Patent Application
20170153202
The present invention relates to electrophoretic separation and analysis of trace and ultra-trace compounds. Specifically the invention is directed to analysis of ionogenic compounds by coupled isotachophoresis and zone electrophoresis on chip with online detection.
Environmental protection agency defines trace analysis as analysis at part-per-thousand level (http://www.epa.gov/esd/chemistry/org-anal/faq.htm).
According to IUPAC definition, trace analysis corresponds to analysis of compounds below 100 ppm (<0.01%). Microtrace analysis corresponds to analysis below 1 ppm (<10−4%), ultra-microtrace analysis to analysis below 1 ppb(<10−7%), and sub-microtrace analysis to analysis below 1 ppt (<10−10%) (J. Namiesnik Trace Analysis—Challenges and Problems. Crit. Rev. Anal. Chem. 32, 271-300, 2002).
According to Fundamental of Analytical Chemistry by Skoog & West, trace analysis represents analysis at 1 ppb to 100 ppm level and ultratrace at <1 ppb level, (Skoog, D. A.; West, D. M.; Hollar, J.: Fundamentals of Analytical Chemistry. 9th edition, Brooks/Cole, Cengage Learning, Belmont, 2013.)
In isotachophoresis (ITP), the concentration of ions in their pure isotachophoretic zones, is set up by their mobilities, the mobilities of the used leading ion and counter ion and the concentration of the leading ion (F. Kohlrausch, Ann. Phys. Chem. 1897, 62, 209-239.) and is independent of the original concentration of analytes in the sample. Thus, low-concentration analytes are concentrated between leading ion and terminating ion, which, in combination with a suitable detection method, makes it a useful tool for a rapid ion analysis (P. Gebauer, V. Dolník, M. Deml and P. Bo{hacek over (c)}ek: Recent trends in capillary isotachophoresis. Adv. Electrophoresis, 1987, 1, 281-359; Bo{hacek over (c)}ek, P., et al., Analytical Isotachophoresis. 1988, Weinheim: VCH Publisher). To achieve a full isotachophoretic separation of analytes, a certain amount of electric charge has to pass through the separation column (Bo{hacek over (c)}ek, P., et al., Analytical isotachophoresis: The concept of the separation capacity. J. Chromatogr., 1979, 160, 1-9.). When so-called effective mobilities of analytes are known, the separation charge and column charge/hold-up can be calculated (Dolník, V., et al., Optimization of isotachophoretic analysis: use of the charge-based transient state model. J. Chromatogr., 1991, 55, 249-266.)
Complex mixtures require larger separation charge to achieve full separation of all analytes. Isotachophoretic separation requiring a large separation charge in a narrow capillary would need rather impractically long separation times. Various techniques were introduced to provide high separation charge in short separation time, including hydrodynamic counter flow, volume coupling, column coupling, concentration cascade/step, and multicolumn ITP.
Hydrodynamic counter flow allows performing isotachophoretic separation in relatively short separation column (F. M. Everaerts, Th. P. E. M. Verheggen, J. L. M. Van De Venne: Isotachophoretic experiments with a counter flow of electrolyte. J. Chromatogr. A, 1976, 123, 1139-148).
The volume coupling is a method, where the isotachophoretic separation is performed in a wide separation channel and detection in a narrow detection channel. (Th. P. E. M. Verheggen, F. M. Everaerts, Volume-coupling in isotachophoresis. J. Chromatogr. A, 1982, 249, 221-230).
The column coupling is a method similar to volume coupling. At the interface between two columns of different width, an auxiliary electrode is connected allowing application of high electric current in the separation step without overheating (F. M. Everaerts, Th. P. E. M. Verheggen, F. E. P. Mikkers, Determination of substances at low concentrations in complex mixtures by isotachophoresis with column coupling. J. Chromatogr. A, 1979, 169, 21-38).
The column-coupling method was also applied to separation on chip (R. Bodor, et al., Isotahophoresis and isotachophoresis-zone electrophoresis of food additives on as chip with column-coupling separation channels. J. Sep. Sci, 2001, 24, 802-809.)
The concentration cascade/step is a method where separation is performed in a channel with a high-concentration leading electrolyte and detection in a channel with a low-concentration leading electrolyte (Bo{hacek over (c)}ek, P., et al., Effect of a concentration cascade of the leading electrolyte on the separation capacity in isotachophoresis. J. Chromatogr., 1978, 156, 323-326.).
Concentration step and column coupling can also be combined. This approach brings possible additional advantages such as changing migration order and eliminating major interfering compounds (V. Dolník, M. Deml and P. Bo{hacek over (c)}ek: Multivalent ion interactions in isotachophoresis and their utilization in a cascade system. In: C. J. Holloway, (Ed.), Analytical and Preparative Isotachophoresis, Walter de Gruyter, Berlin-New York, 1984, pp. 55-62.).
The multicolumn isotachophoresis is a method similar to the column coupling. The separation is performed in a channel with a cross section substantially exceeding the cross-section of the analytical capillary (Dolnik, V., et al., Large sample volume preseparation for trace analysis in isotachophoresis. J Chromatogr, 1985, 320, 89-97, Dolnik, V., et al., Determination of oxalate in human serum by multicolumn isotachophoresis. Electrophoresis, 1988, 9:839-841.). To improve dissipation of generated Joule heat, the separation channel has rectangular cross-section as well as the following tapered channel, in which the profile of isotachophoretic zones is reduced. Only a single auxiliary electrode is connected to the tapered channel. During migration through the tapered channel, the fully separated isotachophoretic zones can be partly mixed and have to be restored by migration through a narrow restoring channel. The system may contain a series of tapered and corresponding restoring channels. The final restoring channel serves also as an analytical channel.
To detect UV absorbing analytes, UV absorption detection can be applied (J. W. Jorgenson, K. DeArman Lukacs: Zone electrophoresis in open-tubular glass capillaries. Anal. Chem., 1981, 53, 1298-1302, M. T. Ackermans, F. M. Everaerts, J. L. Beckers: Determination of aminoglycoside antibiotics in pharmaceuticals by capillary zone electrophoresis with indirect UV detection coupled with micellar electrokinetic capillary chromatography. J. Chromatogr. A, 1992, 606, 228-235.
For a sensitive detection of fluorescent compounds, fluorescence detection has been applied (J. C. Reijenga, Th. P. E. M. Verheggen, F. M. Everaerts: Fluorescence emission and fluorescence quenching as detection methods in isotachophoresis. J. Chromatogr. A, 1984, 203, 99-111). Laser induced fluorescence detection further improves the detection sensitivity (J. V. Sweedler, J. B. Shear, H. A. Fishman, Richard N. Zare, R. H. Scheller: Fluorescence detection in capillary zone electrophoresis using a charge-coupled device with time-delayed integration. Anal. Chem., 1991, 63, 496-502, X. C. Huang, M. A. Quesada, R. A. Mathies: Capillary array electrophoresis using laser-excited confocal fluorescence detection. Anal. Chem., 1992, 64, 967-972).
Mass spectrometry has been used to detect zones in CZE (R. D. Smith, C. J. Barinaga, H. R. Udseth: Improved electrospray ionization interface for capillary zone electrophoresis-mass spectrometry. Anal. Chem., 1988, 60, 1948-1952.) Nuclear magnetic resonance has been also use for detection of analytes in CZE. (D.
L. Olson, M. E. Lacey, A. G. Webb, and J. V. Sweedler: Nanoliter-Volume 1H NMR Detection Using Periodic Stopped-Flow Capillary Electrophoresis. Anal. Chem., 1999, 71, 3070-3076.)
Analytes that do not provide a specific signal can be detected by potential gradient detection (M. Deml, P. Bo{hacek over (c)}ek, J. Janák: High-speed isotachophoresis: current supply and detection system. J. Chromatogr. A, 1975, 109, 49-55) and conductivity detection (F. M. Everaerts, Th. P. E. M. Verheggen: Isotachophoresis: Applications in the biochemical field. J. Chromatogr. A, 1974, 91, 837-851). Recently capacitively coupled contactless conductivity detection (C4D) has been applied particularly to CZE (A. Zemann, E. Schnell, D. Volgger, and G. K. Bonn: Contactless Conductivity Detection for Capillary Electrophoresis. Anal. Chem., 1998, 70, 563-567, J. A. Fracassi da Silva and C. L. do Lago: An Oscillometric Detector for Capillary Electrophoresis. Anal. Chem., 1998, 70, 4339-4343, J. Tanyanyiwa and P. C. Hauser: High-voltage contactless conductivity detection of metal ions in capillary electrophoresis. Electrophoresis, 2002, 23, 3781-3786.)
It may be advantageous to combine isotachophoresis concentrating analytes with zone electrophoresis and more sensitive detection and quantitation. Disc electrophoresis was, in principle, combination of ITP and zone electrophoresis without online detection (L. Ornstein. Disc electrophoresis: Background and theory. Ann. N.Y. Acad. Sci., 1964, 121, 321-349, B. J. Davis. Disc electrophoresis: II. Method and application to human serum proteins. Ann. N.Y. Acad. Sci. 1964, 121, 404-427).
In isotachophoresis, quantitative analysis is typically performed by measuring the length of isotachophoretic zones (Bo{hacek over (c)}ek, P., et al., Analytical Isotachophoresis. 1988, Weinheim: VCH Publisher.). This translates into limited detection sensitivity. Thus, a combination of ITP and capillary zone electrophoresis (CZE) has been introduced, where analytes are concentrated and separated by ITP and detected by CZE (Pant{hacek over (c)}ková, P., et al., Determination of iodide on samples with complex matrices by hyphenation of capillary isotahcophoresis and zone electrophoresis. Electrophoresis, 2007, 28, 3777-3785.). The ITP-CZE combined analysis was also performed on microchip (Kaniansky D, Masar M, Bielcikova J, Ivanyi F, Eisenbeiss F, Stanislawski B, Grass B, Neyer A, Johnck M. Capillary electrophoresis separations on a planar chip with the column-coupling configuration of the separation channels. Anal Chem. 2000 72, 3596-604, 2000).
Electroosmotic flow (EOF) is generated when an electric field is applied to electrolyte in a column that exhibits some electric charged on its inner surface. EOF is detrimental to high-resolutions separations and has to be eliminated.
Chiari (U.S. Pat. No. 6,410,668) disclosed copolymers of various derivatives of acrylamide and methacrylamide with glycidyl group containing monomers to form a highly hydrophilic, dynamic coating that suppresses electroosmotic flow.
Madabhushi et al. (U.S. Pat. No. 5,567,292) disclosed copolymersfor coating suppressing EOF, selected from the group consisting of polylactams, such as poly(vinyl pyrrolidone); N,N-disubstituted polyacrylamides; and N-substituted polyacrylamides.
Dolnik (U.S. Pat. No. 7,799,195) disclosed a permanent wall coating made of thermally immobilized galactomannans to eliminate electroosmotic flow.
The present invention is suitable for analysis of trace and ultra-trace ionogenic analytes by isotachophoresis—zone electrophoresis on a chip made from an electrically insulated material. Disclosed is a setup with a series of side channels connecting electrodes to a tapered channel.
We disclose a device for separation and analysis of ionogenic compounds comprising a separation chip, a multichannel power-supply, a detection system, and a system for data acquisition and analysis, where said separation chip comprises
A device is also disclosed to separate and analyze ionogenic compounds where said separation chip is made from an electrically insulated material selected from group consisting of borofloat glass, fused silica, silicon, poly(methyl methacrylate), polycarbonate, and cyclic polyolefins.
Further we disclose device for separation and analysis of ionogenic compounds, where said injection device is a 4-way injection valve.
We also disclose a device for separation and analysis of ionogenic compounds, where said separation channel and said tapered channel have rectangular cross section and the width of said separation channel is at least forty times larger than the width of said analytical capillary channel.
A device for separation and analysis of ionogenic compounds is also disclosed where connections between said side channels and said tapered channel are made as constrictions of said side channels and inner steps on said tapered channels.
A device for separation and analysis of ionogenic compounds is also disclosed, where said separation channel, said tapered channel, said side channels, said restoration capillary channel, and said analytical capillary channel have a permanent wall coating that eliminates electroosmotic flow.
Further we disclose a device for separation and analysis of ionogenic compounds, where at least three pairs of said side channels are connected to said tapered channel when the first pair of said side channels is connected to the end of the separation channel and the beginning of said tapered channel.
We also disclose a device for separation and analysis of ionogenic compounds, where said tell-tale detectors and said analytical detector are selected from the group of detectors consisting of contact conductivity detector, contactless capacitively coupled conductivity detector (C4D), potential gradient detector, amperometric detector, UV absorption detector, laser-induced fluorescence detector, and mass spectrometric detector.
A device for separation and analysis of ionogenic compounds is also disclosed, where said tell-tale detector is a contact conductivity detector.
Further we disclose a device for separation and analysis of ionogenic compounds, where the height of said separation channel, said tapered channel, and said analytical capillary channel ranges from about 30 μm to about 100 μm, the width of said separation channel ranges from about 10 mm to about 40 mm. and the width of said analytical capillary channel ranges from about 60 μm to about 200 μm.
We also disclose a device for separation and analysis of ionogenic compounds, where said tell-tale detectors are placed at the end of said separation channel, at the end of said tapered channel, and at the end of said restoration capillary channel.
A method to separate and analyze ionogenic compounds in a microfluidic device is also disclosed, where
Further we disclose a method to separate and analyze ionogenic compounds, where said ionogenic compounds are separated and concentrated by isotachophoretic migration in said separation channel at constant current.
We also disclose a method to separate and analyze ionogenic compounds, where said leading ion from said isotachophoretic migration and co-ion from said zone electrophoresis are same compound and are selected from the group of high mobility ions consisting of chloride, sulfate, nitrate, potassium, ammonium, and sodium.
A method to separate and analyze ionogenic compounds is also disclosed, where said counter ion is selected from a group of weak acids and bases consisting of formate, acetate, mandelate, glycolate, nicotinate, citrate, valproate, phosphate, 2-(N-morpholino)ethanesulfonate (MES), 4-(N-morpholino)propanesulfonate (MOPS), diethyl barbiturate, borate, 4-(2-hydroxyethyl)piperazine-1-ethanesulfonate (HEPES), glycine, glutamate, aspartate, β-alanine, nicotinamide, γ-aminobutyrate, ε-aminocaproate, creatinine, histidine, 2,2-bis(hydroxymethyl)-2,2′,2″-nitrilotriethanol (BIS-TRIS), 1,3-bis[tris(hydroxymethyl)methylamino]propane (BIS-TRIS propane), tris(hydroxymethyl)aminomethane (TRIS), and N-methylglucamine.
Further we disclose a method to separate and analyze ionogenic compounds, where said terminating ion is selected from a group of weak acids and bases consisting of formate, acetate, mandelate, glycolate, nicotinate, citrate, valproate, phosphate, 2-(N-morpholino)ethanesulfonate (MES), 4-(N-morpholino)propanesulfonate (MOPS), diethyl barbiturate, borate, 4-(2-hydroxyethyl)piperazine-1-ethanesulfonate (HEPES), glycine, glutamate, aspartate, β-alanine, nicotinamide, γ-aminobutyrate, ε-aminocaproate, creatinine, histidine, 2,2-bis(hydroxymethyl)-2,2′,2′-nitrilotriethanol (BIS-TRIS), 1,3-bis[tris(hydroxymethyl)methylamino]propane (BIS-TRIS propane), tris(hydroxymethyl)aminomethane (TRIS), and N-methylglucamine.
We also disclose a method to separate and analyze ionogenic compounds, where said leading electrolyte comprises from about 5 mM to about 50 mM HCl, and from about 5 to about 100 mM β-alanine, said terminating electrolyte from about 20 mM to about 100 mM mandelic acid, and said background electrolyte from about 5 mM to about 40 mM HCl, and from about 5 to about 40 mM β-alanine.
A method to separate and analyze ionogenic compounds is also disclosed, where viscosity of said leading electrolyte and said background electrolyte is increased by addition of a neutral hydrophilic polymer selected from the group of polymers consisting of hydroxyethyl cellulose, guaran, locust bean gum, dextran, poly(ethylene glycol), poly(ethylene oxide), poly(vinyl pyrrolidone), poly(vinyl alcohol), and poly(dimethyl acrylamide).
Further we disclose a method to separate and analyze ionogenic compounds, where nonionic additives are added to said leading electrolyte and said background electrolyte, selected from the group of small nonionic molecules consisting of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, (2-hydroxypropyl-)-α-cyclodextrin, (2-hydroxypropyl-)-β-cyclodextrin, (2-hydroxypropyl-γ-cyclodextrin, and 18-crown-6 ether.
We also disclose a method to separate and analyze ionogenic compounds according to Claim 11, where said leading electrolyte comprises about 10 mM HCl, about 10 mM β-alanine and about 50 g/L dextran, Mw 2×106, said terminating electrolyte about 20 mM mandelic acid, and said background electrolyte about 10 mM HCl, about 10 mM β-alanine, and about 100 g/L poly(vinyl pyrrolidone), Mw 40,000.
The chip was prepared from borofloat glass wafers 1.1 mm thick with diameter of 10.0 mm. After cleaning the wafers with piranha solution (mixture of 96% sulfuric acid and 30% hydrogen peroxide 9:1) at 120° C. for 20 min, a layer of amorphous silicon was applied in a furnace at 525° C. for 240 min in the presence of SiH4. Then the wafers were coated with hexamethyl disilazane at 110° C. and Shipley photoresist 3612 was applied. A Mylard mask with all the structures drawn on it was used to expose the photoresist layer with UV lamp for 10 s. The exposed photoresist layer was developed and the exposed silicon layer was removed by dry plasma etching in the presence of SF6 and chlorodifluoromethane (F22). Channels were etched with 49% HF at room temperature for 4.5-9 min. Holes of diameter 1.4 mm and 2.0 mm connecting the channels with outer world were drilled with diamond drills on wafers not coated with amorphous silicon. After cleaning all the wafers with piranha solution (mixture of 96% sulfuric acid and 30% hydrogen peroxide 9:1) at 120° C. for 20 min, the upper wafers with drilled holes and lower wafers with etched channels were bonded by anode bonding at 240-300° C. and 1,200 V for 30 min.
Platinum wire with a diameter of 25-75 μm was rolled over with a steel cylinder to make their cross-section elliptic. Then they were inserted into corresponding channels to serve as electrodes for conductivity detection. The sensing electrodes were fixed there by filling the channels with a UV-curable epoxy glue Ultra Light-Weld 3069 (Dymax) and illumination with a UV lamp for 180 s. The electrode reservoirs were attached with the same UV curable epoxy glue.
The chip for isotachophoresis-zone electrophoresis on chip contained said separation channel, which was 16 mm wide and 48 mm long. The height of said separation channel as well as the height of all other channels was approx. 45 μm. There was a sampling four-way valve V placed at the beginning of the separation channel, filled with the sample from said sampling inlet S towards said waste outlet W, behind said terminating electrolyte reservoir. In some setups, said sampling valve was eliminated and high-density samples were simply injected at the bottom of said terminating electrolyte. At the end of said separation channel, a pair of sensing electrodes for said tell-tale detector made from 25-75 μm platinum wire were attached. Behind said separation channel, said tapered channel followed, 24 mm long, reducing the cross section from 16 mm to approx. 130 μm. Four pairs of said side channels connected said tapered channel and leading electrolyte reservoirs. The dimensions of said side channels (length 10-25 mm, width 1 mm) were selected not to significantly contribute to resistance of the electric circuit and simultaneously suppress hydrodynamic flow between said electrolyte reservoirs. Constrictions of said side channels at the connection to said tapered channel suppressed loss of analytes by diffusion out of said tapered channel. Said side channels were connected to said tapered channel with an uneven distribution with a shorter distance between them at the narrower part of said tapered channel. At the end of said tapered channel, said restoring channel (130 μm wide, approx. 40 mm long) was connected. Sharp isotachophoretic boundaries that might have been disturbed during their migration through said tapered channel were restored here. Said restoring channel was connected on the other end to said analytical channel (130 μm wide, effective length approx. 150 mm). A pair of sensing electrodes for said tell-tale detector was attached in front of said leading electrolyte reservoir E, i. e., at the end of said restoring channel or at the beginning of said analytical channel. Three electrolyte reservoirs were connected to said analytical channel: said leading electrolyte reservoir via side isotachophoretic capillary channel, said background electrolyte reservoir F via side zone-electrophoretic capillary channel, and said background electrolyte reservoir G. At the end of said analytical capillary channel, a pair of sensing electrodes made from 25-75 μm platinum wire was connected as said analytical detector. A C4D detector was also used in some setups as said analytical detector. In some experiments, said channels were coated with a galactomannan coating (U.S. Pat. No. 7,799,195) to eliminate electroosmotic flow during analysis.
The analysis by isotachophoresis-zone electrophoresis was typically performed in 6 independent steps. The values for constant current and constant voltage are summarized in Table 1. To speed equilibration of current, initial approximate voltage values were applied at the beginning of a step followed by target constant current values.
First, said analytical capillary channel and said background electrolyte reservoirs were filled with background electrolyte, then said tapered channel, all said side channels, all said leading electrolyte reservoirs, and said separation channel were filled with leading electrolyte. Then said terminating electrolyte reservoir was filled with terminating electrolyte and a sample was applied either with the four-way valve or simply by pipetting it on the bottom of said terminating electrolyte reservoir. When electrodes were connected, a sequence of steps with an 8-channel power supply HVS448 (LabSmith, Inc., Livermore, Calif.) was started. In Step 1, ITP separation was performed. Said tell-tale detector (a contact conductivity detector, Villa Labeco, Spi{hacek over (s)}ská Nová Ves, Slovakia) indicated the end of Step 1. Using a comparator LM393P (Texas Instrument, Dallas, Tex.), a TTL/LTT impuls was sent to the HVS448 and voltages and currents were switched as programmed for Step 2. In Step 2, migration towards electrodes A was disconnected and a low current of 40 μA or less was applied to prevent analytes from entering said side channels connected to said electrodes A. Duration of Step 2, i.e., the time necessary for the colored ITP zone to get in front of said side channels connected to said electrodes B was predetermined with a high-mobility colored marker 2,7-naphthalenedisulfonicacid,4,5-dihydroxy-3-((4-sulfophenyl)azo)-,trisodium (SPADNS). After this time, the sequence switched to Step 3. In Step 3, migration towards electrodes B was stopped and a low current of 40 μA or less was applied on said electrodes B to prevent analytes from entering said side channels connected to said electrodes B. Duration of Step 3 was also predetermined from migration of colored zone of SPADNS. At the end of Step 3, said sequence moved to Step 4 with voltage and current applied as listed in Table 1. Said tell-tale detector (a contact conductivity detector, Villa Labeco, Spi{hacek over (s)}ská Nová Ves, Slovakia) indicated the end of Step 4. Using a comparator LM393P (Texas Instrument, Dallas, Tex.), a TTL/LTT impuls was sent to the HVS448 and voltages and currents were switched to progress to Step 5. Said tell-tale detector (a contact conductivity detector, Villa Labeco, Spi{hacek over (s)}ská Nová Ves, Slovakia) indicated then the end of Step 5. Using a comparator LM393P (Texas Instrument, Dallas, Tex.), a TTL/LTT impuls was sent to the HVS448 and voltages and currents were switched and Step 6 started. During Step 6, analytes migrated in the zone electrophoretic mode towards the destination electrode in said baground electrolyte reservoir G and their zones were detected by analytical detector, either contact conductivity detector (Villa Labeco, Spi{hacek over (s)}ská Nová Ves, Slovakia) or C4D detector (J. A. Fracassi da Silva and C. L. do Lago: An Oscillometric Detector for Capillary Electrophoresis. Anal. Chem., 1998, 70, 4339-4343) with wave generator based on the headstage ET121 and C4D detector ER125 (eDAQ, Ltd., Australia).
Samples were ultrafiltered through Amicon Ultra centrifugal filters (0.5 mL, 30 k, Millipore) by centrifugation at 14,000 RPM for 30 min. Said capillary channels and said corresponding electrolyte reservoirs (E, F, G) were filled with BGE (10 mM HCl, 10 mM β-alanine, 100 mM poly(vinyl pyrrolidone), Mw 40,000), said separation channel, said tapered channel, said side channels and said corresponding leading electrolyte reservoirs (A, B, C, and D) were filled with LE (50 mM HCl, 100 mM β-alanine, 50 g/L dextran, Mw 2,000,000), and said terminating electrolyte reservoir (H) with terminating electrolyte (20 mM mandelic acid in 18 MI water). 10 μL samples were pipetted on the bottom of said terminating electrolyte reservoir and the analysis was performed according to Example 5.
The patent application is based on research sponsored by NIH SBIR grant number 1 R43ES022366-01.
