Electrochemical Evaluation of Cd, Cu, and Fe in Different Brands of Craft Beers from Quito, Ecuador

At a Glance

Metadata	Details
Publication Date	2023-06-04
Journal	Foods
Authors	Oscar López-Balladares, Patricio J. Espinoza-Montero, Lenys Fernández
Institutions	Pontificia Universidad Católica del Ecuador, Central University of Ecuador
Citations	7
Analysis	Full AI Review Included

Executive Summary

This study validates the use of Differential Pulse Anodic Stripping Voltammetry (DPASV) utilizing a Boron-Doped Diamond (BDD) electrode for the rapid and accurate quantification of trace heavy metals (Cd, Cu, Fe) in craft beer.

High Analytical Performance: The DPASV method on BDD demonstrated excellent precision (RSD% < 3%) and accuracy (Recovery R% > 91%) for all three metals, confirming its suitability for trace analysis in complex food matrices.
BDD Material Advantage: The BDD electrode exhibited favorable characteristics, including a granular morphology (300-2000 nm crystals), a wide working potential window (-1.15 V to 1.60 V), and a low double layer capacitance (0.01412 µF cm^-2), minimizing background interference.
Low Detection Limits: The method achieved low detection limits (DL) suitable for regulatory compliance checks: Fe(III) (1.72 µg L^-1), Cu(II) (1.76 µg L^-1), and Cd(II) (6.31 µg L^-1).
Matrix Effect Management: Optimal supporting electrolytes and DPASV parameters were specifically tuned for each metal to mitigate the complex food matrix effects inherent in beer samples.
Regulatory Non-Compliance: Analysis of 13 Ecuadorian craft beers revealed that 5 brands exceeded the permissible limit for Iron (Fe(III) > 0.2 mg L^-1), indicating potential quality and health risks related to brewing ingredients (caramelized/roasted malt) or equipment corrosion.

Technical Specifications

Parameter	Value	Unit	Context
BDD Doping Level	3000 to 5000	ppm	Working Electrode Specification
BDD Crystal Size (Range)	300 to 2000	nm	SEM Characterization
B/C Ratio (Atomic)	0.052	-	EDS Composition
Working Potential Window	-1.15 to 1.60	V	1.0 mol L^-1 KCl, pH 1 (vs. Ag/AgCl)
Double Layer Capacitance (C_dl)	0.01412	µF cm^-2	1.0 mol L^-1 KCl, pH 1
Standard Rate Constant (k°)	2.44 x 10^-2 ± 4.67 x 10^-3	cm s^-1	K₄[Fe(CN)₆]/K₃[Fe(CN)₆] System
Redox Quasi-Reversibility (Ipox/Ipred)	0.99	-	K₄[Fe(CN)₆]/K₃[Fe(CN)₆] System
Cd(II) Detection Limit (DL)	6.31	µg L^-1	DPASV Method
Cu(II) Detection Limit (DL)	1.76	µg L^-1	DPASV Method
Fe(III) Detection Limit (DL)	1.72	µg L^-1	DPASV Method
Cd(II) Reproducibility (RSD%)	1.61	%	Interday (3 days)
Cu(II) Reproducibility (RSD%)	2.94	%	Interday (3 days)
Fe(III) Reproducibility (RSD%)	1.83	%	Interday (3 days)
Cd(II) Average Recovery (R%)	94.94	%	Standard Addition Method
Cu(II) Average Recovery (R%)	91.68	%	Standard Addition Method
Fe(III) Average Recovery (R%)	96.79	%	Standard Addition Method
Fe(III) Regulatory Limit (Ecuador)	< 0.2	mg L^-1	NTE INEN 2263

Key Methodologies

The quantification of Cd(II), Cu(II), and Fe(III) utilized Differential Pulse Anodic Stripping Voltammetry (DPASV) on a Boron-Doped Diamond (BDD) working electrode.

Sample Preparation (Acid Digestion):
- 25 mL beer sample was degassed via ultrasound (20 min at 30 °C).
- Acid digestion performed using 5 mL concentrated HNO₃ (65% m/m) and 2 mL H₂O₂ (30% m/m) at 100 °C until yellow coloration was achieved.
- Digested product was diluted to 25 mL with the selected supporting electrolyte and pH adjusted using 2 mol L^-1 NaOH.
- Samples were purged with 99.99% N₂ for 10 minutes prior to measurement to eliminate O₂ interference.
BDD Electrode Conditioning:
- The BDD surface was cleaned using Cyclic Voltammetry (CV) in 0.2 mol L^-1 HNO₃.
- The electrode was conditioned by running 30 CV cycles in 1 mol L^-1 KCl (pH 1) before each measurement run.
Optimal Electrolyte Selection (DPASV):
- Cd(II): 0.1 mol L^-1 Acetic Acid / 0.055 mol L^-1 Sodium Acetate (pH 4.5).
- Cu(II): 0.1 mol L^-1 KNO₃ / 0.1 mol L^-1 HNO₃ (pH 1.20).
- Fe(III): 0.1 mol L^-1 KNO₃ / 0.01 mol L^-1 HNO₃ (pH 2.10).
DPASV Parameter Optimization (Matrix Effect Considered):
- Cd(II) Quantification: Modulation Amplitude (MA) 0.4 V, Modulation Time (MT) 0.4 s, Time Interval (TI) 0.4 s.
- Cu(II) Quantification: MA 0.7 V, MT 0.7 s, TI 0.7 s.
- Fe(III) Quantification: MA 0.7 V, MT 0.7 s, TI 0.7 s.
- Pre-concentration Time (Cd, Cu, Fe): 15 s (Cd) or 60 s (Cu, Fe) were selected for fast measurement times, despite minimal peak intensity variation at longer times.
Quantification Method:
- Standard Addition Plot method was used for final quantification to accurately compensate for signal distortion and slope changes caused by the complex beer matrix.

Commercial Applications

The use of Boron-Doped Diamond (BDD) electrodes in electroanalysis, particularly for trace metal detection in complex media, is highly relevant across several industrial and environmental sectors due to BDD’s exceptional stability and electrochemical properties.

Food and Beverage Quality Control:
- Rapid, on-site screening for heavy metal contaminants (Cd, Pb, Cu, Fe) in alcoholic beverages, juices, and water, ensuring compliance with strict health regulations (e.g., NTE INEN 2263).
- Monitoring metal content during brewing or food processing to prevent flavor deterioration and spoilage accelerated by transition metals (Fe, Cu).
Environmental Monitoring and Wastewater Treatment:
- High-sensitivity detection of pollutants in industrial effluent and drinking water, leveraging the BDD’s wide potential window and resistance to fouling in harsh chemical environments.
High-Precision Sensor Development:
- Development of robust electrochemical sensors for trace analytes, benefiting from the BDD’s low double layer capacitance (C_dl), which significantly improves the signal-to-noise ratio at low concentrations.
Electroanalytical Research and Development:
- Use as a stable, inert working electrode for fundamental studies of redox kinetics and electrocatalysis, especially in highly acidic or basic solutions where conventional electrodes fail.

View Original Abstract

The presence of heavy metals in craft beers can endanger human health if the total metal content exceeds the exposure limits recommended by sanitary standards; in addition, they can cause damage to the quality of the beer. In this work, the concentration of Cd(II), Cu(II), and Fe(III) was determined in 13 brands of craft beer with the highest consumption in Quito, Ecuador, by differential pulse anodic stripping voltammetry (DPASV), using as boron-doped diamond (BDD) working electrode. The BDD electrode used has favorable morphological and electrochemical properties for the detection of metals such as Cd(II), Cu(II), and Fe(III). A granular morphology with microcrystals with an average size between 300 and 2000 nm could be verified for the BDD electrode using a scanning electron microscope. Double layer capacitance of the BDD electrode was 0.01412 μF cm−2, a relatively low value; Ipox/Ipred ratios were 0.99 for the potassium ferro-ferricyanide system in BDD, demonstrating that the redox process is quasi-reversible. The figures of merit for Cd(II), Cu(II), and Fe(III) were; DL of 6.31, 1.76, and 1.72 μg L−1; QL of 21.04, 5.87, and 5.72 μg L−1, repeatability of 1.06, 2.43, and 1.34%, reproducibility of 1.61, 2.94, and 1.83% and percentage of recovery of 98.18, 91.68, and 91.68%, respectively. It is concluded that the DPASV method on BDD has acceptable precision and accuracy for the quantification of Cd(II), Cu(II), and Fe(III), and it was verified that some beers did not comply with the permissible limits of food standards.

Tech Support

Original Source

DOI: https://doi.org/10.3390/foods12112264

References

2018 - Evaluación de las cervezas artesanales de producción nacional y su maridaje con la cocina ecuatoriana [Crossref]
2020 - Worldwide Contamination of Food-Crops with Mycotoxins: Validity of the Widely Cited ‘FAO Estimate’ of 25% [Crossref]
2019 - Hemocromatosis
2018 - El metabolismo del cobre. Sus consecuencias para la salud humana Metabolism of copper. Its consequences for human health