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6CCVD Research

Quantification of caffeine in coffee cans using electrochemical measurements, machine learning, and boron-doped diamond electrodes

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2024-03-26
JournalPLoS ONE
AuthorsT. Honda, Kenshin Takemura, Susumu Matsumae, Nobutomo Morita, Wataru Iwasaki
InstitutionsSaga University, National Institute of Advanced Industrial Science and Technology
Citations3
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research demonstrates a novel, rapid, and reagent-free method for quantifying caffeine in commercial beverages by integrating Boron-Doped Diamond (BDD) electrochemistry with machine learning (ML).

  • Core Value Proposition: Quantification of caffeine content in complex commercial beverages (canned coffee) was achieved with zero solvent pretreatment, dilution, or electrolyte addition.
  • Performance Metrics: An average prediction accuracy of 93.88% (median 95.95%) was achieved against manufacturer-published values.
  • Speed Advantage: Measurement time was reduced to 2 minutes, significantly faster than conventional High-Performance Liquid Chromatography (HPLC) methods (120 minutes).
  • Electrode Technology: BDD electrodes were utilized due to their high chemical resistance, wide potential window, and long-term stability, which are critical for measuring complex, non-pretreated solutions.
  • Machine Learning Integration: Principal Component Analysis (PCA) and Principal Component Regression (PCR) were employed to analyze the multivariate electrochemical signals, effectively separating the caffeine redox peak (1.6 V) from overlapping noise caused by high concentrations of foreign organic substances (0 V to 1 V peaks).
  • Methodology Advancement: The ML algorithm uses a “graded evaluation” combining both specific coordinate data (concrete information) and broad area data (abstract information) from the SWV spectra to ensure robust quantification despite measurement instability inherent to non-optimized solvents.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
BDD Fabrication MethodHot-Filament Chemical Vapor Deposition (HFCVD)N/AOn Si (100) substrates
BDD Film Thickness2”mWorking electrode layer
Boron Doping Concentration5E20cm-3Heavily doped polycrystalline diamond
HFCVD Filament Temperature2200°CDuring film growth
HFCVD Chamber Pressure1.3kPaDuring film growth
Methane/Hydrogen Gas Ratio3%Gas mixture for growth
Surface TerminationHydrogenN/ABDD surface state
Caffeine Oxidation Peak Potential1.6VMeasured by Square Wave Voltammetry (SWV) vs. Ag/AgCl
Electric Double Layer Capacitance (Cdl)0.18”F/cm2Measured in 1 g/L NaCl solution
SWV Voltage Sweep Range-2.4 to 2.5VWide potential window utilized
Average Prediction Accuracy93.88%Graded ML evaluation
Median Prediction Accuracy95.95%Graded ML evaluation
Measurement Time (This Study)2minZero pretreatment steps
Comparison Time (HPLC Ref. [31])120minStandard method

Key Methodologies

Section titled “Key Methodologies”
  1. BDD Electrode Synthesis: Heavily boron-doped polycrystalline diamond films (2 ”m thick, 5E20 cm-3 B concentration) were grown on Si (100) substrates using HFCVD at 2200 °C and 1.3 kPa, maintaining a 3% CH4/H2 gas ratio.
  2. Electrode Stability Verification: The BDD electrode stability and wide potential window were confirmed via continuous cyclic voltammetry (CV) from -2.4 V to 2.5 V over 50 cycles, demonstrating superior stability compared to gold or glassy carbon electrodes.
  3. Sample Measurement (Direct Injection): Commercial coffee beverages (3 mL) were taken directly from the can and injected into the measuring cell. No solvent pretreatment, filtering, or electrolyte addition was performed.
  4. Electrochemical Data Acquisition: Square Wave Voltammetry (SWV) was performed using the BDD working electrode. Measurements were taken in 0.016 V steps, focusing on the caffeine oxidation peak at 1.6 V.
  5. Multivariate Feature Extraction (PCA): The full voltage-current spectral data was subjected to Principal Component Analysis (PCA) to reduce dimensionality and extract two types of features:
    • Analysis Evaluation (Concrete): Features based on specific coordinates with the highest contribution ratio and variance.
    • Logical Evaluation (Abstract): Features based on the area divided into 17 segments around the caffeine oxidation region (1.55 V to 1.65 V).
  6. Caffeine Quantification (PCR): Principal Component Regression (PCR) was applied to the combined feature sets (Analysis and Logical evaluations). The final quantitative result (Predicted Value) was derived from the median of the stepwise averaged predictions (Ave1, Ave2, Ave3), resulting in the “Graded Evaluation.”

Commercial Applications

Section titled “Commercial Applications”

The combination of chemically inert BDD electrodes and rapid ML analysis is highly valuable for industries requiring fast, accurate, and low-cost chemical quantification in complex matrices.

  • Food and Beverage Safety/Quality Control:
    • Rapid, on-site determination of active ingredients (e.g., caffeine, antioxidants) in finished products without requiring laboratory-grade sample preparation.
    • Verification of manufacturer-published content values for regulatory compliance.
  • Process Analytical Technology (PAT):
    • Real-time monitoring of fermentation, brewing, or extraction processes where solvent composition is complex and rapid feedback is necessary.
  • Environmental and Water Analysis:
    • Detection and quantification of redox-active organic pollutants in industrial wastewater, leveraging the BDD’s wide potential window for simultaneous multi-analyte detection.
  • Pharmaceutical and Nutraceutical Manufacturing:
    • Quick assessment of active pharmaceutical ingredients (APIs) in complex formulations, reducing reliance on time-consuming chromatographic methods.
  • Electrochemical Sensor Development:
    • BDD’s stability and resistance to fouling make it the preferred material for developing robust, long-lifetime sensors for complex biological or industrial fluids.
View Original Abstract

Electrochemical measurements, which exhibit high accuracy and sensitivity under low contamination, controlled electrolyte concentration, and pH conditions, have been used in determining various compounds. The electrochemical quantification capability decreases with an increase in the complexity of the measurement object. Therefore, solvent pretreatment and electrolyte addition are crucial in performing electrochemical measurements of specific compounds directly from beverages owing to the poor measurement quality caused by unspecified noise signals from foreign substances and unstable electrolyte concentrations. To prevent such signal disturbances from affecting quantitative analysis, spectral data of voltage-current values from electrochemical measurements must be used for principal component analysis (PCA). Moreover, this method enables highly accurate quantification even though numerical data alone are challenging to analyze. This study utilized boron-doped diamond (BDD) single-chip electrochemical detection to quantify caffeine content in commercial beverages without dilution. By applying PCA, we integrated electrochemical signals with known caffeine contents and subsequently utilized principal component regression to predict the caffeine content in unknown beverages. Consequently, we addressed existing research problems, such as the high quantification cost and the long measurement time required to obtain results after quantification. The average prediction accuracy was 93.8% compared to the actual content values. Electrochemical measurements are helpful in medical care and indirectly support our lives.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2005 - Determination of caffeine and its metabolites in urine by capillary electrophoresis‐mass spectrometry [Crossref]
  2. 2014 - Beverage caffeine intakes in the US [Crossref]
  3. 2002 - Effects of caffeine on bone and the calcium economy [Crossref]
  4. 1986 - Caffeine consumption during pregnancy and association with late spontaneous abortion. [Crossref]
  5. 2012 - Voltammetric determination of caffeine in beverage samples on bare boron-doped diamond electrode [Crossref]
  6. 2018 - HPLC method for quantification of caffeine and its three major metabolites in human plasma using fetal bovine serum matrix to evaluate prenatal drug exposure
  7. 1999 - Quantitative HPLC analysis of sunscreens and caffeine during in vitro percutaneous penetration studies [Crossref]
  8. 2008 - Measurement of caffeine in coffee beans with UV/vis spectrometer [Crossref]
  9. 2013 - Optimization of a UV-vis spectrometric method for caffeine analysis in tea, coffee and other beverages
  10. 2000 - Quantification of caffeine by off-line TLC-MS

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