This Spanish analytical chemistry paper describes an ultrasound-assisted flow injection method with flame atomic absorption detection for iron, manganese and zinc in water-soluble solids. It applies the method to one soluble cocoa, two soluble coffees and three multivitamin tablets, and compares the food results with a conventional wet acid digestion. The food values are illustrative examples from a handful of products, not a survey.
Key numbers
- Soluble cocoa: zinc 57.90 ± 1.00 µg/g by the new method and 55.41 ± 2.91 µg/g by the official wet digestion method (mean ± SD, n = 3; reported as dry weight) (Table 2, p. 4).
- Soluble coffee 1: zinc 53.18 ± 0.68 µg/g (new method) and 54.14 ± 1.87 µg/g (official method) (Table 2, p. 4).
- Soluble coffee 2: zinc 33.27 ± 0.68 µg/g (new method) and 32.22 ± 1.45 µg/g (official method) (Table 2, p. 4).
- Multivitamin tablets: zinc 15.12 ± 0.03, 2.84 ± 0.02 and 1.55 ± 0.02 mg per tablet against nominal 15.0, 3.0 and 1.4 mg (Table 2, p. 4). The abstract reports the tablet range as 1.55 to 15.12 µg/g, a unit that does not match the table.
- Zinc limit of detection 0.03 µg/mL and limit of quantification 0.1 µg/mL in solution; relative standard deviation 1.2% (Table 1, p. 3).
- Paired t-test against the official method: experimental t 0.92 for zinc versus critical 2.57 (Table 2, p. 4).
Methods (brief)
Samples (5 to 30 mg) were dissolved in water in a continuous ultrasound system at room temperature and injected into a flame atomic absorption spectrometer. Food results were compared with a wet acid digestion reference procedure on the same samples. Products were bought at local markets and pharmacies; brands are not identified.
Evidence fitness
The paper supports method performance for zinc in soluble food powders and shows example zinc levels in one cocoa and two coffee products. Because only three food products were measured in triplicate, it cannot describe market ranges for cocoa or coffee, and it says nothing about exposure or health.
Limitations
Very small product set with no brand, origin or lot detail. The paper states food results on a dry-weight basis but does not report moisture. The tablet unit in the abstract (µg/g) conflicts with the table (mg per tablet).
Related evidence
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