DSpace at VNU: Triple-channel portable capillary electrophoresis instrument with individual background electrolytes for the concurrent separations of anionic and cationic species

DSpace at VNU: Triple-channel portable capillary electrophoresis instrument with individual background electrolytes for...

Accepted Manuscript Triple-channel portable capillary electrophoresis instrument with individual background electrolytes for the concurrent separations of anionic and cationic species Thanh Duc Mai, Minh Duc Le, Jorge Sáiz, Hong Anh Duong, Israel Joel Koenka, Hung Viet Pham, Peter C Hauser PII: S0003-2670(16)30117-9 DOI: 10.1016/j.aca.2016.01.029 Reference: ACA 234369 To appear in: Analytica Chimica Acta Received Date: 30 November 2015 Revised Date: 12 January 2016 Accepted Date: 16 January 2016 Please cite this article as: T.D Mai, M.D Le, J Sáiz, H.A Duong, I.J Koenka, H.V Pham, P.C Hauser, Triple-channel portable capillary electrophoresis instrument with individual background electrolytes for the concurrent separations of anionic and cationic species, Analytica Chimica Acta (2016), doi: 10.1016/ j.aca.2016.01.029 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain -1- ACCEPTED MANUSCRIPT Triple-channel portable capillary electrophoresis instrument with individual background electrolytes for the concurrent separations of anionic and cationic species Thanh Duc Mai1, Minh Duc Le1, Jorge Sáiz2, Hong Anh Duong1, Israel Joel Koenka3, Hung Viet Pham1*, Peter C Hauser3* University of Science, Nguyen Trai Street 334, Hanoi, Viet Nam RI PT SC Centre for Environmental Technology and Sustainable Development (CETASD), Hanoi Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, University of Alcalá, Ctra Madrid-Barcelona km 33.6, Alcalá de Henares, Madrid, Spain 11 M AN U 10 University of Basel, Department of Chemistry, Spitalstrasse 51, 4056 Basel, Switzerland 12 13 * Corresponding authors 16 17 e-mail: Peter.Hauser@unibas.ch; Tel : ++41 61 267 1003; Fax: ++41 61 267 1013 phamhungviet@hus.edu.vn; Fax: ++84 3858 8152 EP 15 TE D 14 Keywords: Capillary clectrophoresis, Capacitively coupled conductivity detection, 19 Concurrent separations, Portable instrument 20 21 AC C 18 -2- ACCEPTED MANUSCRIPT Abstract 23 The portable capillary electrophoresis instrument is automated and features three independent 24 channels with different background electrolytes to allow the concurrent optimized 25 determination of three different categories of charged analytes The fluidic system is based on 26 a miniature manifold which is based on mechanically milled channels for injection of samples 27 and buffers The planar manifold pattern was designed to minimize the number of electronic 28 valves required for each channel The system utilizes pneumatic pressurization to transport 29 solutions at the grounded as well as the high voltage side of the separation capillaries The 30 instrument has a compact design, with all components arranged in a briefcase with dimensions 31 of 45 (w) × 35 (d) × 15 cm (h) and a weight of about 15 kg It can operate continuously for h 32 in the battery-powered mode if only one electrophoresis channel is in use, or for about 2.5 h in 33 the case of simultaneous employment of all three channels The different operations, i.e 34 capillary flushing, rinsing of the interfaces at both capillary ends, sample injection and 35 electrophoretic separation, are activated automatically with a control program featuring a 36 graphical user interface For demonstration, the system was employed successfully for the 37 concurrent separation of different inorganic cations and anions, organic preservatives, 38 additives and artificial sweeteners in various beverage and food matrices 40 41 SC M AN U TE D EP AC C 39 RI PT 22 -3- ACCEPTED MANUSCRIPT Introduction 43 The concurrent separation of anionic and cationic species in capillary electrophoresis (CE) is 44 desirable as it significantly enhances the analytical throughput The time and effort otherwise 45 needed for switching over the task, such as a change of background electrolyte (BGE) and 46 capillary conditioning, are then not required The different techniques for concurrent 47 separations have been discussed in a recent review [1] So far, this has most often been 48 realized on a single capillary employing dual opposite end injections where hydrodynamic 49 sample injection is realized into both ends of the capillary, with detection carried out near the 50 middle of the capillary [1-4] This technique, introduced by Kubáň and Karlberg [5] and 51 Paderauskas and coworkers [6] in 1998, has repeatedly been reported for the simultaneous 52 determination of cations and anions with conductometric detection [7-14] Manual operations 53 and the likelihood of peak overlaps when cations and anions appear on the same 54 electropherogram are nevertheless some issues of consideration when using this technique On 55 the other hand, the employment of more than one capillary at the same time is not much of a 56 complication because of the simplicity and fully electronic principle of CE The only essential 57 components for separation are a capillary and a high voltage power supply module Dual- 58 channel CE, where separations of cationic and anionic species were simultaneously realized 59 on two independent capillaries, was first reported by Bachmann et al in 1992 [15] and has 60 more recently been communicated by several research groups [16-19] The concurrent 61 electrophoretic separation of inorganic anions and cations in two channels has also been 62 reported for microchip platforms [20-22] AC C EP TE D M AN U SC RI PT 42 63 64 In the concurrent CE separation approaches reported so far, generally a common BGE was 65 employed for electrophoresis of both cations and anions However, the use of a common 66 buffer is not always ideal or even possible For example, an acidic BGE (pH ≤ 4) used for the -4- ACCEPTED MANUSCRIPT separation of inorganic cations which may precipitate as hydroxides at higher pH values 68 cannot be employed for the separation of carboxylate anions whose full deprotonation occurs 69 only at pH ≥ (pH higher than their pKa values) The use of different BGEs in a multi- 70 channel CE system can solve this problem Furthermore, this also allows the independent 71 optimization of the electro-osmotic flow (EOF) for different classes of analytes, such as the 72 use of a slow EOF for best separation of cations, or of a high EOF against the mobility of 73 slowly migrating anions While not readily possible for a conventional commercial 74 instrument, the simplicity of CE nevertheless allows the easy extension to more independent 75 channels; and the use of different buffers is not much of an additional complication Such a 76 CE setup, however, has to our knowledge not been reported M AN U SC RI PT 67 77 A further benefit of the straightforward nature of CE is the possibility of its implementation in 79 portable instruments On-site measurements eliminate complications with sample storage and 80 transport and offer better cost effectiveness and rapid availability of results Different portable 81 CE instruments relying on the single-channel CE format have been reported in recent years by 82 several research groups [23-31] Earlier developments have been covered in two review 83 articles [32, 33] Recently, Sáiz et al also reported a portable dual-capillary CE system 84 employing a single BGE [19] Thanks to its positive features of low power consumption, high 85 versatility, high degree of miniaturization, lack of requirement for removal of the capillary 86 coating to create an optical window, easy alignment and movement along the capillary, and 87 ease in construction and operation, capacitively coupled contactless conductivity detection 88 (C4D) has been the detection method of choice and can indeed be considered to have been an 89 enabling factor in the development of these instruments Detailed descriptions of the 90 construction and working principles of C4D can be found elsewhere [34-41] Readers can also 91 find a variety of recent CE-C4D applications covered in several reviews [42-48] Herein, to AC C EP TE D 78 -5- ACCEPTED MANUSCRIPT 92 the best of our knowledge, for the first time a portable triple-channel CE instrument is 93 reported It employs individual BGEs for the concurrent separation of analytes belonging to 94 different catagories 95 RI PT 96 Experimental 98 2.1 Chemicals and Materials 99 All chemicals were of analytical or reagent grade and purchased from Fluka (Buchs, SC 97 Switzerland) or Merck (Darmstadt, Germany) Stock solutions (10 mM) of chloride, nitrate, 101 nitrite, sulfate and phosphate were used for the preparation of the standards of inorganic 102 anions, using their respective sodium or potassium salts Those of the inorganic cations (10 103 mM) (ammonium, potassium, calcium, sodium, manganese, barium, zinc and magnesium) 104 were prepared from the chloride salts Cyclamic acid (cyclohexanesulfamic acid) sodium salt, 105 saccharin sodium salt hydrate, aspartame and acesulfame-K were used to prepare standard 106 solutions of the four artificial sweeteners Histidine (His), acetic acid, lactic acid, 2- 107 (cyclohexylamino)-ethanesulfonic acid (CHES), tris(hydroxymethyl)aminomethane (Tris), 2- 108 (N-morpholino)ethanesulfonic acid (MES) and 18-crown-6 were used for preparation of BGE 109 solutions The separation of inorganic cations was done with a BGE composed of 12 mM 110 histidine and mM 18-crown-6 adjusted to pH 3.7 with acetic acid, using a fused-silica 111 capillary of 25 µm I.D (with a total length, Lt, of 60 cm and an effective length, Leff, of 44 112 cm) The BGE for the inorganic anions was composed of 12 mM histidine adjusted to pH 113 with lactic acid, employing a fused-silica capillary of 25 µm I.D (Lt = 60 cm, Leff = 44 cm) 114 For the artificial sweeteners, the separation was realized with a BGE of 100 mM Tris / 30 mM 115 CHES, pH 9.1 and with a fused-silica capillary of 25 µm I.D (Lt = 54 cm; Leff = 38 cm) 116 Organic anions were electrophoretically separated in a fused silica capillary of the same AC C EP TE D M AN U 100 -6- ACCEPTED MANUSCRIPT internal diameter (Lt = 70 cm; Leff = 54 cm) with the BGE composed of 90 mM His / MES 118 and 20 µM CTAB, pH 6.1 Voltages of 15 kV with appropriate polarities were used for the 119 separations Before use, the fused silica capillaries were preconditioned with M NaOH for 120 10 and deionized water for 10 prior to flushing with buffer The capillaries were then 121 used continuously for successive analyses Deionized water purified using a system from 122 Millipore (Bedford, MA, USA) was used for the preparation of all solutions and for sample 123 dilution if required Carbonated soft drink, fruit juice, beer, wine, tea (with milk aded) and 124 fish sauce were purchased from local shops in Hanoi, Vietnam The beverage and fish sauce 125 samples were prepared by filtering with a 0.02-mm PTFE membrane filter (Chromafil O- 126 20/15 MS, Macherey-Nagel, Oensingen, Switzerland), then diluted with deionized water and 127 ultra-sonicated for 10 prior to CE-C4D measurements M AN U SC RI PT 117 128 2.2 Instrumentation 130 The microfluidic manifolds for each separation channel were machined in poly(methyl 131 methacrylate) (PMMA) plates with the dimensions of 10 cm (w) x 15 cm (l) x 1.5 cm (h) The 132 fluidic channels were milled using a high frequency spindle (R30) from Ray Ltd (Nänikon, 133 Switzerland) at 30'000 rpm with a carbide cutter (Graphograph, Murten, Switzerland) under 134 application of a lubricating oil (Rubin G-8 from Neoval, Hofstetten, Switzerland) The cutting 135 tool had been modified to yield trapezoidal channels with a bottom width of 0.2 mm, wall 136 angles of 18° and a depth of approximately 0.2 mm The channels were sealed with a second 137 PMMA plate of identical dimensions fixed tightly with screws The valves and pumps were 138 mounted on top of the cover plate Access to the fluidic channels was via perpendicular holes 139 in the cover Connections to tubings were made via female ¼-28 UNF threads The solenoid 140 valves (LFVA0030000C-LFVA1230113H and LFRA0030000C-LFRA1230110H) were 141 purchased from the Lee Company (Westbrook, CT, USA) The check valves (CV-3315) were AC C EP TE D 129 -7- ACCEPTED MANUSCRIPT obtained from Upchurch Scientific (Oak Harbor, WA, USA) The miniature peristaltic pumps 143 (RP-Q1-SP45A) were purchased from Takasago Fluidic Systems (Nagoya, Japan) Fluidic 144 connections external to the planar manifold were made with 0.02 inch I.D and 1/16 inch O.D 145 teflon tubing and with polyether ether ketone (PEEK) flangeless ¼-28 nuts (P-235) and 146 ferrules (P-221) (Upchurch Scientific) The polyimide-coated fused silica capillaries (25 µm 147 I.D and 365 µm O.D., from Polymicro, Phoenix, AZ, USA) were fitted to the microfluidic 148 manifolds using adaptor sleeves (F-242x, Upchurch Scientific) Pneumatic pressurization was 149 achieved with a standard cylinder of compressed air, or with an air pump and a reservoir for 150 field measurements [29] The outlet pressure of either system was adjusted to bar with a 151 regulator M AN U SC RI PT 142 152 The electrophoresis section is based on miniature high voltage units (UM20*4) with 154 dimensions of 12 cm (l) x 3.8 cm (w) x 2.5 cm (h) and a weight of 200 g each (Spellman 155 Pulborough, UK) providing a maximum of 20 kV of pre-selected polarities The high voltage 156 ends of the capillaries were isolated in safety cages made from PMMA, which were equipped 157 with microswitches to interrupt the high voltage on opening The high voltage interfaces were 158 machined in PMMA blocks of cm (l) × cm (w) × cm (h) dimensions, and pressurized 159 Falcon tubes (Fisher Scientific, Reinach, Switzerland) served for automated buffer 160 replenishment Detection was carried out with three miniaturized C4D cells built in-house 161 according to a design reported previously [18, 49] The resulting signals were recorded with a 162 12 V-powered E-corder 201 data acquisition system (eDAQ, Denistone East, NSW, Australia) 163 connected to the USB-port of a personal computer For powering the electrophoretic and 164 fluidic parts, a lithium battery pack of 14.8 V and with a capacity of 6.6 Ah (CGR 18650CG 165 4S3P, Contrel, Hünenberg, Switzerland) fitted with a voltage regulator was used to provide a 166 12 V output A separate pair of smaller Li-ion batteries with a capacity of 2.8 Ah each (CGR AC C EP TE D 153 -8- ACCEPTED MANUSCRIPT 167 18659CG 4S1P, Contrel), which was fitted with positive and negative 12 V regulators, 168 provided the split ±12 V supply required for the C4D circuitry 169 2.3 System control 171 The system was controlled with a personal computer using a USB (Universal Serial Bus) 172 connection to an Arduino Nano microcontroller board (Gravitech, Minden, NV, USA) 173 Different outputs of the Arduino Nano board allowed switching of the solenoid valves, of the 174 high voltage, and triggering of the recording of electropherograms with the help of a purpose 175 built electronic interface This also allowed the monitoring of the high voltages and 176 electrophoretic currents A versatile graphical user interface (GUI) written in the Python 177 programming language was used to control the triple channel CE system More details on our 178 software approach (Instrumentino) can be found in recent publications [50, 51] M AN U SC RI PT 170 179 Results and Discussion 181 3.1 System design and operation 182 A simplified schematic drawing of a single channel of the triple-CE system is shown in Fig 183 The three identical channels are based on standard capillaries For each capillary a separate 184 purpose made manifold serves for sample injection and capillary flushing The injection ends 185 of the capillaries are grounded, while the separation voltages are applied at the detector ends, 186 which is not a problem with C4D The high voltage ends of the capillaries are contained in 187 PMMA cages to prevent accidental exposure to the separation voltage and also provides the 188 necessary insulating air space to prevent spurious discharges A specially designed interface 189 allows automated flushing of the BGE at the capillary outlet Propulsion of liquids through the 190 miniature planar injection manifolds and the high voltage interface was carried out by 191 pressurization of the individual BGE reservoirs at both ends of the capillaries Three miniature AC C EP TE D 180 -9- ACCEPTED MANUSCRIPT peristaltic pumps serve to pass the sample to the manifolds for subsequent injection into the 193 capillaries As the three channels are completely separate, the set-up has full flexibility 194 Usually the same sample solution is aspirated concurrently into the three channels, but it is 195 also possible to draw different solutions This feature may be employed if the sample has to be 196 pre-diluted differently for different analytes, but it would also be possible to work on different 197 samples in parallel using identical conditions on each channel The detector cells are mounted 198 outside the high voltage cages and the capillaries can be moved freely for optimization of 199 separation time and efficiency as it is not necessary to remove the polyimide coating of the 200 fused silica capillaries SC RI PT 192 M AN U 201 A more detailed diagram of the fluidic connections of the injection block for a single channel 203 is shown in Fig For automated injection and flushing two pressure levels (low for sample 204 injection, high for capillary flushing) are necessary with an associated number of valves and 205 fluidic connections In order to achieve a triple-channel configuration in a compact and 206 portable design with limited power consumption it was desirable to reduce the number of 207 electromechanical components required for each CE channel compared to the set-up in our 208 earlier systems [18, 29-31] This was achieved by employing two passive check valves as well 209 as a length of narrow tubing to obtain the reduced pressure for controlled sample injection 210 For robustness and in order to limit the number of required tubing connections a planar 211 microfluidic manifold was employed, as illustrated in Fig 2, onto which the different 212 components, including separation capillary and ground electrode, were mounted Two power- 213 consuming valves were required for the injection side of each channel, i.e one stop valve and 214 one 3-port valve (a third valve is required for the flushing of the high voltage interface) A 215 miniature peristaltic pump was employed for sample aspiration into the injection block 216 Compared to microchip electrophoresis, the ‘marriage’ between microfluidic manifolds and AC C EP TE D 202 -19- ACCEPTED MANUSCRIPT 432 [23] 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Meister, R Kava, Low-calorie Sweeteners and Other Sugar Substitutes: SC [59] A Review of the Safety Issues, Compr Rev Food Sci (2006) 35-47 [60] A Zygler, A Wasik, J Namieśnik, Analytical methodologies for determination of M AN U 534 RI PT 531 artificial sweeteners in foodstuffs, TrAC Trends Anal Chem 28 (2009) 1082-1102 538 539 AC C EP TE D 540 -24- ACCEPTED MANUSCRIPT 541 Table Typical operation protocol for one CE channel of the triple-channel system 542 Duration Flushing of the injection interface Flushing of the capillary Flushing of the HV interface Aspiration of sample into the injection interface Hydrodynamic injection Flushing of the injection interface Electrophoretic separation Flushing of the injection interface Flushing of the capillary Settings High V3 Voltage V2 10 s Open Off Off 180 s Open Off Off 5s Closed Off Off 5s Closed Off On variable Closed Off Off 5s Open Off Off variable Closed On Off 10 s Open Off Off 180 s Open Off Off EP TE D M AN U 543 544 545 546 547 AC C Peristaltic pump V1 RI PT Operation SC Step -25- ACCEPTED MANUSCRIPT 548 Table Calibration ranges, detection limits (LODs) and reproducibility for the concurrent 549 determination of different categories of ionic species with the triple-channel CE system 550 ClNO3SO42NO2Aspartame Cyclamate Saccharine Acesulfame-K 1.1 1.4 2.6 2.9 2.4 1.6 3.1 3.3 0.6 0.7 0.8 0.6 3.2 4.4 4.8 3.5 0.3 0.3 0.3 0.3 1.8 2.6 1.1 0.6 0.9 1.2 1.6 1.3 1.2 1.6 1.5 1.4 1.7 1.9 3.5 4.6 4.2 5.3 4.9 3.4 5.6 4.2 4.7 4.1 SC RI PT 0.9 0.8 0.9 0.8 0.9 0.8 0.7 0.8 AC C Oxalate Formate Tartrate Malate Succinate Citrate Pyruvate Acetate Lactate Ascorbate Channel 1: Inorganic cations 10-500 0.999 3.0 10-500 0.999 3.0 5-500 0.999 1.5 10-500 0.999 2.0 5-500 0.999 1.5 5-500 0.999 1.5 10-500 0.999 2.5 5-500 0.994 1.2 Channel 2: Inorganic anions 10-500 0.995 2.0 20-100 0.998 6.0 10 – 100 0.998 3.5 20 – 100 0.997 6.0 Channel 2: Artificial sweeteners 25-1000 0.994 6.5 15-500 0.996 3.7 – 500 0.999 1.5 10 - 500 0.998 2.6 Channel 3: Organic anions 5-100 0.997 1.5 10-100 0.998 2.8 5-100 0.993 1.4 10-100 0.998 1.8 10-100 0.992 1.9 15-100 0.998 4.2 30-500 0.992 10 15-500 0.997 5.5 30-500 0.998 10 50-500 0.993 20 M AN U NH4 K+ Ca2+ Na+ Mg2+ Mn2+ Zn2+ Ba2+ LOD (µM) Precision of Peak Area (% RSD)c (n = 4) TE D + Range (µM)a b Precision of Migration Time (% RSD)c (n = 4) EP Ion Correlation coefficient, r2 551 552 a concentrations 553 b Based on peak heights corresponding to times the baseline noise 554 c Relative Standard Deviations were obtained from the peaks for concentrations of 100 µM 555 -26- ACCEPTED MANUSCRIPT 556 Figure captions: 557 Fig Simplified schematic drawing of the CE instrument showing one of the three separation channels, as well as the pneumatic unit which serves all three channels 559 HV: high voltage; GND: electrical ground; Pt: platinum electrodes; W: waste; V1: 560 electronically actuated 3-way valve for flushing the high voltage capillary interface; 561 C4D: detector cell; BGE: pressurizable containers holding background electrolyte RI PT 558 562 Fig Schematic drawing of one of the micromachined injection manifolds with the SC 563 mounted components V2: electronically actuated stop valve; V3: electronically 565 actuated 3-port valve; CV1, CV2: check valves; Pt: platinum electrode; W: waste 566 The bold lines represent channels milled into the planar manifold, the circles ¼-28" 567 threaded holes for external connections M AN U 564 568 Fig Electropherograms for the concurrent separations of inorganic cations, inorganic TE D 569 anions or artificial sweeteners, and organic anions in standard solutions 571 Channel 1: inorganic cations; NH4+ (200 µM), K+ (200 µM), Ca2+ (200 µM), Na+ 572 (200 µM), Mg2+ (200 µM) Channel 2, Option 1: inorganic anions; Cl- (200 µM), 573 NO3- (50 µM), SO42- (50 µM), NO2- (50 µM) Channel 2, Option 2: artificial 574 sweeteners (50 µM); aspartame (Asp), cyclamate (Cyc), saccharine (Sac) and 576 AC C 575 EP 570 acesulfame-K (Ace) Channel 3, organic anions (50 µM): 1) oxalate, 2) formate, 3) tartrate, 4) malate, 5) succinate, 6) citrate, 7) pyruvate, 8) acetate, 9) lactate and 10) 577 ascorbate Details on CE conditions can be found in section 2.1 578 579 580 Fig Electropherograms for the concurrent separations of inorganic cations (channel 1), inorganic anions (channel 2) and organic anions (channel 3) in wine (A), beer (B) -27- ACCEPTED MANUSCRIPT 581 and tea (C) samples Peak denotations: 1) Oxalate, 2) Formate, 3) Tartrate, 4) 582 Malate, 5) Succinate, 6) Citrate, 7) Pyruvate, 8) Acetate, 9) Lactate and 10) 583 Ascorbate, *) unidentified peak CE conditions as in section 2.1 584 Fig Electropherograms for the concurrent separations of inorganic cations (channel 1), RI PT 585 artificial sweeteners (channel 2) and organic anions (channel 3) in fish sauce (A), a 587 cola beverage (B) and mango juice (C) samples Peak denotations: Asp) Aspartame, 588 Cyc) Cyclamate, Sac) Saccharine, Ace) Acesulfame-K; 1) Oxalate, 2) Formate, 3) 589 Tartrate, 4) Malate, 5) Succinate, 6) Citrate, 7) Pyruvate, 8) Acetate, 9) Lactate and 590 10) Ascorbate, *) unidentified peak CE conditions as in section 2.1 M AN U SC 586 AC C EP TE D 591 Capillary Sample Pt GND C4D W Pt HV W Injection manifold SC HV interface BGE BGE Vent V1 Pressure gauge AC C EP TE D Compressed Regulating air valve Safety cage M AN U RI PT ACCEPTED MANUSCRIPT Figure Separation capillary Pressure-limiting tubing Sample Pt GND V2 BGE CV1 V3 AC C EP TE D M AN U W CV2 SC Miniature peristaltic pump RI PT ACCEPTED MANUSCRIPT Figure ACCEPTED MANUSCRIPT Channel 200 Ca 250 2+ Na 300 Channel + Mg 2+ Mn 2+ 2+ Zn 350 Cl 400 Ba RI PT 10 mV + NH4 K+ 2+ t (s) 450 - Option 50 mV 2- 250 Option 250 Channel 34 400 Ace 300 t (s) 400 20 mV 350 t (s) 400 mV 500 AC C EP TE D 300 350 Sac Cyc Asp 200 300 NO2 M AN U 200 SO4 SC NO3 Figure 10 600 700 t (s) 800 ACCEPTED MANUSCRIPT + Ca + Ch NH4 200 250 Cl 350 K 300 350 K 300 + + 250 2+ 250 EP t (s) 800 400 t (s) 450 2+ 350 Cl - NO3 2SO4 300 350 500 AC C 400 Na Mg 300 Ch 200 700 600 TE D Ch 300 t (s) 400 350 500 Ca t (s) 450 2SO4 M AN U C Ch 400 - t (s) 800 400 200 700 300 mV + Cl Ch 2+ Ca Na Mg2+ 250 t (s) 450 t (s) 400 600 + Ch 400 2- 350 500 250 200 10 mV 50 mV Ch1 200 2+ SO4 400 B Mg 300 34 300 + - 250 Ch Na 300 Ch 200 2+ RI PT K SC A Figure t (s) 400 * 600 700 t (s) 800 ACCEPTED MANUSCRIPT A Ca Na 2+ + 20 mV Ch 300 350 * Ch EOF 150 200 Ch 250 300 B 500 K 300 C Ch 300 200 Ch 400 300 t (s) 450 350 t (s) 400 700 t (s) 800 400 t (s) 450 * 400 K 500 600 Ca + 250 2+ 300 + Na 2+ Mg 350 * 200 Ace 250 400 300 350 500 Figure t (s) 400 10 AC C EP 300 t (s) 800 Sac Ch 150 700 350 250 TE D 200 10 mV M AN U CH t (s) 400 + Cyc 150 * 2+ 2+ Ca Na Mg 250 Ch 350 600 + Ch 200 300 400 + NH4 20 mV Sac Ace t (s) 450 400 RI PT 250 SC 200 600 700 t (s) 800 ACCEPTED MANUSCRIPT Highlights: The use of parallel channels allows the concurrent separation of different classes of analytes • Separate background electrolytes allow individual optimization • The instrument is compact and field portable AC C EP TE D M AN U SC RI PT • ... ACCEPTED MANUSCRIPT Triple-channel portable capillary electrophoresis instrument with individual background electrolytes for the concurrent separations of anionic and cationic species Thanh Duc... composed of 100 mM 298 Tris / 30 mM CHES (pH 9.1) Examples for the separation of standard mixtures of the four 299 classes of species are shown in Fig and the calibration data for the ions of interest... 43 The concurrent separation of anionic and cationic species in capillary electrophoresis (CE) is 44 desirable as it significantly enhances the analytical throughput The time and effort otherwise