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WO1999063335A1 - Interface pour la micro-extraction en phase solide et techniques de microseparation - Google Patents

Interface pour la micro-extraction en phase solide et techniques de microseparation Download PDF

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Publication number
WO1999063335A1
WO1999063335A1 PCT/CA1999/000467 CA9900467W WO9963335A1 WO 1999063335 A1 WO1999063335 A1 WO 1999063335A1 CA 9900467 W CA9900467 W CA 9900467W WO 9963335 A1 WO9963335 A1 WO 9963335A1
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Prior art keywords
interface
passageway
guide
solid phase
fiber
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PCT/CA1999/000467
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English (en)
Inventor
Janusz B. Pawliszyn
Chen-Wen Whang
Original Assignee
Pawliszyn Janusz B
Whang Chen Wen
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Publication date
Application filed by Pawliszyn Janusz B, Whang Chen Wen filed Critical Pawliszyn Janusz B
Priority to AU41252/99A priority Critical patent/AU4125299A/en
Publication of WO1999063335A1 publication Critical patent/WO1999063335A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/447—Systems using electrophoresis
    • G01N27/44704—Details; Accessories
    • G01N27/44743—Introducing samples

Definitions

  • This invention relates to an interface for use with solid phase microextraction and capillary electrophoresis devices to assist in inserting the fiber from the solid phase microextraction device into the capillary electrophoresis device and to a method of constructing and a method of using the interface.
  • a sample preparation step not only isolates the components of interest from a sample matrix, it also brings the analytes to a suitable concentration level, while preconcentration may be the most important factor for clean, dilute samples, interferences removal (or selectivity) is more important in the analysis of complex samples.
  • SPME solid phase microextraction
  • SPME solid phase extraction
  • SFE supercritical fluid extraction
  • SPME is an equilibrium method which does not require total removal of target analytes from the sample matrix.
  • equilibrium extraction strategy is particularly advantageous to speciation analysis in which the equilibrium distribution of the various forms of an element should not be altered during sampling.
  • the amount of analyte extracted in SPME is dependent on the partition coefficient of an analyte between the coating and the matrix.
  • CE Capillary electrophoresis
  • Sample volumes of 1-100 nL are injected directly into the separation capillary, which dramatically reduces system dead volumes because injector valves or column connectors are not required.
  • the small capillary dimensions encountered and the minuscule sample zone generated in CE also lead to relatively poor concentration detection limit.
  • Several large-volume injection techniques such as sample stacking, field amplification and transient isotachophoresis, have been developed to overcome the problem. These techniques yield some sensitivity enhancement but are limited by the amount of sample that can be loaded into a capillary.
  • Other strategies include using a solid phase concentrator or membrane preconcentration cartridge connected on-line with the CE capillary.
  • the analytes were back extracted into a few microliters of an aqueous buffer, followed by conventional CE analysis. Recently, Nguyen and Luong (see Analytical Chemistry 1997, 69,1726) reported a direct connection between SPME and CE.
  • Polycyclic aromatic hydrocarbons (PAHs) in aqueous samples were extracted onto a 150 ⁇ m o.d. x 1 cm length poly(dimethylsiloxane) (PDMS)-coated glass fiber, which was then attached to the inlet end of a 50 ⁇ m i.d. x 350 ⁇ m i.d. x 350 ⁇ m o.d. separation capillary via an adapter.
  • PAHs Polycyclic aromatic hydrocarbons
  • PDMS poly(dimethylsiloxane)
  • the absorbed PAHs were released into the CE buffer stream by injecting a short plug of methanol, followed by cyclodextrin- modified CE separation. Since the analyte-bearing fiber was positioned outside the injection end of the capillary during the solvent desorption step, zero-dead volume connection was not achieved. Significant variations on migration time and peak area for several PAHs were sometimes observed.
  • Figure 1 is a schematic top view of an interface between a solid phase microextraction device and a capillary electrophoresis device
  • Figure 2 is a block diagram showing the use of the interface with a capillary electropherograph
  • Figure 3 is an electropherogram of ten phenolic compounds obtained by SPME/CE;
  • Figure 4A and Figure 4B is an electropherogram of six phenolic compounds
  • Figure 5 A and Figure 5B is an electropherogram of ten pheonlic compounds obtained by SPME/CE using a different fiber from the electropherograms shown in Figure 2;
  • Figure 6 is an electropherogram of serotonin and catecholamines
  • Figure 7 is an electropherogram of six phenols obtained by
  • An interface for use with a solid phase microextraction device and capillary electrophoresis device has a housing having a passageway extending therethrough.
  • the passageway has two ends and a central area between said ends.
  • the passageway has guide means to guide and align the solid phase microextraction device with the capillary electrophoresis device.
  • Said passageway being shaped to receive one of said devices so that said devices are aligned with one another when the solid phase microextraction device is fully inserted into end of said passageway and the capillary electrophoresis device is fully inserted into the other end of said passageway permitting interaction between said devices.
  • the housing is a buffer reservoir and a gap is positioned at the centre of said reservoir.
  • a piece of wire is sealed to a bottom of the reservoir to serve as an anodic electrode.
  • a buffer solution is contained in the reservoir.
  • a method of constructing an interface for solid phase microextraction and capillary electrophoresis devices comprises creating a passage in a housing, said passage having two outer ends and a central area, sizing two guide tubes, one to fit within each end of said passage so that a narrow gap exists between said guide tubes when they are fully inserted, said guide tubes having an inner surface that is conical and tapers toward said central area for each guide tube.
  • a method of using an interface in accordance with the present invention comprising inserting a solid phase microextraction device in an outer guide tube and inserting a capillary electrophoresis device in an inner guide tube, causing a tiny fibre in said solid phase microextraction device to extend through said gap into said electrophoresis device and causing analytes from said fiber to be desorbed into said electrophoresis device.
  • the present invention is not restricted to capillary electrophoresis, but can be used with any suitable microseparation technique.
  • Phenolic standards were purchased from Supelco, Inc. (Bellefonte,
  • PA poly(methyl methacrylate)
  • Stock, solutions of 1000 ⁇ g/mL for various phenols were prepared in methanol and stored in a freezer. Working standards of lower concentrations were prepared daily by diluting the stock solutions with CE buffer. Water samples containing spiked phenols were prepared in 0.01 M HC1 solution saturated with NaCl. The separation buffer was 20 mM sodium borate adjusted to pH 9.9 with NaOH. Poly(methyl methacrylate) (PA) was obtained from Aldrich (Milwaukee, WI). A 3% (w/v) solution of PA was prepared in acetone. All other reagents were of analytical grade. Water, purified with an ultrapure water system (Barnstead/thermolyne, Dubuque, IA), was used for all solutions.
  • Ultrapure water system Barnstead/thermolyne, Dubuque, IA
  • the SPME/CE system developed in this study is depicted in Figure 2.
  • the system consists of three parts: SPME fiber assembly, interface, and CE system.
  • the top view of the interface shown in Figure 1 is enlarged to show its construction in detail.
  • Commercial SPME fibers for CE analysis are not available at the present time. Therefore, all SPME fibers used in this study are custom-made. Preparation of the SPME fiber is similar to that described previously, with some modifications.
  • a PA-coated optical fiber Part no. FHA060072245; Polymicro Technologies Inc., Phoenix, AZ
  • a -2-cm portion of the coating was stripped from one end of the fiber; the remaining silica rod was about 70 ⁇ m in diameter.
  • the stripped fiber end was then cemented into one end of a lOO ⁇ m i.d. x 245 ⁇ m o.d. x 10 cm length fused silica tubing with epoxy glue, leaving about 1.2 cm stripped fiber extruding from the tubing end.
  • the fiber was carefully trimmed to a length of 1.0 cm.
  • the silica fiber was then dipped in a 50% aqueous HF solution to a depth of 0.9 cm, being careful not to immerge the glued part in HF.
  • the fiber was taken out and thoroughly washed with deionized water, followed by drying in a 50 °C oven. Using a microscope, the diameter of the fiber was estimated at -40 ⁇ m.
  • the bare fused silica fiber was then dipped in a 3% (w/v) PA solution to a depth of 0.8 cm for three times. The solvent was allowed to evaporate after each dipping.
  • the thickness of the PA coating was roughly estimated at ⁇ 1 ⁇ m by microscopic comparison with an uncoated silica fiber.
  • the original stainless steel fiber holder in a commercial SPME fiber assembly was removed and replaced with the fused silica tubing-fiber assembly.
  • a small rubber septum was fitted to the other end of the fused silica tubing and served as a plunger cap. This fiber will be designated as the PA-coated fiber in later discussion.
  • Another fiber was prepared from a 250 ⁇ m o.d. acrylic fiber (Edmund
  • a 3-cm piece of the acrylic fiber was vertically soaked in acetone for 30 minutes to etch the diameter down to -80 ⁇ m.
  • the fiber was mounted in the SPME fiber assembly following the procedure described above, and was trimmed to a length of 1.0 cm.
  • the fiber was dipped in acetone again for another 15 minutes to further decrease its o.d. down to -40 ⁇ m. This fiber will subsequently be designated as the PA fiber.
  • the SPME/CE interface was made of a Teflon block (20 x 30 x 10 mm ). Space for accommodating the buffer solution and positioning the SPME fiber and the capillary tubing was tapped with a " , 6 inch thread. Two tunnels with a diameter 2.0 mm each were drilled through both sides of the buffer reservoir, ensuring that the two tunnels are precisely aligned.
  • An Inner-Lok (a trade mark) capillary connector (part no. MLC 150440, Polymicro Technologies) was cut into two halves and two pieces of inner conical tubes were created. The cutting face of one conical tube was carefully polished until a 360 ⁇ m o.d. capillary could barely extrude from it. This piece of conical tube is used as a CE capillary guide in the interface.
  • Another conical tube which is used as a guide for SPME fiber assembly was prepared from the half of a different Inner-Lok (a trade mark) connector (part No. MLC330750, Polymicro Technologies).
  • the two conical guide tubes (with 2.0 mm o.d.) were pressed into the two tunnels respectively from both sides of the interface block until a-l-mm gap was left between them. The gap was positioned in the center of the buffer reservoir. It is crucial to ensure that the two conical guide tubes are perfectly aligned.
  • a short piece of 245- ⁇ m o.d. capillary can be inserted through the guide tubes to check the alignment. Epoxy glue was applied to further secure the guide tubes in position.
  • a piece of 0.5-mm diameter Pt wire was sealed to the bottom of the buffer reservoir and served as an anodic electrode for CE.
  • the interface block was clamped to a stand during experimentation.
  • the inlet end of CE capillary was etched to a conical shape by HF before use.
  • the detection end of the capillary was connected to a glass bottle containing helium pressured to about 20 psi. With helium flowing through the capillary, the inlet end of the capillary was placed in a 50% aqueous HF solution for 20 minutes. The inside of the capillary was etched open to provide an inner conical shape. After etching, the capillary tip was placed in a 1 M sodium carbonate solution to neutralize the acid, followed by washing with deionized water.
  • CE separations were carried out in a Bio-Rad HPE 100 capillary electropherograph (BioRad Lab. Richmond, CA). The original capillary cartridge was modified in order to facilitate the hyphenation between CE tubing and SPME fiber. The separation capillary was 75 ⁇ m i.d., 360 ⁇ m o.d. and 40 cm total length (32 cm to the detector). Each new capillary was pretreated with 0.1 M NaOH for 10 minutes. Before each run, the capillary was rinsed (pressured flow) with buffer for 3 minutes. Detection was carried out at 220 nm. Electropherograms were recorded using either a strip-chart recorder or an integrator. Procedure.
  • a PA-coated fiber was exposed to a stirred aqueous sample containing the spiked phenols for a fixed time of period.
  • the fiber was withdrawn into the protective needle before transferring the fiber assembly to the interface.
  • the needle was inserted into the fiber guide tube until the needle tip butted against the tube wall.
  • a preconditioned and buffer-filled CE capillary was subjected to a 5 s injection of a 0.2 M NaOH solution.
  • the inlet end of the capillary holding the NaOH solution plug was immediately transferred to the interface by inserting it into the capillary guide tube, until the capillary end was 0.1 mm extruding from the guide tube. With the capillary in position, the fiber was carefully inserted into the capillary end by slowly pushing the fiber plunger forward.
  • the PA-coated region of the fiber (-0.8 cm) was completely inserted into the capillary, leaving less than 0.2 cm uncoated part outside the capillary tip. It is important not to block the capillary end by pushing the plunger too far. A microscope greatly facilitated the procedure. Since the capillary end is inner conically enlarged and the two guide tubes are precisely aligned, insertion of a 40 ⁇ m o.d. fiber into a 75 ⁇ m i.d. capillary can be achieved without difficulty. The fiber insertion process generally takes less than 10 s. After fiber insertion, the reservoir was immediately filled with running buffer using a syringe.
  • the capillary-fiber coupling region was completely covered by the buffer solution and potential was applied to perform electrophoresis in the normal manner.
  • the fiber was left inside the capillary for the duration of the analysis.
  • buffer was removed from the reservoir using a syringe.
  • the fiber was then withdrawn into the needle followed by removal from the interface. After washing with deionized water, the fiber was ready for the next extraction.
  • the CE capillary was also removed from the interface and was thoroughly rinsed as described above. Safety Several phenolic compounds used in this study are suspected carcinogens and caution should be exercised when working with these chemicals and their stock solutions. Hydrofluoric acid can cause serious burns, it should be neutralized with sodium carbonate prior to disposal.
  • phenols and poly(acrylate) (PA) were selected as the test analytes and extraction coating, respectively.
  • the determination of priority pollutant phenols in water using SPME with GC analysis is known.
  • the PA phase which is a low density solid polymer of medium polarity, has been shown to be the optimal coating for phenols.
  • the coating-water distribution constants (K) range from 170 for pentachlorophenol to 1.3 for phenol. In general, the more polar the species is, the smaller its K value will be.
  • the chlorinated compounds have a high affinity for the PA coating, and the affinity increases with the number of chlorines on the phenol molecule.
  • Phenol has the smallest K value, which is expected from its high polarity and high solubility in water.
  • the extraction efficiency of phenols can be significantly enhanced by acidifying the water sample to pH 2 and saturating it with NaCl before extraction.
  • the low pH ensures that all of the phenols are in their neutral form while the addition of NaCl salts the analytes out of solution and into the fiber coating.
  • the extraction procedure for SPME/CE is the same as that for SPME/GC or SPME/HPLC.
  • the commercial PA-coated fibers for GC or HPLC analysis are not suitable for CE because their diameters (100 - 300 ⁇ m o.d.) are too large to fit in with the commonly used capillary tubing.
  • Figure 3 shows an electropherogram of ten phenols obtained by SPME/CE analysis using a 40 ⁇ m o.d. PA-coated silica fiber. Extraction was performed for 20 minutes in a stirred water sample containing the spiked analytes. After extraction, the fiber was transferred to the interface and coupled to a 75 ⁇ m i.d. capillary. Potential was then applied to perform electrophoresis in the normal manner and an UV detector was used for detection. Sharp and symmetrical peaks were observed for all the analytes. Additionally, the migration order of the ten phenols is the same as that obtained previously using conventional CE without SPME sample introduction.
  • the desorption procedure is extremely important in SPME/CE because excessive injection band broadening and loss of analyte resolution can be caused by improper selection of desorption conditions.
  • Parameters which control the desorption process in SPME/CE are analogous to SPME/HPLC applications.
  • a judicious combination of the extraction and separation principles could lead to better desorption and selectivity.
  • weak acids/bases in aqueous sample could be extracted either as neutral species using a polar fiber coating or as ions using an ion exchange fiber.
  • Desorption could then be performed by using aqueous buffer followed by normal CE separation, or using organic solvent followed by micellar electrokinetic chromatography (MEKC) separation.
  • MEKC micellar electrokinetic chromatography
  • the desorption kinetics of analytes from the fiber coating into the liquid phase in SPME/HPLC has been discussed previously.
  • L the coating thickness
  • D the diffusion coefficient of an analyte.
  • the thickness of the PA coating is - 1 ⁇ m and the diffusion coefficient of analyte is about 10 * m Is.
  • the desorption time required is thus much less than 1 s, assuming continuously flowing liquid stream and good solubility of analyte in the liquid phase.
  • phenols investigated are weak acids with pKa values ranging from 4.09 (for 2.4-dinitrophenol) to 10.63 (for 2.4- dimethylphenol), a strong base can be employed to ionize and desorbe the phenols from the fiber coating.
  • phenolate anions can be easily separated under counterelectroosmotic CE mode.
  • a 0.2 M NaOH solution was therefore selected as the desorption solvent. With a 5 s injection of NaOH prior to fiber insertion, the first few millimeters of the capillary inlet will be filled with NaOH. After inserting the fiber into the NaOH solution plug, the absorbed phenols ionize and rapidly desorb from the coating into the liquid phase.
  • Figures 4A and 4B compare the electropherograms obtained for the separation of a six phenol mixture using conventional electrokinetic injection (Figure 4A) and SPME sample introduction (Figure 4B). These electropherograms show that little efficiency is lost due to solvent desorption. Quantitatively, the desorption procedure caused a loss in average separation efficiency of about 15% with a range of 0 to 43% for the six analytes studied. The peak shape of phenols in both figures are similar, and their migration order and migration times are almost identical. Additionally, no carryover of analytes was observed in subsequent solvent desorption on the same fiber. These results clearly indicate the feasibililty of NaOH solution as the desorption solvent and a fast desorption kinetics of phenols from the fiber coating into the liquid phase.
  • FIG. 4 shows the electropherograms of a 10 phenol mixture obtained by SPME/CE using a PA fiber ( Figure 5 A) and a PA-coated silica fiber ( Figure 5B). Significant peak tailing was observed for most of the phenols with the use of a PA fiber. This may be attributed to a slow desorption kinetics of analytes from the PA fiber.
  • the PA phase extracts analytes mainly by absorption, which allows analytes to diffuse into the coating, but the diffusion coefficients are generally lower compared to PDMS.
  • the absorbed analytes can quickly diffuse to the coating surface during solvent desorption step.
  • the diffusion paths for analytes become longer and it will take more time to diffuse from the coating interior to the surface.
  • Another problem encountered with the use of a PA fiber is caused by its soft and flexible characteristic, which makes the fiber insertion operation very difficult.
  • the PA-coated silica fiber is rather fragile, it is straight and sturdy enough for direct insertion into the capillary end, with the aid of the interface.
  • SPME can be easily connected on-line to CE by a custom-designed interface.
  • the primary advantage of this interface is its provision of a zero-dead volume connection via direct insertion of the SPME fiber into the CE capillary.
  • the absorbed analytes can be desorbed from the fiber coating into the capillary by a minimum amount of an appropriate solvent without causing significant band broadening.
  • alignment between SPME fiber and CE capillary end can be achieved easily and reliably. Since most microcolumn separation techniques are susceptible to interferences from the complex sample matrices, SPME provides an ideal sampling and sample preparation procedure for the analysis of complicated samples, e.g. clinical urine and sewage sludge samples.
  • the developed interface should also find use in on-line connection between SPME and other microcolumn separation techniques, such as MEKC or capillary electronkinetic chromatography (CEC).
  • MEKC capillary electronkinetic chromatography
  • CEC capillary electronkinetic chromatography
  • FIG 3 there is shown electropherograms of ten phenolic compounds obtained by SPME/CE using (A) a 40 ⁇ m o.d. PA-coated silica fiber and (B) a 40 ⁇ m o.d. bare silica fiber.
  • Peak identities (concentration in sample); (1) 2,4-dimethylphenol (2 ppm), (2) phenol (20 ppm), (3) 4-chloro-3-methylphenol (20 ppm), (4) pentachlorophenol (0.08 ppm), (5) 2,4,6-trichlorophenol (lppm), (6) 2-methyl-4,6-dinitrophenol (10 ppm), (7) 2,4-dichlorophenol (2ppm), (8) 2-chlorophenol (10 ppm), (9) 4-nitrophenol (10 ppm), (10) 2-nitrophenol (2.5 ppm).
  • Figures 4A and 4B there are shown electropherograms of six phenolic compounds.
  • Capillary electrophoresis (CE) in narrow bore (2-75 ⁇ m i.d.) capillaries can be an important teclinique for bioseparation.
  • CE coupled with highly sensitive laser-induced fluorescence (LIF) or electrochemical (EC) detector is ideally suited for single-cell analysis.
  • LIF laser-induced fluorescence
  • EC electrochemical detector
  • FIG. 6 illustrates the separation of serotonin and 3 catecholamines (viz. dopamine, epinephrine and norepinephrine) by on-line coupled SPME/CE using a Naflon-coated silica fiber. Due to their small partition coefficients between the Naflon coating and the aqueous matrix, the recovery of catecholamines is relatively poor. A more specific coating material or a different extraction strategy is probably needed to improve the recovery.
  • the developed interface could also be useful in on-line connection between SPME and other microcolumn separation techniques, such as micellar electrokinetic chromatography (MEKC) or capillary electrokinetic chromatography (CEC).
  • Figure 7 shows the electropherogram obtained by on-line coupled SPME/MEKC.
  • Six phenols are first extracted as neutral species from an acidic (pH 2), salt-saturated aqueous solution using a polyacrylate (PA)-coated silica fiber.
  • PA polyacrylate
  • the absorbed phenols are then desorbed into the capillary by a small amount of methanol, followed by MEKC separation using a phosphate/borate buffer containing sodium dodecyl sulfate (SDS).
  • SDS sodium dodecyl sulfate
  • Figure 6 shows an Electropherogram of serotonin and catecholamines obtained by SPME/CE using a Nafion-coated silica fiber.
  • Conditions extraction time, 30 min, 1000 rpm; desorption solvent, CE buffer; separation column, 75 ⁇ m i.d. x 360 ⁇ m o.d. x 40 cm total length (32 cm to the detector); separation potential, 6 kV; buffer, 20 mM sodium borate at pH 9.9; detection wavelength, 254 nm.
  • Peak identities (1) serotonin, (2) dopamine, (3) epinephrine, (4) norepinephrine. All species are 1 mM in the sample.
  • Figure 7 shows an Electropherogram of six phenols obtained by SPME/MEKC using a PA-coated silica fiber. Conditions: extraction time, 20 min, 1000 rpm; 5 s injection of methanol as the desorption solvent prior to fiber insertion; separation column, 75 ⁇ m i.d. x 360 ⁇ m o.d. x 46 cm total length (38 cm to the detector); separation potential, 4.6 kV; buffer, 10 mM borate/5 mM phosphate/50 mM SDS, pH 7.0; detection wavelength, 220 nm. Peak identities (concentration in sample): (1) methanol, (2) 2-chlorophenol (10 ppm).

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Abstract

La présente invention concerne une nouvelle interface qui permet de coupler la technique d'échantillonnage par micro-extraction en phase solide (MEPS) et l'électrophorèse capillaire (EC). Cette interface facilite l'insertion directe d'une fibre mince de silice dans l'entrée d'un capillaire de séparation, ce qui permet de satisfaire à la coupure entre les techniques MEPS et EC par l'obtention d'un volume mort nul. La performance de l'interface a été évaluée par l'analyse MEPS/EC de phénols, polluants importants, au moyen d'une fibre de silice de 40 νm de diamètre extérieur recouverte de poly(acrylate) (PA), fabriquée au laboratoire, et reliée à un capillaire de séparation de 75 νm de diamètre interne. Les résultats montrent clairement que l'interface est efficace pour un couplage en ligne des techniques MEPS et EC. A la place de l'EC, on peut utiliser avec l'interface d'autres dispositifs de micro-colonnes.
PCT/CA1999/000467 1998-06-01 1999-06-01 Interface pour la micro-extraction en phase solide et techniques de microseparation WO1999063335A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016090064A1 (fr) * 2014-12-05 2016-06-09 Advanced Electrophoresis Solutions Ltd Appareil et procédé pour séparer des molécules

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5453382A (en) * 1991-08-05 1995-09-26 Indiana University Foundation Electrochromatographic preconcentration method
WO1996033405A1 (fr) * 1995-04-17 1996-10-24 Mayo Foundation For Medical Education And Research Pretraiteur d'echantillons

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5453382A (en) * 1991-08-05 1995-09-26 Indiana University Foundation Electrochromatographic preconcentration method
WO1996033405A1 (fr) * 1995-04-17 1996-10-24 Mayo Foundation For Medical Education And Research Pretraiteur d'echantillons

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
AN-LAC NGUYEN: "separation of polycyclic aromatic hydrocarbons by solid phase microextraction/cyclodextrin-modified capillary electrophoresis", ANALYTICAL CHEMISTRY, vol. 69, no. 9, 1997, pages 1726 - 1731, XP002116345 *
WU X -Z ET AL: "AN ON-LINE ELECTROPHORETIC CONCENTRATION METHOD FOR CAPILLARY ELECTROPHORESIS OF PROTEINS", ANALYTICAL CHEMISTRY, vol. 70, no. 10, 15 March 1998 (1998-03-15), pages 2081 - 2084, XP000766182, ISSN: 0003-2700 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016090064A1 (fr) * 2014-12-05 2016-06-09 Advanced Electrophoresis Solutions Ltd Appareil et procédé pour séparer des molécules

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