Fast and accurate quantification of methanol by electrochemical analysis

A group of scientists at the Institute for Tropical Technology, Vietnam Academy of Science and Technology, and the University of Natural Sciences, Vietnam National University, Ho Chi Minh City, has successfully fabricated an electrochemical sensor applied in the quantitative analysis of methanol in alcoholic beverages (beer, wine) and gasoline fuel. The thesis shows the feasibility and advantages of the electrochemical analysis method compared to the chromatographic analysis method (GC/MS) in the quantitative analysis of methanol with a simpler process and more reasonable cost.

Methanol (CH3OH) is the simplest alcohol, light, colorless, volatile, flammable, characteristic taste like white alcohol ethanol (C2H5OH) but sweeter, more aromatic and highly toxic. Due to its strong toxicity, direct contact with methanol can cause dermatitis, rash, psoriasis, blurred vision and blindness, more seriously, local disturbances, irritation of respiratory mucosa, organ damage, neurological disorders, nerve damage to the brain, and can lead to death when used in large amounts.

In industries, methanol is used as an antifreeze agent, a solvent for dissolving production materials, an organic solvent for paints and varnishes, as a raw material for the production of plastics, and for the synthesis of organic substances, used to produce fuels such as gas and biodiesel. Currently, there is a situation of mixing methanol (instead of ethanol) into alcoholic beverages to enhance the taste, mixed with gasoline fuel to reduce costs, for the purpose of profiteering. This causes great and serious consequences for society and human health. This is a matter of great concern in the world in general and in Vietnam in particular.

In order to quickly and accurately analyze the methanol content in alcoholic beverages and gasoline, a team of scientists at the Institute for Tropical Technology, Vietnam Academy of Science and Technology and the University of Natural Sciences, Vietnam National University, Ho Chi Minh City has performed the science and technology project of Ho Chi Minh City level "Manufacturing electrochemical sensors and methanol analysis equipment system in alcoholic beverages and gasoline fuel", code: 114/2019 /HD-QPTKHCN (led by Prof .Dr. Tran Dai Lam, chaired by Institute for Tropical Technology) in the 2020-2021 period. The project has fully completed the objectives and contents set out in the explanation, and was accepted and graded as Pass by the City-level Scientific Council on December 30, 2021.

The goal of the mission is to master the technology of manufacturing electrochemical sensors with suitable specifications, to ensure direct analysis of methanol in alcohol and gasoline fuels, at the same time, to integrate electrochemical meters and sensors in the handheld measuring system for direct analysis of methanol in the field.

Electrochemical sensors for methanol analysis are usually made from precious metals with high catalytic activity but also costly such as Pt, Pd, Ru. This project used metals as catalysts and transition metal oxides of Ni, Cu, which are low cost, to replace precious metals of the Pt family. The use of catalysts that are transition metals and metal oxides combined with a very small amount (0.5-1%) of CNTs or graphene conductors has been shown to successfully solved the problem of ensuring both technological parameters (good catalytic activity) and economic efficiency (much cheaper) in methanol oxidation reaction (MOR).

The methanol oxidation reaction (MOR) in alkaline media, catalyzed by NiO on the modified SPE electrode

Accordingly, the research team designed, fabricated and optimized the printed electrode (SPE) applied as a MeOH analytical sensor. The selection and construction of electrode modification process with conductive polymer PANI and transfer metal catalysts (oxides) to create composites (PANI-Graphene-NiO, PANI-CNTs-NiO, PANI-Graphene-CuO, PANI-CNTs-CuO) and helps to improve the sensitivity and selectivity of the sensor compared to the use of precious metal catalysts such as Pt, Pd, thereby greatly reducing the cost of the modified electrode.

Detection limit and methanol sensitivity of fabricated electrochemical sensors

Comparison of sensor performance compared with GC/MS method (Gas Chromatography-coupled mass spectrometry) showed that the control analysis results of distilled alcohol (white wine) samples with standard addition of 2,000 ppm methanol and A95 gasoline samples standard addition of 10,000 ppm methanol gives quite similar results. The advantage of the sensor method is the direct analysis, which gives fast results, while the GC/MS method requires sample dilution and the analysis time is quite long. In addition, using the sensor to analyze the methanol content in some alcoholic beverage and gasoline fuel samples, it shows that the methanol content is within the allowable threshold according to TCVN and below the detection threshold of the sensor.

Result of methanol detection by electrochemical sensor and GC method

Analysis of methanol in beer, wine, and gasoline samples by potentiostat measuring instrumentation and denatured SPE sensor

The main scientific results of the project were published in 02 prestigious international papers, namely RSC Advances, 2021, 11(46), 28573-28580 (Q1, IF = 3,361) and Journal of the Electrochemical Society, 2021, 168(10), 107509 (Q1, IF = 4.17). In addition, the project also trained 01 Master, and 01 GPHI application was accepted by the National Office of Intellectual Property.

Translated by Phuong Ha
Link to Vietnamese version

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