Fabrication of an All-Solid-State Ammonium Paper Electrode Using a Graphite-Polyvinyl Butyral Transducer Layer

A planar solid-state ammonium-selective electrode, employing a composite mediator layer of graphite particles embedded in a polyvinyl butyral matrix on top of an inkjet-printed silver electrode, is presented in this paper. The effect of graphite powder mass fraction on the magnitude of the potentiometric response of the sensor was systematically verified using a batch-mode and a flow injection measurement setup. Under steady-state conditions, the paper electrode provided a Nernstian response of 57.30 mV/pNH4 over the concentration range of 10−5 M to 10−1 M with a detection limit of 4.8 × 10−6 M, while the analytical performance of the array in flow mode showed a narrower linear range (10−4 M to 10−1 M; 60.91 mV/pNH4 slope) with a LOD value of 5.6 × 10−5 M. The experimental results indicate that the prepared electrode exhibited high stability and fast response to different molar concentrations of ammonium chloride solutions. The pH-response of the paper NH4-ISE was also investigated, and the sensor remained stable in the pH range of 2.5–8.5. The potentiometric sensor presented here is simple, lightweight and inexpensive, with a potential application for in-situ analysis of environmental water samples.

Flow-based System: A Highly Efficient Tool Speeds Up Data Production and Improves Analytical Performance

In this review, we cite references from the period between 2015 and 2020 related to the use of a flow-based system as a tool to obtain a modern analytical system for speeding up data production and improving performance. Based on a great deal of concepts for automatic systems, there are several research groups introduced in the development of flow-based systems to increase sample throughput while retaining the reproducibility and repeatability as well as to propose new platforms of flow-based systems, such as microfluidic chip and paper-based devices. Additionally, to apply a developed system for on-site analysis is one of the key features for development. We believe that this review will be very interested and useful for readers because of its impact on developing novel analytical systems. The content of the review is categorized following their applications including quality control and food safety, clinical diagnostics, environmental monitoring and miscellaneous.

Renewable chemiluminescence optosensors based on implementation of bead injection principle with multicommutation

In this work, the implementation of Bead Injection with multicommutation-based flow systems is reported. A surface renewable chemiluminescence (CL) flow sensor is presented based on the use of CL reaction of luminol with H₂O₂. Dowex 1 × 8 beads with immobilized luminol onto them were injected in the flow system by means of a six-port rotary valve and were accommodated into a 1 mm optical glass flow cell placed just in front of the rectangular photosensor window with the same size than the cell wall. Automatic computer-controlled manipulation of both reagents and sample solutions was undertaken using a multicommutated flow system which comprises five three-way solenoid valves, a home-made electronic interface and a Java-written software. Once the chemiluminescence signal was registered, sensing beads were automatically discarded out with a six-port rotary valve without needing to reverse or stop the flow. As a proof of concept and example, the enhancement of the chemiluminescence signal produced by Co(II) on the luminol-H₂O₂ reaction in alkaline medium was used for illustrating this implementation determining vitamin B₁₂ in pharmaceutical preparations (after mineralization for releasing Co(II)). The analytical performance of the approach was satisfactory, showing a linear dynamic range from 1.7 to 50 µg L^-1, a detection limit of 0.5 µg L^-1, RSD (%) of 5.3%, with a sampling frequency of 11 h^-1. The proposed approach was applied to different samples and the results were consistent with those obtained with a reference method based on ICP-MS. Based on the same reaction (or re-configuring the system to accommodate it to reaction requirements) the approach can also be applied to the determination of other metal ions such as Cr(III) and Fe(II) and appropriately extended to molecules of bioanalytical interest based e.g. in CL immunoassays, given its versatility.

Evaluation of dicationic reagents for their use in detection of anions using positive ion mode ESI-MS via gas phase ion association

Twenty-three different dications were investigated for their effectiveness in pairing with singly charged anions, thereby allowing the electrospray ionization mass spectrometry (ESI-MS) detection of anions as positively charged complexes. Nitrate, iodide, cyanate, monochloroacetate, benzenesulfonate, and perfluoro-octanoate were chosen as representative test anions as they differ in mass, size-to-charge ratio, chaotropic nature, and overall complexity. Detection limits were found using direct injection of the anion into a carrier liquid containing the dication. Detection limits are given for all six anions with each of the 23 dications. Each anion was easily detected at the ppb (microg/L) and often the ppt (ng/L) levels using certain dicationic reagents. The ability of dicationic reagents to pair with anions and produce ESI-MS signals varied tremendously. Indeed, only a few dications can be considered broadly useful and able to produce sensitive results. Liquid chromatography (LC)-ESI-MS also was investigated and used to show how varying the dicationic reagent produced significantly different peak intensities. Also, the use of tandem mass spectrometry can lead to even greater sensitivity when using imidazolium based dications.

Spectrophotometric flow injection methods for zinc determination in pharmaceutical and biological samples

Zinc ions form a yellow complex with di-2-pyridyl ketone salicyloylhydrazone (DPKSH). This complex showed maximum absorption at 376 nm, and it was used to develop spectrophotometric flow injection methods for Zn(II) determination in different samples. Two types of flow systems were proposed. In the first system, a linear analytical curve was obtained in a concentration range from 0.217 to 4.60 mg L(-1) Zn(II), with a detection limit of 48.8 microg L(-1). In the second system, a minicolumn packed with an anion exchanger resin was used to concentrate Zn(II) as a chlorocomplex, and a linear analytical curve within a concentration range from 0.0824 to 2.06 mg L(-1) Zn(II) was obtained, having a detection limit of 13.9 microg L(-1). The developed methods were applied to biological and pharmaceutical samples, and a great compliance was observed by comparing the results with ones obtained by an atomic absorption technique.

Development of a capillary electrophoresis method for the screening of human urine for multiple drugs of abuse

A new capillary electrophoresis (CE) method was developed and validated for the screening of human urine for nineteen drugs of abuse. In order to achieve sufficient separation, the electrolyte composition was modified using beta-cyclodextrin (beta-CD) and organic solvents. To process each sample, a sequential injection-solid-phase extraction (SI-SPE) system was constructed. Using this device, matrix clean-up, extraction, and preconcentration of analytes were performed onto a C(18) cartridge. Optimal separation and detection were obtained using a background electrolyte consisting of 100mM phosphate adjusted to pH 6.0, with 20 mM beta-CD, 5% acetonitrile and 20% isopropanol. Electrokinetic injection was performed at 5 kV for 10s, separation voltage was 25 kV and column temperature was set to 25 degrees C. The separation was carried out in a 67.0 cm x 50 microm fused-silica capillary with UV detection at 214 nm. The combination of SI-SPE and sample stacking showed significant sensitivity enhancement with limits of detection in the range of 5-30 ng ml(-1). A validation study showed good reproducibility of both migration time (RSD=0.003-0.088%) and peak area (RSD=0.54-4.8%). Overall, this automated and miniaturized SI-SPE system provides a rapid, sensitive, and robust procedure for analysis; as well as minimizes sample and solvent consumption.

A hyphenated flow-through analytical system for the study of the mobility and fractionation of trace and major elements in environmental solid samples

A flow-through hyphenated analytical method has been tested that enables not only the accelerated and efficient fractionation of trace elements (TE) species in environmental solids to be achieved but allows real-time studies on the leaching process to be made. Rotating coiled columns (RCC), earlier used mainly in countercurrent chromatography, have been successfully applied to the dynamic fractionation of heavy metals in soil, sediment, and sludge samples. A ground solid sample (about 0.5 g) was retained in a PTFE rotating column as the stationary phase whereas different aqueous eluents, chosen according to recent data on the selectivity of leachants, were continuously pumped through. Elements were determined in the effluent on-line by inductively coupled plasma atomic emission spectrometry (ICP-AES). Since the flow rates used in the RCC are in good agreement with those needed for cross-flow nebulization in the ICP-AES spectrometer, both devices were coupled directly without any additional interface systems. Simultaneous investigation of the elution profiles of trace and major elements has made it possible to study the elements association in separated fractions and hence to prove the efficacy of extractants and their selectivity toward targeted mineralogical phases of samples. The close association of heavy metals with Mn oxides in the sediment and sludge samples was confirmed. The time-resolved dissolution of different organic complexes of metals was observed for the sediment sample. It was found that in sediment and sludge samples the dynamics of iron release under the action of Tamm's reagent is somewhat different from that of aluminium. In addition, the proposed method can also be applied to develop effective leaching schemes and in the analysis of environmental solids for risk assessment of their contaminants addressed to water quality and bioavailability.