Zinc is crucial for various bodily functions, including the synthesis of proteins, carbohydrates, lipids, hormones, and nucleic acids. It also plays a significant role in immune system health, and deficiencies can lead to issues such as growth delays and reduced spermatogenesis. Mineral waters and isotonic sports drinks are common sources of zinc, making accurate detection methods essential for ensuring their safety and nutritional value.
A paper by Costa et al. (2020), “A New Online Pre-Concentration System Using Hydride Generation Atomic Fluorescence Spectrometry (HG AFS) for Zinc Determination in Mineral Water and Isotonic Sports Drinks,” introduces a method that enhances the detection and quantification of zinc in these beverages. It provides a reliable and efficient way to monitor zinc levels in widely consumed drinks.
An Innovative Approach: HG AFS
The research outlines a novel analytical method using Lumina hydride generation atomic fluorescence spectrometry combined with an online pre-concentration system. This method stands out for its simplicity, speed, reliability, sensitivity, and selectivity. The technique achieves impressive limits of detection (LOD) and quantification (LOQ) at 0.03 mg/L and 0.09 mg/L, respectively. Zinc concentrations in samples were found to range from 29.00 to 78.59 mg/L.
By optimizing parameters such as pH, sample flow, and elution flow rate, the researchers developed a system that delivers precise zinc measurements in mineral waters and isotonic sports drinks. With an enrichment factor of 88.92 and a sampling frequency of 51 samples per hour, this method significantly enhances the efficiency of zinc detection.
Methodology
Figure 1 On-line preconcentration system. (a) Sampling state. (b) Elution state. A = sample; P = peristaltic pump; E = eluent; D = disposal; C = column; V = valve.
Sample Preparation:
- Mineral water and isotonic sports drink samples were purchased and prepared by adjusting pH and adding buffer solutions. Key parameters like pH (set at 8.00), Na2CO3 concentration, and flow rates for both sampling and elution were finely tuned using the Box-Behnken design.
- Zinc was pre-concentrated using a mini-column filled with polyurethane foam for effective zinc retention through complexation with 4-(2-pyridylazo) resorcinol (PAR).
Flow Injection Analysis System:
- A flow injection analysis system was set up with a peristaltic pump to control the flow of the sample and eluent through the mini-column and into the Lumina 3300.
Optimization:
- Multivariate optimization was performed to determine the best conditions for zinc detection, including pH, buffer concentration, and sample flow rate.
| Parameter | Optimal condition |
| Light current/mA | 140 |
| Photomultiplier (PMT) voltage/V | 400 |
| Spray height/mm | 8.0 |
| Transport gas flow (argon)/mL min-1 | 400 |
| Protective gas flow (argon)/mL min-1 | 1000 |
| Peristaltic pump speed/rpm | 50 |
Results and Discussion
Accuracy was tested by adding and recovering the analyte in the samples. Additionally, zinc levels were measured using a certified reference material from the National Research Council of Canada (Ottawa, Ontario, Canada), specifically CASS-4 seawater. The results in Table 5 confirm that the method is satisfactorily applicable to the samples studied.
The method developed for zinc determination was applied to 10 samples (4 mineral water samples and 6 isotonic sports drink samples from the same batch, purchased from a local store and supermarket in Salvador, Bahia, Brazil). The results are detailed in Table 9, with a 95% confidence level.
Conclusion
A novel, efficient, and reliable Lumina HG AFS method for zinc determination was developed and validated, which helps ensure that mineral waters and isotonic sports drinks are safe and nutritious. As consumers become increasingly health-conscious, the ability to monitor and control mineral content in beverages will be more critical than ever. Compared to other spectrometric techniques, HG AFS offers superior sensitivity and selectivity at a lower cost, making it an excellent choice for laboratories and quality control environments.
Reference
Costa, M. A. P.; Silva, D. L. F.; Dias, F. S.; Santos Júnior, A. F.; Santos, W. N. L. A New Online Pre-Concentration System Using Hydride Generation Atomic Fluorescence Spectrometry (HG AFS) for Zinc Determination in Mineral Water and Isotonic Sports Drinks. Anal. Methods 2020, 12 (12), 1711–1719. DOI: 10.1039/D0AY00139B.