Concurrent determination of anions and cations in consumer fireworks with a portable dual-capillary electrophoresis system

Application of microfluidic technologies in forensic analysis

The application of microfluidic technology in forensic medicine has steadily expanded over the last two decades due to the favorable features of low cost, rapidity, high throughput, user-friendliness, contamination-free, and minimum sample and reagent consumption. In this context, bibliometric methods were adopted to visualize the literature information contained in the Science Citation Index Expanded from 1989 to 2022, focusing on the co-occurrence analysis of forensic and microfluidic topics. A deep interpretation of the literature was conducted based on co-occurrence results, in which microfluidic technologies and their applications in forensic medicine, particularly forensic genetics, were elaborated. The purpose of this review is to provide an impartial evaluation of the utilization of microfluidic technology in forensic medicine. Additionally, the challenges and future trends of implementing microfluidic technology in forensic genetics are also addressed.

A substantial increase of analytical throughput in capillary electrophoresis throughput by separation-interrupted sequential injections

How to further improve the throughput of capillary electrophoresis (CE) is a fascinating question. Herein an idea to substantially increase the throughput of CE has been proposed together with theory and experimental demonstration. The key is to introduce samples for CE, one after another, by a short suspension of voltage application, which was hence termed separation-interrupted sequential injections (Sisi). The idea was demonstrated to be feasible on a laboratory-built CE instrument coupled with tandem C4D (contactless capacitively-coupled conductivity) detectors. At least 50 injections of a testing sample (mixture of NH4+, K+, Ca2+, Na+ and Mg2+) were successfully separated in only a single run. The separation took 145 min in total, equivalent to 2.9 min per analysis which is only 21% of that of normal CE. Quantification of the separated ions was performed, with a limit of detection of 1.1-2.6 μM, a limit of quantification of 3.2-8.9 μM, and a linear range up to 1000 μM (R2 > 0.99). The recovery was between 88% and 112% measured by spiking standards into samples at low, middle and high levels. The real applicability of Sisi-CE was evaluated by direct injection and analysis of 45 mineral water samples also in a single run. Its clinical application potential was demonstrated by high throughput assay of the calcium and zinc gluconate oral solution formula, and the blood potassium of hyperkalemia and hypokalemia from patients with renal failure disease. This method can be extended to other applications such as omics studies through the use of more suitable detectors. The theory proposed may also be applicable to other high throughput methods.

Advancements in capacitance-to-digital converter-based C4 D technology for detection in capillary electrophoresis using amplified excitation voltages and comparison to classical and open-source C4 Ds

This work introduces new hardware configurations for a capacitively coupled contactless conductivity detector (C⁴ D) based on capacitance-to-digital conversion (CDC) technology for CE. The aim was to improve sensitivity, handling, price, and portability of CDC-based C⁴ D detectors (CDCD) to reach LODs similar to classic C⁴ Ds with more sophisticated electric circuits. To achieve this, a systematic study on the CDCDs was carried out including a direct comparison to already established C⁴ D setups. Instrumental setups differing in electrode lengths, measurement modes, and amplification of excitation voltages were investigated to achieve LODs for alkali metal ions of 4 to 12 μM, similar to LODs obtained by classic C⁴ D setups. Lowest LODs were achieved for a setup with two 10 mm electrodes at a distance of 0.2 mm and an excitation voltage of 24 V. The detection head was exceptionally lightweight with only 2.6 g and covered only 20 mm of the capillary on total. This allowed the use of multiple detectors along the separation path to enable spatial tracking of analytes during separation. The entirely battery-powered detector assembly weighs less than 200 g, and the data are transmitted wirelessly for possible portable applications. The freely accessible hardware and software were optimized for fully automated measurements with real time data plotting and allowed handling multidetector setups. The new developments were applied to quantify the potassium salt of glyphosate in its herbicide formulation.

Low-cost and open-source strategies for chemical separations

In recent years, a trend toward utilizing open access resources for laboratory research has begun. Open-source design strategies for scientific hardware rely upon the use of widely available parts, especially those that can be directly printed using additive manufacturing techniques and electronic components that can be connected to low-cost microcontrollers. Open-source software eliminates the need for expensive commercial licenses and provides the opportunity to design programs for specific needs. In this review, the impact of the "open-source movement" within the field of chemical separations is described, primarily through a comprehensive look at research in this area over the past five years. Topics that are covered include general laboratory equipment, sample preparation techniques, separations-based analysis, detection strategies, electronic system control, and software for data processing. Remaining hurdles and possible opportunities for further adoption of open-source approaches in the context of these separations-related topics are also discussed.

Low-cost automated capillary electrophoresis instrument assembled from commercially available parts

A CE instrument that can be assembled from commercially available components with minimal construction effort is described. Except for the electronic control circuitry no specially made parts are required. It is based on a flexible design of microfluidic, electropneumatic, and electronic sections and different configurations can easily be implemented. Automated injection into the capillary is performed hydrodynamically by the application of a pressure for a controlled length of time. The performance of the device was tested with a contactless conductivity detector by separating different metal ions. In addition, nine metal cations related to the quality of honey were separated in 2.3 min and four honey samples were analysed quantitatively to demonstrate the applicability of the method.

Simultaneous electrokinetic stacking and separation of anionic and cationic species on a paper fluidic channel

On-line enrichment is effective for improving the sensitivity of paper-based analytical devices (PADs). Electrokinetic stacking of ionic species - anionic or cationic species, respectively, on a paper-based fluidic channel has been well demonstrated in the literature. In this work, we further demonstrated that both anionic and cationic species can be electrokinetically stacked and separated simultaneously on the same paper fluidic channel. The feasibility of the proposed method was visually demonstrated by using a colored cationic probe of Rhodamine 6G and an anionic probe of Brilliant Blue. With the introduction of a background electrolyte (BGE) consisting of weak acid and weak base salt, two electric field gradients can be developed on the same paper fluidic channel when a DC voltage was applied. Both of the anionic and cationic species from the reservoirs can be simultaneously stacked as separate bands on the two field gradients, respectively. Under optimized conditions, two orders of magnitude enrichment factors can be achieved for the anionic and cationic probes as characterized by colorimetric analysis by smartphone imaging. The applicability of this method was further demonstrated by stacking and separation of copper ions/nitrite and even amphoteric ions-proteins of phycocyanin (blue, pI 4.4)/cytochrome C (brown, pI 10.2). Potential applications can be found not only for a PAD based point of care test (POCT), but also for sample pretreatment in protein analysis considering the friendliness of the BGE to the mass spectrometer.

A bi-end injection capillary electrophoresis method for simultaneous determination of 37 cations and anions in beers

Capillary electrophoresis (CE) is excellent at separating all the ions in a sample but is rarely used as a result of its detection issue and easy loss of very fast ions by common one-end injection methods. Herein we propose a newly developed method aimed at simultaneous determination of positive and negative ions with a home-made CE device, featuring bi-end injection and contactless conductivity detection at the middle. By simply using 2.5 M acetic acid as a running buffer, the method can separate 37 ions (3 inorganic anions, 8 inorganic cations, 10 biogenic amines, and 16 amino acids) per run, with linearity between 10 and 2000 μM (R² > 0.99), limit of detection of 1.0-16.6 μM, and limit of quantification of 2.3-31.7 μM. The recovery measured by spiking standards into samples at high, middle, and low levels was between 73% and 110%. The intra- and interday repeatability of the 37 analytes ranged from 0.69% to 8.97% and from 0.68% to 11.04%, respectively. The proposed method was evaluated by analysis of 21 beers and, in addition to acquiring the concentration information, the brands of the tested beers were distinguished. This method is of high throughput, fast, and cost-effective. It could be a promising tool for ionomic analysis. Graphical abstract ᅟ.

Recent advances in the capillary electrophoresis analysis of antibiotics with capacitively coupled contactless conductivity detection

This review describes briefly the high rate of counterfeiting of antimicrobial drugs with focus upon its immediate health consequences. The major part of this review encompasses accounts of the improvements achieved in the domain of miniaturization of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D). The application of this principle into the development of portable devices as well as its application to counter the health-system-crippling phenomenon of counterfeit antibiotic formulations, are discussed in the context of developing countries.

Dual-opposite injection capillary electrophoresis: Principles and misconceptions

Dual-opposite injection capillary electrophoresis (DOI-CE) is a separation technique that utilizes both ends of the capillary for sample introduction. The electroosmotic flow (EOF) is suppressed to allow all ions to reach the detector quickly. Depending on the individual electrophoretic mobilities of the analytes of interest and the effective length that each analyte travels to the detection window, the elution order of analytes in a DOI-CE separation can vary widely. This review discusses the principles, applications, and limitations of dual-opposite injection capillary electrophoresis. Common misconceptions regarding DOI-CE are clarified.

Determination of Inorganic Ion Profiles of Illicit Drugs by Capillary Electrophoresis

A portable capillary electrophoresis instrument with dual capacitively coupled contactless conductivity detection (C⁴ D) was used to determine the inorganic ionic profiles of three pharmaceutical samples and precursors of two illicit drugs (contemporary samples of methylone and para-methoxymethamphetamine). The LODs ranged from 0.10 μmol/L to 1.25 μmol/L for the 10 selected cations, and from 0.13 μmol/L to 1.03 μmol/L for the eight selected anions. All separations were performed in less than 6 min with migration times and peak area RSD values ranging from 2 to 7%. The results demonstrate the potential of the analysis of inorganic ionic species to aid in the identification and/or differentiation of unknown tablets, and real samples found in illicit drug manufacture scenarios. From the resulting ionic fingerprint, the unknown tablets and samples can be further classified.

Screening determination of pharmaceutical pollutants in different water matrices using dual-channel capillary electrophoresis coupled with contactless conductivity detection

In this study, the employment of purpose-made dual-channel compact capillary electrophoresis (CE) instrument with capacitively coupled contactless conductivity detection (C(4)D) as a simple and inexpensive solution for screening determination of various pharmaceutical pollutants frequently occurring in surface water and hospital wastewater in Hanoi, Vietnam is reported. Five negatively charged pharmaceutically active compounds, namely ibuprofen, diclofenac, bezafibrate, ketoprofen and mefenamic acid were determined using the first channel whereas three positively charged ones, namely diphenhydramine, metoprolol and atenolol were determined with the second channel of the CE-C(4)D instrument. Two different background electrolytes (BGEs) were used in these two CE channels independently. The best detection limits achieved were in the range of 0.2-0.8mg/L without sample pre-concentration. Enrichment factors up to 200 were obtainable with the inclusion of a solid phase extraction step. Good agreement between results obtained from CE-C(4)D and those with the standard confirmation method (HPLC-DAD) was achieved, with correlation coefficients higher than 0.98.

Microfluidic Breadboard Approach to Capillary Electrophoresis

A breadboard approach for electrophoretic separations with contactless conductivity detection is presented. This is based on miniature off-the-shelf components such as syringe pumps, valves, and pressure controllers which could be set up in a very compact overall arrangement. It has a high flexibility for different tasks at hand, and the common operations of hydrodynamic injection and capillary flushing are automated. For demonstration of the versatility of the proposition, several very diverse configurations and modes of electrophoresis were successfully implemented, namely, standard capillary zone electrophoresis, pressure assisted zone electrophoresis, the simultaneous separation of cations and anions by dual-capillary zone electrophoresis, the separation of cationic amino acids by isotachophoresis, as well as the separation of small carboxylic acids by gradient elution moving boundary electrophoresis. The system also allows fast separations, as demonstrated by the analysis of six inorganic cations within 35 s. The approach addresses respective limitations of either conventional capillary electrophoresis instruments as well as electrophoretic lab-on-chip devices, while maintaining a performance in terms of detection limits and reproducibility comparable to standard instrumentation.

Portable, Battery Operated Capillary Electrophoresis with Optical Isomer Resolution Integrated with Ionization Source for Mass Spectrometry

We introduce a battery operated capillary electrophoresis electrospray ionization (CE/ESI) source for mass spectrometry with optical isomer separation capability. The source fits in front of low or high resolution mass spectrometers similar to a nanospray source with about the same weight and size. The source has two high voltage power supplies (±25 kV HVPS) capable of operating in forward or reverse polarity modes and powered by a 12 V rechargeable lithium ion battery with operation time of ~10 h. In ultrafast CE mode, in which short narrow capillaries (≤15 μm i.d., 15-25 cm long) and field gradients ≥1000 V/cm are used, peak widths at the base are <1 s wide. Under these conditions, the source provides high resolution separation, including optical isomer resolution in ~1 min. Using a low resolution mass spectrometer (LTQ Velos) with a scan time of 0.07 s/scan, baseline separation of amino acids and their optical isomers were achieved in ~1 min. Moreover, bovine serum albumin (BSA) was analyzed in ~1 min with 56% coverage using the data-dependent MS/MS. Using a high resolution mass spectrometer (Thermo Orbitrap Elite) with 15,000 resolution, the fastest scan time achieved was 0.15 s, which was adequate for CE-MS analysis when optical isomer separation is not required or when the optical isomers were well separated. Figures of merit including a detection limit of 2 fmol and linear dynamic range of two orders of magnitude were achieved for amino acids.

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

The portable capillary electrophoresis instrument is automated and features three independent channels with different background electrolytes to allow the concurrent optimized determination of three different categories of charged analytes. The fluidic system is based on a miniature manifold which is based on mechanically milled channels for injection of samples and buffers. The planar manifold pattern was designed to minimize the number of electronic valves required for each channel. The system utilizes pneumatic pressurization to transport solutions at the grounded as well as the high voltage side of the separation capillaries. The instrument has a compact design, with all components arranged in a briefcase with dimensions of 45 (w) × 35 (d) × 15 cm (h) and a weight of about 15 kg. It can operate continuously for 8 h in the battery-powered mode if only one electrophoresis channel is in use, or for about 2.5 h in the case of simultaneous employment of all three channels. The different operations, i.e. capillary flushing, rinsing of the interfaces at both capillary ends, sample injection and electrophoretic separation, are activated automatically with a control program featuring a graphical user interface. For demonstration, the system was employed successfully for the concurrent separation of different inorganic cations and anions, organic preservatives, additives and artificial sweeteners in various beverage and food matrices.

Portable capillary electrophoresis instrument with contactless conductivity detection for on-site analysis of small volumes of biological fluids

A novel, easy to use and portable capillary electrophoretic instrument for injection of small volumes of biological fluids equipped with contactless conductivity detection was constructed. The instrument is lightweight (<5 kg), all necessary parts including a tablet computer are accommodated in a plastic briefcase with dimensions 20 cm × 33 cm × 17 cm (w × l × h), allows hydrodynamic injection of small sample volumes and can continuously operate for at least 10 hours. The semi-automated hydrodynamic sample injection is accomplished via a specially designed PMMA interface that is able to repeatedly inject sample aliquots from a sample volume as low as 10 μL, with repeatability of peak areas below 5%. The developed interface and the instrument were optimized for the injection of biological fluids. Practical utility was demonstrated on the determination of formate in blood serum samples from acute methanol intoxication patients and on the analysis of ionic profile (nitrosative stress markers, including nitrite and nitrate) in the exhaled breath condensate from one single exhalation.

In-house-made capillary electrophoresis instruments coupled with contactless conductivity detection as a simple and inexpensive solution for water analysis: a case study in Vietnam

A simple and inexpensive method for the determination of various ionic species in different water matrices is discussed in this study. The approach is based on the employment of in-house-made capillary electrophoresis (CE) instruments with capacitively coupled contactless conductivity detection (C(4)D), which can be realized even when only a modest financial budget and limited expertise are available. Advantageous features and considerations of these instruments are detailed following their pilot deployment in Vietnam. Different categories of ionic species, namely major inorganic cations (K(+), Na(+), Ca(2+), Mg(2+), and NH4(+)) and major inorganic anions (Cl(-), NO3(-), NO2(-), SO4(2-), and phosphate), in different water matrices in Vietnam were determined using these in-house fabricated instruments. Inorganic trivalent arsenic (As(iii)), which is the most abundant form of arsenic in reducing groundwater, was determined by CE-C(4)D. The effect of some interfering ions in groundwater on the analytical performance was investigated and is highlighted. The results from in-house-made CE-C(4)D-instruments were cross-checked with those obtained using the standard methods (AAS, AES, UV and IC), with correlation coefficients r(2) ≥ 0.9 and deviations from the referenced results less than 15%.

Screening determination of four amphetamine-type drugs in street-grade illegal tablets and urine samples by portable capillary electrophoresis with contactless conductivity detection

A simple and inexpensive method for the identification of four substituted amphetamines, namely, 3,4-methylenedioxy methamphetamine (MDMA), methamphetamine (MA), 3,4-methylenedioxy amphetamine (MDA) and 3,4-methylenedioxy-N-ethylamphetamine (MDEA) was developed using an in-house constructed semi-automated portable capillary electrophoresis instrument (CE) with capacitively coupled contactless conductivity detection (C(4)D). Arginine 10mM adjusted to pH4.5 with acetic acid was found to be the optimal background electrolyte for the CE-C(4)D determination of these compounds. The best detection limits achieved with and without a sample preconcentration process were 10ppb and 500ppb, respectively. Substituted amphetamines were found in different seized illicit club drug tablets and urine samples collected from different suspected users. Good agreement between results from CE-C(4)D and those with the confirmation method (GC-MS) was achieved, with correlation coefficients for the two pairs of data of more than 0.99.

Micro-injector for capillary electrophoresis

A novel micro-injector for capillary electrophoresis for the handling of samples with volumes down to as little as 300 nL was designed and built in our laboratory for analyses in which the available volume is a limitation. The sample is placed into a small cavity located directly in front of the separation capillary, and the injection is then carried out automatically by controlled pressurization of the chamber with compressed air. The system also allows automated flushing of the injection chamber as well as of the capillary. In a trial with a capillary electrophoresis system with contactless conductivity detector, employing a capillary of 25 μm diameter, the results showed good stability of migration times and peak areas. To illustrate the technique, the fast separation of five inorganic cations (Na(+) , K(+) , NH4 (+) , Ca(2+) , and Mg(2+) ) was set up. This could be achieved in less than 3 min, with good limits of detection (10 μM) and linear ranges (between about 10 and 1000 μM). The system was demonstrated for the determination of the inorganic cations in porewater samples of a lake sediment core.