Square-Wave Voltammetric Sensing of Lawsone (2- Hydroxy-1,4-Naphthoquinone) Based on the Enhancement Effect of Cationic Surfactant on Anodically Pretreated Boron-Doped Diamond Electrode
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-12-06 |
| Journal | Acta chimica slovenica |
| Authors | Pınar Talay Pınar, Yavuz Yardım, ZĂŒhre ĆentĂŒrk |
| Institutions | Van YĂŒzĂŒncĂŒ Yıl Ăniversitesi |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study presents a novel, highly sensitive electroanalytical method for the rapid quantification of lawsone (hennotannic acid) using a modified Boron-Doped Diamond Electrode (BDDE).
- Enhanced Sensitivity: The method utilizes an Anodically Pretreated BDD Electrode (APT-BDDE) coupled with the cationic surfactant Cetyltrimethylammonium Bromide (CTAB), which increased the lawsone oxidation peak current by approximately four times.
- Low Detection Limit: The optimized Square-Wave Voltammetry (SWV) technique achieved a low Limit of Detection (LOD) of 0.029 ”M, demonstrating superior sensitivity compared to many previously reported voltammetric methods for lawsone.
- Stable Electrochemical Response: Lawsone exhibits a well-defined, irreversible, and diffusion-controlled oxidation peak at a stable potential of +0.19 V (vs. Ag/AgCl) in acidic phosphate buffer (pH 2.5).
- Robust Platform: The BDD electrodeâs inherent propertiesâwide potential window, low background current, and mechanical stabilityâensure high repeatability (RSD less than 7% for intraday and interday measurements).
- Practical Validation: The methodology was successfully applied for the direct quantification of lawsone in commercial henna samples, yielding high recovery rates (91.8% to 103.7%), confirming its accuracy in complex natural matrices.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Working Electrode Material | Boron-Doped Diamond (BDD) | N/A | Anodically Pretreated (APT) |
| Boron Doping Level | 1000 | ppm | Declared specification |
| Geometric Surface Area | 0.07 | cm2 | 3 mm diameter |
| Anodic Pretreatment Voltage | +1.8 | V | Applied for 180 s in 0.5 M H2SO4 |
| Supporting Electrolyte | Phosphate Buffer Solution (PBS) | 0.1 M | Optimized pH 2.5 |
| Cationic Surfactant | CTAB | 0.1 mM | Cetyltrimethylammonium Bromide |
| Lawsone Oxidation Peak Potential | +0.19 | V | vs. Ag/AgCl |
| Linear Concentration Range (SWV) | 0.1 - 5.0 | ”M | Calibration curve |
| Limit of Detection (LOD) | 0.029 | ”M | Calculated as 3 s/m |
| Square-Wave Frequency (f) | 75 | Hz | Optimized SWV parameter |
| Pulse Amplitude (ÎEsw) | 60 | mV | Optimized SWV parameter |
| Intraday Repeatability (RSD) | 5.43 | % | 10 repeated measurements |
| Interday Repeatability (RSD) | 6.87 | % | 3 consecutive days |
Key Methodologies
Section titled âKey MethodologiesâThe electrochemical sensing platform relies on precise electrode pretreatment and optimized Square-Wave Voltammetry (SWV) parameters:
- Electrode Activation (Anodic Pretreatment): The BDD working electrode was activated daily by applying a potential of +1.8 V for 180 seconds in a 0.5 M H2SO4 solution. This anodic pretreatment (APT) creates a predominantly oxygen-terminated surface, which was found to yield the highest oxidation peak current compared to untreated or cathodically pretreated surfaces.
- Inter-Measurement Cleaning: A 30-second activation program (+1.8 V in 0.5 M H2SO4) was applied between individual measurements to maintain a clean, reproducible surface.
- Electrolyte Selection: Britton-Robinson (BR) buffers, acetate buffers, and phosphate buffers were tested. 0.1 M PBS at pH 2.5 was selected as the optimal supporting electrolyte, maximizing the lawsone peak current.
- Surfactant Enhancement: The cationic surfactant CTAB (0.1 mM) was introduced to the PBS solution. This significantly increased the lawsone oxidation signal, likely due to electrostatic interaction or preconcentration effects at the electrode surface.
- SWV Parameter Optimization: The instrumental parameters for Square-Wave Voltammetry were optimized for maximum sensitivity and peak morphology:
- Frequency (f): 75 Hz
- Step Potential (ÎE): 14 mV
- Pulse Amplitude (ÎEsw): 60 mV
- Sample Preparation: Commercial henna samples were extracted by dissolving 0.1 g in 5 mL ethanol, diluting with pH 2.5 PBS, stirring for 90 minutes, and filtering before analysis via SWV.
Commercial Applications
Section titled âCommercial ApplicationsâThe robust and sensitive electroanalytical platform developed using the APT-BDDE/CTAB system is highly relevant for several industrial sectors requiring rapid chemical analysis:
- Natural Products Quality Control:
- Rapid, on-site quantification of lawsone content in commercial henna products, ensuring regulatory compliance and consumer safety.
- Standardization of active ingredient levels in other natural dyes and plant extracts (e.g., Lawsonia inermis).
- Pharmaceutical and Cosmetic Manufacturing:
- Quality assurance testing for lawsone and related naphthoquinone derivatives used in cosmetic formulations (hair dyes, skin treatments) and potential pharmaceutical agents (antimicrobial, anticancer).
- Environmental and Corrosion Monitoring:
- Lawsone is utilized as a corrosion inhibitor for metals (Al, Fe, Zn, Ni). The BDD sensor offers a stable platform for monitoring inhibitor concentration and degradation in industrial acidic or alkaline process streams.
- Advanced Electrochemical Sensing:
- The methodology (APT-BDDE combined with surfactant enhancement) serves as a template for developing highly sensitive sensors for other electroactive organic pollutants or biological molecules in complex aqueous media.
View Original Abstract
In this reported work, an anodically pretreated boron-doped diamond (BDD) electrode was used for the inexpensive, simple and quick detection of a natural dye, lawsone. Lawsone had a well-defined, irreversible and diffusion-controlled oxidation peak at approximately +0.19 V in phosphate buffer solution (PBS, 0.1 M, pH 2.5) using cyclic voltammetry (CV). The oxidation peak heights of lawsone were significantly increased in PBS using the cationic surfactant cetyltrimethylammonium bromide (CTAB). Under optimized experimental conditions, the calibration curve was linear over a concentration range of 0.1-5.0 ÎŒM with detection limit of 0.029 ÎŒM in 0.1 M PBS (pH 2.5) containing 0.1 mM CTAB by using square-wave voltammetry (SWV). To evaluate the practical applicability of the BDD electrode, it was used for the quantification of lawsone in commercial henna, a natural dye made from the leaves of the henna plant.