Sensitive arsenic speciation by capillary electrophoresis using UV absorbance detection with on-line sample preconcentration techniques

Design and fabrication of La-based perovskites incorporated with functionalized carbon nanofibers for the electrochemical detection of roxarsone in water and food samples

The pentavalent arsenic compound roxarsone (RSN) is used as a feed additive in poultry for rapid growth, eventually ending up in poultry litter. Poultry litter contains chicken manure, which plays a vital role as an affordable fertilizer by providing rich nutrients to agricultural land. Consequently, the extensive use of poultry droppings serves as a conduit for the spread of toxic forms of arsenic in the soil and surface water. RSN can be easily oxidized to release highly carcinogenic As(III) and As(IV) species. Thus, investigations were conducted for the sensitive detection of RSN electrochemically by developing a sensor material based on lanthanum manganese oxide (LMO) and functionalized carbon nanofibers (f-CNFs). The successfully synthesised LMO/f-CNF composite was confirmed by chemical, compositional, and morphological studies. The electrochemical activity of the prepared composite material was examined using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained results confirmed that LMO/f-CNF showed enhanced electrocatalytic activity and improved current response with a good linear range (0.01-0.78 μM and 2.08-497 μM, respectively), exhibiting a low limit of detection (LOD) of 0.004 μM with a high sensitivity of 13.24 μA μM-1 cm-2 towards the detection of RSN. The noteworthy features of LMO/f-CNF composite with its superior electrochemical performance enabled reliable reproducibility, exceptional stability and reliable practical application in the analysis of tap water and food sample, affording a recovery range of 86.1-98.87%.

3D-printed device for the kinetic determination of As(III) in groundwater samples by digital movie analysis

High concentrations of inorganic arsenic in groundwater for human consumption is a worldwide common problem. Particularly, the determination of As(III) becomes important, since this species is more toxic than organic, pentavalent and elemental arsenic forms. In this work, a 3D-printed device that included a 24-well microplate was developed to perform the colourimetric kinetic determination of arsenic (III) by digital movie analysis. A smartphone camera attached to the device was used to take the movie during the process where As(III) inhibited the decolourization of methyl orange. The movie images were subsequently transformed from RGB to YIQ space to obtain a new analytical parameter called "d", which was related to the chrominance of the image. Then, this parameter allowed the determination of the inhibition time of reaction (t_in), which was linearly correlated with the concentration of As(III). A linear calibration curve (R = 0.9995) in the range from 5 μg L^-1 to 200 μg L^-1 was obtained. The method was precise (RSD = 1.2%), and the limits of detection (LOD) and quantification (LOQ) were 1.47 μg L^-1 and 4.44 μg L^-1, respectively. These values were lower than the limit established by the World Health Organization for total arsenic in drinking water (10 μg L^-1). The accuracy of the method was assessed by a recovery study with optimal results (94.3%-104.0%). Additionally, the Analytical GREEnness metric approach was applied, obtaining a score 1.7 times higher than previously published works. The method is simple, portable and low-cost, being in compliance with various principles of green analytical chemistry.

Research on Detection of Sterol Doping in Sports by Electrochemical Sensors: A Review

The use of doping by athletes to improve performance is prohibited. Therefore, doping testing is an important step to ensure fairness in sports. Doping is gradually metabolized in the body and is therefore difficult to detect immediately by a common method. At the same time, the emergence of new doping agents poses a challenge for highly sensitive detection. Electrochemical sensors are a fast, highly sensitive, and inexpensive analytical detection technology. It provides qualitative and quantitative determination of analytes by altering the electrochemical signal of the analyte or probe at the electrode. In this min-review, we summarized the different electrochemical sensing strategies for sterol doping detection. Some of the representative papers were interpreted in detail. In addition, we compare different sensing strategies.

In-line sample concentration in capillary electrophoresis by cyclodextrin to admicelle microextraction

Cyclodextrins (CDs) as a pseudophase in pseudophase-to-pseudophase microextraction (P2ME) in capillary zone electrophoresis (CZE) are proposed. In this P2ME mode called CD to admicelle ME, a long plug of dilute analyte solution prepared in cetyltrimethylammonium bromide (CTAB) at the critical micellar concentration was injected into the capillary. This formed CTAB admicelles at the interface between the solution and the negatively charged capillary surface, where the analytes were trapped. The injection of CD solution released the admicelles and the analytes from the capillary surface due to the formation of stable CD/CTAB inclusion complexes. The analytes are concentrated at the CD front during injection and voltage separation. Various neutral CDs were found to be effective for CD to admicelle ME. To implement this in-line sample concentration technique in CZE, CD concentration, sample injection time, and sample:CD solution injection ratio were optimized. The optimized conditions for five model anionic analytes, namely, 4-bromophenol, sulindac, sulfamethizole, 4-vinylbenzoic acid, and succinylsulfathiazole, were 20 mM α-CD in 20 mM sodium tetraborate (pH 9.2) solution, sample injection time of 370 s, and CD:sample injection ratio of 1:2. The sensitivity enhancement factors (SEFs) were between 112 and 168. The SEFs of sulindac and sulfamethizole in particular were similar to previously published off-line microextraction techniques, which are typically time-consuming. The calculated values of LOQ, intra-/inter-day (n = 6/n = 10, 3 days) repeatability, and linearity (R2) of CD to admicelle ME were 0.0125-0.05 µg/mL, 1.5-4.6%, 1.8-4.8%, and ≥0.999, respectively. Finally, the potential of CD to admicelle ME to the analysis of artificial urine samples was demonstrated.

Application of Capillary Electrophoresis for Determination of Inorganic Analytes in Waters

Aside from HPLC and GC, capillary electrophoresis (CE) is one of the most important techniques for high-performance separations in modern analytical chemistry. Its main advantages are the possibility of using different detection techniques, the possibility of in-capillary sample processing for preconcentration or derivatization, and ease of instrumental miniaturization down to the microfluidic scale. Those features are utilized in the separation of macromolecules in biochemistry and in genetic investigations, but they can be also used in determinations of inorganic ions in water analysis. This review, based on about 100 original research works, presents applications of CE methods in water analysis reported in recent decade, mostly regarding conductivity detection or indirect UV detection. The developed applications include analysis of high salinity sea waters, as well as analysis of other surface waters and drinking waters.

Development of sensitive and accurate solid-phase microextraction procedure for preconcentration of As(III) ions in real samples

We synthesized the poly(methyl methacrylate-co-2-aminoethyl methacrylate (PMaema) amphiphilic copolymer in a form of solid phase adsorbent. Then it was used for separation, preconcentration and determination of trace amount of As(III) ions from foods and waters with hydride generation atomic absorption spectrometry. The PMaema was characterized by fourier transform infrared spectrometer and nuclear magnetic resonance spectrometer. The adsorption of As(III) to the PMaema was also supported using computational chemistry studies. The experimental parameters (pH, PMaema amount, adsorption time and ethanol volume) were optimized using a three-level Box-Behnken design with four experimental factors. We observed linear calibration curve for the PMaema amount in the 10-500 ng L-1 range (R2 = 0.9956). Limit of detection, preconcentration factor and sorbent capacity of PMaema were equal to 3.3 ng L-1, 100 and 75.8 mg g-1, respectively. The average recoveries (spiked at 50 ng L-1) changes in the range of 91.5-98.6% with acceptable relative standard deviation less than 4.3%. After validation studies, the method was successfully applied for separation, preconcentration and determination of trace amount of As(III) from foods and waters.

Ultrasound assisted dispersive solid phase microextraction of inorganic arsenic from food and water samples using CdS nanoflowers combined with ICP-OES determination

Direct determination of arsenic species in real samples is challenging due to their trace concentration and spectral interferences by coexisting ions. Herein, we proposed an ultrasound-assisted dispersive solid phase microextraction (DSPME) procedure for the analyses of the trace inorganic arsenic. The hydrothermally synthesized cadmium sulfide nanoparticles (CdS NPs) completely adsorbed both arsenic species within 20 s at the initial arsenic concentration of 100 µg L^-1. The detection limit (3 S/m) of the proposed method was found to be 0.5 ± 0.2 and 0.8 ± 0.2 ng L^-1 for As(III) and As(V), respectively. The accuracy of the method against the systematic and constant errors was confirmed by the analysis of the Standard Reference Material (SRM) (>95% recovery with <5% RSD). The Student's t-test values were found to be less than the critical Student's t value at a 95% confidence level. The method was successfully employed for the determination of arsenic in food samples.

Design of Fluorescence-Enhanced Silver Nanoisland Chips for High-Throughput and Rapid Arsenite Assay

High-throughput and rapid arsenite (As(III)) monitoring is an urgent task to deal with the critical threat from As(III) contamination in the environment. In this study, an effective, portable, and sensitive As(III) assay was developed using the plasmonic silver (pAg) chips for As(III) detection. The pAg chips were fabricated by a simple seed-mediated method to grow the silver nanoisland films (Ag-NIFs) with the compact nanoislands and adjustable interisland gaps on the large-sized substrates. With appropriate surface functionalization and optimal chip manufacturing, Cy7.5 fluorescence dye can be immobilized on the surface of Ag-NIFs in the presence of As(III) to output the enhanced fluorescence signals up to 10-fold and improve the detection limit of As(III) less than 10 ppb. According to our results, the high-throughput detection measurements and wide dynamic range over 4 orders of magnitude implied the broad prospects of pAg chips in fluorescence-enhanced assays. The proposed As(III) assay has shown great opportunities for the practical application of ultratrace As(III) monitoring.

Enhanced light-emitting diode induced fluorescence detection system with capillary electrophoresis

An enhanced fluorescence detection system of capillary electrophoresis (CE) was equipped with a concave silver mirror, by which the detection sensitivity of light-emitting diode induced fluorescence (LEDIF) can be increased greatly. The silver concave mirror and the cathode window in photomultiplier tube (PMT) were accurately set face to face at the same axis. When the two labeled tumor markers exactly moved to the center of detection window, the emission from analytes are excitated by LED source. Currently, the analytes may be regarded as a luminescent source point. When the source point exactly moves to the focus of the concave mirror, the emission of the labeled sample was collected effectively, enhanced by convergence and reflected by the concave mirror. Then it was sensitively detected by the PMT. The optical mechanism of enhancing detection sensitivity was explored. A simple comparative test on sensitivity was carried out, which aimed to compare sensitivity of the new detection system with concave mirror to that without concave mirror but the other conditions were kept the same. Two tumor markers labeled with FITC were selected for the test, using the simple LEDIF detect system. The results (LOD, 150 nM for L-Leu and L-Val) showed that the detection sensitivity matched with concave mirror reached more 16 times than the detection method without concave mirror.

Rapid extraction of arsenic species from traditional Chinese herbal by dual-frequency ultrasound-assisted enzymatic digestion prior to spectral analysis

Considering the huge difference of biological toxicity, it is extremely significant to recognize the exact content of arsenic species in actual samples. In this paper, a novel pretreatment technique for the efficient extraction of arsenic species from herbal samples is developed by dual-frequency ultrasound-assisted enzymatic digestion (DUED). The preservation of arsenic original form, reduction of the actual analysis time, environmental friendliness and free-interference in subsequent detection make this method over the traditional method such as wet digestion, ashing and some solvent extraction technologies. The combination of DUED and atomic fluorescence spectrometry realize the speciation analysis of arsenic in traditional Chinese medicine. The optimizations of experimental parameters have been achieved, and the potential mechanism is discussed. The experimental data showed that cellulase is suitable for the digestion of herbal matrix than α-amylase and papain. Ultrasound can significantly increase the rate of enzymatic hydrolysis of biological molecules, especially under dual-frequency ultrasound irradiation. The highest relative extraction efficiency can be obtained by combining 40 kHz ultrasonic bath (UB) with 20 kHz ultrasonic probe (UP). Two certified reference materials [CRMs, GBW(E)090066 and GBW(E)090067] and four practical herbs were used to evaluate the accuracy and practicability of the method. Inorganic arsenic, including trivalent arsenic and pentavalent arsenic, was the main species in the four herbal samples.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2016-2018)

One of the most cited limitations of capillary and microchip electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of online/in-line concentration methods in capillaries and microchips, covering the period July 2016-June 2018. It includes developments in the field of stacking, covering all methods from field-amplified sample stacking and large-volume sample stacking, through to isotachophoresis, dynamic pH junction, and sweeping. Attention is also given to online or in-line extraction methods that have been used for electrophoresis.