Electroanalysis

Điện cực graphite-epoxy (GE) được điều chỉnh bằng ống nano carbon nhiều lớp (MWCNTs) và peroxidase củ cải đường (GE/MWCNTs-HRP) đã được sử dụng để xây dựng một cảm biến glyphosate có hiệu suất trong dung dịch nước phụ thuộc vào hoạt động của enzyme. Để chuẩn bị cảm biến, MWCNTs đã được lắng đọng lên bề mặt GE bằng phương pháp điện di sử dụng điều trị oxy hóa (H₂SO₄/HNO₃) có mặt cetyl tributylammonium bromide (CTAB) như một chất hoạt động bề mặt cation. Chất hoạt động bề mặt sau đó đã được loại bỏ khỏi bề mặt MWCNTs bằng cách nhúng điện cực vào dung dịch EtOH/HCl. Việc cố định vật lý HRP và do đó khả năng cảm biến glyphosate đã được thử nghiệm ở pH 4, nơi mà thuốc diệt cỏ chỉ tồn tại ở một dạng duy nhất. Các nghiên cứu phân cực vòng đã gợi ý rằng cấu trúc thứ cấp của HRP thay đổi do tương tác với glyphosate và sự thay đổi này được tăng cường bởi sự kết hợp giữa glyphosate và H₂O₂, điều này có thể giải thích cho việc giảm hoạt động xúc tác của enzyme khi nồng độ glyphosate tăng. Việc định lượng glyphosate trong hạt ngô bị dop rất tái lặp và thể hiện giới hạn phát hiện và định lượng lần lượt là 1.32 pM và 1.63 pM. Cảm biến cũng được đặc trưng bởi độ hồi phục cao (100 %) và độ chính xác (hệ số biến thể <1 %) và có thể được sử dụng trong sự hiện diện của các chất can thiệp như chlorpyrifos (một loại thuốc trừ sâu phospho hữu cơ) và tinh bột.

This article describes anion transfer across a conducting polypyrrole membrane (PPM) using cyclic voltammetry with a four‐electrode system. The transfer process of both chloride and nitrate anions across the polypyrrole membrane used to separate two pools of electrolyte solutions has been studied. A wide potential window beyond 3 V was obtained, and well‐developed voltammograms for the transfer of nitrate and chloride anions appeared within this window. The transfer process depends on the ion size, the ion charge, and the surface characteristics of the polypyrrole membrane. The one‐way transfer phenomenon observed in different potential‐bias directions can be explained by the asymmetrical ion channel model of the polypyrrole membrane.

The effect of 30 phenols and anilines on typical Ru complex electrochemiluminescence (ECL) was systematically investigated under different conditions. It was found that all the tested compounds showed an ECL inhibiting signal. The magnitude of ECL inhibition was related to the position of the substituting group in the benzene ring and decreased in the following order: meta‐>ortho‐>para‐. The oxidation potential of the tested compounds, the ECL spectra and UV‐visible absorption spectra of Ru(bpy)$\rm{ {_{3}^{2+}}}$/tripropylamine (TPrA) in the presence of phenols and anilines, and the direct ECL between Ru(bpy)$\rm{ {_{3}^{2+}}}$ and phenols/aniline were studied. The mechanism of ECL inhibition has been proposed due to energy transfer from the excited state Ru(bpy)$\rm{ {_{3}^{2+}}}$$\rm{{^\cdot}}$ to a quinone or ketone or their polymer formed by electro‐oxidation of phenols and anilines. The potential of analytical application was explored by use of the inhibited ECL. The results demonstrate that numerous compounds are detectable with the detection limits in the range of 10⁻⁸–10⁻⁹ mol/L for Ru(bpy)$\rm{ {_{3}^{2+}}}$/TPrA system and in the range of 10⁻⁶–10⁻⁷ mol/L for Ru(bpy)$\rm{ {_{3}^{2+}}}$/C₂O$\rm{ {_{4}^{2}}}$ system, respectively.

Anodic stripping voltammetry (ASV) and cathodic stripping voltammetry (CSV) were used to determine Mn concentration using metal catalyst free carbon nanotube (MCFCNT) electrodes and square wave stripping voltammetry (SWSV). The MCFCNTs are synthesized using a Carbo Thermal Carbide Conversion method which results in a material that does not contain residual transition metals. Detection limits of 120 nM and 93 nM were achieved for ASV and CSV, respectively, with a deposition time of 60 s. CSV was found to be better than ASV in Mn detection in many aspects, such as limit of detection and sensitivity. The CSV method was used in pond water matrix addition measurements.

Detection of Mn(II) using differential pulse anodic stripping voltammetry (DPASV) on solid silver amalgam electrode is introduced. A well‐defined peak for the oxidation of Mn(0) to Mn(II) was observed around −1.45 V in NH₄Cl (0.05 M) solution. Concentrations down to 1 μg/L were measured in NH₄Cl (0.05 M) with 900 s deposition time at −1.70 V, and good linearity was observed (r=0.993) for standard additions in different concentration ranges (1–3 μg/L, 10 μg/L–60 μg/L, and 50 μg/L–250 μg/L). For all measurements relative standard deviation was within 5% (n=9). Interactions between Mn and Cd, Ni, Cu, Pb and Zn were examined, and it was found that lead and nickel significantly interfere, while zinc, cadmium, copper, and mercury did not interfere within reasonable concentration ranges. The method was demonstrated for online detection of manganese in a contaminated river where the Mn(II) concentration varied between 3 and 15 μg/L. The relation between the Mn(II) concentration in the river water and the vessel traffic was observed due to the presence of high concentrations of Mn(II) in anoxic pore waters.

In this work, we report on the determination of trace manganese (Mn) using cathodic stripping voltammetry (CSV) using a microfabricated sensor with a Pt thin‐film working electrode. While an essential trace metal for human health, prolonged exposure to Mn tends to gradually impair our neurological system. The potential sources of Mn exposure make it necessary to monitor the concentration in various sample matrices. Previous work by us and others suggested CSV as an effective method for measuring trace Mn. The analytical performance metrics were characterized and optimized, leading to a calculated limit of detection (LOD) of 16.3 nM (0.9 ppb) in pH 5.5, 0.2 M acetate buffer. Further, we successfully validated Mn determination in surface water with ∼90% accuracy and >97% precision as compared with inductively coupled plasma mass spectrometry (ICP‐MS) “gold standard” measurement. Ultimately, with stable, accurate and precise electrochemical performance, this Pt sensor permits rapid monitoring of Mn in environmental samples, and could potentially be used for point‐of‐use measurements if coupled with portable instrumentation.

Manganese was determined by differential pulse voltammetry in pre‐enriched solution. The metal was first deposited on the surface of a hanging mercury drop electrode by electrolysis, and after a short oxidation interval, the reformed manganese(II) ions were determined by differential pulse cathodic polarization scan. The detection limit (with 120 seconds deposition) was 2 μg L⁻¹. The only interfering element was cobalt (when present at tenfold concentration excess). Compared with conventional stripping voltammetry the described method has a lower detection limit value, and the analysis is performed during a shorter time interval. The proposed method was applied for the determination of manganese in natural waters.

A carbon paste electrode modified with 1‐(2‐pyridylazo)‐2‐naphthol was fabricated and used to preferentially accumulate Mn(^II) at open circuit. After medium exchange, the accumulated Mn(^II) at the electrode surface was electrochemically oxidized. The hydrated MnO₂ thus formed was then cathodically stripped using differential pulse voltammetry. Various factors influencing the accumulation and stripping were studied. An optimized procedure was then developed for the determination of Mn(^II). Mn(^VII) could also be determined by chemical conversion to Mn(^II) using acidified H₂O₂. Following this, the Mn(^VII) concentration could be obtained by subtraction. Under optimum conditions, a detection limit of 6.9 × 10⁻⁹ M Mn(^II) (0.38 ppb) was found for 200s accumulation. For 8 determinations, each of Mn(^II) concentrations of 1.00 × 10⁻⁶ M, 1.00 × 10⁻⁷ M and 1.00 × 10⁻⁸ M, relative standard deviations of 2.90%, 4.46% and 7.20% were obtained, respectively. Selected metal ions were tested for interferences and it was found that, when determining 1.00 × 10⁻⁶ M Mn(^II) (150s accumulation), Co(^II), Hg(^II) and Fe(^II) at 1.00 × 10⁻⁵M interfered. These interferences were readily eliminated by masking with complexing agents such as sodium citrate and sodium diethyldithiocarbamate. The developed method was tested using a certified sample and then applied to the determination of manganese in seawater.

Ultrasonically enhanced voltammetric measurements have been successfully applied for the detection of a wide range of trace metals. These are reviewed and the beneficial effects of power ultrasound applied to electroanalysis highlighted, most notably the possibility for quantitative analysis in otherwise highly passivating media, where classical electrochemical techniques often fail.