Evaluation of different operating modes of an autosampler for portable capillary electrophoresis.

A compact, inexpensive sampler instrument for portable capillary electrophoresis (CE) was developed and tested to monitor common inorganic ions in drinking water samples. The sampler uses peristaltic and vacuum pumps and pinch and check valves to control liquid flows. The paper also addresses various aspects of CE associated with portability, open access instrumentation and prospects of CE for citizen science. The extensive use of items provided by the electronic and computer industry contributes to this trend.

Autosampler for portable capillary electrophoresis.

A compact, inexpensive sampler instrument for portable capillary electrophoresis was developed for monitoring illegal drugs in human body fluids and evaluated for γ-hydroxybutyric acid (GHB) in simulated saliva samples. The sampler uses peristaltic pumps and pinch and check valves to activate liquid flows. This short communication addresses aspects of CE associated with portability, open access instrumentation, and prospects of CE for citizen science. The extensive use of items provided by the electronic and computer industry contributes to this trend.

The influence of organic solvents on phenylethylamines in capillary zone electrophoresis.

The aim of this study was to investigate the influence of organic solvents on the electrophoretic separation of phenylethylamines. The background electrolyte composition was adjusted with different protic (methanol, ethanol, and 2-propanol) and aprotic (dimethyl sulfoxide and acetonitrile) solvents. Two groups of analytes were studied. The first group contained phenylethylamines with an amine group only, DL-1-phenylethylamine and amphetamine. The second group represented phenylethylamines with both amine and phenolic hydroxyl groups, dopamine and tyramine. Experiments revealed no or minor influence of the organic modifiers on the electromigration behavior of the analytes from the first group (containing only the amine group) and a drastic effect on the second group (containing the additional phenolic hydroxyl group). Dopamine and tyramine showed various electrostatic, hydrophobic, and hydrogen-bonding interactions with both protic and aprotic organic solvents. The dependence of the electrophoretic mobility of dopamine and tyramine on the concentration of the organic solvents provided direct evidence of the formation of hydrogen bonds between dopamine or tyramine and the organic solvent. The baseline separation was achieved by the addition of at least 20% v/v of organic solvent (protic or aprotic) to the background electrolyte. The analyte migration time repeatabilities were within 0.7-4.1% for absolute and 0.2-1.9% for normalised migration times. The proposed bonding mechanism and behavior of phenylethylamines were examined and confirmed by NMR spectroscopy.

Portable fully automated oral fluid extraction device for illegal drugs.

Currently used methods for in-field determination of illegal drugs involve various test kits based mainly on the immunoassay technique, where the presence of a compound of interest is assessed by antibody-antigen reaction and manifested by observable color change. Despite being accepted and widely used by police forces to test the presence of illegal drugs in a suspect person, these tests often suffer from unreliable results (high level of false-positive and/or false-negative) due to the cross-reactivity and difficulties with quantification. Therefore, we have developed a portable capillary electrophoresis instrument to determine illegal drugs in oral fluid collected from a suspected person. However, this drug analyzer has still required manual sample preparation. Therefore, this research aimed to develop, test, and validate a fully automated sample pretreatment (purification, extraction, pre-concentration) prototype compatible with the capillary electrophoresis drug of abuse analyzer and suitable for confirmatory analysis by mass spectrometry. The cotton swab from Salivette® oral fluid collector was examined and integrated into the fully automated extractor prototype. The recoveries for the automated extractor were between 18 and 20%, with repeatabilities within 5-11% for 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxy-N-ethylamphetamine (MDEA), cocaine (COC), and cocaethylene (COET). The developed extraction device was easy to use even for unskilled persons, required minimal liquid handling, and was applicable to use in field conditions.

Capillary Electrophoresis as a Monitoring Tool for Flow Composition Determination.

Flow analysis is the science of performing quantitative analytical chemistry in flowing streams. Because of its efficiency and speed of analysis, capillary electrophoresis (CE) is a prospective method for the monitoring of a flow composition withdrawn from various processes (e.g., occurring in bioreactors, fermentations, enzymatic assays, and microdialysis samples). However, interfacing CE to a various flow of interest requires further study. In this paper, several ingenious approaches on interfacing flow from various chemical or bioprocesses to a capillary electrophoresis instrument are reviewed. Most of these interfaces can be described as computer-controlled autosamplers. Even though most of the described interfaces waste too many samples, many interesting and important applications of the devices are reported. However, the lack of commercially available devices prevents the wide application of CE for flow analysis. On the contrary, this fact opens up a potential avenue for future research in the field of flow sampling by CE.

Complete capillary electrophoresis process on a drone: towards a flying micro-lab.

Hazardous remote places exist in the world. Why should health or life be risked sending a scientist to the investigation site, as the remote analytical instrumentation exists? Different scientific fields require instruments that could be used on-site (in situ), therefore the purpose of this work was to design a fully automated chemical analysis system small enough to be mountable on a drone. Here we show an autonomous analytical system with sampling capability on a drone. The system is suited for the remote and autonomous analysis of volatile and non-volatile chemicals in the air. The designed system weighs less than 800 g. Data are transmitted wirelessly. Collected substances are separated automatically without the intervention of the operator using the method of capillary zone electrophoresis. The analytes are detected using a miniaturized contactless conductivity detector quantifying them down to less than 1 µM. In this work, we demonstrated sampling and separation of volatile amines (triethylamine and diethylamine) and organic acids (acetic and formic acids), non-volatile inorganic cations (K+, Ca2+, Na+), and protein (bovine serum albumin) in the aerosol state. It was shown that the capillary electrophoretic analysis can be performed on a hovering drone. We anticipate our work to be a starting point for more sophisticated, autonomous complex sample analysis. We believe that our designed instrument will enable the investigation of hazardous places in different research fields.

Compensation of the baseline temperature fluctuations for autonomous CE-C4D instrument working in harsh environments.

One of the main problems of the remote complex sample analysis instrumentation is that such systems are susceptible to temperature fluctuations. Temperature regulation is energetically ineffective, and it is not used in most of the field portable analytical systems. Separations performed in a changing temperature environment provide electropherograms with considerable baseline fluctuations, resulting in significant errors in detection and integration of the peaks. This paper describes electropherogram baseline compensation that is suitable for the capillary electrophoresis-contactless conductivity detection analytical method. The baseline compensation utilizes linear or polynomial data processing methods, and can be programmed in-line using simple microcontroller, or on-line and off-line in data acquisition software. This method is targeted for field portable and autonomous analytical systems that are utilized in a fluctuating environment.

Capillary Electrophoresis Sensitivity Enhancement Based on Adaptive Moving Average Method.

In the present work, we demonstrate a novel approach to improve the sensitivity of the "out of lab" portable capillary electrophoretic measurements. Nowadays, many signal enhancement methods are (i) underused (nonoptimal), (ii) overused (distorts the data), or (iii) inapplicable in field-portable instrumentation because of a lack of computational power. The described innovative migration velocity-adaptive moving average method uses an optimal averaging window size and can be easily implemented with a microcontroller. The contactless conductivity detection was used as a model for the development of a signal processing method and the demonstration of its impact on the sensitivity. The frequency characteristics of the recorded electropherograms and peaks were clarified. Higher electrophoretic mobility analytes exhibit higher-frequency peaks, whereas lower electrophoretic mobility analytes exhibit lower-frequency peaks. On the basis of the obtained data, a migration velocity-adaptive moving average algorithm was created, adapted, and programmed into capillary electrophoresis data-processing software. Employing the developed algorithm, each data point is processed depending on a certain migration time of the analyte. Because of the implemented migration velocity-adaptive moving average method, the signal-to-noise ratio improved up to 11 times for sampling frequency of 4.6 Hz and up to 22 times for sampling frequency of 25 Hz. This paper could potentially be used as a methodological guideline for the development of new smoothing algorithms that require adaptive conditions in capillary electrophoresis and other separation methods.

Digital microfluidics platform for interfacing solid-liquid extraction column with portable capillary electropherograph for analysis of soil amino acids.

In this work, the concept of a field-portable analyzer is proposed that operates with milliliter amounts of solvents and samples. The need to develop such an analyzer is not only driven by specific extraterrestrial analysis but also, for example, by forensics applications where the amount of liquid that can be taken to the field is severely limited. The prototype of the proposed analyzer consists of a solid-liquid extractor, the output of which is connected to the micropump, which delivers droplets of extracts to digital microfluidic platform (DMFP). In this way, world-to-chip interfacing is established. Further, the sample droplets are transported to CE capillary inlet port, separated and detected via a contactless conductivity detector. Working buffers and other solvents needed to perform CE analysis are also delivered as droplets to the DMFP and transported through the CE capillary. The performance of the analyzer is demonstrated by analysis of amino acids in sand matrices. The recovery of the spiked amino acids from the inert sand sample was from 34 to 51% with analysis LOD from 0.2 to 0.6 ppm and migration time RSD from 0.2 to 6.0%.

Electrowetting on dielectric actuation of droplets with capillary electrophoretic zones for MALDI mass spectrometric analysis.

An automated fraction collection interface was developed for coupling CE with MALDI-MS. This fraction collection approach is based on the electrowetting on dielectric (EWOD) phenomenon performed on a digital microfluidic (DMF) board; it does not rely on a MALDI spotter. In this study, a four-peptide mixture was used as a sample test, and the separations were conducted in a portable CE instrument with a 150 µm o.d. × 50 µm i.d. capillary and a contactless conductivity detector. The CE instrument was interfaced with a robust DMF board. The CE fractions were directly deposited onto the DMF board at predetermined locations prior to MALDI analysis. The series of experiments determined the lowest concentration that produces a measurable MALDI signal. The concentrations were 0.25, 0.5, 0.05, and 0.05 nmol for bradykinin, angiotensin, ACTH (18-39), and insulin, respectively. The contactless conductivity detector limit of detection for the same analytes was 2.5 µmol.

Electrowetting-on-dielectric actuation of droplets with capillary electrophoretic zones for off-line mass spectrometric analysis.

Present article describes a novel technique based on digital microfluidics that allows collecting fractions of interest after electrophoretic separation and detection for further ESI-MS investigation. In this technique, a mixture is injected into a capillary electrophoresis (CE) apparatus, and microliter droplets are generated at the CE outlet at a frequency high enough to fraction each compound into several droplets, compartmentalizing the CE zones into a sequence of droplets. The droplets are transported from the CE outlet to a storage tube inlet using electrowetting-on-dielectric (EWOD) for droplet actuation. By applying a vacuum at the other end of the storage tube, the droplets form a sequence of plugs separated by air gaps. The plugs stored in the tubing are later analyzed using a standalone spectrometric device. Off-line electrospray ionization mass spectrometry (ESI-MS) was used to characterize the corresponding vitamin and was performed by pumping the segmented plugs directly into a spray emitter tip. The technique could be of interest to laboratories without access to well-equipped facilities (e.g. clean-rooms or lab robots).

Digital microfluidic sampler for a portable capillary electropherograph.

A new sample introduction/analysis approach was developed by combining a digital microfluidic (DMF) device with a portable capillary electrophoresis (CE) analyzer based on short separation capillary and contactless conductivity detection. The DMF sample injection was performed by transporting sample and buffer droplets in succession under the CE capillary inlet end allowing the capillary to be immersed into the sample/buffer droplet, and CE separation was performed by applying a high voltage between the (grounded) buffer droplet and CE outlet reservoir. Electrowetting on dielectric (EWOD) phenomenon was used for droplets actuation. With the use of the DMF sampler, CE separation of a mixture of vitamins was achieved. A droplet evaporation process with simultaneous concentration of sample in the droplet was monitored. It was found that the concentration process closely followed the theoretically predicted function.

Comparison of the contents of various antioxidants of sea buckthorn berries using CE.

The increased interest in sea buckthorn (Hippophae rhamnoides L.) made it possible to investigate the antioxidant content in it. To address this issue, the presence of following antioxidant compounds were analyzed: trans-resveratrol, catechin, myricetin, quercetin, p-coumaric acid, caffeic acid, L-ascorbic acid (AA), and gallic acid (linear range of 50-150 micromol/L) in six different varieties of sea buckthorn berries extracts (sea buckthorn varieties: "Trofimovskaja (TR)," "Podarok Sadu (PS)," and "Avgustinka (AV),") received from two local Estonian companies. Trans-Resveratrol, catechin, AA, myricetin, and quercetin were found in extracts of sea buckthorn. Moreover, AA, myricetin, and quercetin contents were quantified. The biggest average AA content was found in TR (740 mg/100 g of dried berries, respectively). Furthermore, the same varieties gave the biggest quercetin content 116 mg/100 g of dried berries, respectively. For analysis, CZE was used and the results were partly validated by HPLC. Statistically no big differences in levels of antioxidants were consistently found in different varieties of sea buckthorn extracts investigated in this work.

Nonaqueous CE using contactless conductivity detection and ionic liquids as BGEs in ACN.

N,N'-Alkylmethylimidazolium cations have been separated in NACE when one of the N,N'-dialkylimidazolium salts (ionic liquids (ILs)) was used as an electrolyte additive to the organic solvent separation medium. The separated species were 1-methyl-, 1-ethyl-, 1-butyl-, 1-octyl-, 1-decyl-3-methylimidazolium and N-butyl-3-methylpyridinium cations and BGE composed of 1-ethyl-3-methylimidazolium ethylsulfate or 1-butyl-3-methylimidazolium trifluoroacetate [BMIm][FAcO] (A6; B2) diluted in ACN. It was demonstrated that contactless conductivity detection (CCD) may be applied to monitoring the separation process in nonaqueous separation media, allowing to use the UV light-absorbing imidazolium-based electrolyte additives. There could be marked three concentration regions of added ILs; at first ionic strength of BGE below 1-2 mM, and then the actual electrophoretic mobility of analytes rises from 0. At concentrations above 1-2 mM, the added IL facilitated separation. In concentration region of 1-20 mM, the actual electrophoretic mobility of analyzed imidazolium cations was increasing with decrease in separation medium ionic strength. At higher concentrations of BGE (above 30 mM), the conductivity of the separation media became too high for this detector. Some organic dyes were also successfully separated and detected by contactless conductivity detector in a 20 mM A6 separation electrolyte in ACN.