Contactless Conductivity Detection Research Articles

Methods for onboard monitoring of silver biocide during future human space exploration missions.

Silver ions (Ag+) have been proposed as a biocide to treat the water in NASA's next generation of human space exploration vehicles/habitats. One advantage of Ag+ is that it is effective as a biocide in a range (200 to 500 ppb) safe for human consumption. So, monitoring Ag+ is essential to ensure the safety and health of the crew. Here we present two analytical methods based on capillary electrophoresis and capacitively coupled contactless conductivity detection (CE-C4D) to address the need to monitor Ag+ levels in water. Using 5 M acetic acid as a background electrolyte (BGE), 100 ppb of Ag+ could be detected in a simulant of the International Space Station (ISS) water. In addition to Ag+, other inorganic cations (K+, Ca2+, Na+, Mg2+, Ni2+, and Zn2+) frequently found in the ISS potable water can be detected simultaneously using this BGE in less than 4.5 min. By using a BGE composed of 0.5 M acetic acid, levels of Ag+ as low as 25 ppb could be detected in the ISS water simulant in less than 2.5 min. Although in this condition none of the other cations interfered with the detection of Ag+, some of them co-migrated, which could prevent obtaining additional information about the sample composition.

A Flexible Wireless Dielectric Sensor for Noninvasive Fluid Monitoring.

A flexible wireless dielectric sensor is presented here for noninvasively monitoring the permittivity and conductivity of fluids, based on resistor–inductor–capacitor (RLC) resonant circuit and capacitively coupled contactless conductivity detection (C4D) technique. The RLC sensor consists of one single-turn inductor and one interdigital capacitor. The resonant frequency of the device is sensitive to the surrounding environment, thanks to the electric field leaked out between the interdigital capacitor electrodes. Through the high-frequency structure simulator (HFSS) simulation, and experiments on ethanol/water solutions and NaCl solutions, it was confirmed that a fluid’s permittivity and conductivity could be detected by the return loss curve (S11). With great repeatability and stability, the proposed sensor has potential for broad applications, especially in wearable low-cost smart devices.

Determination of 10-Hydroxy-2-Decenoic Acid Content – a Marker in Several Commercial Royal Jelly Products Collected in Vietnam

The optimized capillary electrophoresis (CE) was applied to separate and detect the 10-hydroxy-2-decenoic acid (10-HAD) in royal jelly products. The method only requires that the sample solution need to be centrifuged and filtered before analyzed by the home-made capillary electrophoresis system. Firstly, 10-HDA was separated in a fused silica column with a diameter of 50 um using 20 mM Tris/Acetic buffer (pH 8.5) as a background electrolyte and a separation voltage of -17kV. Then, 10-HDA was detected by capacitively coupled contactless conductivity detection (C4D) with the migration time less than 8 minutes. Nine commercial products of royal jelly with Vietnamese and imported origin including pure royal jelly cream, lyophilized royal jelly (powder and gel) and honey with royal jelly were collected for analysis. The results of this study showed that content of 10-HDA were detected in the range of 0.5 mg/g to 23.1 mg/g. Using paired t test showed that the difference between results obtained from CE-C4D method and from HPLC method as a reference method was not statistically significant.
 Keywords: 10-HDA, royal jelly products, CE-C4D.
 References
 
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Measuring venous-arterial differences of valine, isoleucine, leucine, alanine and glutamine in skeletal muscles using counter-current electrophoresis with contactless conductivity detection

Plasmatic levels of valine, isoleucine, leucine, alanine and glutamine were determined by capillary electrophoresis with contactless conductivity detection. A new kind of covalently coated capillary based on polyacrylamide and (3-acrylamidopropyl) trimethylammonium chloride was employed. The amino acids were separated in the counter-current regime, in which the analytes migrate under counter-current electro-osmotic flow with a value of 5.53 · 10−9 m2 V−1 s−1 in the background electrolyte, 3.2 mol/L AcOH +10% v/v MeOH. The baseline separation of all five amino acids from other plasmatic compounds was achieved in <5 min; the limits of detections are 0.13–0.14 μmol/L for the treated sample and 0.50–0.58 μmol/L for the untreated plasma. The method was used to measure venous-arterial differences of amino acids in hyperinsulinemic patients with cachexia.

Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection for Quantitative Analysis of Dried Blood Spots with Unknown Blood Volume.

Blood volume in dried blood spot (DBS) analysis is assumed to be constant for DBS punches with a fixed area. However, blood volume in the punch is dependent on several factors associated with the blood composition and is preferentially normalized by off-line analysis for quantitative purposes. Instead of using external instrumentation, we present an all-in-one approach for the simultaneous determination of exact blood volume in the DBS punch and the quantitation of target analytes. A DBS is eluted with 500 μL of elution solvent in a sample vial, and the eluate is directly subjected to an automated analysis by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D). The capillary blood volume in the eluate is calculated from the concentrations of the inorganic blood constituents (K+, Na+, or Cl-) determined by CE-C4D, which are linearly proportional to the blood volume originally sampled onto the DBS card. Alternatively, conductivity of the DBS eluate can be used for the blood volume determination by using C4D in a nonseparation flow-through mode. The methods are suitable for the determination of blood volume in unknown DBS samples by punching out the entire DBS or by subpunching a small section of a large DBS with variations of the true vs the determined volume ≤5.5%. Practical suitability was demonstrated by the simultaneous CE-C4D determination of K+ and Na+ (for DBS volume calculation) and amino acids (target analytes) in unknown DBS samples. Quantitative analysis of selected amino acids (related to inborn metabolic disorders) in the unknown DBS was compared with a standard analytical procedure using wet-blood chemistry, and an excellent fit was obtained. The use of CE-C4D represents an important milestone in quantitative DBS analysis since the detection technique is universal, and the separation technique enables the determination of cations and/or anions and the use of multiple detectors, which further enhance selectivity/sensitivity of the analysis and the range of detectable analytes.

Capillary electrophoretic analysis of ionic content in exhaled breath condensate and pH monitoring as a non-invasive method in gastroesophageal reflux disease diagnostics

In this study, the ionic profile and pH of exhaled breath condensate (EBC) in a group of patients with acid and weakly acid reflux and no-reflux controls were compared. A portable sampler was used for non-invasive EBC collection from five exhalations. The ionic profile (anions, cations, organic acids) and pH of the collected EBC samples were measured by capillary electrophoresis with contactless conductivity detection and a pH microelectrode, respectively. Several ions were elevated in the patient groups. Sodium cation was elevated in weakly acid reflux (significance level p < 0.01) and acid reflux (p < 0.05) compared to no-reflux controls. Butyrate and propionate were elevated in both acid reflux and weakly acid reflux compared to no-reflux controls (butyrate: p < 0.01, propionate: p < 0.05). The median values of pH (after de-aeration with N2) were also significantly higher (p < 0.01) in groups with acid reflux and weakly acid reflux than in the control group with no reflux. The ionic analysis and simultaneous pH measurement offer a simple, cheap, fast, and non-invasive approach in gastroesophageal reflux disease diagnostics.

Analysis of bicarbonate, phosphate and other anions in saliva by capillary electrophoresis with capacitively coupled contactless conductivity detection in diagnostics of gastroesophageal reflux disease.

Bicarbonate and phosphate constitute major salivary buffering components, and their importance consists in the neutralization of acidic gastric contents during reflux episodes. In this work, capillary electrophoresis with capacitively coupled contactless conductivity detector was applied for the analysis of bicarbonate, phosphate, and another inorganic (chloride, nitrite, nitrate, sulfate, thiocyanate) and organic anions (acetate, butyrate) to evaluate their levels in saliva. The background electrolytes of different composition and pH between 6.02-9.41 were assessed for the bicarbonate and phosphate determination by comparison of the real analyses of a model solution with the simulation by PeakMaster software. The optimized background electrolyte was composed of 10mM 2-(N-morpholino)ethanesulfonic acid, 20mM arginine, and 30µM cetyltrimethylammonium bromide, pH 8.95. Using this BGE, the anion levels were compared in saliva from 20 patients suffering from gastroesophageal reflux disease (GERD) and saliva from 12 healthy subjects. Bicarbonate levels were significantly elevated in saliva from GERD patients suggesting the possible applicability of bicarbonate as a biomarker in non-invasive diagnostics of GERD by CE-C4 D.

Determination of carbapenem antibiotics using a purpose-made capillary electrophoresis instrument with contactless conductivity detection

In this study, the employment of a purpose-made capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C4D) as a simple and cost-effective approach for simultaneous determination of different carbapenem antibiotics is reported. The developed CE-C4D approach was for the first time applied for quality control of various pharmaceutical formulations in Vietnam, as well as for therapeutic monitoring of these antibiotics in plasma samples from patients under intensive care. Four of the most popular carbapenems in Vietnam, doripenem, meropenem, imipenem and ertapenem, were determined using an electrolyte composed of 10 mM Tris adjusted to pH 8.0 with acetic acid. The best detection limits achieved using the developed CE-C4D method were 0.36 mg/L and 0.45 mg/L for pharmaceutical and plasma samples, respectively. Good agreement between results from CE-C4D and the confirmation method (HPLC-PDA) was achieved, with a coefficient of determination (r2) for the two pairs of data of 0.9967.

Separation and Detection of Trace Fentanyl from Complex Mixtures Using Gradient Elution Moving Boundary Electrophoresis

The current opioid epidemic remains an ongoing challenge, exacerbated by the extreme potency of synthetic opioids (e.g., fentanyl and fentanyl analogues), leading to an increase in adulterated heroin-related deaths. The increasing prevalence of fentanyl and fentanyl analogues in mixtures with heroin and other adulterants, excipients, and bulking agents has placed an emphasis on trace analysis methods for their detection from complex drug mixtures. Here, gradient elution moving boundary electrophoresis (GEMBE), a robust and miniaturized electrophoretic separation technique, was employed for the separation and detection of fentanyl and nine (9) fentanyl analogues from mixtures. GEMBE incorporated a short capillary (5 cm × 15 μm i.d.) for the electrophoretic separation of analytes with an opposing bulk counterflow. As the velocity of the counterflow was varied, analytes with differing electrophoretic mobilities entered the separation channel at different times and were analyzed as moving boundaries by contactless conductivity detection. The continuous injection of sample, driven by a controlled and variable pressure, both provided selectivity of the analytes and prevented contaminants or particulate within the sample from entering the separation capillary. Fentanyl was successfully separated and detected down to 2.5 μmol/L and demonstrated only 50% to 60% signal suppression in dilute binary mixtures with heroin and other common adulterants and excipients at 30:1 (compound/fentanyl) concentration ratios. In addition, GEMBE was successfully applied to a few adjudicated case samples of fentanyl-related mixtures exhibiting dyes and visible particulate. The short capillaries, contactless detection format utilized here, and continuous injection of sample allow for a small footprint platform that is easy-to-use for forensic analyses.

An Integrated Portable Multiplex Microchip Device for Fingerprinting Chemical Warfare Agents.

The rapid and reliable detection of chemical and biological agents in the field is important for many applications such as national security, environmental monitoring, infectious diseases screening, and so on. Current commercially available devices may suffer from low field deployability, specificity, and reproducibility, as well as a high false alarm rate. This paper reports the development of a portable lab-on-a-chip device that could address these issues. The device integrates a polymer multiplexed microchip system, a contactless conductivity detector, a data acquisition and signal processing system, and a graphic/user interface. The samples are pre-treated by an on-chip capillary electrophoresis system. The separated analytes are detected by conductivity-based microsensors. Extensive studies are carried out to achieve satisfactory reproducibility of the microchip system. Chemical warfare agents soman (GD), sarin (GB), O-ethyl S-[2-diisoproylaminoethyl] methylphsophonothioate (VX), and their degradation products have been tested on the device. It was demonstrated that the device can fingerprint the tested chemical warfare agents. In addition, the detection of ricin and metal ions in water samples was demonstrated. Such a device could be used for the rapid and sensitive on-site detection of both chemical and biological agents in the future.

Capillary Electrophoresis and Contactless Conductivity Detection: A Powerful Tool for in Situ Analysis of Samples from Ocean Worlds

The search for life in our Solar System is one of the highest priorities at NASA. Because of the presence of liquid water in the Oceans Worlds such as Jupiter's moon Europa, and Saturn's moon Enceladus, these bodies could potentially harbor life and be the focus of future missions. Liquid-based analytical techniques are particularly attractive for in situ analyses on these locations, since the sample could be analyzed in its natural state (e.g., liquid water or melted ice). Capillary electrophoresis (CE) is a powerful liquid separation technique that has tremendous promise for in situ studies on Ocean Worlds. By using contactless conductivity detection (C4D) a wide number of charged species (both organic and inorganic) can be detected without the need of derivatization. This includes amino acids, which are powerful biosignatures in the search for life beyond Earth as well as inorganic salts that are of primary importance to biological activity and they also determine the thermo-physical properties of any liquid mixture. The characterization of the distribution of inorganic ions is essential to assess the habitability of an extraterrestrial environment and provide sample context for trace detection of amino acids. We are currently developing CE-C4D methods that would be suitable for flight implementation. The first method allows the simultaneous analysis of inorganic cations and amino acids relevant to astrobiology [1]. A second method for analysis of inorganic anions and organic acids is also being developed. The main goal is to use both methods with a single capillary in order to obtain detailed chemical composition of the sample with the simplest configuration possible. Standard mixtures including some of the most relevant analytes for planetary studies were selected and electropherograms for the separations of the positively and negatively charged analytes are presented in the Figure 1A and B, respectively. To demonstrate the potential applications of these methods we have analyzed relevant natural samples of varying salinity. Acknowledgments The research described in this abstract was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Financial support for this project was provided by The Planetary Instrument Concepts for the Advancement of Solar System Observations (PICASSO) Program.

(Invited) Capillary Electrophoresis Instrumentation and Methods for Spaceflight Missions of Exploration

The search for evidence of life beyond Earth is among the highest level goals in planetary exploration. However, despite multiple orbiter and landed missions to extraterrestrial bodies in the solar system, we still haven’t found evidence of life. A powerful approach in this search involves seeking biochemical signatures of life at the molecular level, as distributions of organic molecules. The separation techniques capillary electrophoresis (CE) and its miniaturized version, microchip electrophoresis (ME) overcome the limitations of gas-phase techniques and hold unique promise in the search for signatures of life on other worlds. These techniques offers high resolution separations of molecules dissolved in water and are the simplest of all liquid separation methods to implement for flight. Here we describe CE and ME instrumentation developed at JPL and the steps we are taking to someday enable the its implementation on other worlds. Although multiple detection methods can be coupled to CE and ME, we focus on three detection modes: laser-induced fluorescence (LIF) for state-of-the-art measurements of amino acids, mass spectrometry (MS) for broad detection of ionizable organics, and contactless conductivity detection (C4D) for measurements of inorganic and organic ions. These techniques are complementary of each other and would allow full characterization of the chemical composition of a sample in situ. We are not only developing instrumentation but also analytical methods that could be implemented on a mission scenario. Here we also describe a system we dub The Chemical Laptop, which would provide the sample processing capabilities required for in situ analysis on extraterrestrial destinations with ultra-high sensitivity in a compact, low-mass, and low-power package. The Chemical Laptop is a truly portable, battery-powered, automated, and reprogrammable microchip electrophoresis instrument coupled to laser-induced fluorescence detection. This instrument concept could be adapted to the environmental requirements of a variety of astrobiologically interesting targets like Europa, Enceladus, or Titan. This system also serves as a general prototype that could be reprogrammed for terrestrial-based analyses as well.

A New Contactless Bubble/Slug Velocity Measurement Method of Gas–Liquid Two-Phase Flow in Small Channels

A new contactless bubble/slug velocity measurement method of the gas–liquid two-phase flow in small channels is proposed by extending the contactless conductivity detection technique to the contactless impedance detection (CID) technique. Two kinds of CID sensors with different constructions (tubular construction and radial construction) are developed to obtain the total impedance information (the real part, the imaginary part, and the amplitude) of the gas–liquid two-phase flow. Two bubble/slug velocity measurement systems with different constructions, the tubular three-electrode velocity measurement system and the radial four-electrode velocity measurement system, are developed. With the obtained total impedance information, three initial estimation values of the bubble/slug velocity are determined by the principle of the cross correlation velocity measurement. Then, with the real-time flow pattern identification result implemented by the fuzzy C-means, a corresponding velocity measurement model [which is the linear combination of the three initial estimation values of the bubble/slug velocity and is developed by the penalty function method and the Davidon–Fletcher–Powell algorithm] is applied to obtain the final bubble/slug velocity. Two groups of the bubble/slug velocity measurement system prototypes with three different inner diameters are developed. The bubble/slug velocity measurement experiments are carried out. The experimental results show that the proposed method is effective. For the two bubble/slug velocity measurement systems with different constructions, the maximum relative errors of the bubble/slug velocity measurement are all less than 4.5%. The research results also indicate that making full use of the total impedance information is an effective approach to improve the accuracy of the velocity measurement.

A sensitive photochemical reaction-capacitively coupled contactless conductivity detection system for HPLC and its application in determination of Cyclosporin A

High performance liquid chromatography (HPLC) post-column photochemical reaction (PR) coupled capacitively coupled contactless conductivity detector (C4D) was used for the first time in analysis of weak ultraviolet (UV)-absorbing, non-fluorescence and nonpolar compound. A series of conditions including the radiation power of light source, the length of the reaction tube and the thickness of detection tube were investigated. HPLC-PR-C4D system was successfully applied to the determination of Cyclosporin A (CsA). Consequently, under optimal conditions, the detection system exhibited a detection limit of 0.04 μg/mL and wide linear range from 0.5 μg/mL to 100 μg/mL for CsA detection. Application of the HPLC-PR- C4D system to pharmaceutical formulation and biological samples revealed the system developed maybe reliably applied to clinical studies.

Contactless conductivity detector from printed circuit board for paper-based analytical systems

This work presents a capacitively coupled contactless conductivity detector (C4D) etched out from a printed circuit board (PCB) as potential sensor for paper-based analytical systems. Two lines of any desirable pattern forming 35-μm thick planar copper electrodes were produced on a PCB plate (40 mm × 60 mm) by photolithography. The final PCB plate was covered with polypropylene film to serve as the insulating layer for the C4D detector. The film also protected the copper electrodes from corrosion. Electrodes made in this planar geometry make the PCB-C4D suitable as sensor for flat devices such as paper-based analytical devices. For this work, plain paper strips were employed as sample reservoir and as fluidic channel without hydrophobic pattern. A dried paper strip was first placed over the sensor, followed by dispensing a fixed volume of the liquid sample onto the paper. Entrapment of the liquid sample in the paper strip leads to reproducible size and position of the detection zone of the sample liquid for the capacitive coupling effect. High precision was obtained with %RSD ≤1% (n = 18) for standard solutions of KCl. Soil suspensions could be analyzed without prior filtration by placing a drop onto the paper strip extending away from the detector zone. The paper strip filtered out soil particles at the surface of the paper. Therefore, only soil filtrate moved towards the detection zone by lateral flow. The C4D detection using paper strip showed high tolerance to soil suspension with turbidity up to 6657 NTU, offering direct analysis of soil salinity. Cleaning with moist tissue paper between samples is adequate even for dirty samples such as soil suspension. We also monitored conductivity of acid-base reaction in the microfluidic paper channels, which was later applied to the quantification of bicarbonate in water and in antacid tablet (“Soda Mint Tablet”).

Development of a Passive Capacitively Coupled Contactless Conductivity Detection (PC4D) Sensor System for Fluidic Channel Analysis Toward Point-of-Care Applications

A sensor system based on a modified capacitively coupled contactless conductivity detection sensor is proposed and developed. The proposed system provides a passive and wireless readout technique, through which the conductivity of fluidic flow can be analyzed and foreign objects occurring in the fluidic flow can be detected. The proposed sensor system takes advantage of the series resonance principle and detects shifts in the resonance frequency and reflection coefficient to estimate the conductivity of the fluidic flow. In this paper, the working principle of the device is proposed and analyzed using a multiphysics simulation, and its performance is validated experimentally. The sensing performance is confirmed by measuring the conductivity of the fluidic media and the detection of foreign objects, such as air bubbles or water droplets, occurring in the flow. The influence of the distance between the inductors on the resonance frequency for different solution conductivities is also investigated and reported. The proposed sensor system shows its potential for use in various applications in biomedicine and chemistry, particularly in point-of-care applications, where the sensing chip can be easily set up for measurement and disposed of after use.

Cost-effective capillary electrophoresis with contactless conductivity detection for quality control of beta-lactam antibiotics

A simple and inexpensive approach for determination of various antimicrobial drugs using a purpose-made compact capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C4D) is reported. The objective of the work is to propose an affordable and easily-implemented tool for quality control and detection of counterfeiting of antibiotic formulations in resource constrained developing countries. The design of the purpose-made CE-C4D system was improved according to the feedback from over 10 years of use of our previous instrument. CE-C4D methods were for the first time developed to analyze β-lactam-based antibiotics commonly used in Vietnam, including single- β-lactam antibiotics (i.e. Cephalexin, Cefotaxime Sodium, Cefixime and Sulbactam) as well as β-lactams co-formulated with Sulbactam (i.e. Amoxicillin, Ampicillin, Cefoperazone and Sulbactam). Single β-lactam antibiotics were analyzed using a background electrolyte (BGE) composed of Tris/Ace (10 mM, pH 7.8) whereas β-lactam – Sulbactam combinations were simultaneously separated using a BGE containing Tris/Ace (10 mM, pH 7.5). The best achieved detection limits were 2.0 mg/L and 1.0 mg/L for these two groups, respectively. Good agreement between results obtained from CE-C4D and standard confirmation methods (LCMS) was achieved, with a coefficient of determination, r2, of 0.9991. The applicability of the developed CE-C4D method was demonstrated for quality control of 24 β-lactam-based antimicrobial drugs available in Vietnam.

Design and optimization of a fused-silica microfluidic device for separation of trivalent lanthanides by isotachophoresis.

Elemental analysis of rare earth elements is essential in a variety of fields including environmental monitoring and nuclear safeguards; however, current techniques are often labor intensive, time consuming, and/or costly to perform. The difficulty arises in preparing samples, which requires separating the chemically and physically similar lanthanides. However, by transitioning these separations to the microscale, the speed, cost, and simplicity of sample preparation can be drastically improved. Here, all fourteen non-radioactive lanthanides (lanthanum through lutetium minus promethium) are separated by ITP for the first time in a serpentine fused-silica microchannel (70µm wide×70µm tall×33cm long) in <10min at voltages ≤8kV with limits of detection on the order of picomoles. This time includes the 2min electrokinetic injection time at 2kV to load sample into the microchannel. The final leading electrolyte consisted of 10mM ammonium acetate, 7mM α-hydroxyisobutyric acid, 1% polyvinylpyrrolidone, and the final terminating electrolyte consisted of 10mM acetic acid, 7mM α-hydroxyisobutyric acid, and 1% polyvinylpyrrolidone. Electrophoretic electrodes are embedded in the microchip reservoirs so that voltages can be quickly applied and switched during operation. The limits of detection are quantified using a commercial capacitively coupled contactless conductivity detector (C4 D) to calculate ITP zone lengths in combination with ITP theory. Optimization of experimental procedures and reproducibility based on statistical analysis of subsequent experimental results are addressed. Percent error values in band length and conductivity are ≤8.1 and 0.37%, respectively.

Optimization of background electrolyte composition for simultaneous contactless conductivity and fluorescence detection in capillary electrophoresis of biological samples.

In this article, optimization of BGE for simultaneous separation of inorganic ions, organic acids, and glutathione using dual C4 D-LIF detection in capillary electrophoresis is presented. The optimized BGE consisted of 30mM 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid, 15mM 2-amino-2-hydroxymethyl-propane-1,3-diol, and 2mM 18-crown-6 at pH 7.2 and allowed simultaneous separation of ten inorganic anions and cations, three organic acids and glutathione in 20min. The samples were injected hydrodynamically from both capillary ends using the double-opposite end injection principle. Sensitive detection of anions, cations, and organic acids with micromolar LODs using C4 D and simultaneously glutathione with nanomolar LODs using LIF was achieved in a single run. The developed BGE may be useful in analyses of biological samples containing analytes with differing concentrations of several orders of magnitude that is not possible with single detection mode.

Development and Validation of a CE Method for the Determination of Tetracyclines with Capacitively Coupled Contactless Conductivity Detection

In this study, a simple and robust capillary electrophoresis method with capacitively coupled contactless conductivity detection (C4D) is developed for the determination of the tetracycline antibiotics (1) tetracycline, (2) chlortetracycline and (3) oxytetracycline. An uncoated, fused silica capillary (60.2 cm long, 75 µm i.d.) and a solution of 50 mM tris(hydroxymethyl) aminomethane, 50 mM l-histidine and 5 mM methyl-β-cyclodextrin, without pH adjustment (pH 8.76), was used as background electrolyte. Electrophoresis at + 25 kV showed a rapid analysis with sufficient resolution among the three antibiotics in the order of tetracycline, chlortetracycline and oxytetracycline. Successive inter-injection rinsing (20 psi) of the capillary ensured intra- and inter-day repeatability (0.9–2.2% RSD and 2.0–4.5% RSD, respectively, for relative peak areas). The method showed satisfactory performance in terms of selectivity, accuracy (99.3–101.4%) and linearity (R2 = 0.999). Finally, the method was applied to commercial samples of tetracycline, oxytetracycline and chlortetracycline. This method can be applied for rapid quality control in developing countries in particular, and across the globe in general.