo-'' and mol (10-9-10-11 M), with a linear response spanning 4 orders of magnitude in concentration.
Journal of High Resolution Chromatography, 1997
An on‐line coupling of size‐exclusion Chromatography (SEC), normal‐phase liquid Chromatography (NPLC), and gas Chromatography (GC) for the characterization of complex hydrocarbon mixtures is described. The hyphenated system separates according to size, polarity, and boiling point. The use of size exclusion as the first separation step allows for the direct injection of complex (“dirty”) samples withont prior clean‐up. SEC‐NPLC coupling was realized using an on‐line solvent evaporator based on fully concurrent solvent evaporation (FCSE) using a modified loop‐type interface, vapor exit and co‐solvent trapping. Complete reconcentration of the analytes was realized by the introduction of a cryogenic cold trap. For the subsequent hydrocarbon group‐type separation an ammo‐silica column with n‐heptane as eluent was used. The NPLC‐GC coupling was based on an on‐column interface using partially concurrent solvent evaporation (PCSE) and an early vapor exit. Initial results obtained on the ana...